U. K. Geophysical Assembly 12–15 April 1977

Geophys. J. R. astr. SOC. (1977) 49, 245-312

U.K. GEOPHYSICAL ASSEMBLY

12-1 5 APRIL

1977 Downloaded from http://gji.oxfordjournals.org/

Department of Geophysics

James Clerk Maxwell Building at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 University of Edinburgh

CONTENTS

Preface General (Invited) Lectures Content of Sessions Abstracts Author Index

edited by K.M. Creer 246 U.K.G.A. 1977

1 Preface

In the spring of 1975 I put the suggestion to the Royal Astronomical Society that a national geophysical meeting be held in U.K. at which a wide variety of subjects would be discussed in parallel sessions along the lines of the annual meetings of the American Geonhysical Union held in Washington. A few U.K. geo- Downloaded from physicists expressed doubts as to whether sufficient interesting geophysics was being done in U.K. to sustain such a meeting. Nevertheless when the question of whether such a national meeting would attract their support was put to geo- physicists in U.K. Universities and Research Institutes, it was apparent that wide support would be forthcoming at the grass-roots level. http://gji.oxfordjournals.org/ At this stage Dr. J. A. Hudson, Geophysical Secretary of the R.A.S., proposed to Council that they should sponsor a national geophysical meeting. They agreed to do this and the U.K. Geophysical Assembly (U.K.G.A.) to be held in the Univer- sity of Edinburgh (U.O.E.) between 12 and 15 April 1977 is the outcome.

A Local Organizing Committee was formed with Professor K. P. Creer (Geo- physics, U.O.E.) as Chairman and with the following members: Dr. V. R. S. Hutton (Geophysics, U.O.E.), Dr. D. H. McIntosh (Meteorology, U.O.E.), Dr. P. L. Willmore (I.G.S. Global Seismology), Dr. W. F. Stuart (I.G.S. Geomagnetism), Mr. R.

McQuillin (I.G.S. Marine Geophysics) and Mr. W. Barclay (Oil Exploration (Holdings) at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Ltd.).

Papers were invited on an open basis so that the content of the working sessions would reflect the nature and emphasis of the geonhysical work currently being carried out in U.K. Contributions were grouped under seven section headings. Section convenors were given the responsibility of calling for papers and of composing the working sessions. Local co-convenors were appointed to coordinate the input to the different sections. Section titles, names of convenors and co-convenors, the number of paFers finally contributed to each section and the number of working sessions formed from them are given below.

A Applied Geophysics and Glaciology

Convenor: Prof. D. H. Griffiths, University of Birmingham

Co-Convenor: Mr. R. McQuillin, I.G.S., Edinburgh

15 papers, 2 sessions.

F Magnetohydrodynamics and Meteorology Con ve n o r : Dr. D. J. Tritton, University of Newcastle

Co-Convenor: Dr. D. H. McIntosh, University of Edinburgh

14 papers, 2 sessions.

G Geomagnetism and Palaeomagnetism

Convenor: Prof. R. L. Wilson, University of Liverpool

Co-Convenor: Dr. V. R. S. Hutton, University of Edinburgh

50 papers, 6 sessions. U.K.G.A. 1977 247 L Lithospheric Studies

Convenor: Prof. M. H. P. Bott, University of Durham Co-Convenor: Or. S. A. D. Bamford, University of Edinburgh

39 papers, 5 sessions.

Y Magnetospheric, Ionospheric and Solar Terrestrial Phenomena Downloaded from Convenors: Dr. H. Rishbeth, Appleton Laboratory, and Prof. P. C. Kendall, University of Keele Co-Convenor: Dr. W. F. Stuart, I.G.S., Edinburgh

30 papers, 6 sessions. http://gji.oxfordjournals.org/

P Planetology

Convenor: Prof. A. H. Cook, F.R.S., University of Cambridge

Co-Convenor: Dr. R. G. Hipkin, University of Edinburgh

6 papers, 1 session. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

S Seismology

Convenor: Dr. H. Thirlawqy, A.W.R.E., Blacknest

Co-Convenor: Or. P. L. Willmore, I.G.S., Edinburgh

28 papers, 5 sessions.

Four General Lectures have been invited. They will be delivered to the whole Assembly at 09.00 and at 14.00 on Wednesday, 13 and Thursday, 14 April. The names of the invited speakers and the titles of their lectures are given in Section 2. Norking sessions, run in parallel, will commence at 09.45 and at 14.45 on these days following the General Lectures and will also be held during Tuesday, 12 April after the Opening Ceremony, and during the morning of Friday, 15 April. The content of each of the working sessions is given in Section 3. Abstracts of papers to be presented, grouped section by section, are presented in Section 4. Finally, an author index is given in Section 5. A time-table will be circulated.

The Local Organizing Committee wishes to take this opportunity of expressing its hearty thanks to the Council of the Royal Astronomical Society for generous financial backing without which it would have been .impossible to hold this U,K. Geophysical Assembly. Thanks are also due to the University. of Edinburgh for the many facilities placed at the disposal of the L.O.C. On behalf of all delegates to U.K.G.A., we thank both the City of Edinburgh and the University of Edinburgh for invitations to Receptions offered to delegates respectively on the Tuesday and Wednesday evenings. Thanks are also expressed to Miss Kathy Dodds, my secretary, who typed this copy and who also had to retype many of the submitted abstracts to bring them up to the standard required for reproduction, to Mrs. Inger Banks, the Conference Secretary, and to Mr. S. Ballantyne and Mr. N. Aikman of the University of Edinburgh Audio Visual Services Unit who prepared the copy for the printer.

Edinburgh, K. M. Creer, 10 February 1977 Ch airman , 0 rgani zing Commi t tee. 24 8 U.K.G.A. 2977

2 General (Invited) Lectures

09.00, Wednesday, 13 April 1977:

I3 A Geophysicist's Approach to the Moon and Planets Downloaded from

Professor S. K. Runcomz, F.R.S., Institute of Lunar and Planetaw Science, University of Newcastle upon Tyne. http://gji.oxfordjournals.org/

14.00, Wednesday, 13 April 1977:

I2 Reversals of the Earth's Magnetic Field.

Professor J. A. Jacobs, at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Department of Geodesy and Geophysics, University of Cambridge.

09.00, Thursday, 14 April 1977:

I1 Planetary Atmospheres and the Emerging Perspective.

Dr. G. E. Hunt, Meteom logical Office, Braeknelt .

14.00, Thursday, 14 April 1977:

14 Marine Magnetic Anomal ies .

Professor F. J. Vine, F.R.S., SchooZ of Environmental Sciences, University of East Anglia. U. K. G.A. 1977 249 3 Content of Sessions

SESSION A1 Applied Geophysics Chaim: Dr. M. A. Khan

A9 Holographic Mapping of Coal Seams Using Channel Waves. I. M. Mason and D. J. Buchanan Downloaded from

A3 3-D Data Collection and Display. M. J. G. Cox and W. R. Cotton

Al In Situ Seismic Measurements of Crack Anisotropy.

D. Bamford and K. R. Nmn http://gji.oxfordjournals.org/

A10 A Shallow Land Seismic Reflection System Using a Vibrator Source. E. G. Webb and K. R. Nmn

A7 Marine Geophysical Surveying in Engineering Studies of Coastal Zones. D. M. McCann and R. A. Floyd

A5 In-Situ Electrical and Acoustic Measurements - An Aid to Rapid Geotechnical Mapping on the Sea-Floor. P. D. Jackson md R. Baria at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

A6 Transformation of Magnetic into Pseudo-Gravity Anomalies iJsing an Inter- active Graphics Terminal. C. McCann

All Joint Modelling of Gravity and Magnetic Anomalies Using Non-Linear Optimization. G. K. Westbrook

SESSION A11 Applied Geophysics and Glaciology

Chairman: Dr. R. F. King

-42 The Use of Geophysical Methods in Locating Buried Valleys in N.E. England. J. D. Cornwell, E. M. Andrew, C. Johnson and M. K. Lee

A8 A Comparison of I.P. Transient Shapes over Disseminated and Massive Sulphide Sheets in the Lower Pillow Lavas of Cyprus. G. Maliotis and M. A. Khan

A12 A Borehole Controlled Source Induction Procedure for the Determination of Electrical Conductivity Structure. M. H. Worthington

A4 A Deep Resistivity Sounding at Rookhope Co. Durham. G. M. Habberjam

A13 Surface Strain Rate Measurements of Sea-Ice and Glaciers. D. J. Goohan

A14 The Radio Frequency Bi-Refringence of Polar Ice Sheets. N . D . Hargreaves

Al5 Radar Techniques in Glaciology and Other Fields - A Review. D. T. Meldnun U. K. G.A. 1977

SESSION FI

Magnetohydrodynamics and Meteorology

Chairman: Dr. D. Tritton

F8 A Study of the Stratification in the Earth's Outer Core T. G. Masters Downloaded from

F9 Hydromagnetic Effects Near a Bumpy Core-Mantle Interface. H. K. Moffatt

F3 Generation of Magnetic Fields by Fluid Motions of Global Scale. D. Gubbins http://gji.oxfordjournals.org/

F1 Magnetohydrodynamic Wave Energy Flux. J. A. Adam

F5 The Transport of Ozone in a Time-Dependent, Two-Dimensional Model. R. S. Hamood and J. A. PyZe

F1O Prognosis of Ozonolytic Pollution. R. 5'. Scorer

F7 On Detached Shear Layers and Western Boundary Currents in a Rotating at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Homogeneous Liquid. L. M. Hocking and R. Hide

SESSION FII

Magnetohydrodynami cs and Yeteorology

Chairman: Dr. D. H. McIntosh

F12 Convection in Rapidly Rotating Fluid Spheres. A. M. Soward

F13 Internal Gravity in a Shear Flow. S. A. Thorpe

F2 The Spectrum of Lee Waves in Stratified Flows. F. H. Berkshire

F11 Non-Linear Baroclinic Disturbances to Mid-Latitude Zonal Flows. A. J. Simns and B. J. Hoskins

5'6 Thermal Convection in a Rotating Fluid Subject to a Horizontal Temperature Gradient: Spatial and Temporal Characteristics of Fully Developed Baroclinic Waves. R. Hide, P. J. Mason and R. A. Pl&

F4 The Observed Flux of Potential Vorticity in the Stratosphere. R. S. Hawood

F14 Aspects of Geophysical Turbulence. J. D. Woods U.K.G.A. 1977 251

SESSION GI

Geomagnetic Main Field and Secular Variation

Chairman: Mr. S. R. C. Malin

G1 Does the Geomagnetic Field Have a Significant Monopole Component?

D. R. Barraclough Downloaded from

C2 A Definitive Model of the Geomagnetic Field of Epoch 1975. D. R. Barraclough, J. M. Hawood, B. R. Leaton and S. R. C. Mazin

G3 Synthetic Plots Obtained from an Oscillating Alldredge-Hurwitz Radial Dipole Model. K. M. Cwer and T. E. Hogg http://gji.oxfordjournals.org/

G4 The (IN) Significance of the Correlation between the Earth's Gravitational and Magnetic Fields. F. J. Lmes

G50 A Geomagnetic Test of Maxwell's Equations. R. L. Wilson, C. R. Johnson, A, G. MacCormck and D. R. Barraclough

SESSION GI1 at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

Geomagnetic Field Behaviour Studies

Chairman: Professor R. L. Wilson

G5 A Layman Looks at Dynamo Theory. F. J. Lmes

G2 8 Speleornagnetism - The Paleomagnetic Record Carried by Cave Sediments. J. S. k'opper

G31 Preliminary Results of a Palaeomagnetic Investigation of Lake Sedimnts from Poland. E. Niedziolka, P. Tucholka and T. E. Hogg

G2 5 Secular Variations Obtained from French and Swiss Lakes 0-6000 Years B.P. T. E. Hogg

G35 Geomagnetic Field Fluctuations Recorded in Sediment from Lake Trikhonis, Greece. P. W. Reachan

G30 Palaeomagnetic Studies of Varved Clays from Poland. E. Niedziolka

G33 Post-Depositional Remanent Magnetization in Sediments from the Greek Lakes. S. Papamarinopoulos

Gl9 A New Method for Determining the Magnitude of the Earth's Magnetic Field Using Sun-Dried Bricks. K. P. Games

G20 Geomagnetic Archaeomagnitude Measurements from Peruvian Ceramics. N. M. Gunn 252 U.K. G.A. 1977 ~16 Experiments Relating to Fundamental Problems in Archaeomagnetic Field Strength Measurements. M. F. Barbetti, K. P. Flu& ad J. M. W. Fox

G30 Archaeomagnetic Intensity Measurements Using a Squid Magnetometer. D. Walton and M. J. Aitken

SESSION GI11 Downloaded from Younger Palaeomagnetism

Chaimn: Dr. A. E. Mussett

G2 3 Magnetic Fabric of Marine Sediments. http://gji.oxfordjournals.org/ N. Hami I ton

G32 Some Uses of Induced Magnetic Measurements in Lake Sediments. F. OZdfieZd, J. A. Dearing, T. A. Rmmeqj and R. Thorpson

G36 Low Temperature Denmgnetization 1nvestigatj.ons into the Carriers of Stable Natural Remanent Masetization in Some Finnish Lake Sediments. J. C. Stober and R. Thompson

G37 A Statistical Approach to Curve Fitting and Correlation of Serial Data at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Distributed on a Sphere. R. Thompson and R. M. CZark

G22 Quaternary Palaeomagnetic Results from DSDP Sites 379 and 380 in the Black Sea. E. A. Hailwood and N. Hamilton

G24 Late Neogene Magnetic Stratigraphy Evidence from DSDP Mediterranean Sea Sites 372, 374 and 376. N. Hamilton and E. A. Hailwood

G17 Polarity Sequence of Mull. P. Dagley and A. E. Mussett

G29 Problems of Polarity in the British Tertiary Igneous Province. A. E. Mwsett

G2 7 Palaeomagnetic Investigations of Tertiary Volcanic Activity in Lower Silesia, Poland. M. JeZenska, M.. Kadzialko-Hofhrokl and J. Kruczyk

SESSION GIV

Geo?ogical Uses of PaJaeomagnetism

Chairman: Professor J. C. Briden

G26 Continental Drift Between the Palaeozoic and Mesozoic. E. Irving

G34 Palaeomagnetic Studies of the Pre-Cambrian: Britain, South Greenland and Scandinavia. J. D. A. Piper and J. E. F. Steam U.K. G.A. 1977 253

G18 Palaeozoic Palaeomagnetic Results from Jersey, C.I. B. A. Duff

G21 Mesozoic Geomagnetic Field Configuration and C ircumAtlant i c Continent a1 Reconstructions. E. A. Hdlwood

G15 Chemical Demagnetisation Studies of the Alderney Sandstone, Channel lslands. J. A. Banner and E. A. Hdlwood Downloaded from

SESSION GV

Rock Magnetism http://gji.oxfordjournals.org/ Chaimm: Dr. W. O'ReiZly

G40 A Method for Preparation of Iron-Titanium Single Crystals. Z. Hazrptm

G42 Laboratory Simulation of Maghemitization and Deuteric Oxidation of Titano- magnetite-Influence on Coercive Force and Other Magnetic Properties. J. B. O'Donovan at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 G45 A Magnetic Study of Synthetic Titanomagnetite Substituted by Aluminium. 0. Ozdemir

G41 Oqgen Fugacity Values and Curie Temperatures for the Middle Members of the Cubic Titanomagnetite S.S. Series. 2. Hauptman and A. L. Campbell

G39 An Experimental Study of Ti Diffusion in Xagnetite. R. Freer and Z. Hauptrnan

G47 Magnetic Properties of Titanomagnetite Single Crystals. P. Tucker

~4 8 Magnetic Interaction Between Iron and Ulvospinel. R. Veitch and A. Stephenson

~46 Magnetic Properties of Ulvospinel. P. W. Reahan

G44 Magnetic Anisotropy of Deformed Calcite Aggregates. W. H. Owens and E. H. Rutter

G4 3 Rotational Hysteresis in Haematite. W. H. Owens

G49 A RotatingHead Torque Magnetometer Controlled by a Microprocessor D. Wilson 254 U.K.G.A. 1977 SESSION GVI

Geomagnetic Induction Studies

Chairman: Dr. R. Banks

G6 Effect of Conductivity Anomalies in Devon on Micropulsations. C. C. F. Adcock, A. M. Hart, C. D. Honebon and W. C. V. Rosser Downloaded from

G11 The Interpretations of Geomagnetic Variation Observations in Scotland Using the Hypothetical Event Technique. V. R. S. Hutton, J. Sik, A. G. Jones and D. Rooney

G12 A Method for the Processing of Magnetotelluric Data.

A. G. Jones http://gji.oxfordjournals.org/

G13 A Comment on Methods of Solution of Oceanic Induction Problems. P. C. KendaZZ

G14 Lunar Geomagnetic Tides and the Ocean Dynamo. D. M. Schlapp G7 The Representation of Internal Fields by Equivalent Currents in Thin Sheets: Application to GDS Array Studies in Kenya. R. J. Banks D. Beamish and at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

Ga Local Conductivity Effects on the Magnetic Fields Due to Sea Tides. A. M. Hart

G9 First Order Solutions of Oceanic Induction Problems. R. C. Hewson-Bruwne and P. C. Kendull

G10 The Electrical Conductivity of the Moon: An Application of Inverse Theory. B. A. Hobbs

SESSION LI

General Geophysics (U.K.)

Chairmen: Pmfessor M. H. P. Bott, Dr. M. A. Khan

L22 Caledonian Granites : A Rare Thermal Event. J. Hennessy and G. C. Brown

L27 Geophysical Modelling and Petrogenesis of the Shap Granite. C. A. Locke and G. C. Brown

~26 A Geomagnetic Induction Study at Micropulsation Periods in the Southern Uplands of Scotland. A. G. Jones and V. R. S. Hutton

L23 A Gravit'j Survey of the South Midlothian Coalfield and Southern Uplands Fault System. R. G. Hipkin

Geophysical Investigation of the Pre-Carboniferous Basement of the Askrigg Block Yorkshire. J. D. Cornwell, J. M. Allsop, M. K. Lee and D. Patrick U.K.G.A. 1977 255 ~16 The Acquisition and Interpretation of a Garmna-Ray Survey over the Loch Doon Granite. J. CassiCty, G. C. Bwn and J. Hennessy

L31 A Geomagnetic Deep Sounding Study in Northern Scotland. J. M. Sik and V. R. S. Hutton

L24 Secular Variation of Gravity in Scotland. R. G. Hipkin Downloaded from SESSION LII

Seneral Geophysics (Offshore U.K.)

Chairman: Professor M. H. P. Bott http://gji.oxfordjournals.org/

L2 8 Results of Gravity and Magnetic SurveF in the Forties Area of the North Sea. A. K. Rochester

L17 Geophysical Evidence on the Structure of the Faeroe-Shetland Escarpment. J. A. Chalrners, A. Dobinson, A. Mould and D. K. Smjthe

Ll9 An Interpretation of Gravity and Magnetic Data in the English Channel

Around the Isle of Wight. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 S. E. Deegan and A. Dobinson

Laboratory and Theoretical Studies

Chaimn: Dr. R. F. King

L 36 Isostatic Compensation of a Continental Scale: Local Versus Regional Mechanisms. R. J. Banks

L37 Amplification of Upper Lithospheric Stresses by Underlying Vlscoelastic Creep with Application to Continental Splitting Mechanism. M. H. P. Bott and N. J. Kasznir

L 39 Seismic Wave Propagation in Anisotropic Media: Importance for Lithospheric Gtudies. S. Crampin

L38 Laboratory Measurements of Seismic Velocities and Electrical Resistivity of Rocks in Upper Crustal Conditions. P.'N. Chroston, C. Evans and C. Lee

L35 Laboratory Measurements of Seismic Velocities in Lewisian Metamorphic Rocks. F. M. AI-Haddad

SESSION LIII

Explosion Seismology (Continents )

Chairmen: Dr. D. Bmford, Dr..R. B. Whitmarsh

L11 The Crustal Structure Beneath Northern Britain. K. Nunn (The LISPB Working Group) 9 256 U.K.G.A. 1977 L2 S Waves in the LISPB Crustal Profiles. M. Asswnpcao and D. Bmford

~6 Observations of PS Reflections from the Moho. A. W. B. Jacob and D. C. Booth

L5 Lewisian Units Seismic Traverse. J. Hall

L13 Seismic Refraction Studies of the Upoer Crust in the.East Midlands. D. N. Whitcode Downloaded from

L4 Long Seismic Lines in the Bristol Channel Area. M. Brooks, M. BayerZy and D. J.. LkwelZyn

L3 Long-Range LISPB Observations. D. Bamford (The LISPB Working Group) http://gji.oxfordjournals.org/

L7 On the Inversion of Long Range Seismic Profiles. B. L. N. Kennett

SESSION LIV

Explosion Seismology (Margins and Oceans)

Chairmen: Dr. D. Bamford, Dr. R. B. fiitmarsh at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

L1 The Hebridean Margin Seismic Project of 1975. A. R. Amour md id. H. P. Bott

L10 Display and Processing of Seismic Wide Angle Reflection Data from Disposable Sonobuoys . P. R. Miles

La Towards a More Detailed Seismic Picture of the Oceanic Crust. B. L. N. Kennett

L14 Detailed Studies of the Upper Oceanic Crust Using a Large Air Gun and Bottom Receivers. R. B. Whitmarsh

L9 Thin Crust in the Philippine Sea. K. E. Louden

L12 P Wave Structure of the Lithospheres (0-10 m.y.) North of the Azores. L. Steinmetz, R. B. @itmarsh and V. Moreira.

