"Seismic Investigations of Glaciers on Axel Heiberg Island" Submitted To

Home , Ice divide

"Seismic Investigations of Glaciers on Axel Heiberg Island"

Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Master of Science Degree

B. B. Redpath McGill University Department of Geology August 1964 TABLE OF CONTENTS Page ACKNOWLEDGMENTS 1

INTRODUCTION 2

GEOGRAPHY AND GEOLOGY OF AXEL HEIBERG ISLAND AND EXPEDITION AREA 3

REFRACTION ME THODS 10

REFLECTION METHODS 24

CONCLUSIONS 42

APPENDIX A - INSTRUMENTS 44

APPENDIX B - LOGISTICS 48

BIBLIOGRAPHY 52

ACKNOWLEDGMENTS

The author wishes to thank Dr. Fritz Müller, leader of the Arctic

Research Expedition to Axel Heiberg Island, for his leadership in the

field and his encouragement during the writing of this paper. Gratitude

is also expressed towards Dr. Vincent Saull for initially suggesting the

project and for his continuing interest and many helpful suggestions.

The author also wishes to thank Keith Smith, who provided valuable

assistance in the field; Alex Becker, whose help in the field and gravity

data were greatly appreciated; Colleen Doyle, who assisted with much of

the drafting and preparation; the Carnegie Institute, which provided

financial assistance for the project; and the Physics Department of the

University of British Columbia which made the seismic equipment avail

able on loan. Grateful thanks are also expressed to many other in

dividuals who, by their contribution of time, effort and needed advice, all helped in the execution of this phase of the Arctic Research Expedition to Axel Heiberg Island .. 2

INTRODUCTION

The work outlined in this the sis was a part of the pro gram of glacial studies undertaken by the Arctic Research Expedition to Axel Heiberg

Island, N. W. T. , during the summer of 1960. The expedition was organized for the purpose of investigating the fields of glaciology, geol ogy, meteorology, bot an y and other closely related subjects as they applied to Axel Heiberg Island.

An undertaking of this nature does not set a precedent in the broad field of Arctic studies: there is a rather extensive history of high latitude studies to r r to. It is felt, however, that this expedition differs from many other s in that the re was a conscious effort t o integrate and cor relate the various field sciences in or der to effect more efficient field operations and achieve a more comprehensive and unified result.

The use of seismic methods to investigate glaciers is a fairly well established field technique. Seismic investigations have been carried out on almost every large body of ice in the world; there is no claim to originality in either application or method of seismic sounding. The purpose of the seismic work was to establish ice depths to be used in the study of the glaciological regime of Axel Heiberg, as well as to provide control for the gravity survey which was carried out concurrently. 3

GEOLOGYandGEOGRAPHY of AXEL HEIBERG ISLAND and EXPEDITION AREA

Axel Heiberg Island is a remote and fairly inaccessible region of the

Canadian arctic. The island forms a single geographical unit with Ellesmere

Island, from which it is separated only by the narrow waters of Eureka

Sound. Its area is sorne 15, 000 square miles, about the size of Swit zerland; it is the fourth large st of the Que en Elizabeth Islands. Axel

Heiberg was discovered in 1899 by a sledging party of Sverdrup 1 s 1898 -

1902 expedition. Fig. 1 shows the location of Axel rg Island and the primary transport routes.

The island can be roughly divided into three topographie regions: a central mountain region, large1y covered by ice; a smooth1y sloping area in the east; and a generally hilly region in the west. (Dunbar, 1956).

Aerial views of portions of the central region are shown in Fig. 2.

A brief comment on the geology of the expedition area is quoted from

Kranck, 1961:

"The central parts of the island around Strand Fiord and Expedition

Fiord consist of highly folded Jurassic and Cretaceous sediments intersected by basic igneous rocks forming flows and sills. The olde st sediments visible are quartzitic sandstones with a few plant fossils

(Jurassic}. On top of this very thick horizon follows soft carbon rich 4.

Map 1 LOCATION OF HEIBERG ISLAND, N.W.T. WITH TRANSPORT ROUTES .

Air Routes lee Breoker Route l' '\

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Fig. 1. 5

Pig. 2a

Fig. 2b.

Fig. 2. Topography of Central Region of Axel Heiberg Island

1. 6

black shales and thereafter a few hundred metres of mixed strata of

shales and sandstone. These strata are comformably overlaid by

volcanic lava ( Cretaceous ), with beds of columnar ba salt alternating

with highly vesicular and tuffitic material. They form a very striking

horizon in the landscape as erosion has usually reached clown to the

level of the main basalt, which, therefore, often forms the crest of the

mountains. Particularly in synclines younger sediments are found on

top of the lava. The other main factor controlling the topography is

gypsum which occurs in enormous quantities, mainly in the centre

of each anticline. In the central parts of the island it is everwhere in

allochthonous position, intruded in the sediments as diapirs. The

original age is probably Pennsylvanian. 11

The two glaciers which were surveyed by geophysical methods are

described by MÜller as follows:

"The White Glacier is a medium size ice stream with a well defined

accumulation basin ..... this north-south running, alpine type, valley

glacier measure s 14. 5 km. in length, having a width of 5 km. in the

accumulation basin and averaging l km. in width in the ablation zone

..... the surface of the White Glacier drops in three gentle steps in the accumulation are a and in four steps, which have almost the char

acter of ice falls, in the ablation zone. The gradient for the whole

glacier ave rages 10 per cent. n 7

''The Thompson Glacier is one of the largest outlet glaciers from the

7250 square kilometres of highland ice, the northern or 1 McGill lee

1 Cap • The glacier measures 35 km. in length from the ice divide,

~!< >:;:: which is at an elevation of approximately 1600 m. , to its terminus

The gradient averages about 4 per cent. for the whole glacier, but

only about one per cent. for its lower half. The width varies between

3 and 5 km. 11 (Müller, 1961 ).

