PROGRAMME

This provides an outline for the day, but times are approximate.

Note: the venue is Cotton 217

1.10 pm - 1.30 pm Introduction 1.30 pm - 2.00 pm Seismology (Martha Savage) 2.00 pm - 2.30 pm Geodesy and Neotectonics (Simon Lamb and Tim Little) 2.30 pm - 3.00 pm Exploring the Deep Earth (Tim Stern) 3.00 pm - 3.30 pm Aerogravity and Groundwater Studies (Euan Smith) 3.30 pm - 4.00 pm Afternoon tea 4.00 pm - 4.30 pm Geomagnetism and Paleomagnetism (Gillian Turner) 4.30 pm - 5.00 pm Ice Physics (Huw Horgan) 5.00 pm - 5.30 pm Meteorology and Atmospheric Physics (Jim Mcgregor and Jim Renwick) 5.30 pm - 6.00 pm Break and drinks 6.00 pm - 6.30 pm Overview of geophysical research at the Institute of Geophysics (Tim Stern) 6.30 pm - 7.30 pm Discussion, posters, and drinks/food.

Institute of Geophysics Symposium 2013

TALKS

Seismology Martha Savage

We are lucky to be able to use the GeoNet network, specialised field studies and also to collaborate with other groups throughout the world to use to study volcanoes and other structures in the crust and mantle. Specialised studies on the Alpine , the Wellington region and Ruapehu have been supplemented with portable seismometer deployments. The Geonet network has been used to determine the anisotropic structure of the and to determine the stress state throughout . A broadband seismic deployment after the Darfield allowed us to: 1) delineate fault structures within the aftershock sequence before the rupture, 2) determine a rotation of stress directions along the Greendale fault; and 3) use cross-correlation of seismic noise to find the origin of previous enigmatic strong amplification in basins as caused by higher mode Rayleigh waves. Passive seismic studies in the Wellington region complement the controlled source studies in the SAHKE deployment, and current recordings of the Seddon earthquake sequence will allow us to continue such analysis along the strike of the plate. Collaborations with investigators in the US, France and Japan have enabled us to use ocean bottom seismometers to study mantle anisotropy, and to use other countries’ volcano networks to examine the evolution of cracks on volcanoes in relation to eruption. PhD student Adrian Shelley will give a brief presentation on his efforts to model the effects of stress on crack orientation and anisotropy on Asama volcano in Japan.

Institute of Geophysics Symposium 2013

Geodesy and Neotectonics Simon Lamb: Using geodesy to understand deformation in the New Zealand plate-boundary zone.

New Zealand has a rich data-base of geodetic deformation, over the past 100 years, from retriangulation surveys and campaign and continuous GPS. These measurements primarily record the build up of elastic strains, that ultimately will be redistributed during earthquakes. Simple elastic models of slip at depth on a single plate interface at the relative plate motion, without any knowledge of the pattern and rate of surface faulting, have been remarkably successful in describing this deformation. In this talk, I will review what geodesy does and does not tell us about the longer term pattern of active faulting in the New Zealand plate-boundary zone.

Tim Little: Measuring the slip rates of active faults and their application to New Zealand

In this talk I will review methods for assessing slip rates on active faults with particular emphasis on displaced fluvial terrace flights. Challenges for such an analysis include an understanding of how fault slip has interacted with river erosion in time and space, and the need to project displaced (and now eroded) three dimensional landforms to the fault plane, estimation of errors, and dating of faulted landscape surfaces. I will illustrate these techniques with examples from the North Island Dextral Fault belt and the and finish with a current summary of Late Quaternary Slip Rates across central New Zealand.

Institute of Geophysics Symposium 2013

Exploring the Deep Earth

Tim Stern

Over the past 21 years the Institute of Geophysics(IoG) has been involved with exploring the crust and mantle structure of New Zealand with both active and passive seismic methods. Our goal is to learn about fundamental processes in the earth, conduct underpinning research for resource rich parts of New Zealand and address some of the fundamentals of earthquakes. For example the joint NZ-US South Island Geophysical Transet (SIGHT) was directed at understanding continental transform and collision. More recently the SAHKE project (NZ-Japan-US) was directed to unraveling the structure of a subduction zone (beneath Wellington) that is locked. Earthquake studies have also featured over the past two decades with studies of structure, upper mantle seismic wave-speeds and seismicity in both central South and North Islands. In the past few years we have worked with international collaborators to use data from ocean bottom seismometers to extend our reach beyond the shoreline. We also have used links with GNS and industry to study offshore in frontier areas like deep-water Taranaki and Canterbury basins. Some key discoveries are:

 The thickness of the crust beneath the Mt Cook area is about 42 km and the thickness of the lithosphere is about 200 km (twice normal).  The thickest crust is beneath the Wanaka area and is ~ 48 km.  Beneath the central North Island (Taupo –Rotorua area) the original crust has been thinned to a minimum of ~ 15 km and

Institute of Geophysics Symposium 2013

has been under-plated by new mafic rocks , 10 km thick and of P-wave speed of ~ 6.8-7.1 km/s.  The upper mantle P-wave speed (Pn) at ~ 7.4 km/s under the central North Island is one of the lowest recorded anywhere on the continents.  Geological and geophysical data showing rock uplift of ~ 2.5 km in western and central North Island at ~ 5 Ma .  Onshore-offshore seismic work shows the Raukumara Basin to be one of the thickest sequences of sediments in our EEZ.  A significant (~ 8 -10 km) buildup, or underplating, of sediments on top of the subducted plate beneath both Wellington and East Cape, which appear to be the origin and support for the Axial Ranges of the North Island.  A uniform crustal thickness of about ~ 25 km north and west of a line between Mts Taranaki-Ruapehu then north to Opotiki. Across the Taranaki-Ruapehu line there is 7 km step in the thickness of the crust and step in the lithospheric thickness of at least 100 km.  Microearthquake studies in central South Island have discovered seismic tremor and low frequency earthquakes deep on the