General Geophysics (Oceans)

Chairman: Professor M. H. P. Bott

L 30 The Structure of King's Trough, North-East Atlantic, from Seismic and Gravity Data. R. C. Searle and R. B. Whitmarsh

L34 Variation in Crustal Structure Along the Lesser Antilles Island Arc. G. K. Westbrook

L29 The Structure and Origin of Kurchatov Fracture Zone, North Atlantic Ocean. R. C. SearZe md A. S. Laughton U. K. G. A. 1977 257 SESSION LV

General Geophysics (Rift Valleys)

Chairman: Dr. M. A. Khan

L21 Recent Geophysical Studies of the Gulf of Aden. R. W. Girdler and P. Styles Downloaded from L15 Krisp 1975. Seismic Profiles Within the Gregory Rift Valley, Kenya. 7'. J. Wilton

L33 A Gravity Map of Kenya. C. J. Swain and M. A. Khan http://gji.oxfordjournals.org/ L32 Regional Gravity Anomalies Over the East African Rift System. W. T. C. Souerbutts

L2 5 Geomagnetic Induction Studies in Kenya. V. R. S. Hutton, D. Rooney, I. M. Brazier and E. Mbipom

L20 Crustal Development of the Central West Greenland Bnbayment. J. W. Elder at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 SESSION MI

Atomic Oqgen in the Mesosphere and Lower Thermosphere. P. H. G. Diekinson

The Scattering of Smlight from Noctilucent Clouds. M. Gadsden

Some Characteristics of Cirrus Clouds Observed with a Steerable Lasar Radar. A. J. Gibson, L. Thomas and S. K. Bhattaeharyya

M10 Noctilucent Cloud Movements. A. D. Jenkins

M11 Atmospheric Water Vapour of Extraterrestrial Origin. D. M. WiZlis

M12 Theory of the Near Infra-Red Nightglow Continuum. P. C. Wraight

SESSION MI1

M15 Outer Radiation Zone Structure in a Simple Magnetospheric Model. S. W. H. Cowley

~16 Recent Results on Magnetic Merging in Collisionless Plasmas. S. W. H. Cowley 258 U.K.G.A. 1977 M21 Focusing of Whistlers by a Varying Magnetic Field. M. J. Laird

142 3 The Role of Hot Plasma in Magnetospheric Convection. D. J. Southwood r429 Temporal Variations in Total Equatorial Plasmaspheric Content and their Relationship to the Ring Current Intensity and the Plasmapause. D. C. Webb and L. J. Lanzemtti Downloaded from SESSION IIIII http://gji.oxfordjournals.org/ M1 Electrons and Positive Ions Associated with an Auroral Arc. D. A. Bqant, D. S. Hall, D. R. Lepine and R. W. N. Mason

M2 Image Intensified Observations of Auroral Pulsating Patches. J. crawford, P. Rothwell and R. Thomas

M3 Suprathermal Particle Fluxes Associated with an Auroral Arc. A. D. Johnstone and J. J. Sojka

MI+ Observations of Pulsating Aurora. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 D. J. McEwen and D. A. Bnjant

M5 Energised Auroral Suprathermal Electrons. J. J. Sojka and A. D. Johnstone

SESSION MIV

MIST

M6 Instability of a Field-Aligned Electron Beam. R. J. Strangeuay

M13 Relative Flow of H+ and O+ Ions in the Topside Ionosphere at Mid- Latitudes. R. J. Moffett, G. J. Bailey and J. A. Murphy

M14 Ti Troughs in the Equatorial Topside Ionosphere. H. Rishbeth

M19 Possible Effects of I.M.F. Sector Polarity on Sq. J. G. Greener Fd D. M. Schlapp

M30 Stochastic and Dynamic Temperature Changes in the Interplanetary Gas. M. K. Wallis and M. A. Hassan

SESSION MV

M17 Hydromagnetic Eigenmodes in a Simple Model Plasmasphere with a Thin Lower Ionosphere. A. H. Craven and J. A. Lahe U.K.G.A. 1977 259 M18 Localised Pcb's which Occur at High Latitudes in the Midnight-Dawn Quadrant. C. A. Green and W. F. Stuart

M20 A Pc4 Pulsation Observed Near Midnight at Geostationary Orbit. W. J. Hughes, R. L. MePherron and J. N. Barfield

M22 Sources of Damping of Pc's. R. S. Newton

M24 Particle Flux Variations Produced by Magnetospheric Hydromagnetic Waves. Downloaded from D. J. Southwood and M. G. KiveZson

M2 5 Seine Global Characteristics of Pulsation Activity. W. F. Stuart and C. A. Green

~26 Secondary Resonance in Pie's. http://gji.oxfordjournals.org/ W. F. Stuart and P. M. Mills

M27 Long Period Continuous Pulsations at High Latitudes. M. R. Warner and D. Orr

M28 A Comparison of ULF and VLF Measurements of Magnetospheric Cold Plasma Densities. D. C. Webb, L. J. Lanzerotti md C. G. Park at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 SESSION XVI

Invited papers describing experiments currently proposed for the U.K. research programme using EISCAT European Incoherent Back Scatter Facility will be presented. Contributed papers will also be welcoiwd.

SESSION PI

P1 anetology

Chaimn: Professor A. H. Cook, F.R.S.

P3 Towards a New Semi-Literal Theory of the Lunar Librations A. H. Cook

~6 The First 100 Million Years. G. Turner, P. H. Cadogan and M. C. Enright p5 Large Scale Processes on the Moon. G. Fielder

P4 Determination of the Temperature and Duration of Some Apollo 17 Boulder Shadows Using Themluminescence Methods. S. A. Durrani

P1 Micrometeorite and Solar Wind Erosion of the Lunar Surface. D. G. Ashworth

P2 Evaporative Sources for Track Components of Planetary Atmospheres. P. Brirrbleeorbe and K. Hunter 260 U.K. S. A. 1977 SESSION SI

The Source

Chairman: Dr. J. A. Hudson s4 Seismology in the Oceanic Microseism Band. A. Douglas Downloaded from s5 Earthquake Synthesis. K. J. Fahm'

512 Fault Plane Solutions Using P and pP Relative Amplitudes. R. G. Pearce

S1Q Ocean Bottom Seismograph Observations on the Mid Atlantic Ridge at 45%. http://gji.oxfordjournals.org/ R. C. LiIwaZZ, T. J. G. Francis and I. T. Porter s6 Ocean Bottom Seismograph Observations Near the Eastern End of the St. Paul's Fracture Zone. T. J. G. Francis, I. T. Porter and R. C. Lilwa11

The Transmission Path at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Computed Characteristics of Seismic Surface Waves for Anisotropic Models of Oceanic Structure. S. Kirkwood

SESSION SII

Chairman: Dr. M. H. Worthington

52 Seismic Wave Propagation in Anisotropic Media: I. Computations. S. Crampin s3 Seismic Wave Propagation in Anisotropic Media: 11. Observations. S. Crampin

S8 A New Approach to Surface Wave Dispersion. N. J. Kerry and B. L. N. Kennett s7 The Structure of Seismic Scattei-ed Waves. J. A. Hudson and J. R. Heritage s1 Scattering at the 650 km Boundary. B. J. BarZey s11 Is P Velocity an Indicator of Q,? P. D? Marshall U.K.G.A. 1977 261 SESSION SIII

Instrumentation and Networks

Chairman: Professor T. Murphy

S14 A Seismic Network in Ireland. A. W. B. Jacob, T. Murphy and G. WaZZace Downloaded from S15 CWF - A Seismic Station in the Midlands. P. K. H. Maguire

513 An Experiment with a U.K. Seismological Data Centre. F. H. Grover http://gji.oxfordjournals.org/ s16 Development of Miniature Wide-Band Force-Balance Seismometers. M. J. Usher

S17 Recent Developments in Portable Seismograph Equipment. P. L. Willmore

SESSION SIV

Seismic Risk at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

Chairman: Mr. A. Douglas

521 Microzoning in Space and Time. P. L. WiZZmore

S 19 Seismicity and Associated Risk in the United Kingdom. P. W. Burton

S18 Induced Seismicity in the United Kingdom. C. W. A. Bmitt s20 Earthquake Parameters from Extreme Value Statistics. C. MakropouZos and P. W. Burton

Regional Studies s22 Seismicity of the South Sandwich Islands Region. C. P. Brett

524 Teleseismic Delay Times, Bouguer Anomalies and Inferred Thickness of the African Lithosphere. J. D. Fai rhead

SESSION SV Chairman: Dr. T. J. G. Francis

528 Teleseismic Delw Tims for Underground Nuclear Explosions to Seismograph Stations in Britain. A. S. White and J. D. Fairhead 26 2 U.K.G.A. 1977 s26 Resonances in Microseismic Noise Spectra. D. T. Meldnun

S25 Determinations of Q for Direct Paths from the Urals to the U.K. R. W. Hurley

527 A Surface Wave Study of the Structure of the North Sea and Scandinavia. G. W. Stuart

S23 Lateral Variations of P Wave Velocity Structure Within the Eurasian Region P. C. England and M. H. Worthington Downloaded from http://gji.oxfordjournals.org/ at Dept Applied Mathematics & Theoretical Physics on September 15, 2013

4 Abstracts

Abstracts of papers accepted for presentation at the working sessions of the Assembly are presented below. They are grouped under the seven section headings defined in the preface. Reference numbers are prefixed by an initial letter, A, F, G, L, M, P or S defining the section. Subgroups within the larger sections have been defined and are labelled. Within each subgroup, abstracts are presented in alphabetical order of the name of the first author. U.K.G.A. 1977 263 ted to major tectonic changes. In spite GENERAL (INVITED) LECTURES of these increased benefits to the geologist, the physics of the reversal I1 Qechanism is still not well understood. PLANETARY Al24OSPHERES AND THE EMERGING ?'he detailed behaviour of the magnetic PERSPECTIVE field during a polarity transition is described as well as the more recently G. E. Hunt, Meteorological Office, observed phenomenon of excursions of the Bracknell, Berkshire field. Physical and mechanical modelsof the geodynamo are examined in some detail

There is considerable interest at this in so far as they may affect reversals. Downloaded from time in determining the mechanisms and The statistical sequence of geomagnetic feedback processes associated with clim- reversals is also discussed. atic change of the Earth's atmosphere. We do not know whether man's activities 13 may have any effect or whether external effects such as solar activity can modi- A GEOPHYSICIST'S APPROACH TO THE MOON fy the climate. But the Earth's weather AND PLANETS http://gji.oxfordjournals.org/ and climate are complicated by the effects of oceans, continents and mour- S.K.Runcorn, Institute of Lunar and tains. Consequently, it is no longer Planetary Sciences, School of Physics, possible nor desirable to consider the The University, Newcastle upon Tyne. Earth's atmosphere in isolation from other planetary atmospheres. The geophysicist, geochemist and There are now four planets, Earth, Mars, planets as bodies to test the theories Venus and Jupiter that have been examin- developed over the last two centuries to ed at close range by spacecraft in addi- explain the global properties of the tion to the studies performed by Earth Earth. Indeed an essential part of the at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 based instrmnts and they reveal a con- scientific method in geophysics and siderable diversity in atmospheric geology as in othe sciences must be to phenomena. In this lecture we review test the theories outside the field for our current understanding of planetary which they have been developed. atmospheres and discuss the observations that are still necessary to resolve the Perhaps the two most profound and outstanding meteorological problems, for difficult theories of geophysics example Jupiter's Great Red Spot and developed in the last generation are the climatic change on Mars, the super rota- dynamo theory of the generation of the tion of the upper atmosphere of Venus geomagnetic field due to Elsasser and and the structure and composition of the Bullard and the convection theory of Titanian atmosphere. In this wa~we continental drift and plate tectonics. treat the planetary atmospheres of the Much remains unsolved in both theories, solar system as natural laboratories to but the new data being obtained by space test our understanding of atmospheric missions and renewed astronomical phenomena present on the Earth in exten- observations, both visual and radio, is ded surroundings in order to provide a giving new impetus to theory. Can the greater insight into atmospheric system present magnetic fields of Mars, in general. Jupiter, Saturn, Mercury and possibly Venus give us any insight into the 12 dynamo process. Does the ancient magnetic field of the Moon inferred REVERSALS OF THE EARTH'S MAGNETIC FIELD from the remanent magnetization of the Apollo rocks and its decrease with time J.A. Jacobs. Department of Geodesy and help? Why do all the terrestrial Geophysics, University of Cambridge. planets and the Moon possess non- hydrostatic low harmonic terms in their This review summarizes the progress in figures? Does this imply convection OUT knowledge of reversals of the Earth'r- and if so why does the Moon, Mercury and magnetic field since Bullard's Bakerian Mars show no sign of continental drift Lecture to the Royal Society in 1967. although like the Earth hemispherical Reversals have played a major role inthe asymmetry. Is Venus the other planet changed outlook in geological thinking with moving plates? through the development of the conceptof plate tectonics. The mean frequency of reversals has also shown marked changes in the past and these may well be rela- 26 4 U.K.G.A. 1977 ta MARINE MAGNETIC ANOMALIES

F.J. Vine School of Environmental Sciences, University of East Anglia Initial interpretations of marine magnetic anomalies concentrated on defining plausible limits for the intensity of magnetisation and geometry of the Downloaded from causative bodies in the crust. With the realisation that the remanent component of magnetisation is dominant and that many of these anomalies could be explained by a combination of sea floor spreading and reversals of the Earth's magnetic http://gji.oxfordjournals.org/ field, interest shifted to deducing the evolution of the ocean basins and the times of magnetic reversals during the past 200 m.y.. Such studies reveal that virtually all deep sea floor has been formed by a spreading process with the possible exception of that beneath certain magnetically 'quiet' areas adjacent to passive continental margins. Because of the at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 dominance of remanent magnetisation it has also been possible to deduce palaeolati tudes of formation for older oceanic areas by analysis of the linear anomalies developed over them or the isolated anomalies associated with uniformly magnetised sea- mounts. More recently there has been a return to consideration of the vertical extent and geometry of magnetisation contrasts in the crust. Measurements on material from ophio- lites and drilled samples from layer , 2 indicate that a greater thickness of crust is involved than has commonly been assumed. Detailed studies of the way in which the crust is formed, and the phase-shifting of the anomalies produced as a result of a change in latitude and/or orientation both suggest that the boundaries between normally and reversely magnetised crust are sloping rather than vertical but at very different angles at different depths. U. K. G.A. 1977 265 APPLIED GEOPHYSICS IN- A3 CLUDING GLACIOLOGY 3-D DATA COLLECTION AND DISPLAY

A1 M. J .G . Cox and W. R. Cotton, Geophysical IN SITU SEISMIC MEASUREMENTS OF CRACK Service International ,: Bedford. ANISOTROPY During the last few years several techniques D. Bamford, Department of Geophysics, University of Edinburgh have been introduced into the geophysical K. Nunn, Department of Geological Sci- industry to collect and process seismic data in Downloaded from ences, University of Birmingham 3-dimensions. One of these techniques which utilizes almost equal sampling on the earth's The physical properties of rocks, espec- surface in both the x and y directions over the ially their seismic velocity, are con- complete prospect will be discussed. The trolled to a great extent by cracks and quantity of data collected and processed in fractures. There are many reasons why http://gji.oxfordjournals.org/ such cracks and fractures may have a this manner, over a given prospect, is an order preferred orientation which should then of magnitude greater than that with convent- result in a significant velocity aniso- ional techniques. Several ways which can tropy. We have applied interpretation provide the geophysicist with a total inter- techniques developed for the study of pretive view of his prospect, not biased by any- anisotropy in the crust and upper mantle one's personal judgement, will be presented. to the in situ measurement of possible Two methods utilizing conventional vertical velocity anisotropy of fractured Carbon- cross sections and one method where the seismic iferous Limestone in Northwest England, using conventional refraction equipment data is displayed as horizontal cross sections and a weight-drop source. Compressional will be shown on data from two prospects. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 wave velocity measurements indicate that velocity anisotropy of 10-20% is present with directions of maximum and minimum A4 velocities that can be directly related A DEEP RESISTIVITY SOUNDING AT ROOKHOPE to the mapped orientations of joints and CO. DURHAM fractures. It seems that velocity anisotropy measurelnents have considerable G.M. Habberjam and C. Thanassoulas potential for the assessment of in situ Department of Earth Sciences, University crack and fracture properties. of Lezds An account is given of the technique used to conduct a deep resistivity A2 sounding (up to electrode spacings of THE USE OF GEOPHYSICAL METHODS IN LOCA- 5 km) at Rookhope. Effectively the TING BURIED VALLEYS IN N.E. ENGLAND sounding was crossed and the method of deriving the potential curve to obtain J.D. Cornwell, E.M. Andrew, Miss C. resistivities in conventional Johnson and M.K. Lee, Applied Geophysics Schlumberger terms is described. A Unit, Institute of Geological Sciences measure of the orientational variation of the sounding results is also given. Channels formed during the period of the An interpretation of the final sounding last glaciation in N.E. England were curve is discussed in relation to the frequently not re-occupied when the nearby Rookhope borehole. river system was restored and exist as drift-filled valleys in a bedrock made up of Middle and Upper Carboniferous A5 sediments. Although the existence of IN-SITU ELECTRICAL AND ACOUSTIC MEASURE- the valleys has been proved in places MENTS - AN AID To RAPID GEOTECHNICAL by boreLoles, their form and continuity MAPPING ON THE SEA-FU)OR can be checked efficiently by geophysical methods aimed at determining the P.D. Jackson and R. Elaria Institute of death to bedrock. With examples from Geological Sciences, Exhibition Road, the Tyne and Dement valleys, the use London of gravity, seismic and resistivity methods and the intenretation of the Electrical resistivity and sound speed results are described. measurements have been made on the sea- floor using two geophysical probes which 266 U.P.G.A. 1977 are both designed to produce minimal A7 disturbance. 'Ihese measurements have been related to porosity using empirical MARINE GEOPHYSICAL SURVEYING IN correlation curves produced on the basis ENGINEERING STUDIES OF COASTAL U)NES of laboratory analyses. The resistivity probe employs automatic current control- D.M. McCann hgineering Geology Unit, lers to focus current into the seabed. Institute of Geological Sciences, The acoustic probe has two transmitters London and four receivers which are forced into R.A. Floyd Marine Geophysics Unit, soft sediments. ?he maximum depth of Institute of Geological Sciences, investigation varies linearly with the Edinburgh Downloaded from size of each probe and at present is in the range 0.5 - 1.0 m. Good agreement The application of various marine geo- has been found between values of poros- physical techniques to engineering stud- ity inferred from 'acoustic and resistiv- ies in coastal and estuarine environ- ity measurements, made in the Forties ments is considered. In the estuary of Field, and measurements made on cores the River Crouch (South Essex) a continuous seismic profiling survey revealed taken nearby. Also, it has been possib- http://gji.oxfordjournals.org/ le to map changes in sediment type in the presence of a deep buried Pleisto- the Irish Sea using the resistivity cene channel somewhat misaligned with probe, the in-situ porosity being contr- the course of the present day estuary. olled largely by the size of the sedi- This informatior. was produced for the ment. preliminary assessment of possible major highway routes across the estuary to the airport on Maplin Sands. In the Lyme A6 Regishest Bay area in Dorset an apprai- sal of the engineering characteristics TRANSFORMATION OF MAGNETIC INTO PSEUDO- of the near-shore environment was carri- GRAVITY ANOMALIES USING AN INTERACTIVE ed out in connection with coastal engin- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 GRAPHICS TERMINAL eering studies in this area. Seabed morphology was examined using an echo- C .HcCann ,Dept . of Geology,University of sounder and sideways looking sonar in Reading conjunction with sampling of the sea- floor sediments and rocks. In the Wash, The lfpseudo-gravityff anomaly of a body continuous seismic profiling surveys of uniform density and uniform magnetis- were carried out to determine the thick- ation may be computed from the Fourier ness of superficial sediments above the transform of the total magnetic field bedrock in an engineering feasibility anomaly via the magnetostatic and gravi- study into water storage. ty potentials.Generally the direction of magnetiaation of the body is not known, but is simply determined as that which A8 gives a one-signed pseudo-gravity anoma- A COMPARISON OF I.P. TRANSIENT SHAPES 1y.An interactive BASIC computer program OVER DISSEMINATED AND MASSIVE SULPHIDE is given for carrying out this procedure SHEETS IN THE LOWER PILLOW LAVAS OF The Fourier transform of the magnetic CYPRUS anomaly is input from a file,followed by a sequence of assured directions of mag- G. Maliotis, Hellenic Mini-ng Co.,Cyprus netiaation graphics terminal. from the M.A. Khan Department of Geology, The each direction the pseudo-gravity lor University, Leicester anomaly is computed and plotted on the acreen for the user assess terminal to A number of Time-Domain I.P. traverses when the anomaly becomes one-signed.App- were carried out across 2 parallel lications of the method to magnetic ano- mineralised sheets in the Lower Pillow malime over Dartroor and the Nalverns Lavas, near Mitsero, Cyprus with Huntec are given.Other fields of application of Mark 111 equipment using the pole-dipole the interactive graphics terminal in array. In one sheet the mineralisation geophysical research and teaching are was disseminated (2%S), and in the other demonstrated. it was massive (30% s). At the n = 2 separation, the transients were recorded at a number of points to give the complete shape of the curves and a number of features compared. The normal- ised time integrals were anomalous over the two sheets but they were not siqnif- U.K.G.A. 1977 267 icantly different, the highest values underground experiments. In the latter being observed over the disseminated case, explosive sources have been used sheet. Both sheets were also associated and the recording system was specially with high electromagnetic components of designed for use in an underground the decay curve. The chargeability values environment. The coal seams examined obtained over the disseminated body were to date are sufficiently homogeneous to considerably higher. The chargeability/ enable numerical holographic techniques resistivity ratio was also of value in to be used in data processing. The discriminating between massive ore configuration of scatterers or sources disseminated mineralisation and barren can be deduced by compressing the sig- rock. The values of P2and P3for the two nals in time and space, and then con- Downloaded from bodies were also compared (P,'. and P3 structing the maps interactively on a being defined by P2 = M1 - M3 and P3 = mini-computer. These methods will be discussed more fully in the talk. M2

M2 - M4 , where M1 to Mq are the amplitud- ~10 http://gji.oxfordjournals.org/ M3 A SHALLOW LAND SbISMIC REFLECTION SYSTH'l USING A es of the decay curve at the 4 points, 55, 130, 280 and 580 millisecs respectively). For the massive ore, P was inversely E.G. hebb and K.R. Nunn related to M but for the disseminated ore, Department of ~~~l~~i~~lsciences P was independent of M. University of Birmingham

A9 The development is described of

an experimental shallow seismic at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 HOLOGRAPHIC MAPPING OF COAL SEM USING reflection system for the depth CHANNEL WAVES range 10-60m. The system uses an electromagnetic vibrator as a I.M. Mason, Department of Electronics source and a digital averager for and Electrical Engineering, University stacking and digitisation of College London records prior to recording on magnetic tape. Field techniques D.J. Buchanan, National Coal Board, and processing techniques so far Mining Research and Development Estab- tried are described. Processing li shment includes deconvolution for pulse compression and velocity It is important, for both economic and filtering. The system has been safety reasons, to be able to predict field tested on several sites in the layout of the strata ahead of advan- the U. I... cing coal faces. A number of different physical methods have been proposed but, to obtain the required resolution and A1 1 longterm prediction, it appears that JOINT MODELLING OF GRAVITY AND MAGNETIC underground seismology at the coal face ANOMALIES USING NON-LINEAR OPTIMISATION must be practised. It has been shown that the acoustic impedance contrast of G.K. Westbrook Department of Geological coal compared with the surrounding Sciences, University of Durham. strata results in a channelling of seismic waves within the coal seam. A technique is presented in which struc- This means that if a seismic source is tures producing gravity anomalies and placed within a seam then a considerable magnetic anomalies are modelled simul- proportion of the energy is restricted taneously to produce an optimal fit of to the seam, thereby increasing the the calculated gravity and magnetic ano- probability of detecting reflected waves malies to the observed anomalies. To from any in-seam discontinuity such as a achieve this a function embodying the geological fault or old water-filled squares of the residuals of the gravity workings. One disadvantage, however, is and magnetic anomalies is minimised us- that the waves are dispersive and this ing iterative techniques such as the must be taken into account in the subse- Simplex method of Nelder and Mead, and quent data processing. the Davidon variable matrix algorithm. It is particularly effective when only We have conducted both laboratory and parts of any structure produce a magn- 26 a U.K.G.A. 1977 etic anomaly, and when various bounds A14 and constraints are placed on the model. RADAR TECHNIQUES IN GLACIOLOGY AND OTEER Examples of the technique applied to FIELDS - A REVIEW theoretical models and real cases are discussed. D T Meldrum, Scott Polar Research Insti- tute, University of Cambridge A1 2 Radar sounding of ice and snow has become A BOREHOLE CONTROLLED SOURCE INDUCTION established as a major fool in the inves- PROCEDURE FOR THE DETERMINATION