The expedition area is shown in Fig. 3; a more detailed map of the

southern portion of the expedition area is shown in Fig. 4.

>:~The name 11 McGill lee Cap" has been changed to 11 Akaioa lee Cap. 11

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REFRACTION METHODS

Three refraction lines were shot during the course of the field work; one at

Beaver Profile (730 m. long) in the accumulation zone of White Glacier; one at Moraine Profile (710 m. long) near the equilibrium zone of White

Glacier; and one at Upper lee Profile (1925 m. long) on the Akaioa lee

Cap. The primary purpose of these surveys was to determine longitudinal wave velocities, although the refraction line on the ice cap was also in tended to provide a positive value of the depth of rock, since reflections in this area were either not obtained or were somewhat indefinite.

A detailed description of the seismograph and the function of its various components will be found in Appendix A; Fig. 11 shows the instruments mounted on a small tobboggan. Comments on transportation of personnel and equipment in the field will be found in Appendix B.

The seismograph was operated without filtering or AGC for all of the re fraction work. The blaster unit was connected to the camera by means of wire wound on a commutated reel. As a result of experience with this method, radio communication, including transmission of the shot break, is recommended for this type of operation since it permits a much greater degree of freedom in movement, and allows long, detailed reversed re fraction lines to be run without being hampered by long lengths of 1phone wire.. ll

A geophone spacing of 15 meters was employed on all refraction lines, this spacing being the largest that could be obtained with the seismic cable used. A larger spacing would have been an advantage on the ice cap. Charge sizes ranged from approximately 500 gms. to 15 kg, depend ing on the shot distance. The seismic stations were surveyed with a Wild

TO theodolite, a light weight and rugged instrument well suited for this type of work. Distances were measured by stadia.

The initial portions of each of the three travel-time curves are shown in

Fig. 5. The similarity between the curves for Beaver and Moraine

Profiles was not expected; surface conditions were quite different in the two zones; Beaver Profile is four km. up-glacier and 400 m. higher in elevation than Moraine Profile. The travel-time curves for Beaver and Moraine Profiles indicate a nearly uniform velo city with increasing depth; the curve for the Upper lee Profile shows a definite velocity in crease with depth.

Least squares calculations were performed for the straight line portion of each of the three curves in order to arrive at an accurate velocity representative of the areas where the refraction lines were run. The following velocities resulted: Upper lee Profile 3900 m/ s. ; Beaver

Profile, 3765 m/ s.; Moraine Profile, 3735 m/ s. A mean value of

3750 m/ s. is used for White Glacier and Thompson Glacier. These values are considered correct to within one per cent.

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When p1otting the travel-time curves it was found that there was a small

amount of time mismatch between coïncident points in adjacent groups of

12 points (i.e. the 12 detectors on the sei smic line ). This mismatch is

the result of using a progressively more distant shot point and keeping

the detectors fixed. Ideally the same shot point should be used each time

and the detector s should be moved, this would in sure that the ray path

near the shot point would be nearly the same for each shot and would

eliminate the effect of surface variations in the ice from one location to

another. However, it was felt that the additional time and effort that

would have been required to relocate the instruments and cable for each

shot was not warranted.

The travel-time curve for the Upper lee Profile was integrated according

to the Herglotz-Weichert-Bateman equation:

D 1 -1 Vd H - -rr-. scosh Vx dX 0 in which H the depth at which the velo city is V d

Vd =the velocity (on travel-time curve) corresponding to a distance D from the shot point

V x =the velo city (on travel-time curve) corresponding to any distance X from the shot point

X = distance from shot point

The integration is performed graphically by choosing a particular 14 distance D and the corresponding velocity Vd (obtained from the tangent

-l Vd to the travel-time curve at distance D), and plotting values of cash Vx against X, where X is any distance less than D. The area under the re- sulting curve, when multiplied by ~ , is the depth at which the velocity is Vd. The graphical integration is repeated for decreasing values of D, and a gr a ph is drawn of the variation of velo city with depth. The values of D chosen for the ice cap were: 5, 15, 25, 35, 45, 60, 80, l 00, 130, l 70, 210, and 250 m. The resu1ting curve of ve1ocity vs. depth is shawn in Fig. 6.

The curve of ve1ocity vs. depth may be converted into one of ice density vs. depth by means of the relation: -4 density = 2. 21 x 1 0 ( 1 + O. 00061 T )V p + O. 059 in which T =temperature of ice in Oc

V p= ve1ocity of longitudinal waves in ice. (Robin, 1958).

