THE STRUCTURE OP THE EARTH'S CRUST IN THE VICINITY OP VANCOUVER ISLAND AS ASCERTAINED BY SEISMIC AND GRAVITY OBSERVATIONS By WILLIAM ROBERT HUGH WHITE M.A., The University of Saskatchewan, 195^ A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OP PHILOSOPHY in the Department of Physics We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1962 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia, Vancouver 8, Canada. Date The University of British Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION PUBLICATIONS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 1. Milne, W.G. and W.R.H. White. A seismic investigation of mine "bumps" in the Ciiews- nest Pass Coal Field. The Canadian Mining of and Metallurgical Bulletin, 51, No. 559, 1958. WILLIAM ROBERT HUGH WHITE 2. Milne, W.G. and W.R.H. White. A seismic survey in the vicinity of Vancouver Island, British Columbia. Publications of the B.A. Hons., University of Saskatchewan, 1951 Dominion Observatory, XXIV, No. 7, 1960. M.A., University of Saskatchewan, 1954 3. Scrimger, J.A., W.G. Milne and W.R.H. White, | MONDAY, JULY 23, 1962, at 2:30 P.M0 Sub-bottom velocities in the Esquimalt ! IN ROOM 303, PHYSICS BUILDING Lagoon, British Columbia. Report 61-4, Pacific Naval Laboratory, Esquimalt, B. C, 1961. COMMITTEE IN CHARGE Chairman: F.H. SOWARD J„A„ JACOBS R„D0 RUSSELL V.Jo OKULITCH W.F. SLAWSON G.L. PICKARD R„W. STEWART W_HC WHITE External Examiner: J0H„ HODGSON Dominion Observatory, Ottawa GRADUATE STUDIES Field of Study: The Crustal Structure of the Earth in Western Canada THE STRUCTURE OF THE EARTH'S CRUST IN THE VICINITY OF VANCOUVER ISLAND FROM SEISMIC AND GRAVITY OBSERVATIONS Advanced Geophysics J.A. Jacobs Nuclear Physics J.B. Warren ABSTRACT Introduction to Dynamic Oceanography G.L. Pickard A seismic explosion programme has been carried out in the Vancouver Island-Strait of Georgia area of Advanced Dynamic Oceanography .... R.W. Stewart Western Canada. The programme included a relatively intensive survey in the Strait of Georgia between Campbell River and the south end of Texada Island, as Related Studies: well as a number of longer range refraction lines ex• tending from Kelsey Bay along the coast as far south Geodesy H.R. Bell as northern California, and east through the mountains to a distance of 700 km. Gravity readings were ob• Electronic Instrumentation F.K. Bowers tained at intervals of about ten km. along the east coast of Vancouver Island as well as for a number of Computational Methods C. Froese east-west traverses. Readings were also obtained for a few locations on the British Columbia mainland. Except for a marked positive trend in the Victoria area the regional value of the Bouguer anomaly for the Vancouver Island area is nearly zero. The average structure for the area, derived from the seismic refraction observations consists of a layer of volcanic and granitic strata less than five km. in thickness, and an intermediate layer 46 km. thick with a constant velocity for compressional waves of 6.66 km/sec. A velocity of about 7.7 km/sec. for the mantle has been observed along unreversed refraction lines, both along the coast and east through the moun• tains. Interpretation of the refraction observations has been based mainly on first arrival phases. The observed regional gravity anomaly is compatible with the crustal model obtained from the seismic results. - i - ABSTRACT A seismic explosion program has been carried out in the Vancouver Island- Strait of Georgia area of Western Canada. The program included a relatively- intensive survey in the Strait of Georgia between Campbell River and the south end of Texada Island, as well as a number of longer range refraction lines extending from Kelsey Bay along the coast as far south as northern California, and east through the mountains to a distance of 700 km. Gravity readings were obtained at intervals of about ten km. along the east coast of Vancouver Island as well as for a number of east-west traverses. Readings were also obtained for a few locations on the British Columbia mainland. Except for a marked positive trend in the Victoria area, the regional value of the Bouguer anomaly for the Vancouver Island area is nearly zero. The average structure for the area, derived from the seismic refraction observations consists of a layer of volcanic and granitic strata less than five km. in thickness, and an intermediate layer