OF tigation of sub-ice geology, ice dynami- Downloaded from ELECTRICAL CONDUCTIVITY STRUCTURE cs and ice physics; and is being further developed to encompass applications in M.H. Worthington Department of Geology sea ice studies and in the sounding of and Mineralogy, Parks Road, Oxford. ice-free areas. A review is given of A.R. Kuckes Department of Physics, Uni- the techniques currently in use, their versity of Cornell, U.S.A. applications and limitations, and future

developments are discussed with reference http://gji.oxfordjournals.org/ Electrical conductivity values have to possibly more general geophysical been obtained for structure away from studies. the immediate vicinity of a borehole. This is achieved by using a horizontal loop induction source on the surface A1 5 and borehole horizontal and vertical magnetometers and gradiometers. Sig- THE RADIO FREQUENCY BI-PEFRINGENCE OF nals from the borehole receivers and POLAR ICE SHEETS a reference from the source are D supplied to a lock-in amplifier and N Hargreaves, Scott Polar Research amplitude and phase variations of the Institute, University of Cambridge at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 magnetic field with depth are determined. Conductivity estimates are Radio-echo sounding of polar ice sheets achieved by numerical modelling has shown that they are bi-refringent at assuming a plane layered structure. radio frequencies. The optical bi-ref- Information on lateral variations of ringence of ice is well established, and structure is also obtained. a discussion is given of the expected level of electrical anisotropy of a single ice crystal at radio frequencies. A1 3 Polar ice sheets are polycrystalline, SURFACE STRAIN RATE MEASUFENENTS ON SEA- with preferred orientations of the ice ICE AND GLACIERS. crystals determined by the strain field of the ice sheet. A theoretical treat- D.J. Goodman, Physics and Chemistry of ment is derived which may be used to ob- Solids Group, Cavendish Laboratory, tain the effective bulk dielectric tensor University of Cambridge. of polycrystalline ice. A comparison is then made between the observed and expec- Results of a three year programme tQ ted levels of radio frequency bi-refrin- develop the use of geophysical wire gence. strainmeters to measure surface strain rates on glaciers and sea ice will be presented. Improvements in the technique will be outlined in the light of field trials carried out in Greenland, the Barnes Ice Cap, Baffin Island, and sea ice in Labrador (the details of which will be published elsewhere). A new instrument, which uses a 1 m Invar bar as a length standad, will be described. It is shown that the technique can either detect the directions and magnitudes of the principal strain rate axes on the surface of a glacier if these are greater than strain per day or the directions and magnitudes of strains produces by the action of sea waves on sea ice. Future applications are outlined. U.K.G.A. 1977 269 MAGNETOH YDRODYNAMICS the atmosphere the effect of such drag may be apparent at great heights. AND METEOROLOGY F1 F3 MAGNETOHYDRODYNAMIC WAVE ENERGY FLUX GENERATION OF MAGNETIC FIELDS BY FLUID MOTIONS OF GLOBAL SCALE J.A. Adam, Department of Applied Mathematics, University of St. Andrews David Gubbins, Department of Geodesy & Geophysics, University of Cambridge. Results are presented concerning the Downloaded from stability of certain magnet oatmospheric There are many examples of fluid motions systems (in which the restoring forces that give kinematic dynamos in an infin- of buoyancy, compressibilityandmagnetic ite medium, but very few cases of dyna- fields are important) in the presence mos in an electrical conductor of boun- of shear. The basic linearised equa- ded extent. This curious observation is tions enable a convenient description to investigated by numerical calculation. http://gji.oxfordjournals.org/ be made of the behaviour of the net up- Two significant effects are revealed. ward energy flux in such a system. From An insulating boundary is found to cause a detailed consideration of the energy a current sheet to form near it and this flux function a numbe? of results are inhibits magnetic field generation. Also established, including the extension of the ratio of poloidal to toroidal corn- the well-known semicircle theorem to ponent of fluid flow must lie in a shear along a horizontal magnetic field certain range for dynamo action to occur, in a stratified compressible atmosphere. because otherwise the diffusive effects This places an upper bound on the range of the separate components dominate the of t,he complex phase velocity of un- regeneration mechanism which requires a stable modes. It is also shown that combination of both. These two effects at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 purely convective modes (Re(w) = 0) do help account for some of the difficult- not in general exist. A sufficient ies encountered in constructing kine- condition is given for stability, which matic dynamo models, and are relevant is not necessarily limited to the case to the problem of generation of magnetic of convectively stable atmospheres, and field by thermal convection in a rotat- this is compared with those derived on ing system. the basis of the energy method. The behaviour of the energy flux function F4 in convectively stable regions is also discussed. THE OBSERVED FLUX OF POTENTIAL VORTICITY IN THE STRATOSPHERE F2 R.S. Harwood Department of Meteorology, THE SPECTRUM OF LEE WAVES IN STRATIFIED University of Edinburgh FLOWS Because it is possible to obtain the F.H. Berkshire, Department of Mathe- poleward flux of momentum from a matics, Imperial College, London knowledge of the fluxes of heat and potential vorticity, it is important Linear lee wave theorf nas demonstrated in constructing 2-dimensional models how significant stationary gravity waves, of the atmosphere to know to what produced by the flow of a density - extent the flux of potential vorticity stratified fluid over an obstacle, can can be parameterised. This paper appear in the form of a discrete spectrum presents some observations of poten- of modes with real wavenumber and with tial vorticity fluxes in the mid- amplitude decaying with height. Here it stratosphere and seeks to relate is indicated how the continuous spectrum them to the zonal mean distribution. of wavenumbers which give internal waves In particular it is shown that there at all heights may often be assessed in is not always a simple down-gradient terms of complex 'modes' which have de- transport anticipated by several two- caying amplitude in the downstream dir- dimensional models. ection. For a given obstacle these waves max dominate the real modes - if the latter are present -.and may produce an important contribution to the drag produced by the obstacle on the flow. In 2 70 U.K.G.A. 1977

F5 ture variation around a circle concentric with the walls of the annulus. THE TRANSPORT OF OZONE IN A TIME- The time-averaged azimuthal spectra thus DEPENDENT, TWO-DIMENSIONAL MODEL obtained show that in the regular regime, where the flow is dominated by a single ___-R.S. Harwood" and J.A. Pyle, Department Fourier mode of wavenumber M (say), sig- of Atmospheric Physics, Oxford nificant "ener@y" is found not only in University the harmonics, which describe the jet stream structure of the flow, but also A two-dimensional, time dependent in the side-band modes of wavenumber M numerical model of the atmosphere has -+ 1, which describe the observed azimu- Downloaded from been used to investigate the ozone thal modulations in the amplitude and/or budget. The photochemistry includes phase of the wave. At the high-wave- catalytic destruction of ozone by the number end of those spectra for which oxides of hydrogen and nitrogen with the an inertial sub-range can be resolved, source and sink terms linearized about the "spectral energy" follows a "wave- the equilibrium values. The behaviour length cubed" law. The time-dependent

the modelled ozone is quite satis- http://gji.oxfordjournals.org/ of' behaviour of the phases of the side- factory especially in low and mid- bands and the main baroclinic mode is latitudes. Many of the observed details such that a special frame of reference have been reproduced includinq hemi- spneric asymmetries of the total ozone can be found in which the instrinsic frequencies of the modes are equal. amounts. Photochemical production in These results can be interpreted with the model takes place in the mid strato- the aid of simple wave-interaction the- sphere in low latitudes with destruction ory, which suggests that the side-bands in the hi& latitudes of both hemi- interact strongly with baroclinically- spheres. The mean motion fluxes are the stable long waves, but in such a way

most important transport term in equa- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 that in equilibrium the net transfer torial latitudes. Polewards the eddies into the long waves is small. become relatively more important. In middle and high latitudes there is near cancellation between mean and eddy flux F7 divergences. The hemispheric asymmetry ON DETACHED SHEAR LAYERS WESTERN in the total ozone amount results in AND BOUNDARY CURRENTS IN A ROTATING HOMO- part from the high latitude mean circu- GENEOUS LIQUID lation driven by the eddy fluxes of angular momentum. Tropospheric pro- L.X. Hocking, Department of Applied cesses also are responsible for some Mathematics, University College London differences between the hemispheres. R. Hide, Geophysical Fluid Dynamics Attention is drawn to the difficulty of Laboratory, Meterological Office, describing the vertical transoorts in a Bracknell, Berks. one-dimensional model. This paper reports a combined experi- * Now at Department of Meteorology, mental and theoretical study of slow University of Edinburgh. motions produced mechanically in a rapidly rotating homogeneous liquid by the F6 differential rotation of the rigid walls of the container when the side-wall is a THhRMflL CONVECTION IN A ROTATING FLUID circular cylinder of radius b', one of SUBJECT TO A HORIZONTAL TEMPERATURE the two plane end-walls is inclined at GRADIENT: SPATIAL AND TEMPORAL CHARAC- an angle Il/2 - a to the axis of the cyl- TERISTICS OF FULLY DEVELOPED BAROCLINIC inder (which is also the axis of basic WAVES rotation with angular speed 0) and the other end wall is perpendicular to the R. Hide, P. J. Mason and R. A. Plumb, rotation axis and is split at a distance Geophysical Fluid Dynamics Laboratory, -a from the axis so that the inner part Meterological Office, Bracknell, of the end wall can be rotated with Be rks hire relative angular speed R. The, invest:- ation thus extends to cases when a f 0 Lktailee studies of the azimuthal struc- and a f b' extensive previous studies of ture of fully developed waves in a diff- detached shear layers in systems having erentially-heated rotating fluid annulus a = 0 and a f b' and of western boundary have been carried out with the aid of currents in systems having ci = 0 and inst rurnent ati on canable of providing a = b' (sliced - cylinder). A full frequent determinations of the temuera- account of the experiments, which cover- U.K. G. A. 1977 271 ed a wide range of Rossby number lCl and wave modes, two of which have a Ekman number E f v/Qa? (where v is the bounda.ry-layer character , the coefficient of kinematical vi s cos ity) third being a diffusion mode which will be deferred until a numerical study penetrates well into the core. The of the non-linear governing equations przsence of the bumps can lead to has been completed. The experiments led an increase in the tangential to the analytical study of the linear stress exerted by the core on the case when 161 = 0 discussed in the pre- mantle and so to an increase in sent paper. Thus study shows how the the rate of transfer of angular general flow pattern changes as a in- momentum from core to mantle. Est- creases, revealing three flow regimes imates of these effects will be Downloaded from typified by the limiting cases tan a << given ir, terms of the mean bump En, EY << tan a << E4 and tan a >> amplitude. E" . It also provides some information on non-linear effects, including the magnitude of It( at which linear theory F10 should break down in each flow regime PROGNOSIS OF OZONOLYTIC rOLLUTION http://gji.oxfordjournals.org/ and the relative importance of non- linear effects in different parts of the R.S. Scorer, Dept. of Mathematics, flow. Imperial College. Predictions of effects of NO and C1 F8 on stratospheric O3 using lDXmodels are misleading for aircraft exhaust and A STUDY OF THE STRATIFICATICN IN THE photochemically released C1. Dilution EARTH'S OVl'ER CORE mechanics and secondary photochemical and dynamical effects are omitted and T.G. Masters. Department of Geodesy and influence of natural levels under- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Geophysics, University of Cambridge. estimated. The prospects of obtaining an adequately parameterised 3D model The inversion theory of Backus and are negligible and we have to learn Gilbert is applied to the determination to live with ignorance. There are good of the stratification in the outer core. reasons for ignoring the scares raised Various measures of the stratification by the 1D model, whose predictions have been considered, the most satis- can never be tested. Machinery of factory, for numerical purposes, being many governments is too unsophisti- Bullen's rl which has been determined cated to handle this situation. using seismic data. In view of recent results, the effect of dissipation on F11 the inversion of modal data is investigated with particular emphasis on the NON-LINEAR BAROCLINIC DISTURBANCES TO anelasticity of the inner core. Impli- MID-LATITUDE ZONAL FLOWS cations of the results for the thermal and chemical state of the outer core are A.J. Simmons and B.J. Hoskins Depart- discussed. ment of Geophysics, University of Reading

F9 A series of numerical simulations of HYDROMAGNETIC EFFECTS NEAR A BUMPY atmospheric behaviour has been made CORE-MANTLE INTERFACE using as idealized initial conditions zonal jets given small-amplitude per- H.K. Moffatt Department of Mathe- turbations of normal-mode form. Dis- matics, University of Bristol. turbances subsequently grow by baroclinic instability, and display frontal Flow over bumps at the core-mantle formation and occlusion in agreement interface in the presence of a with both simpler theoretical models and predominantly toroidal magnetic synoptic experience. As baroclinic field leads to magnetic field per- growth ceases they become decoupled in turbations which are correlated the vertical, and decay barotropically, (with a phase-shift in longitude) strengthening the upper-level zonal flow. with the gravitational perturba- Eddy heat and momentum fluxes averaged tions caused by the same bumps over the whole life cycle of disturbances (Moffatt & Dillon 1976, F'hys-Earth differ significantly from those suggested Planet. Inter., 13, 67-78). The by linear stability analysis, and exhibit flow is characterised.by three much more variation with zonal wavenumber 272 U.K.G.A. 1977 then with the flow profile. The dominant F14 eddy transfers are in good agreement with atmospheric stat istics . ASPECTS OF GEOPHYSICAL 'IWRBULENCE .T.D. Woods Institut fcr Meereskunde an F12 der Universitht Kiel

CONVECTION IN RAPIDLY ROTATING FLUID The motion on all scales from milli- SPHERES metres to megametres in the atmosphere and ocean appears to be turbulent. The A.M. Soward Department of Applied

aim of this paper will be to examine Downloaded from Mathematics, University of Newcastle some of the statistical properties of upon Tyne this turbulence, taking into account the effects of stratification 'large of instability for a self- The onset Richardson number), rotation (low Ross- gravitating Y internally heated, fluid. by number) and the Earth's curvature sphere of radius r at large Taylor 0. (p effect). A preliminary attempt is number, T Y is investigated. According made to derive the form of the climato- http://gji.oxfordjournals.org/ to approximate linear theory it is well logical distribution of turbulent kin- known that convection sets in first as etic energy in the four Fourier dimens- overstability and that the ensuing ions /i.e. meridional, zonal and vertic- notion corresponds to the Eastward pro- al wavenumbers and frequency) from /a) pagation of Rossby waves, which have a observations and 'b) classical turbul- short wave length of order T-g6r 0' ence nypotheses concerning the cascade These waves are concentrated close to a of energy through the spectrum. In order cylindrical surface, SY coaxial with the to achieve this it is necessary to int- diameter of the sphere parallel to the roduce assumptions concerning the rel- angular velocity. The above theory is ationship between the local properties at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 revised and new results are obtained for of the flow and the mean statistics, the particular case, in which the and concerning the definition of freq- Rayleigh number, RY exceeds its critical uency. value, R 3 by an amoudt of order T-*R , the linegr theory predicts that conditions for convection are favourable in a layer of width T-G8rC) about the surface, S. Here according to non-linear theory, Rossby waves propagate steadily within distinct sublayers of width Y 9 T"kr 0 which, in general drift slowly across the Tm1bB-convection layer.

F13 INTERNAL GRAVITY WAVES IN A SHEAR FLOW

S.A. Thorpe, Institute of Oceano- graphic Sciences, Godalming

The presence of a current which varies with depth in the ocean (or a model atmosphere) modifies the structure and speeds of possible internal gravity waves. We describe a non-linear, normal mode, analysis with numerical results being obtained for a fluid with a single (not necessarily narrow ) ther moc line at which the shear is concentrated. These conditions are easily produced in the laboratory, and experimental results are presented which demonstrate, in particular , the breaking of internal waves (in a cine film). U. K. G. A. 1977 273 can their strength and radial distance. GEOMAGNETISM The field at any point on the earth's General surface is then calculated by skng the effect of each dipole over even G1 intervals of time. The synthetic curves so obtained are compared with curves DOES THE GEOMAGNETIC FIELD HAVE A derived from cores of Holocene sediments. SIGNIFICANT MONOPOLE COMPONENT ? The effect of varying the different parameters will he shown and the char D.R. Barraclough. Geomagnetism Unit, acteristics of simulated geomagnetic Institute of Geological Sciences. excursions will be described. Downloaded from

The zero degree and order term (go)0 of a spherical harmonic model of the geomag- G4 netic field could, if significantly THE 'IN) SIGNIFICANCE OF THE CORRELAT- different from zero, be interpreted as arising from monopolar sources. Exten- ION BETWEEN THE EARTH'S GRAVITATIONAL

sive data sets for 3 epochs have been AND MAGNETIC FIELDS http://gji.oxfordjournals.org/ analysed so as to include the g: term, whose significance is discussed. The F.J. Lowes Department of Geophysics and Planetary Physics, University of time changes of the 'monopole' coefficient over a period of 30 years have Newcastle upon Tyne. also been studied using a homogeneous argued that the most relevant series of observatory data. It is radius at which to perform the correlation is that of the core-mantle inter- G2 face, and that the physically most relevant quantities are the gravitat- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 A DEFINITIVE MODEL OF THE GEOMAGNETIC ional potential 'which reflects the FIELD FOR EPOCH 1975 'bumps') and the magnetic vertical intensity ii.e. the flux leaving the D.R. Barraclough, J.M. Harwood, B.R. core). The maximum correlation is then Leaton and S.R.C. Malin. Geomagnetism only 0.583, with a probability of this Unit, Institute of Geological Sciences. occurring by chance of 28%, compared with the usually quoted values of 0.837 and A spherical harmonic model of the main 2.4% for the magnetic potential at the geomagnetic field and its secular varia- Earth's surface. tion has been derived, to degree and order 8, using all available data from the period 1955 to 1975. This definit- G5 ive model is compared with the original A LAYMAN LOOKS AT DYNAMO THEORY International Geomagnetic Reference Field (IGRF 1465). The new model is F.J. Lowes Department of Geophysics and extrapolated down to the core - mantle Planetary Physics, University of interface and the significance of the Newcastle upon Tyne. extrapolated coeffici-ents is discussed. Various phys i cal features associated It is now well established that dynimo with the model are also investigated. action will occur if the fluid motion in the core is 'sufficiently' vigor- G3 ous and 'sufficiently' asymmetric, and it is not unreasonable that sufficient SYNTHETIC PLOTS OBTAINED FROM AN OSCIL- power is available from heat sources in LATING ALLDREDGE-HURWITZ RADIAL DIPOLE the core. But as yet dvnamo theory MI DEL provides only very weak constraints on the necessary core size/fluid velocity/ K.M. Creer and T.E. Hogg, Department of speed of rotation, cannot explain the Geophysics, University of Edinburgh relative magnitude of the dipole and non-dipole fields or why the dipole Attempts have been made to simulate long magnitude remains so constant over geol- period secular variations using an osci- ogical time, and is not able to predict llating eccentric radial dipole model. the reversal spectrum. This model allows eight radial dipoles as positioned by Alldredge and Hurwitz (1964) to oscillate as a sine function. The aeriod and uhase of the oscillations can be varied for each dipole, as 274 U.K.G.A. 1977 G50 Sounding investigations can be reduced A GEOMAGNETIC TEST OF MAXWELL'S to maps of the internal fields EQUATIONS produced by regional current flow at selected azimuths, by predicting the response from inter-station transfer R.L. Wilson, C.R. Johnson, A.G. functions. The internal field maps MacCormack and D.R. Barraclough. Dep- can be replaced by equivalent currents artment of Geophysics, University of in a thin sheet at some selected depth. Liverpool. In the wavenumber domain, the current system is obtained by the use of a

Einstein's unified field theory predicts Downloaded from downward continuation filter. We use that, for a sufficiently large-scale this technique to generate internal experiment, deviations from Maxwell's current maps from the results of an equations should become apparent. In array study of the Kenya Rift Valley. particular, a toroidal field, and a poloidal field with a curl, both become possible even in non-conducting regions G8 like the earth's atmosphere. We have http://gji.oxfordjournals.org/ analyzed the geomagnetic field for such LOCAL CONDUCTIVITY EFFECTS ON THE phenomena. If they exist, they lie in MAGNETIC FIELDS DUE TO SEA TIDES fields of .order 10 gamma or less, for the case of the earth. A. H. Hart, Department of Physics, University of Exeter.

Induction Measurements of the 12.42 lunar variation in the North-South (H) and G6 vertical (Z) components of the geo- EFFECT OF CONDUCTIVITY ANOMALIES IN magnetic field at a coastal site at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 DEVON ON MICROPULSATIONS. (Sidmouth), and a site 10 km inland (Exeter) have been made using two C. C. F. Adcock, A. Me Hart, rubidium vapour magnetometers in a C. D. Honebon and W. G. V. Rosser. gradiometer configuration. For the vertical component, the difference The ratios of the North-South (H) between the sites is one third of the components of the magnetic fields of value at Exeter. For H, the difference micropulsations of period 20 to 150 s is about the same as the total variation at stations in the vicinity of Exeter at Sidmouth. Such differences are to the values at Sidmouth is approx- attributed primarily to electric imately 1.4. This difference must be currents flowing in the land, and are due to electric current flowing beneath thus subject to local conductivity some of the stations. The vertical (Z) anomalies. components show a complicated variation between stations. For example, Z reverses direction between Exeter and G9 Bickleigh Castle, which is 10 km North FIRST ORDER SOLUTIONS OF OCEANIC of Exeter. At Sidmouth Z is complicated INDUCT1ON PROBLEMS by the English Channel. The probable causes of these differences are (1) R.C.Hewson-Browne, Department of Applied diversion of current by the Dartmoor Mathematics and Computing Science, The granite, (2) the Crediton Trough, a University, Sheffield S10 2TN small rift valley running East-West P. C. Kendall, Department of Mathematics just North of Exeter (3) the English University of Keele, Staffs ST5 5BG Channel ~ A model ocean is considered on a globe G7 with a perfectly conducting, smaller, THE REPRESENTATION OF INTERNAL FIELDS concentric globe beneath. This model BY EQUIVALENT CURRENTS IN THIN SHEETS: is immersed in an oscillating external APPLICATION TO GDS ARRAY STUDIES IN e.m. field. We show how to calculate KENYA the magnetic flux passing beneath the ocean, to the first order, for varia- R.J.Banks and D.Beamish Department tions of period L l?h (say). Analytic of Environmental Sciences, University solutions can be readily obtained for of Lancaster simple geometries such as the well known spherical cap. These first order solu- The results of Geomagnetic Deep tions are satisfactory when compared U.K.G.A. 1977 2 75 with “exact” spherical harmmic solu- G12 tions. The method can be used to A METHOD FOR TKE PROCESSING OF MAGNETO- provide boundary conditions for strip TELLURIC DATA problems which simulate local edge effect problems. Alan G. Jones, Department of Geophysics, University of Edinburgh G10 In the analysis of recent magnetote1l.u- THE ELECTRICAL CONDUCTIVITY OF THE MOON: ric observations from the southern up- AN APPLICATION OF INVERSE THEORY lands of Scotland, more high frequency Downloaded from information has been extracted than is E.A. Hobbs, Department of Geophysics, possible using standard techniques. University of Edinburgh The method involves dividing the data segment into sub-sets of the required Inverse theory of Backus and Gilbert is length and computing freqcency domain used to analyse the day-side electro- parameters for each sub-set. This re- magnetic response of the moon to magnet- presents a frequency domain version of http://gji.oxfordjournals.org/ ic fluctuations in the solar wind. The the sonogram analysis of Swift (1967) data consist of two transfer functions, and Hermance (1973) but, in execution, both tangential to the lunar surface, it results in much less effort and com- and in the theoretical development, the puter time. Also new forms of coher- required Fre chet derivatives correspond- ence functions are defined - these are ing to these transfer functions are more practical than the standard forms determined. The ensuing calculations when constant Q or logarithmic windows show that the data are sufficiently good are applied to the data. Examples of to determine the conductivity down to a the applications of these techniques to depth of about 600 km. The results are

the Scottish M-T data are presented. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 very encouraging and it is suggested that as newer theories of lunar induction are developed to consistently G13 interpret the day- and night-side measurements, they should be used in the A COMMENT ON METHODS OF SOLUTICIN OF above enlightened manner. OCEANIC INDUCTTON PROBLEMS