The curve of ice density versus depth, based on the above formula and the velocity-depth curve obtained from the refraction line on Akaioa lee

Cap, is shawn in Fig. 7; an arbitrary temperature of -l5°C was used in the calculations. If a temperature of -21Pc is used, which is the temperature measured at a deptr• of l Om. on the ice cap, then the curve is shifted to the right by less than one per cent. Using the maximum velo city measured on the ice cap of 3900 m/ s and the measured temperature of -21 °C, a value of O. 91 results as the density of ice at depth on e e

VELOCITY ( METERS PER SECOND) 1000 2000 3000 4000 0 1 1 -o~ -..,~ 10- ~

20- U) -0:: ~ ~ ::E ...... _30- a· Ul J: t a. LaJ 0 .\ 4o- \ 0

~ 50- VARIATION OF SEISMIC VELOCITY WITH DEPTH AKAI OA ICE CAP \

60~------.J Fig.6 16

DENS1TY ( GRAMS/CC) 0.4 0.5 0.6 0.7 0.8 0.9

20 0

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4 ( DENSITY• 2.21 11 10- ( 1+0.00061 T) Vp + 0.0!19) \

VARIATION OF' 1CE DENSITY WITH DEPTH AKAIOA ICE CAP

Fig. 7 17

the ice cap. Similarly a velo city of 37 50 m/ s and a temperature of -l5°C

results in a value of O. 88 for the density of ice at depth in the region of

Moraine Profile on White Glacier.

It is possible to construct a diagram of the wave front generated by an

explosion in an inhomogeneous medium, such as the top 50 or 60 m. of

ice on the ice cap; the required data are the travel-time curve and the velocity vs. depth curve. The procedure for deriving a wave front dia

gram will be given below along with an illustration of its use in computing

depth to rock on the ice cap.

Using reciprocal values of velocity (dH/ dt) obtained from the depth vs. velocity curve, the variation of dt/ dH with depth is plotted; this new curve

is then graphically integrated to obtain the curve showing vertical travel time vs. depth, as shawn in Fig. 8. It is now possible to determine three points on a wave front for any given time. A point vertically beneath the explosion corresponding to a time T may be read off the curve vertical travel-time vs. depth. A second point at time T on the horizontal axis

(i.e. the surface) may be read directly from the travel-time curve. The third point may be determined from the depth vs. velocity curve. If it is assumed that at time T the ray has penetrated to the deepest point on its path, then it will also have reached one half of the horizontal distance which corresponds to a time 2T on the travel-time curve, and the tangent to the travel-time curve at this distance (corre sponding to 2T) will give the 18

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10 ro so 50 60 DEPTH (METERS)

DEPTH-TIME CURVE FOR A SEISMIC WAVE AKAIOA ICE CAP

Ft o. a 19 velo city of the wave at time T; with this velo city the depth of penetration may be obtained from the depth vs. velo city curve, · the two coordinate s necessary to define the third point on the wave front for time T are now given. The wave front diagram constructed from the data pertaining to the Akaioa !ce Cap is shown in Fig. 9.

An illustration of the wave front diagram is given by the calculation of depth to rock on the Upper !ce Profile, using the data from the refraction line which was run from station C24 to station Cl8. The refractions from rock ( 5200 m/ s. ) were plotted on the travel-time curve and extrapolated to intersect the first arrival plots (3900 m/ s. ) at a critical distance of

3690 m., and extrapolated back to a time intercept of. 263 sec. See Fig.

1 O. Computing the depth to rock by means of the standard time intercept formula results in a depth of 775 m., whereas a depth of 697 m. results when when the standard critical distance formula is used. These calculations do not take into account the gradual increase of velocity with depth for the first 50 or 60 m. of ice; this accounts for the large difference in the two values.

To correct for the variation of velocity with depth it is assumed that the ice has a uniform velocity below a depth of 80 m. ; we are therefore interested in the corrections to be made to the time intercept and critical distance to compensate for the variable velocity in the top 80 m. of ice. 20

HORIZONTAL DtSTANCE {METERS) to 10 10

::z:, t a. LtJ 0

SEISMIC WAVE .. FRONT AND RAY PATH DIAGRAM AKAIOA ICE CAP •vt- ftlltONTS AAE 5, 10, 1!, 20, 25,30,35 MILLISECONDS AFTEft Dr1'0NATION

FIQ. 9 21

From the ratio of the velocity of ice to that of the rock (3900: 5200), a critical angle of 42° at the ice-rock interface is obtained, therefore a ray on the wave front diagram that emerges at 42° to the vertical at a depth of 80m. will closely approximate the true situation; it is found that a ray meeting these requirements will take . 033 sec. to penetrate to a depth of 80 m. See Fig. 9. It follows that the refraction from bedrock must be lowered on the travel-time curve by twice this amount, or . 066 sec. , and that the direct wave must be lowered by the time intercept of its straight line portion, or . 027 sec. , in order to reduce the travel-time curve to a datum of -80 m. Refer to Fig. 1 O. A new time intercept for the refraction of . 197 sec. and a new critical distance of 3080 m. will result from the above operation; depths below the -80 m. datum of 581 and 582 m. respectively are the result of using these new values in the standard formulas, giving a total depth to rock of approximately 660m. e e

ctor Surface Shot ooinf

------~-\------80m dotum/ '-.·033sec. trovel tlme for first EK>m.

N Cl) N 0 z 0 (.) Reduced eritieal diatonce laJ Cl) =3080m. 1 laJ Time lntercept ~ ...

0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 DISTANCE - METERS

TRAVEL-TIME CURVE REDUCTION FOR COMPUTING DEPTH TO ROCK- AKAIOA ICE CAP Flg.IO 23

c ro 0'1 8' ...0 ...0 0 H ...... ro E Cl) c 0 'U .....

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REFLECTION METHODS

Reflection stations were located at varying intervals along the profiles which had been selected for study by the glaciological team as a whole.

The major profiles were: Beaver, Moraine, and Anniversary Profiles on the White Glacier; Eureka Profile on the Thompson Glacier; Upper lee

Profile on the Akaioa lee Cap. The seismic stations are shown on each profile cross section as well as on Fig. 4.