with a constant velocity for com- pressional waves of 6.66 km/sec, 46 km. thick. A velocity of about 7.7 km/sec. for the mantle has been observed along unreversed refraction lines, both along the coast and east through the mountains. Interpretation of the refraction observations has been based mainly on first arrival phases. The observed regional gravity anomaly is compatible with the crustal model obtained from the seismic results. - iv - ACKNOWLEDGMENT The author is especially indebted to Dr. J. C. Savage who suggested an outline for the program discussed in this thesis, assisted in the field operations and supervised the research throughout. The author would also like to express his indebtedness to Mr. W. G. Milne of the Dominion Observatory staff who assisted in a number of ways and in particular organized the seismic field program of May I960. Thanks are also due to Dr. P. L. Willmore, formerly of the Dominion Observatory staff, who kindly supplied data for the Ripple Rock explosion. Mr. Malcolm Bancroft of the Dominion Observatory operated two field stations during the May I960 program. The Gravity Division of the Dominion Observatory, in cooperation with this program, carried out observations for a network of base stations in the survey area. This part of the survey was carried out by Mr. A. K. Goodacre. Arrangements for ship time were made by Mr. E. P. Fleischer, Coordinator of Research Ships at the Pacific Naval Laboratory, and Mr. J. S. Williams, Supervisor of Auxiliary Vessels. Thanks are due to Captain J. E. Francois of C. N.A.V. Laymore and Captain D. M. McFarlane of C.N.A.V. Whitethroat and the crews of these two vessels for handling the explosives and carrying out the navigation. The explosives for the November 1961 program were handled by LCDR D. B. Perrin, R.C.N., of the Underwater Weapons, Fleet School, H.M.C.S. Naden, and LT D. B. Hope, R.C.N., of the R.C.N. Diving Establishment (West). A number of the members of the staffs of the Dominion Astrophysical Observatory and the Institute of Earth Sciences at the University of British Columbia assisted in the field programs. These include B. Caner, R. Hemmings, C. Hemmings, H. Draper, C. Sansbury, J. White, R. Bennett, H. McNaughton, L. Manslhna, C. Westphal, B. Whittles and W. McReynolds. Mr. H. Draper and Miss T. Thompson assisted in the preparation of the thesis. - V - A number of submarine gravity readings have been used by permission of Professors Worzel and Ewing of the Lamont Geological Observatory, and one gravity reading by permission of Dr. G. D. Garland of the Department of Physics, University of Alberta. The research in this thesis has been supported by the Dominion Observatory and through grants made to the University of British Columbia by the National Research Council. - ii - TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1 Definition of the Earth's Crust 1 1.2 Methods of Investigation of Structure in the Earth's Crust 2 1.2.1 Seismic reflection and refraction surveys 2 1.2.2. Analysis of surface waves 4 1.2.3 Gravity measurements 4 1.2.4 Other methods 6 1.3 Some General Aspects of Crustal Structure Studies 6 1.3.1 History of pioneer refraction studies 6 1.3.2 Continental and oceanic crustal structure 8 1.3.3 The reality of the intermediate layer 10 1.3.4 Velocities of compressional waves in the mantle 10 1.3.5 Investigations of the earth's continental crustal structure J 11 2. RESULTS OF SOME SURVEYS IN WESTERN NORTH AMERICA 13 3. THE SEISMIC PROGRAM 23 3.1 General Description 23 3.2 Instrumentation and Recording Techniques 25 3.3 Reduction of Data 28 3.4 Accuracy of Measurements 29 3.5 Additional Data 32 3.6 Seismograms 33 .3.7 Amplitudes of Recorded Energy 33 3.8 Shorter Range Refraction Data for the I960 and 1961 Programs 35 3.8.1 Profile I 36 3.8.2 Profile II 43 3.8.3 Profile III 44 3.8.4 Prpfile IV 44 3.8.5 Profile V 44 3.8.6 Profile VI 46 3.8.7 Profile VII 47 3.8.8 Profiles VIII to XI 47 - iii - 3.9 Ripple Rock Data 51 3.9.1 Profile XII 51 3.10 Longer Range Data 53 3.10.1 Profiles XIV to XVII 53 3.11 Methods of Interpretation 56 3.12 Interpretation and Discussion of the Refraction Data 59 3.12.1 Results for the Strait of Georgia area 61 3.12.2 Results for the Kelsey Bay and Johnstone Strait area 64 3.12.3 Estimated thickness of granitic and volcanic strata 66 3.12.4 Results of the longer range data 68 3.12.5 Ripple Rock-east data 72 3.12.6 Lg waves 72 4.