P.C.Kendal1, Department of Mathematics, G11 University of Keele, Staffs ST5 5BG THE INTERPRETATION OF GEOMAGNETIC VARI- ATION OBSERVATIONS IN SCOTLAND USING THE Recently, Hobbs and Brignall claim to HYPOTHETICAL EVENT TECHNIQUE have significantly modified the method of shifting the spectrum. They imply V.R.S. Hutton, J. Sik, A.G. Jones and that this has somehow rendered the D. Rooney, Department of Geophysics, oceanic induction problem more conver- University of Edinburgh gent. In fact, the convergence rate is the same as for the method of shifting Since 1973, a continuing programme of the spectrum; and this was to be expect- geomagnetic induction studies has been ed, as the method is in fact the same. undertaken in Scotland. For time vari- The convergence of all methods is poor ations of period > 10 min, it has com- for micropulsation periods, but it is prised the simultaneous operation of 20 reasonable for the daily variations. 3-component magnetometers in each of N. Nevertheless, calculations have been and S. Scotland and subsequent single carried out for high frequencies, and station and small array geomagnetic re- the iterations do in fact converge in a cording; for shorter period phenomena, practical sense. T > 10 s, observations have also been made at 13 locations traversing the G14 southern uplands. In this paper, the results of the various studies are syn- LUNAR GEOMAGNETIC TIDES AND THE OCEAN thesised using the hypothetical event DYNAMO technique proposed by Bailey et al. (1974). The interpretation which D. M. Schlapp, Department of Physics, follows is compared with other methods University of Exeter. of presentation of geomagnetic induction data. For S. Scotland, the manner Some preliminary results of the lunar in which it complements the M-T analy- tide analysis of long series of sis (Jones and Hutton, 1977) is discussed 276 U. K. G. A. 1977 geomagnetic data are presented. The the other an oxidizing atmosphere. M2 tide at midnight is found to show This was in cooperation with Peter a seasonal variation at certain Reynolds of the Butser Ancient stations. After consideration of Farm Project. Significant disto- possible complications due to the 01 rtions of remanent direction tide, it is concluded that the source were observed and their implica- of the night-time geomagnetic tide tion for archaeointensity meas- must be at least partly external in urements are discussed. origin as well as oceanic. Laboratory experiments designed Palaeomagnetism to produce the weathering effe- Downloaded from cts found in magnetic samples have also been undertaken. G15 The specimens were placed for per- CHEMICAL DEMAGNETISATION STUDIES OF THE iods up to 3 months in a dig- ALDERNEY SANDSTONE, CHANNEL ISLANDS estion bomb with distilled water undgr pressure at approximately http://gji.oxfordjournals.org/ Jacqueline A. Banner and Ernest A. 120 c. Hailwood, Oceanography Department, University of Southampton G17 An investigation into the use of acid POLARITY SEQUENCE OF MULL leaching for demagnetisation (with particular reference to the Alderney P.Dagley and A.E.Mussett, Sub-depart- Sandstone) is presented. The effect of ment of Geophysics, University of the following conditions on the leaching Liverpool process has been studied:- orientation, at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 field-free space. acid strength, On present evidence the magnetic pol- temperature, rock type. In these arity sequence is: all plateau lavas are experiments acid leaching resulted in reversely magnetised, as are the earl- greater intensity and direction changes iest members of the first centre. The than A.F. demagnetisation, but a stable rest of the central complex is normal Y direction of magnetisation could not be magnetised but dykes which post-date t isolated for all samples. A period of are reverse. 200 hours appeared to be critical, since after this time there was a significant This sequence and the significance of decrease in the rate of decay of NRM the Fishnish dykes are discussed. the total amount of iron leached out approached 100% available iron, and stable directions of remanence were Gfa recovered in some cases. The remanent PALAEOZOIC PALAEOMAGNETIC RESULTS FROM magnetisation measured is used to define C.I. a palaeopole position which corresponds JERSEY, closely with a recently published Duff, Departmnt of Earth Sciences, Devonian pole for Normandy and Brittany B.A. University of Lee& (van der Voo, 1976) and with the mean Devonian pole position for North West Palaeomagnetic results have been obtain- Europe. ed from a range of lower Palaeozoic rocks from Jersey, relating to the late G16 Precambrian /Cambrian Cadomian 0 ro geny . Systematic variations of stable NRV in EXPERIMENTS RELATING TO FUNDAMENT- diorites stoped by granite are attribu- AL PROBLEMS IN ARCHAEOMAGNETIC ted to blocking of PTRM during cauldron FIELD STRENGTH MEASUREMENTS subsidence and rotation. Three late- orogenic granites (c. 570-490 m.y. ), M. F. Barbetti, K. P. Flude and unconformably overlying red shales J. M. W. Fox. Research Laboratory (probably Cambrian), and lamprophyre for Archaeology, Oxford University dykes, all yield pole positions at variance with the lower Palaeozoic To investigate the distorting fie- polar wander curve for Great Britain, ld produced within pottery samples and are interyeted in terms of raoid clay rings were fired in reconstr- Cambrian aolar wandering relative to ucted archaeological kilns, one Jersey and adjacent regions. Of three having a reducing atmosphere and grouns of palaeomagnetic directions’ in U.K.G.A. 1977 277 crosscutting dolerite dykes, two are Existing palaeomagnetic data from consistent with Ordovician/Silurian and the four ciycum-Atlantic contin- Carboniferous data from Britain. ents (Africa, South America, North America and W. Europe) will be used to explore the validity G19 of different Mesozoic predrift A NEW METHOD FOR DETERMINING THE I4AGNI- reconstructions and possible TUDE OF THE EARTH'S MAGNETIC FIELD USING geomagnetic field configurations. SUN-DRIED BRICKS In particular an attempt will be made to investigate the extent to K.P. Games, Sub-deoartment of Geophysics which an offset dipole geomagnetic Downloaded from Live rpool University field model might apply to Mesozoic times. Palaeomagnetic pole A new method of determining the magni- positions for the above continents tude of the Earth's magnetic field have been recalculated on the basis using sun-dried bricks is outlined, and of a dipole source, offset r km Some of the magnetic prooerties of these northwards along the geographic http://gji.oxfordjournals.org/ bricks are described. The method has axis, and the dispersion of poles been tested on a modern adobe brick from from the four continents examined Lima and was found to be accurate and as a function of r, for different regeatable. Results of palaeomagnitude continental reconstructions. In from Peruvian bricks are presented and the case of the South Atlantic it compared with palaeomagnitudes obtained will be demonstrated that available from Ceramics. Some prelimiqary results Mesozoic palaeomagnetic data are from Egyptian bricks are also given. more consistent with a centred dipole than an offset dipole field source, but that currently accepted G20 reconstructions of the pre-drift at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 GEOMAGNETIC ARCHAEOMAGNITUDE tEASURE- positions of South America and MENTS FROX PERUVIAN CERAMICS Africa in Mesozoic times may require substantial modification. N.M. Gun, Sub-department of Geoohysics, Liverpool University G22

The application of Shaw's Method to QUATERNARY PALAEOMAGNETIC RESULTS FROM archaeological ceramics is briefly DSDP SITES 379 AND 380 IN THE BLACK'SEA explained, with reference to its advantages in certain resnects over thermal E. A. Hailwood, Department of demagnetisation methods. The two major Oceanography, University of Southampton obstacles of multiple remanence and N. Hamilton, Department of Geology, thermal instability in the specimens University of Southampton are mentioned, together with an account of their relative prevalence among Preliminary palaeomagnetic studies on a different types of pottery shards. closely-spaced series of samples from a For the fraction of specimens passing 6 metre section of rhythmically banded all tests, the field magnitude results sediment at a depth of 800 metres sub- are presented on a diagram plotted bottom at DSDP site 380A, have revealed against time. A provisional assessment the presence of a stable reversed of the data is offered, including com- component of magnetisation overprinted parison of the general trend observed by a less-stable normal component. A here with results from other sources, cyclical change in inclination of the and some comment on the reality of stable reversed component may be oossibly short-term fluctuations in interpreted as a record of palaeo- field magnitude. secular variation of the geomagnetic field during the Matuyama epoch. G21 Additional palaeomagnetic information from more-widely spaced samples at Site MESOZOIC GEOMAGNETIC FIELD 380A and 379 provide constraints on the CONFIGURATION AND CIRCUM-ATLANTIC possible location of the Brunhes- CONTINENTAL RECONSTRUCTIONS Matuyama epoch boundary within the Black Sea sedimentary sequence, and E. A. Hailwood, Department of demonstrate the potential value of Oceanography, University of magnetic polarity stratigraphy for Southampton. dating DSDP sediment cores. 278 U. K. G.A. 1977 G23 tion cover one cycle and correlate well between lakes. Variations in the decli- MAGNETIC FABRIC OF MARINE SEDI- nation record show one and a half to two MENTS cycles in this tim interval and correlation between lakes is more difficult. N. Hamilton Department of Intensity and susceptibility measure- Geology, University of mnts correlate well in each lake. Southampton These records are compared with those from Lake Windermere and some problems Variability in magnetic grain arising from attempts at correlation

fabric style of clastic marine will be discussed. Downloaded from sediments reflects the conditions of sediment accumulation and subsequent deformation. Detailed G26 studies of the magnetic fabric of CONTINENTAL DRIFT BETWEEN THE PALAEOZOIC Tyrrhenian Sea sediments of Holo- AND MESOZOIC cene age are used to demonstrate http://gji.oxfordjournals.org/ the usefulness of this magnetic E.Irving Earth Physics Branch, Energy property for sedimentological Mines and Resources, Ottawa, Canada investigations. Palaeomagnetic result for the Lower G24 Jurassic (175 m.y.) fit Pangaea very well. Upper-Carbonif erous to Mid-Triassic (300- LATE NEOGENE MAGNETIC STRATI- 215 Ma) do not and systemmatic polar dis- GRAPHY EV~DENCEFROM DSDP crepancies of up to 15" occur. Maps have MEDITERRANEAN SEA SITES 372, 374 been prepared that account for these des- AND 376 crepancies by rearranging the continents without the creation of intervening at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 N. Hamilton Department of oceans. Their main features are the oc- Geology, University of currence of about 3000 lan of dextral Southampt on shear along the Hercynian-Appalachian E.A. Hailwood Department of foldbelt, and about IOOOkm of shear (XM) Oceanography, University of between Eurasia and North America between Southampton the middle Permian and Late Triassic (250-200 Ma). The maps are based on a new Detailed biozonat ion of sedimen- global synthesis of the palaeomagnetic tary sequences recovered during data which, for the first time, have been deep sea drilling on Leg 42A in reduced to a uniform time basis. It is the Mediterranean Sea provide a suggested that the absence of ocean rid- unique .opportunity to correlate ges may account for the world-wide re- observed magnetic polarity se- gression at the beginning of the Mesozoic quences with an established which may in turn have caused whole-sale geomagnetic time scale. Impli- extinctions. The shear XM may provide a cations of such tentative corre- useful kinematic framework within which lations, their palaeomagnetic to discuss the origin of oil-bearing rift reliability and possible ambig- structures of the North Sea. uities are discussed. This provisional magnetic chronology is used in defining the duration G27 of the 'Messinian' evaporitic PALAEOMAGNETIC INVESTIGATIONS OF phase within the Mediterranean. TERTIARY VOLCANIC ACTIVlTY IN LOWER SILESIA, POLAND G25 M. Jelenska, M. Kadzialko-Hofmokl, SECULAR VARIATIONS OBTAINED FROt4 FRENCH J. Kruczyk, Institute of Geophysics of AND SWISS LAKES 0-6000 YEARS B.P. Polish Academy of Sciences, Warsaw

T.E. Hogg, Department of Geophysics, The Lower Silesian basaltic rocks form University of Edinburgh the eastern boundary zone of the central European Tertiary volcanic province. Results from 6 m 'Mackereth' cores from They occur in two groups, along the Lakes Geneva, Bourget, Morat and Annecy Odra Fault and along the Sudetic Bound- covering the period 0-6000 years B.P. ary Fault. The magnetic fraction of are presented. Variations in inclina- the investigated rocks comprises titano- U.K.G.A. 1977 2 79 magnetites containing from 0% to 80% Attempts to make stratigraphic correl- approximately of ulvospinel, oxidized to ations using magnetic polarity run into different degrees. In some exposures a number of problems: i) why are there oxidation processes have taken place at no normally magnetised lavas correspond- high temperatures while in other expos- ing to the normal dykes? ii) why is ures low temperature oxidation to a there no correlation between dyke pol- non-stoichiometric phase is evident. In arity and geochemical or other group- some samples ferri-ilmenite occurs in ings, and iii) why is there a predomin- addition to spinel phases. The results ance of reverse magnetisation even of our investigations of the magnetic though activity spanned several periods? fraction combined together with the re- Downloaded from sults of our investigations of the stab- These questions and possible solutions ility of the NRM and of the scatter of are discussed. its directions lead to the conclusion that at several exposures the primary NRM has been presemed. Since the pola- G30 rities and pole positions obtained from the various exposures differ, the vol- PALAEOMAGNETIC STUDIES OF VARVED CLAYS http://gji.oxfordjournals.org/ canic~studied are not synchronous. The FROM POLAND palaeomagnetic data are related K-Ar ages carried out on the same material. Elzbieta Niedziolka, Institute of Geo- All of these results have served to for- physics, Polish AcadenIy of Sciences, mulate an hypothesis concerning the Warsaw evolution of volcanic activity in the region of the Lower Silesian faults. The magnetic properties of varved clays deposited at Mochty and Plecewice in the Warsaw Basin during the Middle Polish

G28 Glaciation about 150,000 years ago are at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 described. Thennomagnetic and mineral- SPELEOMAGNETISM - THE PALEOMAGNETIC ogical studies identify magnetite as the RECORD CARRIED BY CAVE SEDIMENTS carrier of remanence.

J.S. Kopper, Anthropology Department, Long Island University G31

This paper will describe the paleomagne- PRELIMINARY RESULTS OF A PALAEOMAGNETIC tic records obtained from a number of INVESTIGATION OF MESEDIMENTS FROM cave sites as they relate to the condi- POLAND tions of deposit. Both archaeological and non-archaeological cave sediments E. Niedziolka and P. Tucholka, Institute are represented and it is found that of Geophysics, Polish AcadenIy of Sciences, this new sampling context has distinct Warsaw, Poland advantages and unique disadvantages as T.E. Hogg, Department of Geophysics, compared with conventional sampling University of Edinburgh situations. Among the advantages of certain deposits are minimal post de- Fifty-nine six-metre cores were collected posi.tiona1 disturbance, constant ambi- from ten lakes in northern Poland during ent temperatures and humidity, aopar- the summer of 1976 using a Mackereth-type antly simple diagenetic sediment pneumatic corer. The NRM of cores from changes, observable sediment geometry some of the lakes is stable and well and often archaeological time indica- defined patterns of inclination and de- tors. . Variable sedimentation rates and clination changes are obtained. There is hiatuses in deposition are two recog- generally good agreement between cores nized problems and are compounded by from the same lake, correlations being the general absence of materials for confirmed by matching variations in the absolute dating. NRM intensity and low-field susceptibility. The stability and origin of the remanence will also be discussed. G29 PROBLEMS OF POLARITY IN THE BRITISH TERTIARY IGNEOUS PROVINCE

A.E. Muasett, Sub-department of Geo- physics, University of Liverpool 280 U.K.C.A. 1977 G32 ments, continental distributions, and geomagnetic field behaviour in much SOME USES OF INDUCED MAGNETIC MEASURE- as detail as possible. Results are out- MENTS IN LAKE SEDIMENTS lined from the Gardar Igneous Province of Greenland covering lava successions F. Oldfield, J.A. Dearing, T.A. Rummerj, (>131O m.y. ), dyke swarms (1245 m.y.) Department of Geography, University of related to the Mackenzie episode within Live rpool the Laurentian Shield, and 1175-1160 R. Thompson, Department of Geophysics, m.y. dyke swarms, University of Edinburgh giant dykes and plutons. In Britain results cover Magnetic susceptibility, IN4 and related thermal demagnetisation studies of strat- Downloaded from igraphic sections through the Torridonian measurements provide rapid means of core Sandstones, dyke swarms within the and sample correlation and can be used Lewissian foreland, N.W. Scotland, and to improve the basis on which alloch- northern outcrops of the Late Precambrian thonous input to lakes can be both quan- tified and characterized with regard to Unriconian rocks of the Welsh Borderlands. Results from gabbrmanorthosite complexes

type and source. The speed of the tech- http://gji.oxfordjournals.org/ and slowly-cooled basement terrains with- niques now available and the environmen- in the Baltic Shield are also noted. tally diagnostic nature of some of the induced magnetic parameters measured make magnetic studies a useful comple- G35 ment to stratigraphic, palaeobotanical and chemical analyses. Magnetic arop- GEOMAGNETIC FIELD FLUCTUATIONS RECORDED erties can also be used as a basis for IN SEDIMENT FROM LAKE TRIKHONIS, GREECE studying substrate-soil-sediment link- ages and transformations within lakes P.W. Readman, Department of Geophysics, and their drainage basins. Results have University of Edinburgh at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 been obtained from a wide range of tem- perate and tropical lakes. Palae omagne t i c measurements on s i x-metre cores spanning the time period 1000-6000 B.P. from Lake Trikhonis in Greece will G33 be presented. There is very good agreement between cores from different places POST-DEPOSITIONAL REMANENT MAGNETIZATION in the lake. The NRM intensity is be- IN SEDIMENTS FROM THE GREEK LAKES tween 10 and 100 pG with median destructive fields of -300 Oe. A well defined S. Papamarinopoulos, Department of Geo- peak in the NRM intensity and the low- physics, University of Edinburgh field susceptibility indicates the position of an ash horizon which is probably The effect of time and applied field from the Santorini eruption -3500 B.P. strength on post-depositional magnetiza- Although an oscillatory pattern of in- tion processes have been investigated clination changes exist, the present using sediments from the Greek Lakes. dating controls preclude concluding The stability characteristics of the whether or not they are periodic. PDRM acquired are similar to those of the NRM. An attempt to recomr the palaeointensity record along a complete G36 core is described and the results com- TEMPERATURE DEMAGNETIZATION INVESTI- pared with those obtained using the ARM LOW GATIONS INTO THE CARRIERS OF method. STABLE NATURAL REIQNENT MAGNETIZATION IN SOME FINNISH LAKE SEDIMENTS G34 J.C. Stober and R. Thompson, Department PALAEOMAGNETIC STUDIES OF THE PRG of Geophysics, University of Edinburgh CAMBRIAN: BRITAIN, SOUTH GREENLAND AND SCANDINAVIA Finnish, Holocene sediments from deep lakes carry a stable remanent magnet- J.D.A.Piper and J.E.F.Stearn Sub-depart- ization. Geochemical, thermomagnetic ment of Geophysics, University of Liver- and coercivity studies have been carried pool out in order to delimit the origin of magnetization. The NRM, ARM, IRM and Comprehensive sampling of these regions initial susceptibility of samples from is continuing with the aims of defining selected Finnish lake sediment cores Precambrian apparent polar wander move- are compared. The carriers of reman- U.K.C.A. 1977 ence, in organic rich sedimnt, cannot Rock Magnetism be determined by thermal demagnetization because of chemical change nor by alter- G39 nating field demagnetization because of the low variation in coercivity spectra. AN EXPERIMENTAL STUDY OF Ti DIFFUSION IN Harever, cooling of the remanences in MAGNETITE zero magnetic field has yielded information about the carriers. The origin of R. Freer, Z. Hauptman, Department of the magnetization is discussed. Geophysics and Planetary Physics, Uni- versity of Newcastle upon Tyne Downloaded from G37 Diffusion coefficients of Ti4+ in single A STATISTICAL APPROACH TO CURVE FITTING crystal magnetite have been determined AND CORRELATION OF SERIAL DATA DISTRI- over the temperature range 600 .- 13Oo0C BUTED ON A SPHERF, at constant po2. Interdiffusion experiments were performed on couples of Feg04 R. Thompson, Department of Geophysics, (single crystal) - Fe2.8 Ti0.2 O4 (pow- University of Edinburgh der) under defined atmospheres. Pro- http://gji.oxfordjournals.org/ R.M. Clark, Department of Mathematics, files of Ti and Fe were obtained by Monash University electron probe microanalyses, and D calculated by the Boltzmann-Matano meth- The theory of cross-validation smoothing od. Diffusion coefficients and activa- developed by Clark has been applied to tion energy for the process are reported serial palaeomagnetic directions. The and compared with previous indirect esti- method objectively produces a best fit- mates. Data obtained are useful for ting curve and confidence limits. estimating rates of oxidation, and trans- Palaeomagnetic data, from Lake Winder- formation of titanomagnetites to other mere (11000 - 0 BP), have been used as phases. Combined with data for Fe diff- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 a master curve for dating other sedimen- usion a better understanding of kinetics tary sequences. Analyses of this data of the system will be gained. are shown. Statistically significant oscillations are found and interpreted in terms of variations in the geomaaet- G40 ic field. These oscillations are objec- li h?ETIiCD FOR P?FSL!ATI31; OF XECK-TXTaI- tively distinguished from minor fluctu- I'bl SDTGLE CRYSTALS ations which cannot be justified by the data and cannot be assumed to have been Z.Eauptman Department of Geophysics and produced by changes in direction of the Flnnetary Physics, University of Few- ancient field. castle upon Tyne.

A novel xethod preparation of single G38 for crystals fro? the melt has been develop- ARCHAECMAGNETIC INTENSITY MEASURE- ,?d tc provide ;naterials for research in- MENTS USING A SQUID MAGNETOMETER to thermoremznent properties of titsnc- mgnetites. In order tc apm-oach mre D. Walton Physics Department, clcss1;y the comaosition c-f natural tit'i- McMaster University. cc,-nagnctites it, is noczasary to spthe- M. J. Aitken Research Laboratory size not cnl.:. -,me titancmgxetitcs hut for Archaeology, Oxford University a 1 so their substituted e ;;uiva 1en t s, i .e ., containin;: mimr elements (:;g,AI, Cr, The high sensitivity of a SQUID ..). ATI alaost comnlet,c lac]. of enui- magnetometer permits the use of libriuin data for those more complex sy- such a small sample that the stems is a seri0u.s difficclt:. for ccn- heating time in the Thellier -7mtic:iill ,grcning nethods from melts. technique can be shortened to ?'he grcwhg apparatus described mak.es it less than a minute. This makes pcssible to assess the solid-melt-foz it practical to heat the sample in equilibria in situ orior to growing,and -situ within the magnetometer and- thus enables a good rate of succcss in in turn this makes it possible to nrcdncing single phase crystals. Compo- modifv the Thellier techniaue in sitional zonixg in the "as-grow'' crys- 282 U.K.G.A. 1977 G41 the optical limit but could be resolved by the electron microscope. The hyste- OmGX; %TSACITY vfi1L"3s L.iD C:?LE TBPE- resisloops of the mosthighly RITLjS ?OR TilE; LiIDDLh' TrlF&B~..SOF THE samplesare typicalof dispersed mono- CIBIC TITA;YOMAGIIITITE S.S. SBIES domain magnetite rods. Z .!Iauptmn, A.L.Campbel1 Department of Geophysics and Planetary Physics, Uni- G43 versity of 2ewcastle upon Tyne. ROTATIONAL HYSTLRGIS IN HAUIATITY

Previously, an unusually steep slcpe of Downloaded from W.H. Owens Department of Geological T, as a function of f02 had been observed in the titanomagnetite FelkTi, (TM Sciencea, University of Birmingham 60) which was padually oxidized at high Adopting a model for fine-grained haema- temperature (1573 K) over its single phase stability field and quenched. The stu- tite, in which the magnetization is re- dy has now been extended over the range stricted to the basal plane, within which there is single easy direction, TM4O - TM60. The steepness of the Tc-foz a http://gji.oxfordjournals.org/ plot increases even more towards the iron torque curves have been calculated for a richer member. Within the same compositi- range of basal plane inclinations, easy directions and field strengths. These onal region, i.e., TM40-!M60 the S.S. series shows a marked departure from Vegar- show that the model provides a simple ds rule: when Tc for stoichiometric ti- explanation for the well-known persist- tanomagnetites are plotted against compo- ence of rotational hysteresis to very sitional parameter x an almost straight high fields. It also predicts that an- line results for O(x40.4 and 0.64xL isotropy of rotational hysteresis should occur for distributions of hematite 1 .C with slope A Tc/d x N 700 K. The tvo grains showing preferred orientation. straight parts appear to be offset by 35- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 A0 K over the 0.4 < x 0.6 range. Hystere- This haa been verified by torque-meter ses of similar magritude for Tc deterini- measurements on Cambrian slates from ned from susceptibility - termeratwe North Wales. plots have been occasionally observed. At present, investigation are being carri- ' G44 ed out in a search for uossible order-dis- order transitions or similar phase trans- B"AGmTIc ANIsoTRon OF Duomm formation phenomena. AGGREGATES