An L-shaped seismic cable configuration was employed at nearly all of the reflection stations; six detectors (each consisting of a single geophone) were used in each arm of the L. Shots were detonated off both ends of each arm at varying distances from the nearest detector, typically about

100 m.

Different instrument settings of gain, AGC, and suppression were tried at each location until what were felt to be usable records had been obtained.

A frequency passband of 50 eps to 90 eps w as used for almost all of the reflection work. An ice drill of the coring type was used to bury the dynamite (60% gelatin) charges one to two meters beneath the soft surface snow and where necessary; charges were of the order of 500 gm. to l kgm. The geophones were also placed beneath this soft surface layer where it existed. The shot break was transmitted by 1phone wire to the seismograph. During the latter part of the summer and on the lower 25 elevations of the glaciers the charges were laid on the surface of the ice.

Laying the charge on the ice surface made it necessary to increase the size of the charge; a part from a slight increase in the amplitude of the surface waves generated by the explosion, the overall quality of the seismic records was not affected too adversely. Much time was saved by surface shooting because drilling with the type of coring drill used proved to be a time consuming procedure.

Surface wave velocities generally varied over a range of 800 to 1750 ml s., the lower values being obtained on Beaver and Upper lee Profiles. Very strong surface waves with a velocity of 800 to l 000 ml s. were present on the records from the Upper lee Profile.

No shear waves were recognized on any of the records. A direct shear wave, having a velocity very close to that of surface or Rayleigh waves, would be entirely masked by these surface waves at small shot distances; a shear wave arriving at the surface at an angle close to the vertical

(say 40°} would be attenuated by the vertically sensitive geophones since the particle motion of such a wave would be essentially horizontaL

The three seismograms shown in Fig. 12 illustrate feature s that are common to the majority of the records obtained. The three seismic re cords in Fig. 12 were recorded at the same location: Station M9, Moraine

Profile, White Glacier. The distance from each shot to each trace is 26

•Fig. 12. Sei smic Records from Moraine Profile 27 shown on the individual traces. All 12 detectors were in line; shots were fired to the north of the seisrnic line on the first two records and to the south on the last. Note that the detector spacing on the last record is less than the spacing on the first two. Tirne lines are . 005 sec., with heavier line s every . l 00 sec. The shot break, or zero tirne, is aligned on the three records.

It is difficult to say whether the event rnarked R on the top record (i.e.

MV21) is a refraction or a r ction from bedrock. The apparent velocity of 6600 rn/ s. seerns high for the velocity of bedrock, but not out of reason, especially if a ba salt underlies the ice. If the event R is considered to be a reflection, then the 1 step-out 1 tirne, from first detecter to last, is less than would be expected. ·It is possible that a reflection and a re fraction have arrived alrnost sirnultaneously. The overall evidence is in favour of R being a refraction but in either case an average depth to rock of 260 rn. is the result. Strong surface waves with a velocity of

1720 rn/ s. begin to arrive at . 290 sec.

The middle record (i.e. MV71) illustrates the effects of the autornatic gain control (AGC). The darnping effect of the AGC is apparent after the arrivai of the surface waves. A strong burst of energy, i.e. the sur face waves, irnrnediately reduces the gain and the output of the arnplifiers to a suitable recording level, however, it takes a finite arnount of tirne, approxirnately. 035 sec., for the AGC to release and allow the arnplifiers 28 to return to a higher leve! of amplification; during this recovery time a comparatively weak event like a reflection will not be recorded. From the depth obtained on the top record, a reflection would be expected at about . 135 sec. on this record; there is an indication of a reflection at approximately this time (. 139 sec.) on tr-aces 7 to 12 (i.e the bottom six traces). Traces 1 to 6 show nothing ·at this time since the AGC has not yet released on these traces, having just brought the surface waves under control. If there were no AGC at all, then this record would appear much the same as the top record does after the arriva! of the surface waves, that is, the traces would swing clear off the recording paper.

The bottom record {i. e. M4ll) shows an •event at about . 130 sec. The strong and probably spurious event at . 185 sec. is unaccounted for, although it is stronger and more apparent than the reflection, it does not occur on any of the other records shot at this location; it is possible that it is the result of a chunk of ice from the explosion falling near the seismic cable. A possible multiple reflection occurs at time . 250 sec.

Reflection depths were computed with the equation:

in which H = depth V p = velocity of e

T = total reflection time

D shot distance 29

In some cases where appreciable non-parallelism of the ice surface and the rock surface was felt to exist, a simple graphical method was employed whereby elliptical arcs were drawn with the shot and detector stations as the two focii of an ellipse and the total reflection path {i.e. reflection time x velocity) as the sum of the two radii; the line of tangents drawn to these elliptic arcs represents bedrock surface.

The depth vs. time curve for Upper lee Profile, Fig. 8, was used in com puting the ice thickness beneath station C24 on this profile, where a fairly reliable reflection was obtained at . 275 sec. As was the case in the refraction ca:nputations, this time was converted to a depth by taking into account the variable velocity of the surface ice. A ray travelling almost vertically (i. e. a reflected pulse where the shot distance is short com pared to the depth of ice) would require . 023 sec. to travel the fir st

60 m. , and this much again on the return path; if . 046 sec. is subtracted from the total reflection time of . 275 sec., then the ray will tra',·el at 3900 m/ s for . 229 sec. , which is equi·v'alent to a depth of 446 m. , hence a total depth of 506 m. is obtained at C24.