Institute of Geophysics Symposium 2013

Atmospheric Physics and Meteorology

James McGregor Meteorology research at Institute of Geophysics

A brief overview will be given of recent and current meteorological research at the Institute of Geophysics. Particular attention will be given to past and present studies of precipitation and atmospheric water vapour. Current research includes an investigation of monsoons in South-east Asia, winter precipitation in North-west India, and examines the performance of precipitation forecasts from high resolution global scale weather models in Australia and New Zealand.

James Renwick Climate dynamics research in SGEES

Abstract: This presentation will give a brief overview of large scale atmospheric dynamics research and teaching undertaken in the Physical Geography group in SGEES. It will touch on atmospheric circulation, the Southern Annular Mode, and interactions between the atmosphere and the Antarctic sea ice field. Research topics to be discussed include large-scale wave motions over the southern oceans, atmospheric forcing of Antarctic sea ice, and recent changes in the seasonality and distribution of regional climate over New Zealand.

Institute of Geophysics Symposium 2013

Palaeomagnetism and Geomagnetism

Gillian Turner Students: Annika Greve, Rimpy Kinger, Elizabeth Cairns, Ben Dixon, Maha Alfhied, Ruth Corkill

Virtually all rocks, sediments and fired archaeological materials contain small proportions of ferrimagnetic minerals, such as magnetite or haematite. These materials are thus capable of retaining records of the magnetic field from the time of their formation or firing, and hence constitute valuable archives of the prehistoric geomagnetic field. Palaeomagnetic studies at Victoria began in the late 1950’s with an astatic magnetometer housed in a wooden hut at Moore’s Valley, 30 km out of the city. With the acquisition of an early model cryogenic magnetometer in the later 1970’s, research moved to New Zealand’s sequences of weakly magnetized, uplifted Neogene marine mudstones, and there ensued numerous integrated studies of their magneto- and bio-stratigraphy, as well as the tectonic significance of their sometimes anomalously rotated palaeomagnetic directions. Since 1999 the Palaeomagnetism and Geomagnetism research group has been based in the School of Chemical and Physical Sciences. It enjoys close links and shares students and projects with the School of Geography, Environment and Earth Sciences. Our main current research project, Unlocking the Secrets of the Geodynamo: the South West Pacific Key, is an investigation of geomagnetic secular variation in the South West Pacific region over the past 10,000 years. Strands of the project include palaeomagnetic studies of lava flows, lake sediments and a novel study of the thermo remanent magnetization of hangi stones. We work closely with

Institute of Geophysics Symposium 2013

volcanologists, limnologists and archaeologists, particularly in the collection of samples. Eighteen months into this Marsden-funded project we are in a position to evaluate our first results – both directions and intensities of the palaeomagnetic field – as shown in some of the accompanying posters. We are also working on regional models of the geomagnetic field – currently from historical records, but with the intention of extending the models back through the Holocene with our palaeomagnetic data. Other members of the research group use palaeomagnetism in their studies of tectonic rotations in the plate boundary zones around Papua New Guinea, emplacement mechanisms (including temperature) of volcanic debris flows on Mount Taranaki, and the magnetic properties of rocks that make up the Kermadec submarine volcanoes.

Ice Physics Huw Horgan : Ice Sheets, Glaciers and Geophysics

Geophysical methods have played a role in understanding the form and flow of glaciers and ice sheets ever since seismic and radar soundings first established their thickness. More recently geodesy and remote sensing have revealed a plethora of surprising glacial phenomena from fast-flowing ice streams with speeds that are modulated by the tides, to active subglacial lakes that exist beneath kilometers of ice and fill and drain on timescales of minutes to years. Here we highlight some of our recent contributions to the study of ice dynamics; all of which have been made possible by geophysical methods. We first track the distribution of water and sediment beneath the West Antarctic Ice Sheet, paying special attention to the transition between the grounded ice sheet and the floating ice shelf. We then examine the ice interior and show that seismic techniques

Institute of Geophysics Symposium 2013

reveal surprising complexity within the ice column. We finish on Tasman Glacier in the Southern Alps, where geodetic observations reveal the interplay between climate and dynamics, and simple correlations mask complex physical relationships.

Mathematical Modelling in Geophysics and Statistics Euan Smith

PhD candidate Jack McCubbine will give a progress report on his project to undertake an aerogravity survey of New Zealand. The project is a collaboration between Land Information NZ, GNS and VUW, with the first objective of providing a more accurate vertical datum (Geoid) for New Zealand, for surveying and earth structure research. To date about 1/3 of the country has been flown and jack will present some preliminary modelling results.

MSc student Grant O’Brien will present his project to model the water level responses to earthquakes in monitoring bores at Lake Dunstan. Similar responses have been observed elsewhere, but the relationship between the bores where level falls and those where it rises in the bores at Clyde is distinctive. Preliminary modelling suggests a common response mechanism but with different time constants for different earthquakes. POSTERS There will be posters on display illustrating aspects of current geophysical research at the Institute of Geophysics.

Institute of Geophysics Symposium 2013