G42 Y1.H. Owens Department of Geological Sciences, University of Birmingham LABORATORY OF MAGHEMITIZAT1oN E.H. Rutter Department of Geology, Imp- AND DELPTERIC OXIDATION OF TITANOMAGNE- erial college, university of London TITE-INFLUENCE ON COERCIVE FORCE AND OTHER MAGNETIC PROPERTIES High-field torque-meter measurements of diamagnetic susceptibility anisotropy of J.B. O'Donovan, Department of Geophysics a suite of samples of Carrara 3rble, and Planetary Physics, University of axially shortened at 1.5-3.C 10 Pa con- Newcastle upon Tyne fining pressure and 20-5OO0C (usually 4CC°C) by amounts up to 5Wb, have been (i)Maghemitization: Twenty samples were compared with optical measurements of c- prepared by oxidizing finely ground axis preferred orientation. Given the (-0.1 urn) titanomagnetite, containing up anisotropy of calcite, quantitative com- to 0.35 Mg2+ ions per formula unit, in parison is posaible. Calcite anisotropy air at temperatures below about 35OoC. has been measured on undeformed and de- Hysteresis loops indicate the monodomain formed single crystals. It is found state with coercivity ranging from 1.5 x that optical and magnetic measurements lo5 AIM in near stoichiometric material agree only if allowance is rmde for de- to lo4 AIM in the most highly oxidized. forrmtion as well as reorientation of Rotational hysteresis parameters simi- the calcite grains. larly fall with progressive magnetization. (ii)Deutoric oxidation: Samples were prepared by oxidation of coarse ground (-10 vm) titanomsgnetite in air at temperatures up to 7OO0C. The scale of the resultant intergrowths was at or below U.K. G. A. 1977 283

G45 crystals were homogeneous and showed well defined Curie points. The crystals A MAGNETIC STUDY OF SYNmTIC lTlWJOM- were formed into spheres 1-1.5m in AGNETITE SUBSTI?UTED BY ALUMINIUM diameter and orientated for magnetic .. .. measurements. These include the temp- 0. Ozdemir Dept. of Geophysics and erature dependence of coercive force, Planetary Physics, University of determined using a vibrating sample Newcastle upon Tyne. magnetometer, equipped witb a vacuum furnace, and curves of acquisition of Sintered PolYcrYStalline specimens in thermoremanence against applied field.

the systems Fez.,,-& Alr Ti..& 0, and Downloaded from A16 Ti..,, 0, (04 s s 0.2) were prepared by a method of partial self- G48 buffering with two firings at 13OO0C. MAGNETIC INTERACTION BETWEEN IRON AND X-ray powder pictures and Curie point uLvtjspINEL determinations confirmed that the prepared samples are single phase spin- R. Veitch and A. Stephenson. Institute http://gji.oxfordjournals.org/ el s. Both Curie temperature and unit of Lunar and Planetary Sciences, cell edge decrease with increasing A1 School of physics, university of N~~- concentration. The materials were ball- castle upon me. milled to produce samples in the monodomain or pseudo-single domain size Samples of ulv'dspinel containing large range to be used for testing models for iron inclusions of various shapes have the acquisition of thermoremanent mag- been prepared. mey were then maweti- netization. zed at different temperatures and in different directions. Marked differenc-

es in the behaviour of the remanent at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 G46 magnetizations of the composite samples MAGNETIC PROPERTIES OF ULVOSPINEL were observed as they were cycled through the ulvospinel Curie point. This P.W. Readman, Department of Geophysics, is interpreted as being due to magnet- University of Edinburgh ostatic interaction between the two phases. Low temperature magnetisation curves for synthetic polycrystalline ulv6spinel will be presented. The spontaneous mom- G49 ent below 60 K is < 0.3 emu/g and at 4 K A MRQmMAGNETOMEER the magnetisation curve up to the maxi- CONTROLLED BY A MICROPROCESSOR mum field of 24 kOe is linear. Between 60-120 K a weak ferromagnetic moment is D. Wilson School of Physics, University, present with a maximum value of 1.8 emu/g Newcastle upon Tyne. at 100 K. When the sample is cooled in the presence of a high magnetic field, The present instrument, which incorpor- the thermomagnetic curve has the appear- ates a taut dual fibre suspension and ance of a N6el N-type with a 'compensa- photocell bridge detector handles tion temperature' of about 40 K. torques up to 3xlO-*N-m with a noise level of 10-'N-m. A novel feature is 647 that the torque head rotates and the electromagnet remains stationary. The MAGNETIC PROPERTIES OF TITANOMAGNETITF microprocessor is used to control the SINGLE CRYSTALS sampling interval and rotation rate, to store the data in digital form and can P. Tucker Department of Geophysics and also be used for in-situ data analysis Planetary Physics, University of Newcast- eg. calculation of areas under curves le upon Tyne. (rotational hysteresis loss). The data is available as a visual display or A suite of single crystal specimens of print out/punched paper tape. For more approximate composition Fe elaborate calculations the data tapes iiTiO. were prepared from the "el?' by 6'4 may be read into a large computer. the "micro-Bridgman" technique. The zoned "as-grown" crystals were analysed using the electron microprobe and suit- able atmosphgres chosen for after-treatment at 1300 C. After such treatment the 284 U.K.G.A. 1977 LITHOSPHERIC STUDIES L3 LONG-RANGE LISPB OBSERVATIONS Explosion Seismology The LISPB Working Group (presented by L1 D. Bamford, Department of Geophysics, THE HEBRIDEAN MARGIN SEISMIC University of Edinburgh) PROJECT OF 1975 The special effort made during the LISPB A.R. Armour and M.H.P. Bott experiment to secure good quality long range data resulted in excellent ohserv- Department of Geological Downloaded from ations to distances of kms. These Sciences, University of Durham lOC0 clearly show that the Pn phase refracted from the uppermost mantle dies out be- The Hebridean Margin Seismic yond 250 to 300 kms distance, and is re- Project focussed on an east-west placed by a sequence of later, faster line along 58ON from Rockall phases of varying horizontal persistence

Trough to the east coast of the returned from the lower lithosphere. http://gji.oxfordjournals.org/ mainland. Time term analysis After careful correction by ray-tracing for variations introduced by lateral yields Pn of 8.09 km/s and aver- crustal inhomogeneities, these phases age Pg of 6.1 km/s. time P9 can be intecreted in terms of velocity terms vary up to 0.4 seconds and contrasts in the depth range 50-100 kms correlate closely with gravity using theoretical travel-time and syn- and magnetic anomalies. Pn time thetic seismogram modelling. These re- terms average 2.7 seconds on the sults seem to confirm earlier results shelf and Outer Hebrides, 3.1 obtained in France which suggested that

seconds over the Minch, and they the lower lithosphere has a hitherto at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 unexpected fine structure. increase eastwards across Scot- land from 2.5 to 3.0 seconds. The average time term for Rockall L4 Trough at 58ON is 2.97 seconds LONG SEISMIC LINES IN THE BRISTOL representing a crustal thickness CHANNEL AREA of about 8 km beneath 3 km of sediments. M. Brooks, M. Bayerly and D.J. Llewellyn Department of Geology, University Coll- ege of Swansea

A report is given of long seismic lines S WAVES IN THE LISPB CRUSTAL PROFILES established in the Bristol Channel area during the past three years. Quarry M. Assumpcao and D. Bamford - Department blast recordings in South Wales provide of Geophysics, University of Edinburgh a network of profiles up to 45km long giving information on the local depth Many shots in the LISPB profiles produ- to Precambrian basement. Large charges ced shear waves with large amplitudes of Aquaflex explosive cord detonated in which were recorded by 3-component sta- the Bristol Channel have been recorded tions. A preliminary crustal model for along several lines from Pembrokeshire S velocities is presented for the seg- to the Mendips and in North Devon. A ments ALPHA and BETA (Loch Eriboll to maximum range of nearly 1OOkm has been Carlislel The phases best observed were . achieved. Provisional geological inter- usually Sg and SMS, but to S conver- P pretation of selected lines will be pre- sion at the Moho was also recorded. Tra- sented, and the case for a major thrust vel times of these phases give Poisson under Exmoor will be re-examined in the Ratio in the range 0.240 to for 0.255 light of the new data and of a re- the middle and upper crust, whereas sed- interpretation of the gravity gradient mentary basins seem to require values across Exmoor. greater than 0.26 and possibly as high as 0.30. Multiplication of horizontal and vertical components was used and its usefulness in determining S wave onsets is reassessed. U.K.G.A. 1977 285 L5 University of Cambridge LFWISIAN UNITS SSISMIC TRAV?L!RSE The use of controlled sources has mark- J. Hall Department of Geology, Univers- edly improved our knowledge of the ity of Glasgow seismic structure of the lithosphere. In particular the recent use of relative- A 40 lan refraction line was shot from ly closely spaced recording stations has Badcall Bay to Durness in M.I Scotland shown the existence of fine structure in across the Laxford F'ront separating var- the character of the seismic wave field. iably-retrogressed Scourian granulites Both travel time inversion and waveform (of average composition equivalent to analysis may be used to construct vel- Downloaded from intermediate igneous rocks) from re- ocity distributions but the final struct- worked acid quartzo-feldspathic meis- ure obtained will be dependent on the ses, in order to discover whether the attention structure. Improved knowledge granulites continue at shallow depth of lithospheris structure in complex areas depends on making allowances for below the acid gneissos BS predicted by lateral variation in crustal structure

gravity and magnetic models. Each of http://gji.oxfordjournals.org/ 89 vertical seismometer stations was along a profile. Topography at the used to record errivals from four shot crust mantle interface can have a signif- points. Time-distance plots of first icant effect on the recorded wavefield. zrrivals show a scatter of 0.01s about smooth curves to be interpreted by ray- tracing methods. The velocity struct- L8 ure is compared with results of other TOWARDS A MORE DETAILED SEISMIC PICTURE in-situ measurements of velocity and CF THE OCEANIC CpUST lab. measurements on hand-specimens at B.L.N. Kennett Department of Applied

variable pressure. So far, there is at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 no clear evidence of laterally-extens- Mathematics and Theoretical Physics, ive granulites under the gneisses at University of Cambridge depths less than 4 km, though some high-velocity patches are present. For many years a very simple picture of the oceanic crust divided into four uniform seismic layers has prevailed. L6 Recently however the use of greater shot OBSERVATIONS OF PS REFLECTIONS FROM densities and more sophisticated inter- THE XOHO pretation techniques is beginning to change the model of the crust. System- A.W.B.Jacob and D.C.Booth , I.G.S., atic travel time inversion and detailed Global Seismology Unit, Edinburgh. analysis of recorded wave forms using synthetic seismograms place additional In a study on the absence of PS constraints on the velocity distribution reflections in crustal record sections within the oceanic crust. Fuchs(1975) has recommended that a search for PS reflections on reoord L9 sections be carried out,since the results should give more information THIN CRUST IN THE PHILIPPINE SEA on the nature of the Moho than is available from P wave data only. h. E. Louden Department of Geodesy & Observations of a PS phase on a Geophysics, University of Cambridge section in MJ Scotland are presented here, with recommendations as to how Much of the 'Philippine Sea is signifi- the phase may be more clearly detected and observed by signal processing. cantly deeper than would be predicted by its ages and the depth vs. age curve Referenoe: Fuchs,K. J,Geophys.,&445 for the Pacific. This may imply that -462, (1975). its crust is significantly thinner than that of normal ocean basins. In July L7 1976 on the joint expedition "Indopac" between Scripps Inst. of Ocean. and ON THE INVERSION OF LONG RANGE SEISMIC the National Taiwan Univ. we shot 7 PROFILES reversed or split two- ship refraction D.L.N. Kennett Department of applied lines in the Parece Vela and West Phil- Mathematics and Theoretical Physics, ippine basins to test this possibility. 286 U.K. C.A. 1977 Tnese new results suggest that the total transition (< 2 kms) in the north to a crustal thickness may be 2 to 3 km gradational change (> 5 kms ) in the thinner than Pacific crust of a similar south . age. This is primarily due to an "oceanic" layer (v=6. 7 km/sec) only L12 3. 1 km thick as opposed to 5. 3 for km P WAVE STRUCTURE OF THE LITHOSPHERES normal oceans of tnis age. These (0 - 10 M.Y.) NORTH OF THE AZORES crustal differences when isostatically compensated can produce a large frac- L. Steinmetz, Inst. de Physique du Globe, Downloaded from tion, but not the entirety, of the depth 4 Place Jussieu - Tour 14, 75230 Paris anomalies in these basins. R.B. Whitmarsh, Inst. of Oceanographic Sciences, Wormley, Surrey, GU8 5UB V. Moreira, Servico Meteorologico L10 Nacional, Lisboa, Portugal DISPLAY AND PROCESSING OF SEISMIC WIDE

seismic refraction lines up to 400 http://gji.oxfordjournals.org/ ANGLE REFLECTION DATA FROM DISPOSABLE Four km long indicate the upper lithosphere SONOBUOYS structure of the Mid-Atlantic Ridge close to the Azores. Although energy P.R. Miles, Institute of Oceanographic propagates across the ridge axis within Sciences, Wormley, Godalming, Surrey the crust the axial region prevents propagation within the mantle. A pro- A new method for displaying disposable file along the m.y. isochron shars, sonobuoy data on a variable area 4 below a km layer, a low velocity recorder has been developed after 7.6 zone underlain by an 8.3 km s-l refrac- identifying the need to improve data

tor km depth. Higher velocities at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 display comparable with recording and at 9 interpretation techniques. Each signal found on east-west lines shot towards trace is digitised, processed and the ridge can be attributed to this re- delayed using a mini-computer capable fractor if it dips away from the ridge. of shipboard operation. The final A 9 m.y. isochron profile detected an display flattens the reflection hyper- 8.3 km s-l refractor at 30 km depth. bolae and enables improved trace We explain our data by using a velocity correlation and reflector digitisation. model based on a petrological model The method has particular application which incorporates significant hydration to interpretation of poor quality reactions. records.

L13 L11 SEISMIC REFRACTION STUDIES OF THE UPPER THE CRUSTAL STRUCTURF BENEATH NORTHERN CRUST IN THE EAST MIDLANDS BRITAIN D.N. Whitcombe Department of Geology, The LISPB Working Group (presented by University of Leicester. K. Nunn, Department of Geological Sci- ences, University of Birmingham) The paper is a report on a part of the Leicester University Charnwood Block Interpretation of data from the 1974 Project, the aims of which are to invest- LISPB experiment (Bamford w.,1976, igate the nature of Charnwood with GJFUS, 3,145) has resulted in a de- respect to the surrounding geology, and tailed seismic cross-section of the to study the deep structure by means of crust and uppermost mantle beneath Nor- earthquake data collected from an eiqht- thern Britain. The main features in station seismic array which was oper- this section are ational on Charnwood for five months. (i) a possible horizontal discontinuity Two reversed seismic lines using quarry in the Pre-Caledonian basement, between blasts as sources, were set up during the the Southern Uplands Fault and the Stub- summer of 1976. The first of these was lick Line, undertaken in collaboration with the IGS (ii)a lower crustal layer, velocity in and was between Mancetter quarry near excess of 6.7-6.8 kh/s, which appears to Nuneaton and Bardon Hill quarry to the NE shallow beneath the Southern Uplandsf in Charnwood. Twenty-two vertical seis- Midland Valley, and mometer stations were set out along the (iii)a change in the nature of the twenty-four kilometer line. Mancetter Mohorovicic discontinuity, from a sharp quarry fired an 1800 lb. shot split U.K.G.A. 1977 287 between seven 17 ms. relays. Bardon the Rift, of length 50 kms, between Lake quarry fired a 2900 lb. unrelayed shot. Baringo and the Kerio Valley. Recording Quarry blasts from The Croft and Whitwick positions were at 600 m. intervals along quarries were also recorded by 15 and 6 these lines with shot points at Lakes Geostore stations respectively. The Hannington and Baringo (2 shot points in second line was NNW from Bardon to Ball- each) for the N-S line and at Lake idon quarry near Ashborne in Derbyshire. Baringo and the River Kerio with two This was to investigate the basement intermediate points for the E-W line. ridge extending southwards from the Interpretation of the seismic data for Derbynnire Dome to Charnwood as suggest- both lines indicates an essentially two ed by the gravity data. The paper layered structure. On the N-S line, an Downloaded from discusses the results obtained from the upper layer (lavas with sediments) of Mancetter-Bardon seismic line. A time velocity 2.4 km/s rests on basement of term analysis was applied to this data, velocity 5.75 km/s. The interface is together with quarry blast data recorded fairly flat at about 1.5 km. depth but by the Charnwood array. A preliminary deepens to 3.5 km. towards Lake Baringo. interpretation shows a basement of velo- The E-W line crosses the main structural city 5.6 km/s. The line crosses a 7 km. trends and is understandably more compli- http://gji.oxfordjournals.org/ wide horst bounded by faults with throws cated. At the eastern end of this line of .5 km. at a depth of approximately the surface layer (mainly Baringo sedi- 1.5 km. The centre of this structure is ment) velocity is about 2.30 km/s and 9 kms. from Bardon Hill quarry. The this increases to 3.63 km/s at the west- position of this upfaulted block coin- ern end where lavas are dominant. The cides with the Southern extension of the basement velocity along this line is gravity high that exists to the south of lower than that along the N-S line at the Derbyshire Dome. 5.45 km/s. Gravity was also measured at each seismic recording site and together

with the gravity data already available at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 L14 and the control provided by the seismic DETAILED STUDIES OF THE UPPER OCEANIC work, an interpretation of a detailed CRUST USING A LARGE AIR GUN AND BOTIOM nature became possible. When the gravit- RECEIVERS ational field computed for the E-W seismic model is compared with the observed R.B. Whitmarsh Institute of Boug’ier Anomalies, a large positive res- Oceanographic Sciences, Wormley, idual is seen centred on 36OE. This has Surrey GU8 5UB. been interpreted in terms of a basic intrusion whose top surface varies from Over the last 5 years a number of 6 to 9 km in depth. This compares with seismic refraction profiles have been similar intrusions penetrating to within recorded by 10s pop-up bottom seismic 3 km. of the surface which have been recorders (PUBS) using a 16 1 airgun postulated further to the north and as a sound source. The gun was fired south from gravity data alone. Thus the every 1 or 2 minutes while being axial intrusion appears to be continuous towed at 4 to 5 knots. Refracted through this area although the gravity arrivals are often detectable to data alone does not show this. ranges of over 20 kms. Some examples of these airgun profiles will be presented and the upper crustal General Geophysics structures deduced from them will be L16 discussed. THE ACQUISITION AND INTERPRETATION OF A GAMMA-RAY SURVEY OVER THE LOCH DOON L15 GRANITE. KRISP 1975. SEISMIC PROFILES WITHIN THX GREGORY RIFT VALLEY, KENYA J.Cassidy, G.C.Brown and J-Hennessy. Sub-Department of Geophysics,University T.J. Wilton Department of Geology, of Liverpool. University of Leicester Field gamma-ray measurements over the In the summer of 1975, two reversed Loch Doon granite pluton,Southern Scot- refraction lines were shot within the land, show a qualitative similarity with Rift Valley in Central Kenya. One line available petrochemistry and emphasise was N-S in the middle of the Rift, about the gradational change from the tonalite 30 kms. long between Lakes Hannington margins to two distinct granite cores and Baringo. The other was E-W across within the intrusion. A technique for 288 U.K.G.A. 1977 calibrating the field spectrometer in at depth and giving the intrusion an terms of K, U and Th concentrations has overall east to west elongation. been devised using neutron activation Strong magnetic anomalies abutting the analysis of selected samples. The Bouguer anomaly low suggest that the present results considerably amplify granite has beer intruded in places radioactive element distribution maps through a magnetic horizon in the base- previously determined using only neutron ment. This was intersected by a bore- activation data. The origin of the gran- hole in 1976. ite by partial melting in the lower Geophysical models for the granite and crust or upper mantle with subsequent the host rocks are presented and their fractionation and/or roof assimilation geological significance discussed. Downloaded from will be discussed in the light of available geophysical and petrochemical data. L19 AN INTERPRETATION OF GRAVITY AND L17 MAGNETIC DATA IN THE ENGLISH GEOPHYSICAL EVIDENCE ON THE CHANNEL AROUND THE ISLE OF WIGHT STRUCTURE OF THE FAEROE-SHETLAND http://gji.oxfordjournals.org/ ESCARPMENT S E. Deegan and A Dobinson, Marine Geophysics Unit, J A Chalmers, A Dobinson, A Mould Institute of Geological Sciences and D K Smythe, Marine Geophysics Unit, Institute of Geological A gravity map of the Isle of Sciences. Wight area is interpreted in terms of structure underlying New geophysical evidence, the known surface geology. refraction and reflection seismics Magnetic results are used to gravity and magnetics, suggest, indicate the regional at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 that the Faeroe-Shetland significance of this structural Escarpment is formed by a wedge analysis. of Palaeocene lavas overlying a considerable thickness of Mesozoic sediments. The L20 implications of these results CRUSTAL DEVELOPMENT OF THE CENTRAL for the plate-tectonic history WEST GREENLAND EMBAYMENT. of area are discussed. J. W. Elder. Department of Geology, University of Manchester. L18 GEOPHYSICAL INVESTIGATION OF THE PRE- A quasi-hydrostatic model of the develop- CARBONIFEROUS BASEMENT OF THE ASKRIGG ment of an intra-con tinent rift zone is BLOCK YORKSHIRE described, based on geological and geophysical measurements of the Cretaceous- Lower J.D. Cornwell, Mrs. J.M. Allsop, M.K. Tertiary sedimentary and volcanic embayment Lee and D. Patrick, Applied Geophysics of central West Greenland. A gravity contrast Unit, Institute of Geological Sciences reaching 170 milligal across the embayment The gent1 y- dipp ing lower Carbon i f e rous is interpreted as a crustal thinning up to 80%. limestones of the Askrigg Block almost 'The model is calibrated against: seismically completely conceal the basement rocks determined terrestrial sediment thickness; which give rise to strong magnetic and thickness of early pillow breccias; height Bouguer gravity anomalies. Detailed of the lava pile; and ultimate water depth. gravity and magnetic surveys and inter- Superb field data allow a detailed investiga- pretations of the results carried out to help in the siting of two deep boreholes tion of models of this type. have revealed more details of the distribution of the basement rock types. l.21 The most likely cause of the pronounced RECENT GEOPHYSICAL STUDIES OF THE GULF Bouguer anomaly low in the centre of the OF ADEN block was thought to be a large granite intrusion whose existence was subsequent- R.W. Girdler and P. Styles, School of ly proved by the Raydale Borehole in Physics, The University, Newcastle upon 1973. A gravity survey of the area over Tyne, NE1 7RU the granite revealed a central cupola with deeper cupolas on two sides joined In 1975, a new geophysical survey was U. K. G. A. 19 77 289 made aboard the RRS SHACKLETON with the terminated under the Midlothian Coalfield specific objectives of discovering more Roslin-Vogrie Fault System. This appears about the sea floor spreading history of to have either pre-dated it or moved con- the Gulf and the evolution of young con- temporaneously, although movement continental margins. In the westernmost tinued throughout Carboniferous times. part, 16 continuous profiles of bathy- metry, total magnetic intensity and gra- Neither the conventional offset of the vity were made along N.32O, i.e. the S.U.F.S. along the Cockmuir Fault to join direction of separation of Arabia and the Lmermuir Fault, nor the Lammemuir Somalia. The profiles extend as far to Fault itself are defined gravitationally the shores as practicable, i.e. to 3 n. above the 5 gu level. Downloaded from mls off Somalia to 12 n.mls off Arabia. Analyses of the profiles reveal that the A provisional interpretation of the present active centre has been spreading regional field is made in terms of the for only a few million years and that deep structure of the Southern Uplands. there was a previous earlier phase of spreading in the Oligocene. The magnet- http://gji.oxfordjournals.org/ ic lineations are found to extend almost L24 as far as the shorelines and the signi- SECULAR VARIATION OF GRAVITY IN SCOTLAND ficance of this for the evolution of continental margins is discussed. R .G. Hipkin, Department of Geophysics, University of Edinburgh

L22 Tests with the LaCoste-Romberg gravity CALEDONIAN GRANITES: A RARE THERMAL meter G-275 show that random reading EVENT errors generate a standard deviatfon of about 0.02 pu (2 pgal) under normal J.Hennessy and G.C.Brown Sub-Department microseismic conditions, although re- at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 of Geophysics, University of Liverpool. producible systematic errors are commonly an order of magnitude larger, Knowledge of the thermal regime of due mainly to thermal and residual continental crust, and of geochemical tidal disturbances. Non-equilibrium and isotope data leads to a conceptllal temperature response gives characteris- model for the site of genesis of the tic instrumental drift of typically large granitic batholiths of the world. 0.3 gu over a 2 hour period, but can be From a consideration of both steady eliminated by calibration. Non-elastic state and dynamic heat flow and water earth tides vary rapidly near the coast diffusion models, and knowing the bulk and are the principal difficulty with properties of the end result, we can British secular gravity experiments. attempt to specify the physical proper- Preliminary analysis suggests that this ties of this source region,and to out- may be overcome statistically. If a line the form of a numerical solution 0.02 gu uncertainty can be achieved in for the problem of granite genesis. Britain, then estimates of post-glacial uplift in Scotland should generate significant relative gravity changes in a L23 2 to 10 year period, on a simple iso- A GRAVITY SURVEY OF THE SOUTH MIDLOTHIAN static hypothesis. Preliminary results COALFIELD AND SOUTHERN UPLANDS FAULT by Petersson and Kiviniemi from Fenno- SYSTEM scandia may imply regional variation of lithospheric response, with excess R.G. Hipkin, Department of Geophysics, rates of change to the west, so that University of Edinburgh British variations could be more rapid. Seven gravity stations associated with Approximately 1000 gravity observations O.S. Fundamental Bench Marks east to have been made near the S.U.F.S. east of west between Dunbar and Bowling (Glas- the Lanarkshire border. A 400 element, gow), and north to Crubenmore (Newton- three-dimensional inversion of this data more) are being measured as the basis will be presented as a model for part of of a secular gravity study. the S.U.F.S. and the Midlothian Coalfiela.