The individual reflection profiles are discussed below.

Beaver Profile - Fig. 1:1

This profile, located in the accumulation basin of White Glacier, was the first profile to be surveyed by seismic and gravity methods. The reflec- tians were, in general, easily identified, except a.t station B6 where 30 positive reflections could not be identified. The excellent agreement be-

tween the depths derived by seismic and gravity data lends support to the concept of providing the occasional control point with the seismograph

and filling in the interme details with the gravimeter, at least in

areas such as Beaver Profile, where the local topography is not pro nounced and does not create problems in terrain corrections for

gravity data. Two sample records are reproduced in Fig. 18 and 19.

Possible multiple reflections were noted on a number of records, as the one in Fig. 18.

Moraine Profile - Fig. 14

This profile lies in a narrow valley with fairly high walls, this fact,

combined with the suspected presence of a gravity gradient, could account for the disagreement of the seismic and gravity results. There is no

seismic evidence to support the gravity interpretation, except between

stations M9 and Ml O. Reliable reflections were not obtained at all of the

surveyed points, particularly M6 and M7.

Anniversary Profile - Fig. 15

Marked disagreement between the seismic and gra·~-ity interpretations is again evident on this profile. r etions recorded between station:a

A3 and A4, and between stations A5 and A6 are reliable. See Fig. 20 for a sample record from this profile; the reflections obtained at station A9 are not as positive, probably because of the curvature and 31 slope of the valley wall. It cannat be positively stated that the gravity data are incorrect; any reflections arriving from a depth corresponding to the gravity information would be completely obscured by surface waves and AGC on all of the records taken on this profile.

Snout of White Glacier

Two reflection stations were occupied on the snout of White Glacier, but no reflections were recorded; this is possibly the result of the snout being underlain by morainal mate rial and the lack of a defini te ice -rock contact; this is supported by the temperature profiles taken in this area, in which the projected rature at a depth of only 55 m. is 0°C.

Eureka Profile - . 16

This profile has been drawn on the basis of the gravity results. Positive reflections were obtained at station E7 only, and the computed depth agrees very well with the gravity depth value, although it would appear that the gravity profile is slightly too deep. This profile is r to

Beaver Profile in the respect that it has a great ral extent compared to the local relief.

Upper lee Profile - Fig. l 7

This profile was characterized by an almost complete lack of identifiable reflections and has also been drawn on the basis of gra"'çity A long refraction line was run to provide a positive depth determination, and ...

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Scale

...

900

PROFILE

--····

(Q)

SECTION

GLACIER

::·

Fig.l4

800

......

meters--

•

(Q)

Mï

WHITE

CROSS

...

700

MORAINE

····

...

1 •

:':

··

....

··

600

··-··

o-@-0

500

400

•

300

;

-_,-

. .

200

--~

100

1-----+--

1------t--

500~---+-

6001-----+- 700

900

800

1000

(/) Q)

Q) E

....J

l.IJ ....J

l.IJ

<[ l.IJ (/) CD

w ....J >

0 z ~

l.IJ

l.IJ 1400

1300

•

. •

">.

1200

•

Al\

6._6~

A\0

1100

\8)

depth

station

depth

stake

1000

Gravit_y

Seismic

Profile

Seismlc

•

-o_-8-

900

•

-6-

800

PROFILE

•

5,000

GLACIER

SECTION

1: 1:

700

meters

Fig.l5

•

Scole

•f_®-L

600

WHITE

CROSS

•

ANNIVERSARY

500

6-@-

•

400

•

300

200

~~b

::~·:·:~

100

-----

t--1

1------+----

t------+----+--

1-----f--

100

400

600~----~------~-----

500 3001t--- 200

...

Cl) Cl)

(/)

__J w w >

.....J

w > w w .....J >

(/)

0 ~

Il Il

•• ••

E E

3000 3000

.. ..

2800 2800

depth depth

station station

•.. •..

b b

stoke stoke

. .

EIO EIO

. .

Profile Profile

Seismic Seismic

Grovity Grovity

2600 2600

.. ..

b b

e e

@ @

.. ..

. .

b b

. .

E9 E9

2400 2400

2200 2200

b b

ES ES

2000 2000

...... •...... •...

~ ~

b b

E7 E7

1800 1800

' '

...... •...... •.

GLACIER GLACIER

1600 1600

····· ·····

10,000 10,000

PROFILE PROFILE

16 16

SECTION SECTION

1: 1:

6 6

. .

E6 E6

35 35

Meters Meters

Fig

le: le:

Seo Seo

1400 1400

...... •...... •.

CROSS CROSS

EUREKA EUREKA

THOMPSON THOMPSON

b b

E5 E5

1200 1200

······•·· ······•··

......

1000 1000

:,;· :,;·

b b

E4 E4

. .

....• ....•

......

800 800

b b

E3 E3

600 600

~: ~:

:: ::

......

400 400

b b

E2 E2

200 200

El El

0 0

-L© -L©

0 0

200 200

-200~~~-----+------+-

......

Q) Q)

tl) tl)

~ ~

.....J .....J

w w

> >

w w

~ ~

0 0

z z

<( <(

0 0 w w (]) (])

> >

.....J .....J

w w

(/) (/)

.....J .....J

w w <( <(

w w > >

. .

·: ·:

~ ~

; ;

cr cr

8.4 8.4

.··.·~~··.-'

...•.. ...•..

. .