The north-westerly downthrow of the S.U.F. (s.s.) has a gravitational expression of typically 70 gu. Displacement was very largely pre-Namurian and active during Upper Old Red Sandstone times. It is 290 U. K. G.A. 1977 L25 Gravity and magnetic data collected from GEOMAGNETIC INDUCTION STUDIES IN KENYA the area of the Shap granite instrusion have been used to produce a 3-dimension- V.R.S. Hutton, D. Rooney, I.M. Brazier a1 model of the pluton. The model of and E. Mbipcm, Department of Geophysics, the detailed subsurface structure formed University of Edinburgh using the gravity data broadly resembl- ing an inverted cone was used in conjun- Magne totelluri c and magne tovariational ction with palaeomagnetic and suscept- masurements in the period range 10-1000 ibility measurement. in an attempt to seconds have been made at 12 locations locate the source of a strong local in- Downloaded from in and around the Kenya Ri.ft Valley. duced magnetic anomaly. It appears that The data have been processed in a number the granite is either vertically inhomo- of ways, including the evaluation of (a) genous, with decreasing acidity and maximum and minimum response functions hence increasing susceptibility with and (b) apparent resistivity versus depth or that stable magnetic minerals period curves and the plotting of hypo- are present at the expense of silicate

thetical event contours. For each pro- phases beneath outcrop level. The http://gji.oxfordjournals.org/ cedure, the results are qualitatively relative importance of these suggestions consistent with the existence of a good will be discussed in the context of the conductor below the Rift Valley extend- petrogenesis of this intrusion. ing into the upper mantle from shallow crustal depths. The results of this L28 study are discussed in association with those of other induction studies in the RESULTS OF GRAVITY AND MAGNETIC Great Rift Valley of Africa and of other SURVEYS IN THE FORTIES AREA OF geophysical investigations in Kenya. THE NORTH SEA

A K Rochester, Marine Geophysics at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 L26 Unit, Institute of A GEOMAGNETIC INDUCTION STUDY AT MICRO- Geological Sciences PULSATION PERIODS IN THE SOUTHERN UPLANDS OF SCOTLAND The results of marine gravity and magnetic surveys in the A.G. Jones and V.R.S. Hutton, Department Forties area of the northern of Geophysics, University of Edinburgh North Sea are interpreted and discussed in relation to deep The existence of a major electrical con- geological structure, ductivity anomaly in the region of Esk- particularly that which is dalemuir has previously been indicated by associated with Jurassic geomagnetic deep sounding studies using volcanic activity. periods greater than 12 minutes (Edwards et al.. , 1971). This has now been follow- L29 ed by magnetotelluric measurements at 13 locations along lines perpendicular and THE STRUCTURE AND ORIGIN OF KURCHATOV parallel to the strike of the proposed FRACTURE ZONE, NORTH ATLANTIC OCEAN anomaly using periods extending down to 10 seconds. The use of the magnetotell- R.C. Searle and A.S. Laughton Institute uric as well as geomagnetic deep sound- of Oceanographic Sciences, Wormley, ing techniques and the analysis of shor- Godalming GU8 5UB ter period phenomena has aided the deli- neation of the crustal conductivity stru- Kurchatov Fracture Zone (40'30") has a cture in this region. One- and two- 20 km dextral offset and appears to be dimensional interpretations of the res- at least 100 km from the nearest ults are presented and their tectonic neighbouring fracture zones. Long- implications are discussed. range side-scan sonar and other geophysical methods suggest it is being produced by oblique spreading within L27 the offset zone, rather than by a transform fault. The fracture zone GEoPHYSICAL AND PETROGENESIS walls are composed of NE-SW scarps en- OF THE SHAP GRANITE echelon..~ giving them a serrated outline in plan. A model to account for the C.A. Lockf? and G*C- Brown, Sub-depart- bathymetric reliefof the fracture ment of Geophysics, University of zone is presented and is tested Liverpool against observed gravity anomalies. U.K.G.A. 1977 291 L30 of Z is observed at stations lying on THE STRUCTURE OF KING'S TROUGH, NORTH- the ophiolitic suites running through EAST ATLANTIC, FROM SEISMIC AND GRAVITY the Grampians and is indicated to a DATA lesser extent by the sparser data in the far north. The analyses of the R.C. Searle and R.B. Whitmarsh, data will be presented with a tenta- Institute of Oceanographic Sciences, tive interpretation where possible. Wordev, Godalming, GU8 5m L32 King's Trough is a linear, NW-SE trending feature about 460 km long, situated REGIONAL GRAVITY ANOMALIES Downloaded from 500 km northeast of the Azores. It con- OVER THE EAST AFRICAN RIFT sists of a series of basins, each 50 to SYSTEM 100 km long, about 15 km wide, and trending E-W to NW-SE. These are flank- W. T. C. Sowerbutts , Department of ed by two linear ridges. Although the Geology, University of Manchester

whole structure is roughly symmetric http://gji.oxfordjournals.org/ The nature and extent of regional gra- about its axis, in detail the southwest side appears more complex, and rises vity anomalies over the section of the from shoaler sea-floor. King's Trough East African Rift system between appears to be part of an ancient plate Central Africa and midway along the boundary which joined the Mid-Atlantic Red Sea are described. The extent Ridge to the Pyrenean compression zone. of regional negative Bouguer anomalies However, the precise relative motions at allows an outer limit to be placed on the boundary are unclear, though the the area underlain by low density upper total displacements probably did not mantle. This area includes places exceed a few tens of kilometres. We present models of the deep structure of where there is little surface evidence at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 the Trough based on gravity and seismic of rifting . data, and we combine these with other geophysical data to discuss possible origins of the feature. L33 A GRAVITY MAP OF KENYA

L31 C.J. Swain and M.A. Khan Department of A GEOMAGNETIC DEEP SOUNDING STUDY IN Geology, University of Leicester NORTHERN SCOTLhND This map is based on over 9000 gravity J.M. Sik and V.R.S. Hutton, Department observations, made principally by the of Geophysics, University of Edinburgh University of Leicester in the last ten years with a La Coste Romberg gravity Scotland is a tectonically complex area meter as part of a study of the deep and this is reflected in the magnetic structure of tne African Rift. The field time variations recorded by two station interval varies from <1km in arrays of Gough-Reitzel magnetometers. the rift, to >lo km elsewhere and has These arrays were operated in 1973 and been determined by the availability of the first arrey consisted of twenty roads. Other measurements were made instruments deployed over that area of from rail cars along railway lines, Scotland lying North of the Highland from a boat along the shore of Lake Boundary Fault. Nine simultaneous Turkana, on foot, and by helicopter. events have been digitized for this Most of the station elevations were array. Various aspects have been stud- determined barometrically. Terrain ied: the magnetograms themselves ; maps corrections were carried out using a of Fourier amplitudes and phases of the newly developed programme in which local magnetic field components for each of corrections are computed by interpolation the events; transfer functions ; hori- between 1 km grid points. The Bouguer zontal field polarizations and hypo- anomaly map to be presented was obtained thetical event analyses. All the using automatic interpolation for estim- treatments reveal, superimposed on ating the values at regular grid points effects due to seas and source fields, based on Briggs' method of minimum striking variation anomalies. Some of curvature. The regional gravity field these effects may be attributed to is satisfactorily fitted by a 7th order major structures such as the Great orthogonal polynomial surface which Glen (where further work is in pro- contains a NW - SE elongated saddle in gress), but an interesting attenuation the North-east and a bowl-shaped 292 U.K.G.A. 1977 minimum in the South-west coincident specimens from the Precambrian Lewisian with the culmination of the Kenya Dome, metamorphic complex, N.V. Britain, have suggesting regional isostatic comparison. been measured in the laboratory to A spectral study of the gravity and topo- reveal the dependence of velocity on graphic data is in progress. The minerel constituents and crack closure. residual gravity map shows a number of Effective velocities and densities of features which clearly correlate with constituent minerals have been found by the visible geology. There are lows multiple-regression analysis. The associated with the light sediments in results are compared with those of In- the Kavirondo trough, and the light Situ velocity measurements, of the volcanics near Mount Kenya. An irregular 'Levisian Units Seismic Traverse', and Downloaded from high in the north-east extends for 500 km of other crustal profiles in the area. and is attributed to high density basement Further east a step anomaly of 80 mgal occurs indicating a fault with a throw of L36 several km. An intermittent gravity high ISOSTATIC COMPENSATION ON A, is present along the rift axis and a CONTINENTAL SCALE : LOCAL VERSUS number of large and prominent calderas REGIONAL MECHANISMS http://gji.oxfordjournals.org/ lay on it. Seismic refraction data suggests that the high is obscured in R.J.Banks Department of Environmental places by light sediments near the surface Sciences, University of Lancaster The indications are that the rift axis is underlain by a continuous axial intrusion. Using linear programming methods, the isostatic response function for the continental U.S.A. is shown to be L34 incompatible with any local VARIATION IN CRUSTAL STRUCTURE ALONG compensation model. A simple regional

THE LESSER ANTILLES ISLAND ARC. compensation model that treats the at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 lithosphere as a thin elastic plate G.K. Westbrook Department of Geo- overlying a liquid is investigated. logical Sciences, University of If only positive density gradients Durham. are allowed in the plate, the response of this model fits the data Gravity, magnetic, seismic refraction at the 95% confidence level, provided and reflection data show that in add- the flexural rigidity of the pl ition to individual variations betw- lies in the range 10" to N m. een islands, the gross structure of These bounds imply that at most only the Lesser Antilles arc changes sig- a thin surface layer of the nificantly along its length. The arc lithosphere can be treated as elastic. can be divided into 3 main segments. The southern part has a single line of islands with a crustal root 30 km L37 deep. The middle contains the volcanic AMPLIFICATION OF UPPER LITHOS- arc and east of it a buried ridge: PHERIC STRESSES BY UNDERLYING both have roots. The northern segment has two arcs with outside them a bath- VISCOELASTIC CREEP WITH APPLI- ymetric shelf which does not have the CATION TO CONTINENTAL SPLITTING same structure as the volcanic is- MECHANISM lands. The deformed sediment complex in front of the arc also shows corres- M.H.P. Bott and N.J. Kusznir, ponding structural changes. The poss- Department of Geological ible reasons for these variations are Sciences, University of Durham. discussed. The rheology of the lithosphere Laboratory and Theoretical Studies can be crudely modelled by an L35 upper elastic layer about 20 krn thick above a lower viscoelastic MEASUREKENTS OF LABOiUTORY SEISMIC or "Bingham" layer about 60 km VCLOCITIES Ll3'ISIh.N NETN40RPHIC 9OCKS IN thick. Finite element analysis F.M. Al-Haddad Dep:ir-Lmant of Gc,olom, applied to such a model shows Univei-nity of G1mgo.oi: that equilibrium deviatoric stresses in the elastic layer Seismic velocities in suites of had- produced by boundary stresses U. K. G.A. 1977 29 3 or gravitational body forces are examining the polarization anomalies amplified relative to a purely suggested by numerical calculations. elastic lithosphere, by a factor These anomalies are very sensitive to about equal to the ratio of even very weak anisotropy and may provide information about depth, lithospheric to elastic layer thickness, orientation, and internal thickness. The time constant is structure of any anisotropic layering. about 0.2 My for a viscosity of The implications of anisotropy in Pa s. Local variation of the upper mantle are discussed. elastic layer thickness is associated with inverse variation Downloaded from in deviatoric stress. In the elastic layer of an isostatically plateau uplift structure deviatoric stresses of over 100 MPa (1 kbar) can occur due to http://gji.oxfordjournals.org/ surface loading and compensating upthrust. Such a stress system provides a mechanism for continental spl’itting within this setting.

L38 LABORATORY MEASUREMENTS OF SEISMIC VELO-

CITIES AND ELECTRICAL RESISTIVITY OF at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 ROCKS IN UPPER CRUSTAL CONDITIONS

P.N. Cnroston, C. Evans and C. Lee, School of Environmental Sciences, Uni- versity of East Anglia

Equipment has been developed at this University for meas wing simultaneously seismic velocities and electrical conductivity of rock samples in upper crustal conditions. Confining pressure and pore water pressure can be varied up to 4 kb and temperature up to 30OoC. In this paper we outline the results and discuss the implications of measurements made on some oceanic and on some (Brit- ish) continental crust samples. Parti- cular attention will be paid to the effects of temperature on P velocity.

L39 SEISMIC WAVE PROPAGATION IN ANISOTROPIC MEDIA: I11 IMPORTANCE FOR LITHOSPHERIC STUDIES

Stuart Crampin, Institute of Geological Sciences, Edinburgh

Detailed measurements of velocity anisotropy in the upper mantle can be interpreted in petrological terms. The method is limited by the difficulty of obtaining sufficient high- quality data. A more fruitful way of investigating upper mantle anisotropic structure appears to be by 29 4 U. K. C. A. 1977 a few seconds) and directions of drift MAGNETOSPHERIC, IONO- of the various patches seen in the sky SPHERlC AND SOLAR- at any one time differed considerably, Estimates of the energy of the particles TERRESTRIAL producing a particular patch could be Aurora made from the bounce period. Electric fields perpendicular to the magnetic M1 field lines could be deduced from the ELECTRONS AND POSITIVE IONS ASSOCIATED drift velocities. The horizontal dim- WITH AN AURORAL ARC ensions of the patches at auroral

heights could also be estimated. The Downloaded from D.A. Bryant, D.S. Hall, D.R. Le-pine and nature and the scale of the magneto- R.W.N. Mason, Appleton Laboratory spheric phenomena responsible for these observations will be discussed. Measurements of electrons and positive ions of 0.5 - 25 deV obtained on 21 November 1976 during the flight from M3

Andoya in Norway of the first Skylark SUPRATHERMAL PARTICm FLUXES http://gji.oxfordjournals.org/ sounding rocket to reach an altitude of ASSOCIATED WITH AN AURORAL ARC 715 km are employed to investigate the structure of an auroral arc and the A.D. Johnstone and J.J. Sojka Department processes that lead to its formation. of Physics and Astronomy, University It is shown that the arc was formed at College London the boundary between two source plasmas - to the south, the plasma sheet with Preliminary results from suprathermal electron and ion temperatures equivalent (5eV to 500eV) particle detectors on to 2 keV and 10 keV respectively; and to the first Skylark 12 firing, SL 1422, the north, the high-latitude magnetotail on 21 Nov 1976 are presented. The at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 where the ?articles were less energetic. rocket was high enough at apogee (714 The arc appears to have been formed kms) to ensure that all but the lowest primarily by acceleration of electrons energies of particles with magneto- from the plasma sheet, though in some spheric origin could be detected before regions ions were accelerated apparently interacting with the neutral atmosphere. simultaneously. Field aligned currents Substantial fluxes of both electrons and carried by the energetic particles are protons, both upgoing and downcoming, evaluated. were detected.

M2 M4 IMAGE INTENSIFIED OBSERVATIONS OF OBSERVATIONS OF PULSATING AURORA AURORAL PULSATING PATCHES, D.J. McEwen, University of Saskatchewan, J. Crawford, P. Rothwell and Canada R. Thomas. D.A. Bryant, Appleton Laboratory, Physics Department, University Science Research Council of Southampton. Pulsating auroras have been considered An image intensifying isocon TV to be caused by very energetic elec- camera, fitted with an all sky trons. The characteristic energy of lens, and an associated time lapse video electrons causing the optical pulsations, recorder were used to make observations inferred from measurements of the inten- of auroral pulsating patches in Fair- sities of 427.8, 557.7 and 630.0 nm banks, Alaska, in January 1976 and in emissions in pulsating aurora observed AnGya, N, Norway, in November 1976, at Andoya, Norway in Nov. 1976, was much Pulsating patches occur after the break- lower than predicted. One stable event -up phase of an auroral substorm, with pulsations each 20 2 2 sec was ob- equatorward of the discrete arcs, in the served in the magnetic zenith. The pul- region of diffuse aurora, They are gen- sations were 0.5 kR above a 2 kR diffuse erally associated with VLF chorus emis- auroral background. They were apparently sion and PC1 micropulsations, The caused by 6 keV electrons wh’ile the dif- pulsating patches, seen intensified on fuse aurora resulted from electrons of the TV screen, had a variety of dis- characteristic energy 3 keV. tinctive forms which appeared to switch Accompanying TV all-sky pictures show on and off as they drifted across the the pulsations to be wave-like, appear- sky. The pulsation periods (typically ing then travelling rapidly poleward. U.K.G.A. 1977 295 These and other observations are dis- Aeronomy cussed in relation to recent particle measurements in pulsating aurora. M7 ATOMIC OXYGEN IN THE MESOSPHERE AND LOWER THERMOSPHERE M5 ENERGISEO AURORAL SUPRATHERNAL ELECTRONS P.H.G. Dickinson, Appleton Laboratory, Science Research Council 3.3.SOJKA and A.D.JOHNSTONE Department of Physics and Astronomy, University The current status of the ADpleton Lab-

College London oratory/University College of Wales, Downloaded from Aberystwyth programme of rocket borne The observation of field aligned supra- measurements of atomic oxygen will be thermal 'bursts' from several rockets reviewed. In particular the analysis flown through various forms of auroral methods used to compare the concentra- activity gives a strong indication of tions on different occasions will be the frequent presence of small sca1.e described. The results will be presen- electron energisation mechanisms. The ted and the sources of error in the http://gji.oxfordjournals.org/ electron signature of these subvisual measurements will be discussed. auroral events being the enhancement of In addition a preliminary report will be the field aligned electron flux comp- given on the (at time of writing, pro- onent. This results in the electron posed) S. Uist rocket campaign in Feb- spectrum having a bump in it at small ruary 1977. pitch angles,somewhere in the suprathermal energy range. A study of electron data obtained below 250 km indicates M8 that the mechanism is at times situated THE SCATTERING OF SUNLIGHT F'RGM NOCTI-

at these altitudes, while at others it LUCENT CLOUDS at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 extends above 700 km. The variable duration of the 'bursts' indicates that the M. Gadsden, Department of Natural mechanism is turbulent in both its spat- ?hilosophy, Aberdeen University, ial and temporal properties which prob- Aberdeen AB9 2UE ably implies that the ionospheric plasma over this region is near the limit of Determination of the sizes and shaDes of stability for this energisation mech- the particles making up noctilucent anism. clouds will probably be decided by observation of sunlight scattered from them. I consider the temperatures M6 necessary for the clouds to form and the INSTABILITY OF A FIELD-ALIGNED ELECTRON likely form of the ice crystals that BEAM will grow at these temperatures. Recent observational data support the hypo- R.J. Strangeway Blackett Laboratory, thesis that the cloud particles are not Imperial College, University of London only needle-like in shape but also show some preference in their orientation. A previously published formulation for waves on a thin field-aligned electron beam of "Top Hat" profile is summarjzed. M9 Solutions are sought between the back- SOME CHARACTERISTICS OF CIRRUS CLOUDS ground plasma hybrj d frequencjes . These OBSERVED WITH A STEERABLE LASER RADAR are radjating modes except in a band between the electron gyrofrequency and A.J. Gibson L. Thomas and plasma frequency in which ducted solu- S.K. Bhattacharyya, Appleton Laboratory tjons exist. The mjnjmum beam thick- Slough ness is dependent on the mode which varies most rapidly across the beam, Measurements with a laser radar system in and is half the wavelength of thjs mode. S.E. England have shown cirrus clouds The effect of parallel temperature on (sometimes subvisible) to be present at the beam thickness is investjgated and 10-12 km on about 50% of otherwise clear found to be small. Varjous modifi- nights. The measured backscatter and cations to the model are possible and extinction coefficients of cirrus for progress on an attempt to include per- different angles of elevation of the pendj cular temperature is reported. laser beam have been found inconsistent with models consisting of spherical or randomly-orienta ted irregular- shaped 294 U.K. G.A. 1977 particles. The results have been Philosophy, Aberdeen University, interpreted on the basis OE a model of Aberdeen AEi9 2UE. long cylindrical crystals orientated in a horizontal plane with arbitrary Observations are reviewed which indicate azimuthal angle, and show the importance that there is a component in the night- of taking into account the directional glow continuum which rises in intensity dependence of the backscatter/extinction from near 0.6~to 1.0~. It is suggested ratio in the interpretation and ex- that the source of this continuum is ploitation of laser radar data. radiative association of atomic oxygen to the ground state via the (largely repulsive) 'II state. Model calculations Downloaded from M10 indicate qualy t a t ive agreement with 1JOC 2ILUCEIIT CLOIJD I.IOVEI.E:TS observation. There is also support from laboratory measurements. Implications Alastair D Jenkins Department of IIatural for the physics of the lower thermosphere kilosophy, University of Aberdeen are discussed. http://gji.oxfordjournals.org/ TJoctilucent clouds have been ph,?to- ,yaph,-d frc)rii Aber-leen, with a 35 Ionosphere and Movements the.-lapse mo tion-pic ture camera with effective focal 1en::th ~10r.m and aper- M13 tue S/4. Die rnovernents of the noctiluc- RELATIVE FLOW OF H+ AND 0' IONS 1N THE ent clouds revealed by this system are discussed . TOPSIDE IONOSPHERE AT MID-LATITUDES R.J. Moffett and G.J. Bailey Department M11 of Applied Maths. and Comp. Sc., University of Sheffield at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 ATMOSPHERIC WATER VAPOUR OF J.A. Murphy Department of Mathematics, EXTRATERRESTRIAL ORIGIN University of Aston in Birmingham D. M. Willis, Appleton Laboratory, Theoretical results on the daily varia- Ditton Park, Slough 9JX SL3 tion of H+ and O+ field-aligned velocities in the topside ionosphere are The speculative suggestion that the in- presented. The results are for an L=3 flux of extraterrestrial hydrogen to the magnetic field tube under sunspot mini- Earth's atmosphere constitutes a sigai- mum conditions at equinox. They come ficant variable source of atmospheric from calculations of time-dependent H+ water-vapour, which can be invoked to and continuiiy and momentum balance explain Sun-weather relationships, is O+ in a magnetic fieId tube which extends examined in detail and found to be un- from the lower F2-region to the equat- tenable. The continual influx of solar- orial plane. The magnitude of the ion flare protons with energies in the range velocity difference is such that sig- 1-100 MeV makes an absolutely negligible nificant heat flow may be induced in contribution to the normal water-vapour the ion gases, as suggested by St. - concentration in the upper stratosphere Maurice and Schunk. There are occasions and the mesosphere. The continuous when ion counterstreaming occurs, with influx at the magnetospheric clefts of the O+ velocity upward and H+ velocity solar-wind protons with a mean energy downward, as observed at Arecibo by of about 1 keV, which cannot penetrate Vickrey, Swartz and Farley. The cond- below I50 km and hence cannot form water itions causing this counterstreaming vapour directly, only constitutes a are described. highly-localized reduction, or reversal, of the global efflux of hydrogen atoms from the Earth's atmosphere. Other extraterrestrial sources of atmospheric M14 water vapour or atomic hydrogen are also Ti TROUGHS IN THE EQUATORIAL TOPSIDE insignificant. IONOSPHERE