C28 C28

• •

7.8 7.8

depth depth

station station

depth depth

stake stake

C26 C26

Seismic Seismic

Profile Profile

Seismic Seismic

Gravity Gravity

7.2 7.2

• •

6 6

@ @

1 1

C24 C24

C22 C22

line line

6.0 6.6

C20 C20

refraction refraction

5.4 5.4

1 1

Cl8 Cl8

,. ,.

·· ··

4 .8

CAP CAP

Cl6 Cl6

PROFILE PROFILE

000 000

SECTION SECTION

17 17

4.2 4.2

ICE ICE

30,

:·

36 36

1 1

iz~;;·r,:I~::J,j;i;,!~;"

ICE ICE

l4 l4

= =

Fig. Fig.

Kilometers Kilometers

ale ale

'''·''r'~ '''·''r'~

Sc Sc

3.6 3.6

CROSS CROSS

AKAIOA AKAIOA

Cl2 Cl2

UPPER UPPER

3.0 3.0

......

CIO CIO

....•...... •..

. .

.. ..

2.4 2.4

,.. ,..

..:·::

C8 C8

......

. .

·····•···· ·····•····

1.8 1.8

......

. .

.. ..

C6 C6

1.2 1.2

C4 C4

0.6 0.6

[email protected]®--b-b--b-6:::.....6-

.. ..

C2 C2

......

M.. M..

CO CO

0 0

600 600

300 300

900 900

1200 1200

1500 1500

1800 1800

E E

OJ OJ

C/1 C/1

~ ~

:::> :::>

w w

~ ~

....J ....J z z

0 0 w w

Œl Œl

w w

<{ <{ w w

Cf) Cf)

w w

....J ....J

~ ~

....J ....J > > 37 the depth computed agrees very well with the depth provided by the

gravity survey; this again supports the logistic advantage of the

gravimeter in areas having little local topo.graphy. A reasonably good reflection (see Fig. 22) recorded at station C24 gives a depth of

506 m. which agrees well with the depth according to gravity information.

A number of se1ected seismograph records are briefly discussed be1ow.

Fig. 18 This record clearly shows the arrivai of a reflection

R, and what is very probably a multiple reflection,

M. The clark areas on this and other records are due

to light leaking into the seismograph camera.

Fig. 19 This record was taken at the reflection station

adjacent to the one where the record in Fig. 18 was

recorded, but it was recorded with a gain l Odb lower.

The reflection R, although still clear, is not as

obvious as it is in 18.

Fig. 20 The event marked R on the bottom six traces is

a reflection, it doe s not appear on the top six

traces because of AGC damping.

Fig. 21 Surface waves with a velocity of 1730 m/s, and marked

S, are clearly shown on this record. reflection

R is apparent on the lower six traces, but is part1y

obscured by noise on the upper six trace s. 38

Fig. 22 This record shows the slow surface waves S with

a velocity of about 1000 rn/ s that were recorded on the

ice cap. What appears to be a reflection R, is masked

by surface noise and the air wave on the bottom six

traces.

Fig. 23 This is a refraction record taken to determine the ice

thickness on the Upper lee Profile. The arrivai of the 3900

ml s direct wave, is clear, as is the arrivai of the

refraction, R, with a velocity of 5200 ml s. 39

111 11111 1111111

IIEAVER PROFILE SHOT BREAl< .t. MCORO M51 • 822 OEQ SPACING • !Ill "L" SHOT OIST. • !10 M.

... R r~

Fig. 18. Record from STN B22 - Beaver Profile

BEAVER PROFILE RECORD Bllll• 818 GEO. SAIICING •!!M. ' L" SHOT OIST. • !1011.

, .t. rrr~~~.LJ R .-H.-H1f+++H-+++++-++t++-++f-H.+H~++ 1 1 11 1 Il 1

Fig. 19. Record from STN 818 - Beaver Profile 40

::~RED~:. =~E ...t.+++-i-+-+-1-+-1-+-!.+'Ul GED SPACING • !!M. "L' +-l-+++++4--1-t++-HI\ SHOT DIST. • 90 M.

Fig. 20. Record from STN A6 - Anniversary Profile

1 1 1 l i l l 1 I l I l l 1

1 1 EUREKA PROFILE l RECORD E 143 • E7 OED. Sf'jiClNG •!!M. "L' 1-+4-+-1~+\

Fig. 21. Record from STN E7 - Eureka Profile ,....., e e

~- -- ,-·,

UPPER IŒ PROFILE RECOfiO C341 • C24 GEQ SPACING • !SM..._ . SHOT DISt • 90 Il .

4,.._1 ..,.~ "V"!"· "

,.j:o.. . 1.: 1 1 1 1 1 IJ' 1 1 1 1 1 iJI 1 \1 • 1 1 1 1 11111 , 1 1 1 1 11111 1 1 1 I l l t' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I l l I l l 1 1 1• 1 1 ,_.

fig. 22. Record from STN C24 - lee Cap

lll\l\1\l\1.\\lli(J~ l1111111111111IMIIIH lllllll fltoflllllllllflllll Hli ~ltt++Htltt-NttiliW'+~

UPPER ICE PROFILE RECORD ICY·IeC (REFRACTION) GEO. SfiiQ NG• I!I M. (I NLINE) SHOT DIST. • 176010.

rfig. 23 . Record from lee Cap Refraction Line 42

CONCLUSIONS

The seismic survey on Axel Heiberg Island has provided most of the information that was sought after. Cross sections of White Glacier, Thomp son Glacier and Akaioa lee Cap have been constructed on the basis of seismic and gravity information. The general agreement between the two geophysical methods is reasonably good, but notable differences, such as Anniversary and Moraine profiles on White Glacier, also exist.