H. Rishbeth, Appleton Laboratory, Slough M12 THEORY OF THE NEAR INFRA-RED NIGHTGLOW The ion-trap aboard OGO-6 recorded mark- CONTINUUM. ed depressions of ion temperature on certain occasions as the satellite P.C.Wraight, Department of Natural crossed the magnetic equatorial region U.K.G.A. 1977 297 at heights of 700 - 1100 km. These Ti MI7 troughs are about 400 wide in latitude HYDROMAGNETIC EIGENMODES IN A and up to 1200 K in depth; their occur- SIMPLE MODEL PLASMASPHERE WITH A rence varies with longitude, LT and season. They are attributed to adiaba- THIN LOWER IONOSPHERE tic cooling of F-region plasma driven along geomagnetic field lines by trans- A.H. Craven and J.A. Lawrie, equatorial winds. The directions of Mathematics Division, University of Sussex. these winds, as deduced from current thennospheric models, is consistent with

Damped hydromagnetic eigenmodes have Downloaded from the occurrence of the Ti troughs. (Co- been calculated for a simple model ooerative project with University of Texas at Dallas and NOAA, aoulder, plasmasphere with a thin lower ionosphere. Colorado.) Further toroidal solutions have been cal- cula ted with spat ia l attenuation transverse to the magnetic field lines; 'but steady state

solutions have not been obtained. If steady http://gji.oxfordjournals.org/ Magnetosphere state toroidal solutions do exist, they appear M15 to be strongly attenuated. OUTER RADIATION ZONE STRUCTURE IN A SIMPLE MAGNETOSPHERIC MODEL M18

S.W.H. Cowley Blackett Laboratory, LOCALISED Pc 4's WHICH OCCUR AT HIGH Imperial College LATITUDES IN THE MIDNIGHT-DAWN QUADRANT C. A. Green and W. F. Stuart Institute The structure of the outer radiation of Geological Sciences, Edinburgh at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 zone has been calculated using the sim- plest steady-state model of the convect- Packets of peculiarly highly coherent Pc ing magnetosphere (dipole magnetic field 4 occu at Kiruna and Tromso. They occur plus uniform convection electric field). predominantly in the midnight-dam time The development of anisotropies in the sector with a maximum occurrence between plasma will be discussed in relation to local midnight and 03.00. Their period microinstabilities, together with the range is 80 to 150 seconds and were prev- variation of plasma bulk parameters with iously classified P L and the effects of the forbidden zones G' (Alfvgn layers). Particular emphasis Relative amplitude of the vertical componellt will be placed on the proton 'nose' is shown to relate to period range and structures observed by Explorer 45. It appears to be in agreement with generation has been found that the inclusion of by a hipJly localised field line resonance. strong proton losses is necessary to re- Phase and Polarisation characteristics are concile the model with observations. discussed together with the relationship of these pulsations to night time magneto- M16 spheric conditions. RECENT RESULTS ON MAGNETIC MERGING IN COLLISIONLESS PLASMAS M19 S.W.H. Cowley Blackett Laboratory, POSSIBLE EFFECTS OF I.M.F. SECTOR Imperi a1 College POLARITY ON Sq

The properties of one-dimensional steady- J. Go Greener and D. M. Schlapp, state current sheets in a collisionless Department of Physics, University plasma will be discussed, using analyti- of Exeter. cal models based on Eastwood's (1972, 1974) numerical results. The problem Previous workers have suggested that of maintaining charge neutrality in the in addition to the well-established current layer will be emphasized. It effects in polar regions, there is is shown that there exists no solutions some control of midlatitude S by of this problem in which particles re- the I.M.F. Some results are 9 main adiabatjc in the current layer. presented based on daily ranges for The relevance of the results of this a number of Northern hemisphere study to the properties of collision- stations. The statistical signi- free X-type systems will also be dis- ficance of the results is marginal cussed. but if the effect is real, its sign 29 8 1i.K.G.A. 197? appears to change from year to year M22 and season to season. SOURCES OF DAMPING OF Pc's

R.S. Newton Blackett Laboratory, M20 Imperid College, University of London A Pc 4 PULSATION OBSERVED NEAR MIDNIGHT AT GEOSTATIONARY ORBIT Ionospheric damping of continuous pulsations is considered with the aid of W. 3. Hughes Blackett Laboratory, numerical solutions of the uncoupled Imperial College, University of London poloidal mode. The program assumes a R.L. McPherron Institute of Geophysics dipole field and the ionospheric boun- Downloaded from and Planetary Physics, University of dary condition 4xC E/c = b where E and California, Los Angeles b are field perturgations and Zp is a J.N. Barfield, Space Environment Labora- height integrated co ductivity. A den- tory, National Oceanic and Atmospheric sity model of p = L- f: is used. The Administrati on relationship between damping rate and

C is studied. Typically, for a day- http://gji.oxfordjournals.org/ P We describe the observation and analysis side value of conductivity the damping of a narrow band continuous geomagnetic rate is found to be weak (e.g. y/w - pulsation of about 60s period (Pc 4). whilst far a nightside value the The observation was made by three geo- dam ing rate is more severe (e.g. y/W - stationary satellites with a total 10-B ). Collisionless damping by inter- longitudinal separation oi 20°, located action with resonant particles is also just prior to local midnight. The pul- discussed as is the asymmetric case of sation lasted for about 90 minutes and different ionospheric conductivities at had a large compressional magnetic field either end of a field line. component. It was found that the signals were not coherent over the whole at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 satellite array which indicates a rapid M23 azimuthal phase variation. This pul- THE ROLE OF HOT PLASMA IN MAGNETOSPHERIC sation is unusual because of (a) its CONVECTION occurrence near local midnight when continuous pulsations are not normally D.J. Southwood, Blackett Laboratory, observed and (b) the very monochromatic Imperial College, University of London nature of the signal. The implications of this event will be discussed in the Several authors have earlier shown that light of theory. the presence of hot plasma in the magnetosphere can severely modify an im- posed convection Dattern and even pre- M21 vent its penetration to low latitudes. F0CU:;ING OF WHISTLERS BY A Here it is argued that the important VAXYING DGLWETIC FIELD parameters governing such effects are hot particle pressure, number density bi. J.Laird Department of Iviathem- and the ionospheric conductivity with atics, King's College, London the result that the shielding phenomenon can be pictured in a fluid manner. Such he consider the propagation of a description is given. The effects of whistlers when the ambient mag- ring current pressure on ring current netic field g is a fundtion only injection are discussed in the fluid of the x coordinate. We examine picture. The limitations of the fluid ray paths from a source at the approximation, the development of steady origin, where H, and Hz are state flow patterns and the effects of taken to vanish, and discuss the collisionless plasma behaviour are qual- focusing of rays with small init- itatively described with the aid of ial wave-normal angle, and the simple theoretical models. The role of associated caustic surface. Ne particle loss is also discussed. show that for a wave frequency equal to half the electron pyro- M24 frequency at the origin, there is a ray path alone the field PARTICLE FLUX VARIATIONS PRODUCED BY line. The t,ieory is related to MAGNETOSPHERIC HYDROMAGNETIC WAVES recent observations of magnetospheric chorus. D.J. Southwood Blackett Laboratory, Imperial College, University of London U.K.G.A. 1977 299 M.G. Kivelson Department of Earth and M27 Space Science, University of California LONG PERIOD CONTINUOUS PULSATIONS Los Angeles, L.A. Ca. 90024 AT HIGH LATITUDES

Magnetospheric hydromagneti c waves M.R. Warner and D. Orr Department of generally produce flux variations in energetic particle distributions. Physics, University of York Potentially these oscillations can yield information on wave modes. We show High latitude geomagnetic field lines that the oscillation amplitude is differ significantly from a dipole strongly dependent on the particle geometry. Time of flight calculations Downloaded from erierm, the background particle distri- using the Mead-Fairfield model of the bution, the symmetry of the wave distur- geomagnetic field are presented. bance and its wavelength by examining Ground based observations of long theory. Examples of observations from period Pc 4 and Pc 5 pulsations the spacecraft OG05 and ATS6 are dis- support the suggestion that some of cus sed . these waves are guided hydromagn3tic waves in the plasmatrough. The http://gji.oxfordjournals.org/ location and period of the waves are M25 consistent with an association with SOME GLOBAL CHAUCTERISTICS OF PULSATION regions of enhanced proton density ACTIVITY (detached plasma).

W. F. Stuart and C. A. Green Institute of Geological Sciences, Edinburgh M28 A COMPARISON OF ULF AND VLF MEASUREMENTS From a preliminary scruting of pulsation OF MAGNETOSPHERIC COLD PLASMA DENSITIES recordings made in Newfoundland, UK, and at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Scandinavia examples are shown which D.C. Webb Department of Physics, illustrate some aspects of the global University of York morphology of pulsation activity. Sim- L.J. Lanzerotti Bell Laboratories ultaneous 'switch on' and 'off' of New Jersey 01974 pulsations over a large global area is C.G. Park Radioscience Laboratory, demonstrated and the range of coherence Stanford University of pulsation signals over 6 hours of local time is discussed. Variation of N-S and Equatorial cold plasma density profiles E-W characteristics of Pi 2's are shown to determined fro% VLF whistlers propagating be dependent on, among other things, the in magnetospheric ducts are compared degree of impulsiveness in the apparent with densities computed from the obser- s t imulus . vations of ULF hydromagnetic waves (geomagnetic pulsations). The densities obtained by the ULF technique, are M26 based on the identification of resonant SECONDARY RESONANCE IN Pi 2's geomagnetic field lines, assumed to be driven by a monochromatic source. The W.F. Stuart and Paul M. Mills Institute of ULF results thus obtained agree well Geological Sciences, Edinburgh with the whistler results throughout the period, June 11-20, 1913. The ULF obser- Characteristics of the mid-latitude vations show that at mid-latitudes resonance in Pi 2's appears to indicate shorter period resonances can be supp- that in the pre- midnight sector it orted in the plasma trough region, while occus within the plasmapause and that those of longer period can occur past midnight the resonance is outside the inside the plasmasphere. plasmapause. Spectral studies show that mid latitude Pi 2's have no systematic latitude dependence of period. M29 TEMPORAL VARIATIONS IN TOTAL EQUATORIAL Impulsive Pi 2's (dpi's) have several PLASMASPHERIC CONTENT AND THEIR spectral components and these cases appear RELATIONSHIP TO THE RING CURRENT to support the interpretation of mono- INTENSITY AND THE PLASMAPAUSE chromatic Pi 2's as being due to field line resonance. Possible implications about source characteristics are dis- D.C. Webb Department of Physics, University of York cussed. L.J. Lanzerotti Bell Lahoratories, New Jersey 300 U.K.G.A. 1977 Measurements of the plasmaspheric electron content (N 1 as monitored by the ATS 6 Radio geacon Experiment during the interval July 1974-May 1975 have been used to study the effects of ring current intensity and geomagnetic storms on the plasmasphere. Values of N measured at local midday are compared with values of two geomagnetic indices Dst and Kp. At geomagnetically active

times when the plasmasphere has been Downloaded from eroded and the plasmapause has moved close to the earth, different models of equatorial plasma distrubution, varying as R-” are used to compute a value for the plasmapause position. Reasonable values of the plasmapause position are found if it is assumed http://gji.oxfordjournals.org/ that the plasma density at 1000 kms varies in direct proportion to the plasmapause position.

Inter planetary M30 STOCHASTIC AND DYNAMIC TEMPERATURE CHANGES IN THE INTERPLANETARY GAS at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 -Max K. Wallis, Mathematical Institute, Oxford University M.A. Hassan, Department of Mathematics, University of Khartoum, Sudan

Exact solutions of the Fokker-Planck equation representing stochastic velocity changes have been found, to describe particles moving in an inverse square central force field under an inverse square collision frequency. The solutions for velocity distribution contain a combination of collisional and dynamical heating. At a general position there are two populations each with three distinct temperatures. Inter- planetary helium gas that reaches around 1 AU in the downstream wake, where the density is enhanced through the gravitational lens effect, is heated by several 100°K; that poFulation reaching 1 AU from the sun perpendicular to the initial direction along indirect orbits is heated to several 1000°K. In the interpretation of sky background radiation observations, these effects have to be carefully considered. The purely dynamical changes in the velocity spread have also to be taken into account for hotter helium gas, for which Doppler shifts relative to the solar emission line are significant. As the background Lyman-a radiation is conditioned by heating of the approaching hydrogen gas outside the heliosphere, current determinations of local interstellar gas parameters are most uncertain. U.K.G.A. 1977 301 PLANETOLOGY spheres. The contribution that evaporation of surface minerals is likely to P1 make to the atmosphere of the planet Mercury is considered in more detail. MICRUETE4RITE AM) SOLAR WIND EROSION OF mLuu9RsuRmcE P3 D.G. Ashworth Electronics Labraiories, TOWARDS A NEW SEMI-LITERAL THEORY OF THE University of Kent at Canterbury, Kent. LUNAR LIBRATIONS

Current lunar crater production and A.H. Cook, Department of Physics, Uni- Downloaded from equilibrium distribution curves are versity of Cambridge reviewed Equilibrium distribution curves, lunar crater erosion rates, and A brief account will be given of pro- rock lifetimes on the lunar surface are gress in the development of a new theory derived from the production curves by of the lunar librations, in which a com- using proven analytical techniques. It puter system of algebraic manipulation is sham that the equilibrim curves (CAMAL) is used to develop algebraic http://gji.oxfordjournals.org/ are in good agreement with equilibrim expressions. distributions measured on lunar rocks and with other statistically derived distributions. 'Ihe predicted erosion P4 rates on the lunar surface are also in DETERMINATION OF THE TEMPERATURE AND very good agreement with erosion DURATION OF SOME AP3LLO 17 BOULDER measurements made on typical lunar SHADOWS USING THERMOLUMINESCENCE METHODS rocks. It is shown that ambiguity still exists between the curves S.A. Durrani Department of Physics, derived from lunar rock crater counts University of Birmingham at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 and those derived from satellite measurements. The natural thermcjluminescence (TL) retained by soil samples collected from P2 the shadows of certain Apollo 17 bould- ers has been compared with that of a EVAPORATIVE SOURCES FOR TRACE COMPONENTS nearby sunlit sample. The shaded OF PLANETARY ATMOSPHERES samples have been kept continuously refrigerated, since soon after their re- Peter Brimblecombe and Keith Hunter, trieval, to preserve their natural TL. School of Environmental Sciences, Uni- By experimentally determining the versity of East Anglia, Noiwich various TL parameters of the relevant trapping levels, we have attempted to Evaporation of substances into atmos- calculate the temperature (TI) in the pheres from planetary surfaces is usu- shade and the duration (tl) of the shad- ally considered only for those sub- ow cast on the samples. We obtain the stances, such as liquids or ices which values TI = 256K and tl '~4.0~10~- 5.7~ are volatile in terms of terrestrial lo4 yr, based on a dose-rate of 10 rad experience. Recently it has been yr-1 in the shade. On applying various suggested that some trade heavy metals corrections for the fading of the natur- found in the Earth's atmosphere might be al TL over the intervening $3 yr, a present due to the evaporation of such value of tl 2.6.5~104 yr is obtained. non-volatile compounds as metal oxides These values of the storage time in the or sulphides. Determination of the mag shade confirm the relatively recent nitude of contributions from evaporation arrival of the boulder concerned at its is hampered by the lack of vapour pres- present location, as was indicated by sure data for minerals of interest, par- the freshness of its tracks. ticularly at relatively low temperatures, and is further complicated by the effects of the matrices within which they are present. However it is clear that evaporation rates which may be quite high under a vacum are lowered by boundary layer effects when an atmosphere is present. Evaporation of minerals can thus be expected to make more significant contributions in very tenuous atmo- 30,s U. ii. G.A. 1977 P5 LARGE SCALE PROCESSES ON THE MOON

-~G. Fielder, Lunar and Planetary Unit, Department of Environmental Sciences, University of Lancaster

Recent research on the viscous dissipation mechanism involved in the gravita- tion& adjustment of geological struc- Downloaded from tures has lent new weight to the dualis- tic hypothesis of the formation and development of certain large lunar craters. The craters in question - distinct from those which are essentially of impact origin and from those which are purely volcanic in origin - have suffered pro- http://gji.oxfordjournals.org/ tracted developments involving volcanic activity preceded, millions of years earlier, by major collisions. ionsider- ation is given to the application of this hypothesis to the problem of the origin of Mare Inbrium, using rock ages from the Apollo programme.

P6 at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 TH6 FIRST 100 MILLION YPAE

G.Turner, P.H.Cadogan and M.C.Enright Department of Physics, Yheffield Uqiversi ty. Three major classes of events which occurred within the first 100 million years of Solar System history can now be Rccurately dated by radiometric methods. They are; the formation and thermal metamorphism of primitive solid objects ( chondrites) , magmatic procesr- es caused by an undetermined heat source and producing chemically diff- erentiated objects (achondrites, irons) and, high velocity collisions producing fragmented bodies (breccias). Recent advances in our understanding of the relative and absolute times of these events will be presented. U. K. G.A.~~ 1977 30 3 waves may have almost equal amplitude SEISMOLOGY SH (or SV) components. Earthquake Source and Transmission Path

s1 s3 SEISMIC WAVE PROPAGATION IN SCATTdRING AT Tm 630Kli BOUNDARY ANISOTROPIC MEDIA: I1 OBSERVATIONS

B.J. Barley, KOD(PE), Blacknest, Stuart Crampin, Institute of Brimpton, Reading RG7 4RS, Berks Geological Sciences, Edinburgh Downloaded from Complexity and simplicity of the P Seismic anisotropy in the oceanic seismogrms of eleven deep earthquakes upper mantle has been recognised since in the Izu-Bonin Is., observed at the 1964. There are now two observations medium aperture seismic array of seismic anisotropy in the upper Warramunga, Australia (49< A<53), mantle beneath Eurasia: Bamford (1977) correlate with negative and positive has found 7% velocity anisotropy ben- mb rcs idual s (me asured-expect ed) eath the Rhinegraben, and Crampin and http://gji.oxfordjournals.org/ respectively. The negative mb King (1977) have observed diagnostic residuals are attributed to direct coupling of the Third Generalized mode P leaving the focal sphere close to indicating aligned anisotropy beneath a node of P. An association between the whole of the Russian Shield area. negative mb residuals and complexity is Unfortunately, these surface wave expected if scattered energy in the coda studies have not yielded a direction remains fairly constant in amplitude as of symmetry, but do suggest that the the absolute P amplitude falls due to orientation of the anisotropic sym- the radiation pattern. This background metry changes only gradually over energy might be produced by scattering Eurasia. at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 of S to P; this hypothesis is supported by five observations of a high frequency (1-2Hz) emergent phase arrivine; about s4 30s after P, which is coherent across SEISMOLOGY IN THE OCEANIC MIGROSEISM Warramunga, has dT/a and arrival BAND azimuth clow 'L.O P, and a variation of arrival time with hypocentral depth A. Douglas BIOD(PE), Blacknest, Brimpton consistent with S to P scattering at a Nr Reading, Berks, RG7 4RS rough interface between 650 and 700kni beneath the Izu-Bonin Is. To demonstrate the advantages of broad hand recording, thc seismic body wave s2 signals from a series of earthquakes and explosions as recorded on conventional SEISMIC WAVE PROPAGATION IN narrow band short period and long period ANISOTROPIC MEDIA: I COMPUTATIONS seismographs are compared to the same signals recorded on a broad'band seismo- Stuart Crampin, Institute of graph (with displacement amplitude Geological Sciences, Edinburgh response flat from about 0.1 to 10.OHz). When the broad band signal is recorded Propagation of seismic waves in aniso- with adequate signal to noise then: tropic media is fundamentally differ- (1) the shape of the pulses radiated by ent from that in isotropic solids, the seismic source can be observed although the effects may be subtle and directly; (2) the surface reflections easily overlooked. Coupling between such as pP and SP are more easily sagittal and horizontal transverse identified than on narrow band records; motion writes anomalous signatures and (3) the polarity and onset time of on the seismogram. These are illus- arrivals can be read with less possib- trated by numerical computations from ility of error than on narrow band models containing anisotropy in the records. upper mantle. Most surface waves show very few effects except for the Third The bizgest drawback to broad band Generalized mode (equivalent to the rccording is the very hi;;h noise levels isotropic Second Rayleigh mode), which that are usually present in thc band has distinctive and diagnostic coupl- 0.125IIz4.167Hz thc so-callcd oceanic ing. Incident P waves have anomalous microsc im band. Thcx no is(? ar:ipl itudes SH arrivals after the S-P delay thro- may be no largc as to swamp all but .the ugh the crust. Incident SV (or SH) vcry largest sixnals. Ebrtunatcly iiiuch 30 4 0. K. G.A. 1977 of this noise is oftcn propqating as S? coherent wave trains and array processing can be used to reduce these coherent THE STRUCTURE OF SEISMIC SCATTERED WAVES components virtually to zero. Examplcs arc shown of the application of array --J.A. Hudson and J.R. Heritage, Depart- processins nethods to broad band ment of Applied Mathematics and Theore- recordings to obtain the bcst estimates tical Physics, University of Cambridge of signals in the presence of noise with both random and coherent components. The first part of the paper consists of an investigation of the conditions under which first-order scattering theory may Downloaded from s5 be regarded as reliable as a method of predicting the amplitudes and shapes of EARTHQUAKE SYNTHESIS waves scattered from heterogeneities in the Earth. The second part-concerns the Khalid J. Fahmi Dept of Geophysics, expressions for scattered wave displace- University of Edinburgh and the ments, and, in particular, the effect of Institute of Geological Sciences

wavelength and the relationship with http://gji.oxfordjournals.org/ Edinburgh calculations from ray theory. An attempt is made to take account of the effect of a *'design earthquake" antici- sg pated to OCCUT in a seismically and tectonically active area. One way of achiev- A NEW APPROACH TC SURFACE WAVE DISPER- ing this aim would be to try to predict SION the waveform of a large event before it OCCUTS. This can be done by the simple N.J. Kerry and B.L.N. Kennett Depart- addition - after introducing the necess- ment Of Applied Mathematics and Theoret- ary time delays - of microtremor records, ical Physics, University of Cambridge at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 enough in quantity and of the desired quality to sample the whole source region A new approach to the calculation of of a major earthquake. By the applicat- surface wave dispersion has been devised ion of this summation procedure it is 'based on the determination of the reflect. expected that the destructive inter- ion response of an elastic half space. ference of high frequencies and the The new technique 1s computationally very concomitant build-up in low frequencies convenient and appears to be cornpetiti.se and in wavepattern, would transform the with the fastest existing methods. waveform of the microtremors into an approximation to that of the large s9 event. COMPUTED CHARACTERISTICS OF SEISt4IC SUR- S6 FACE WAVES FOR ANISOTROPIC MODELS OF OCEANIC STRUCTURE OCEAN BOTTOM SEISMOGRAPH OBSERVATIONS "EAR THE EASTERN END OF THE ST'. PAUL'S S. Kirkwood, Department of Geophysics, mcm ZONE Univers i ty of Edinburgh