It is noted that the two methods disagree in those cases where comparatively large terrain corrections are required for the gravity data. In areas with little topographie relief the agreement between the sei smic depths and gravity depths is very good. This strongly supports the allied use of both methods in regions where gravity corrections are not large and where the definite logistic superiority of the gravimeter may be employed to advant~ age.

The seismograph used was very well suited to the nature of the survey, i. e. shallow reflection work. It proved to be a rugged and dependable instrument. The seismic cables had a detector take-out spacing measured in feet, since the metric system was used exclusively on the expedition, a cable with a convenient metric would have been preferable, as would have been a cable with a lar r spacing than that a.vailable. 43 Due to generator breakdowns, some difficulty was experienced in charging

the 12. volt storage batteries required to power the seismograph; it is felt

that a small four cycle generator would have been more reliable than the

two cycle machine used.

The ice drills used for placing shots were very slow and were eventually

abandoned in favour of surface shooting with some sacrifice of record

quality. A light, manually powered ice drill of an improved type would

have been a definite advantage in speeding operations and improving

record quality.

A radio equipped blaster and seismograph would have been a logistic

advantage for certain portions of the work, however, the direct wire link

between the blaster and the seismograph proved to be a trouble free and

rapid method for transmitting the shot break for small shot distance s.

In those cases where the seismic and gravity interpretations disagree

markedly, there is no seismic evidence in favour of the gravity version,

however, in the case of Anniversary Profile where the gravity data result in shallower depths, any seismic event supporting the gravity data would be obscured by shot noise (surface waves) and AGC damping 44

APPENDIX A

INSTRUMENTS

The seismograph, a 12 channel, high resolution, reflection type, was manufactured by Texas instruments Ltd. of Houston, Texas. The functions of the various components are briefly described below. A block schematic of the seismograph is shown in Fig. Al.

Detectors: The geophones are of the velocity or moving-coil type with a natural frequency of 30 eps. The geophones used had a spike base which is not suitable for use on hard ice, a tripod base is preferable.

Input Unit: This unit connects the seismic cable to the amplifier inputs.

It measures the resistance of the cable, the geophone, and the primary side of the amplifier input transformer. It provides a test signal variable from one microvolt to O. 1 volt in 10 db steps. The input unit has a meter for reading the voltage of the test oscillator, the output "\;·oltage of the amplifiers, and the battery voltages.

Amplifiers: The amplifiers must operate within rather strict require= ments, viz: they must be distortion free; they must give a nearly con stant output for input voltages of from less than one micrm?olt to O. 1 volt, i.e. a dynamic range of l 00 db. Constancy of output over this wide range is achieved by automatic gain control (AGC which itself must produce no distortion, and must act fast enough to permit the recording of ev-ents 45

of greatly different amplitudes occurring within . 030 sec. or more of

each other. At the instant before the shot is fired the amplifiers are

receiving only background noise, and so the gain is at a maximum. When

the shot is fired large signais are applied to the amplifier, and these

signais must be brought under control within . 030 sec. This severe re

quirement is met by providing initial attenuation to the amplifier before

the shot is fired and removing the attenuation after the shot has been fired.

This function is performed by the initial control unit described below.

Initial Control Unit: This unit reduces the gain of the amplifiers before the shot is fired and returns full AGC action afterwards. It controls the

gain of the amplifiers when operated without AGC, and it limits the gain of the amplifiers to any desired value.

The initial con,trol unit produces a 5000 eps signal which is fed into the amplifiers just behind the filters. The AGC adjusts the gain to a level necessary to bring the 5000 eps signal under control. The seismic

signal will then be applied to an amplifier whose gain has been set by the initial control voltage; the 5000 eps frequency of this control voltage is too high to interfere with the seismic signais.

The control unit also has a tripping amplifier, the function of which is to receive a s smic signal from the output of the amplifier, amplify and rectify this signal so as to bias the tubes to eut off the 5000 eps signal, and thus to bring the amplifier to fully automatic gain control. e e

INITIAL CONTROL AND TRIPPING AMP.

1 -----,

l Ilot INPUT INPUT UNIT STAGE

L ______l -----...-----...... ------.... (AMPLIFIER) ~ ....----..... 0' ,.....----... ,...... --....

CHARGE~

(Tl ME BREAK)

BLOCK SCHEMATIC OF SEISMOGRAPH

Fig. Al 47

Filters: High-cut and low-cut filters are provided for each bank of six amplifiers so that a desired pass band may be selected. The low-cut frequencies are 30, ·40, 50, 70, 90, 120, 160, 210, 270, and 360 eps; the high-cut frequencies are 60, 90, 140, 210, 320, and 480 eps. Filte:r' type may be selected from single section constant K, single section M derived, double section K, double sectio11 M, and K=M combination.

Output Unit: This unit receives the output from all amplifiers and drives the recording galvanometers; the unit also provides for 50o/o mixing of the outputs.

Recording Oscillograph: The oscillograph records the amplifier outputs against a time base on photographie paper; it also records the instant of explosion. The recording paper is fed past the galvanometers at 30 inches per second. The time base consists of a 100 eps tuning fork which modula tes the rate of rotation of a slotted drun1 containing a light source; time lines are spaced every . 005 sec. on the recording paper.

Blaster: The blaster is of the condenser discharge type; it produces a pulse which is fed to the oscillograph to record the instant of detonation of the explosive charge. 48

APPENDIX B

LOGIS TICS

The matter of transportation merits special mention because the trans

portation of men and materials consumes a large part of the total time

available for field work.

Long distance moves, such as from one area of study to another, were

accomplished with small aircraft equipped with skiis or oversize balloon

tires. See Fig. B3. Such aircraft approach the helicopter in versatility,

and have the advantage of less cost per flying mile and less maintenance.

Short moves over ice and snow were made with 12 foot Nansen sleds pulled by a motor tobboggan under favourable conditions, and by man power under less favourable conditions. The Nansen sled is remarkable for its simplicity, maneuverability and stability; the sled has a high load

capacity, of the order of 400 kg. , and its durability under the roughest

conditions is very good. The Nansen sled was used over the entire length of White Glacier. See Fig. Bl.

The motor tobboggan is somewhat restricted as far as operating conditions are concerned. It has a high tractive force on hard packed

snow and smooth ice, but is not well suited to conditions of rough ice,

such as on the lower portion of White Glacier, where the tobboggan eventually failed and was replaced by manpower. See Fig B4. 49

Fig. B 1. Nansen Sled Cros sing Meltwater Stream

Fig. B2. Probing for Crevasses with lee Axe on White Glacier 50

Small wooden tobboggans were tried on the Thompson Glacier, but they proved to be too flimsy and were abandoned. These same tobboggans served quite well on the ice cap, where conditions are ideal for almost any form of transportation; they were limited only by their small load capa city.

Crevass regions pose particular problems and necessitate the use of skiis or snowshoes and the roping together of individuals. Progress was slowed in the upper region of White Glacier by the pre sen ce of crevasses, and it was often necessary to probe every few feet of the way with an ice axe. See Fig. B2. In the lower regions of the glacier, and during the later part of the summer, the snow bridges over the crevasses had fallen in, and so any hidden danger was removed. Large melt-water streams occurring in the later part of the season proved to be barriers that were difficult to overcome, especially with a heavily loaded sled. 51

Fig. B3. Piper Aircraft Equipped with Large Balloon Tires

Fig. 84. The Elia son Motor Tobboggan 52

BIBLIOGRAPHY

ALLE;N, C. R., ( 1953), Seismic and Gravity Investigations on the Malaspina Glacier, Alaska, Trans. A. G. U., Vol. 34, No. 5

BECKER, A. ( 1961 ), Gravity Measurements, in Preliminary Report, Jacobsen-McGill Arctic search Expedition (B. Muller ed.) McGill University, Montreal.

BECKER, A. ( 1963 ), Gravity Measurements on Axel Heiberg Island, PhD Thesis, McGill University, MontreaL

BEHRENDT, J. C., (1963), Seismic Measurements on the lee Sheet of the Antarctic Peninsula, Journal Geophy Res., Vol. 68, No. 21.

BENTLEY, C. R., Pomeroy, P. W., and Dorman, H. S., (1957), Seisrnic Measurements on the Greenland Cap, Annales de Geophysique Tome 13, Fasc. 4.

CRARY, A. P., (1956), Geophysical Studies along Northern Ellesmere Island, Arctic, Vol. 9, No. 3.

DOBRIN, M. B. (1952), Introduction to Geophysical Prospecting, McGraw Hill Book Co. , Inc. , Toronto

DUNBAR, M. and Greenaway, K. R., (1956), Arctic Canada from the Air, Defense Research Board, Ottawa, Canada.

HEILAND, C.A. (1940), Geophysical Exploration, Prentice Hall, Inc., New York.

HOBSON, G. D., (1962), Seismic Exploration in the Canadian Arctic Islands, Geophysics, Vol. XXVII, No. 2.

HOEN, E. L. W. (1963}, The Anhydrite Diapirs and Structure of Central Western Axel Heiberg Island, Canadian Arctic Archipelago, PhD Thesis, McGill University, MontreaL

HOLT ZSCHERER, J. J., ( 1 954), Contribution a la Connaissance de l'Inlandis du Groenland, Expedition rancaises, . III Paris. 53

KRANCK, E. H., (1961 ), Gypsum Tectonics on Axel Heiberg Island, Preliminary Report, Jacobsen-McGill Arctic Research Expedition (B. Muller ed. ), McGill University, Montreal.

MULLER, F., (1961), The Areas Selected for the Glaciological Studies, Preliminary Report, Jacobsen-McGill Arctic Research Expedition (B. Muller, ed. }, McGill University, Montreal.

REDPATH, B., (1961), Sei Jacobsen- Mc Gill ------~------·A retie Re se arch McGill University, Montreal.

ROBIN, G. de Q., (1958), Seismic Shooting and Related Investigations, Glaciology III-Norwegi.an, British, Swedish Antarctic Expedition Scientific Resuits, VoL V - Published by Norsk Polarinstitutt, Oslo.

ROTHLISBERGER, H. (1955), Glacier Physics, Studies on the Penny lee Cap, Baffin Island, Part III, Journ. Glac. Vol. 2, No. 18.

THIEL, E. and Ostenso, N. A., (1961 ), Sei smic Studies on Antarctic Ice Shelves, Geophys s, Vol. XXVI, No. 6.

WEBER, J. R., (1960), son of Gravitational and Seismic Determinations on the Gilman Glacier and Adjoining Ice Cap in Northern Ellesmere Island, Report Hazen ll, Defense Research Board, Canada.