T.J.G. Francis, I.T. Porter and Dispersion and particle motion charac- R.C. Lilwall, Inst ikute of Oceano- teristics have been computed for the graphic Sciences, Blacknest first four normal modes of surface wave propagation in plane-layered models An array of four OBS was operated in late where at least one layer is anisotropic 1974 near the junction of the St. Paul's and the surface layer is liquid. Re- Fracture Zone with the median valley of sults suggest that even large mounts the Wid-Atlantic Ridge to the south. of anisotropy in the uppermost mantle Zarthquakes were detected both on the would not alter the fundamental Ray- Fracture Zone and in the median valley. leigh mode significantly. Anomalous Many events occurred close to or within particle motion, with Coupled radial the-confines of the array and for these and transverse components, is likely precise focal depths have been obtained. for modes corresponding to isotropic The tectonic siy-nificance of the distri- higher Rayleigh modes and is possible, bution of epicentres and focal depths with coupled transverse and vertical obtained will be discussed. conponents, for modes corresponding to isotropic fundamental and higher Love U.X.G.A. 1977 305 nodes. Only small azimuthal variations sP. Here this information is of Dhase velocity are likely for funda- utilized in a new method of computing mental Rayleigh or Love modes. fault plane solutions. The procedure is demonstrated usin,: earthquakes with mb as low as 5.0. While the s10 method enables double couple solutions to be computed using only OCZAN BO'MW SEISNOGRAPH OBSXRVATIONS a few seismograms, the inclusion of ON TKr: KID ATLANTIC RIEE AT 4S0N many stations imposes strict limitations on the source radiation

R.C. Lilwall, T.J.G. Francis, and Downloaded from pattern, and so provides a means of I.T. Porter, Institute of Gceano- testing different mechanisms against graphic Sciences, Blacknest observation. Seisrricity at 45ON appears to be restricted to a zone only 5km wide. lnstrumentakn and Networks Epicentres determined from teleseismic data can be reconciled with this zone. http://gji.oxfordjournals.org/ Both swarm like and aftershock type S13 sequences were observed with all A.I: XWRIl2NT iIITH A UK SEISMOLOGICAL similar b values. The b value for DATA CdtJTRE teleseisrnically observed events is greater but this difference can be F. H. Grover PZ/LTOD Blacknest, Brimpton, explained by differences in the Near Readin;, Berkshire ma,gnitude scales employed. The observations are in agreement with a A basic objective of the expcriment has Caldera collapse model of the Nedian been to evaluate rncthodw of inonitorins

Valley with movement restricted to the at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 interaational coi:iplianc& with possible inner faults. a comprehensive nuclear Test Ban Treaty. Usini; data supplied by a seisnioiiieter s11 array station in the UII and 3 other arrays overseas, with which 1on;r- IS Pn VELOCITY AN INDICATOR OF €& standin; liaison for ReCD studies already existed, it has been possible to make a P.D. Marshall, liIOD(PE), Blacknest, pilot study of an operational monitoring Brimpton, Reading, Berks RG7 4RS systei., based on a small but well- distributed network. An empirical relationship between the velocity of Pn and amplitude residuals Important features of the experiment havc has been established for N. America. As been iinprovcment of communications to it seems reasonable to suppose that the provide rapid and rcgular flow of data, amplitude variations are caused by 4 establishment of data exchange li&.s variations it is concluded that Qr and with other centres, strengthening the the velocity of Pn are correlated. data contribution from within the UK and the creation of a database on computer files to which collaborating centres Eay s12 havc access. FAULT PLANE SOLUTIONS USING P AND pP RELATIVE AMPLITUDES S14

R.G. Pearce, School of Physics, A SEISI-1IC NETWORK IN IRELAND University of Newcastle Upon Tyne A.W.B. Jacob, T. Murphy and G. Wallace, (and Blacknest) Dublin Institute for Advanced Studies

P wave polarity observations sample A triangular seismic network is being only a small fraction of the inform- established in Ireland. This includes at ion contained in seismograms. a recorder at a site near Dublin and Comparison of observed and theoret- two radio-linked outstations, the ical seismograms for shallow earth- pattern being an equilateral triangle quakes has confirmed that there are of side about 50 km. All stations will other features of P wave codas which have both broad-band and high-gain are sensitive to source orientation, short period instrumentation. Sites notably the relative amplitudes of P are required which have (1) low general and the surface reflections pP and background noise levels and (2) low 306 U.K.G.A. 1977 signal generated noise levels. Site capability with much smaller masses testing is.being carried out and results suspended at shorter periods. Such from this are presented. instruments are valuable for borehole applications or where many instruments must be rapidly set up. S15 The problems of the design of miniature CWF - A SEISMIC STATION IN THE MIDLANDS wide-band force-feedback seismometers are discussed and two such instruments are wuireDepartment of Geology, described. Both instruments use a University of Leicester capacitive displacement transducer to Downloaded from detect the displacement of a mass of A permanent, three component, short about 5Ogm having a natural period near period seismic station CWF, has been one second. A force-feedback system installed on the Precambrian volcanics maintains the mass stationary with of Charnwood Forest. Signals are record- respect to the instrument frame and the ed on a multichannel, slow speed tape device has an output flat to acceleration http://gji.oxfordjournals.org/ recorder, the Geostore. Although situ- from dc to 10Hz. A single miniature ated only 1.8 km from a major motorway, instrument can thus provide data over the and about 4 km from four industrial whole of the seismic range. towns, noise levels are low, typically 10-15 nm during the week, falling to Details are given of the experimental half that value at weekends. The station difficulties encountered and of a was operational from October 1974 to comparison of the instruments with April 1975, and then from October 1975 to conventional seismometers. the present. For five months during the winter of 1975-6, it was supplemented by seven other stations forming a small, S17 at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 5 km aperture array. Arrivals were obtained from blasts at 11 quarries, whose RECENT DEVELOPMENTS IN PORTABLE shot instants were timed. Following the SEISMOGRAPH EQUIPMENT dismantling of the array, CWF has proved valuable in estimating shot times of un- P.L. Willmore IGS, Global Seismology Unit, timed quarry blasts recorded on two Edinburgh seismic projects in the vicinity of Charnwood. As well as quarry blasts (50- The options available for field work in 100 each week) 423 regional and tele- earthquake seismology have been extended seismic events have been picked from CWF in several directions. The first is an records. From analysis of a selective electronic feedback system which can in- set of events, there appears to be crease the natural period of Willmore considerable azimuthal variation in the Mark I11 seismometers to about 50 secs. P - wave delay relative to Eskdalemuir, The second is a modification to the con- ESK. Between 350 to 140 degrees, all the trol circuitry of Racal-Thermionic mag- measured delays are negative at CWF netic tape recorders to permit single- relative to ESK with a mean of -0.26 2 channel operation for up to 7 months with- 0.05 secs. Between 250 and 320 degrees out change of tape. The third is a the relative delay is positive. Seven of miniaturised smoked- f i lm recorder which these events are from the Nevada test can produce a transparency, having resolution comparable that of a site giving a relative delay of W.65 _+ to 70-mm 0.05 secs. From the available data, the film chip, from a battery-powered package delay does not appear to vary with measuring only 240mm x 12Omm x loom distance . Seismic Risk S16 S18 DEVELI)PhENT OF MINWJTJW WIDZ-BANU FORCE- BALANCE SEISMONEmRS INDUCED SEISMICITY IN THE UNITED KINGDOM

M.J. Usher, Department of Engineerink: and C.W.A.Browitt Global Seismology Unit, Cybernetics, University of Reading, Rerks Institute of Geological Sciences, Edinburgh Conventional seismometers employ masses of several kilof

a sparsely instrumented country is Downloaded from demonstrated. s21 MICROZONING IN SPACE AND TIME s19 P.L. Willmore IGS Global Seismology Unit SEISMICITY AND ASSOCIATED RISK IN THE Edinburgh UNITED KINGDOM http://gji.oxfordjournals.org/ Conventional seismic zoning starts with Paul W Burton, Global Seismology Unit, a historical pattern of earthquake occurr- Institute of Geological Sciences, ence in a seismic region, and computes EDINBURGH therefrom the expected distribution of earth-motion parameters on the assumption The results of a seismic risk analysis .in of uniform attenuation throughout the a region of relatively low activity like region and of stationary statistical the United Kingdom necessarily largely expectation of earthquake occurrence. depend on historical catalogues of Microzoning seeks to determine vari- earthquakes with whatever inaccuracies ations in attenuation over the affected at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 these contain. Nevertheless it is poss- region, with particular reference to ible to mitigate against the effects of near-surface effects which can introduce incompleteness in the macroseismic repeatable anomalies into the zoning sample and variability in the human map. Prediction is the end-point in the population by using extreme value anal- process of recognising non-stationary ysis. The ensuing results for return features in the pattern of regional period analysis at given magnitude seismicity, but useful results can be levels allow the estimation of tne mag- obtained at an earlier stage in the nitude of those naturally occurring recognition of time variations in the earthquakes which are likely'to be rate of strain release. Concerted IGS sel-ioualy damaging in the United effort is directed towards the ultimate Kingdom. With this information from goal of producing "design seismograms", historical data it is then possible with expectation of occurrance, tailored to examine the ground motion char- for a particular structure on a part- acteristics of more recent and instru- icular site. mentally recorded earthquakes which are in this magnitude range. Regional Studies

s 20 s22 EARTHQUAKE PARAMETERS FROM EXTIlFME VALUE STATISTICS SEISMICITY OF THE SOUTH SANDWICH ISLANDS REGION Costas Makropoulos Department of Geo- physics, Edinburgh University and the C .P . Brett, Department of Geological Institute of Geological Sciences, Sciences, University of Birmingham Edinburgh. Paul W Burton Global Seismology Unit, South Sandwich Island earthquakes have Institute of Geological Sciences, been relocated for the period 1964 - mid Edinburgh. 1974. Travel-times modified by station corrections, computed by applying the The application of extreme value statis- joint epicentre method to the major tics to the analysis of seismicity is events, have been used. This results in discussed md the paper presents results the definition of the active zone, aris- for both the circum-Pacific, and Greece. ing from the subduction of the South It is shown that Gumbells third assymp- American plate beneath the young Sand- totic distribution gives an excellent and wich plate, being greatly improved. The informative fit to the data. Values 30 8 U.K.G.A. 1977 detailed features of the seismicity are delay times are thus considered to interpreted in terms of the tectonics of arise from structures within the upper the area, and new evidence is presented mantle. One possible source is lateral which suggests that the penetration variations in thickness of the astheno- depth of the subducted slab may be deeo- sphere which is assumed in this study to er than previously recognised. manifest itself as a variation in thickness of the overlying lithosphere. The delay time map is tentatively used to s23 derive a man of lithosphere thickness LATERAL VARIATIONS OF P-WAVE VELOCITY which takes into account lateral vari- STRUCTURE WITHIN THE EURASIAN REGION ations of velocity within both the Downloaded from lithosphere and asthenosphere. The P.C. England Department of Geodesy and lithosohere thickness model indicates a Geophysics, Madingley Rise, Cambridge. major zone of thin lithosphere (thick M.H. Worthington Department of Geology asthenosphere) is associated with the and Mineralogy, Parks Road, Oxford. East African Rift System and its continuation into southern Africa. Con- http://gji.oxfordjournals.org/ T-A curves have been obtained for P- comitant seismicity, volcanism and high waves arriving at the Norwegian Seismic heat flow further suggest that incipient Array in three ditferent azimuth ranges. separation of the continental plate is Thgse are: 40-120 , 120-200 and 250- taking place along the axis of this 20 for rays bottoming under Western zone. Russia, southeast and central Europe and the North Atlantic ocean and conti- S25 nental margins, respectively. These three regions yield travel time curves DETERMINATIONS OF & FOR DIRECT PATHS of significantly different character F'RON THE URAIS TO THE UK. and indicate appreciable variations in at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 velocity structure within the region to R.W. Hurlex, MOD(PE), Blacknest, Brimpton depths greater than 400 km. Reading, RG7 4RS

Qd is estimated for direct body wave s24 paths from the Urals to the UK using P TELESEISP4IC DELAY TIMES, BOUGUER ANOMA- to PcP ratios. An attempt to segment LIES AND INFERRED THICKNESS OF THE the paths according to their Q AFRICAN LITHOSPHERE contribution is presented.

J.D. Fairhead, Department of Earth S26 Sciences, University of Leeds RESONANCES IN MICROSEISMIC NOISE SPECTRA Teleseismic P-wave travel time residuals (delay times) have been determined for D T Meldrum, Scott Polar Research Inst- 38 African seismograph stations using a itute, University of Cambridge total of 104 Russian underground nuclear explosions, 92 from East Kazakhstan and A simple experiment is described whereby 12 from Novaya Zemlya. The delay times the seismic background noise at a varie- (TI for seismograDh stations situated on ty of sites was measured. The amplitude Precambrian crust within the interior of spectra of the records made on top of a Africa, where surface erosion is mini- large sill show strong peaks in the 1- mal, appear to be linearly related to 100 HZ band which are substantially ab- both stations elevation (E) and Bouguer sent at other nearby sites. It is shown anomaly (B) such that T = (1.12 t 0.32) that these peaks are consistent with the E - (1.81 ? 0.44) .. (l), T = (0.012 2 normal modes of a simple model of the 0.005)B - (1.81 2 0.60) (2), where T is sill, and a value for its thickness is in seconds E in kilometres and B in derived which is in reasonable agreement milligals. Equation 2 has been used to with other observations. Alternative predict delay times more generally over explanations are also discussed. Africa using the Bouguer anomaly map of Slettene et al. Although previous gravity studies have shown the African crust is in approximate isostatic equilibrium, the above relationships cannot be explained purely in terms of Airy- Heiskanen isostasy. The variations in U. K. G.A. 1977 S27 A SURFACE WAVl STUDY OF 'THZ STURC'IVRE OF 'ThX NORTH %A AND SCANDINAVIA.

G.W. Stuart, kpartment of Earth Sciences University of keds

The variation in the shear wave velocity structure of the crust and upper mantle

(surface to 400h) of North-West Europe Downloaded from is determined from the phase velocity dispersion of fundamental Rayleigh waves along profiles between the WWSSN statioris of ESK, COP, KON, UbE, NUR and KEV. Inversions of the regional phase velocity curves by the *'Hedgehog*' method indicate that the North Sea region is character- http://gji.oxfordjournals.org/ ised by a low velocity zone of 'S-wave velocity of 4.35-4.45h.s-' between depths of approximately 85-2001~11, while Scandinavia has a low velocity zone reaching down to about 4OOkn1, which begins at depths of 140-240km if its S-wave velocity is 4.51~11.~'~ and at depths of 190-290h if its S-wave velocity is 4.41ai.s-1. Significantly

hi::her velocities are found for western at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 as compared to eastern Scandinavia.

S28 TELESEISMIC DELAY TIXES FOR UNDERGROUND NUCLEAR EXPLOSIONS TO SEISMOGRAPH STA- TION IN BRITAIN

A.S. White and J.D. Fairhead, Department of Earth Sciences, University of Leeds

Analysis of teleseismic P-wave travel time residuals from American and Russian underground explosion test sites to fif- teen stations in Britain has been made, using the Jeffreys-Bullen travel time tables. Observations of first arrivals were obtained fron ISC bulletins and directly from seismograms for more recent events. For Russian exalosions a least variance technique was used to minimise systematic errors due to inaccuracies in orie;in times and egicentre locations. The results of the analysis indicate that residuals for Low net stations in Scotland are predominantly more negative than Eskdalemuir station while stations in the south of England are slightly more gositive. The residuals determined for Lownet, using the Russian eslosion data, are sufficient to give an indication of their station correction terms. 310 U. K. G.A. 1977 5 Author Index

Reference numbers of papers of which Crawford, J., 92 I11 abstracts are presented in the fore- Creer, K.M., G3 I going pages are appended to the author's names below. The session to D which each paper has been allocated is indicated by the Roman numeral. Dagley, P., G17 I11 Dearing, J.A., G32 II! Downloaded from Deegan, S.E., L19 I1 A Dickinson, P.H.G., M7 I Dobinson, A., L17 11, L19 I1 Adam, J.A., F1 I Doug1 as, A., S4 I Adcock, C.C.F., 66 VI Duff, B.A., 618 IV Aitken, M.J., G38 I1 Durrani, S.A., P4 I Al-Haddad, F.Y.., L35 I1 http://gji.oxfordjournals.org/ Allsop, J.M., L18 I E Andrew, E.M., A2 I1 Amour, A.R., L1 IV Elder, J.LJ., L20 V Ashworth, D.G., P1 I Enright, M.C., P6 I Assumpcao, M., L2 I11 Evans, C., L38 I1

B F

Bailey, G.J., M13 IV Fahmi, K.J., S5 I Barnford, D., A1 I, L2 111, L3 I11 Fairhead, J.D., S24 IV, 528 V at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Banks, R.J., G7 VI, L36 I1 Fielder, G., P5 I Banner, J.A., G15 IV Floyd, R.A., A7 I Barbetti, Y.F., 616 I1 Flude, K.P., G16 I1 Barfield, J.N., M20 V Fox, J.M.K., 616 I1 Baria, R., A5 I Francis, T.J.G., S6 I, S10 I Barley, B.J., S1 I1 Freer, R., 639 V Barraclough, D.R., G1 I, G2 I, G50 I Bayerly, M., L4 111 G Beamish, D., G7 VI Berkshire, F.H., F2 I1 Gadsden, M., M8 I Bhattacharyya, S.K., M9 I Games, K.P., G19 I1 Booth, D.C., L6 I11 Gibson, A.J., M9 I Bott, Y.H.P., L1 IV, L37 I1 Girdler, R.W., L2'1 V Brazier, I.M., L25 V Goodman, D.J., "3 I1 Brett, C.P., S22 IV Green, C.A., Y18 V Brindlecornbe, P., P2 I Grover, F.H., S13, I11 Brooks, M., L4 I11 Gubbins, D., F3 I Browitt, C.W.A., S18 IV Gunn, N.Y., 620 I1 Brown, G.C., L16 I, L22 I, L27 I Bryant, D.A., M1 111, 1.14 I11 H Buchanan, D.J., A9 I Burton, P.W., S19 IV, S20 IV Habberjam, G.M., A4 I1 Hailwood, E.R., G15 IV, 621 11, 622 C I11 Hall, D.S., M1 I11 Cadogan, P.H., P6 I Hall, J., L5 I11 Campbell, A.L., 641 V Hamilton, N., 622 111, 623 111, 624 Chalmers, A.K., L28 I1 I11 Chroston, P.N., L38 I1 Hargreaves, N.D., A14 I1 Cook, A.H., P3 I Hart, A.M., 66 VI, G8 VI Cornwell, J.D., A2 I1 Harwood, J.Y., GP I Cotton, W.R., 43 I Harwood, Q.S., F4 11, F5 I Cowley, S.W.H., M15 11, Y16 I1 Hassan, M.A., V30 IV Cox, M.J.G., A3 I Hauptrnan, Z., 639 V, 640 V, 641 V Crampin, S., L39 11, S2 11, S3 I1 Hennessy, J., L16 I, L22 I Craven, A.H., M17 V Heritage, J.R., 57 I1 U.K.G.A. 1977 311 Hewson-Browne, R.C., G9 VI Makropoulos, C., 520 IV Hide, R., F6 11, F7 I Yalin, S.R.C., 62 I Hipkin, R.G., L23 I, L24 I Maliotis, G., A8 I1 Hobbs, B.A., G10 VI Marshall, D., S11 I1 Hocking, L.M., F7 I Mason, I .M. , A9 I Hogg, T.E., 63 I, 625 11, G31 I1 Mason, P.J., F6 I1 Honebon, C.D., 66 VI Mason, R.W.N., M1 I11 Hoskins, B.J., F11 11 Masters, T.G., F8 I Hudson, J.A., S7 I1 Mbipom, E., L25 V Hughes, W .J. , M20 V Meldrum, D.T., A15 11, S26 V Hunt, G.E., I1 Miles, P.R., L10 IV Downloaded from Hunter, K., P2 I Mills, P.M., Y26 V Hurley, R.W., S25 V Moffatt, H.K., F9 I Hutton, V.R.S., Gll VI, L25 V, L26 I Moffett, R.J., M13 IV Moreira, V., L12 IV I Vould, A,, L17 I1

Murphy, J.A., M13 IV http://gji.oxfordjournals.org/ Irving, E., G26 IV Murphy, T., S14 I11 Mussett, A.E., G17 111, 629 I11 J MC Jackson, P.D., A5 I Jacobs, A.W.B., L6 111, S14 I11 McCann, C., A6 I, A7 I Jacobs, J.A.-, I2 MacCormack, A.G., 650 I Jelenska, M., 627 I11 McEwan, D.J., M4 I11 Jenkins, A.D., M10 I McPherron, R.L., M20 V Johnson, C., A2 I1 Johnson, C.R. , G50 I N at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 Johnstone, A.D., M3 111, M5 I11 Jones, A.G., G11 VI , 612 VI, L26 I Newton, R.S., M22 V Niedziolka, E., 630 11, 631 I1 K Nunn, K., A1 I, A10 I, L11 I11

Kadzi a1 ko-Hofmokl , M. , 627 I I I 0 Kasnir, N.J., L37 I1 kendall, P.C., 69 VI, 613 VI O’Donovan, J.B., 642 V Kennett, B.L.N., L7 111, L8 IVY S8 I1 Oldfield, F., 632 I11 Kerry, N.J., S7 I1 Orr. D., M27 V Khan, N.A., A8 11, L33 V Owens, W.H., 643 V, 644 v Kirkwood, S., S9 I Ozdemir, O., 645 V Kivelson, M.G., M24 V Knuckes, A.R., All I P Kopper, J.S., 628 I1 Kruczyk, J., 627 I11 Papamarinopoulos, S. , 633 I1 Park, C.G., M28 V L Patrick, D., L18 I Pierce, R.G., S12 I Laird, M.J., M21 I1 Piper, J.D.A., 634 IV Lanzerotti, L.J., M28 V, 1129 I1 Plumb, R.A., F6 I1 Laughton, A.S., L29 IV Porter, I.T., S6 I Lawrie, J.A., M17 V Pyle, J.A., F5 I Leaton, B.R., 62 I Lee, C., L38 I1 R Lee, M.K., A2 11, L18 I Lepine, D.R., M1 I11 Readman, P.bl., 635 11, 646 V Li’lwall, R.C., S6 I, S10 I Rishbeth, H., M14 IV Llewellyn, D.J., L4 I11 Rochester, A.K., L28 I1 Locke, C.A., L27 I Rooney, D., 611 VI, L25 v Louden, K.E., L9 IV Rozser, W.G.V., 66 VI Lowes, F.J., 64 I, 65 I1 Rothwell, P., M2 I11 Rumnery, T.A., 632 I11 M Runcorn, S.K., I3 Rutter, E.H., 644 V Maguire, P.K.H., S15 I11 312 U. K. G. A. 1977 S Schlapp, D.M., G14 VI, M19 IV Scorer, R.S., F10 I Searle, R.C., L29 IVY L30 IV Sik, J., Gll VI Simnons, A.J., Fl1 I1 Smythe, D.K., L17 I1 Sojka, J.J., M3 111, M5 I11 Southwood, D.J., M23 11, 'I24 V

Soward, A.M., F12 I1 Downloaded from Sowerbutts, W.T.C., L32 V Stearn, J.E.F., 634 IV Steinmetz, L., L12 IV Stephenson, A., 648 V Stober, J.C., G36 111 Strangeway, R.J., Y6 IV Stuart, G.W., S27 V http://gji.oxfordjournals.org/ Stuart, W.F., I418 V, M25 V, M26 V Styles, P., L21 V Swain, C.J., L33 V T

Thanassoulas, C., A4 I1 Thomas, L., M9 I Thomas, R., M2 111 Thompson, R., 632 111, 636 111, 637 at Dept Applied Mathematics & Theoretical Physics on September 15, 2013 111 Thorpe, S.A., F13 I1 Tucholka, P., G31 I1 Tucker, P., G47 V Turner, G., P6 I

Usher, M.J., S16 111 V

Veitch, R., G48 V Vine, F.J., I4

Wallace, G., S14 111 Wallis, M.K., M30 IV Walton, D., G38 I1 Warner, M.R., !427 V Webb, D.C., !428 V, M29 I1 Webb, E.G., A10 I Westbrook, G.K., All I, L34 IV Whitcombe, D.N., L13 I11 White, A.S., S28 V Whitmarsh, R.B., L12 IV, L14 IV, L30 IV Willis, D.M., M11 I Willmore, P.L., S17 111, S21 IV Wilson, D., G49 V llilson, R.L., G50 I Uilton, T.J., L15 V Woods, J.D., F14 I1 Worthington, M.H., A12 11, S23 V Wraight, P.C., !412 I