Volume 7, No. 3 March 1996

CREWES News

The Consortium for Research in Elastic Wave Exploration Seismology

Upcoming CREWES Presentations

CSEG National Convention, Calgary, May 7-9, 1996 58th EAGE Conference , Amsterdam, June 3-7, 1996

Reflection/Refraction Laws, Raytracing and Traveltime Inversion in Weakly Anisotropic Media

Michael Slawinski

Editor's Note: This is an abstract of Michael's Ph.D. thesis presentation, given on March 19, 1996, at the University of Calgary. The complete hardbound thesis will be distributed at the Sponsors Meeting in October, 1996.

An analytical method relating incidence, reflection and transmission angles at an interface between anisotropic media is presented. The method relies on the continuity conditions relating tangential components of phase slowness across the interface, and on the fact that the ray is perpendicular to the phase-slowness surface. The rather familiar concepts of vector calculus are used in a template for calculating phase and group angles. The angles involved in wave propagation through layered anisotropic media are, at times, significantly different than their isotropic counterparts. Thus the trajectories derived in raytracing by the isotropic versus the anisotropic approach differ significantly. This template is used to derive analytic expressions for phase and group angles, and to elaborate a raytracing scheme for qP, qSV and qSH waves using expressions for phase velocities under the assumption of weak anisotropy. The retracing method can be used to calculate travel times for layered weakly anisotropic media composed of TI materials. The results of a physical laboratory experiments, which involved propagation in the symmetry plane of an orthorhombic material with known characteristics, have been compared with theoretical calculations. The comparison indicates that the anisotropic approach yields a significantly better prediction than an isotropic one. The analytical approach is further extended to provide a traveltime inversion scheme for the anisotropic parameter characterizing qSH waves. The inversion method can be used in multilayer media and account for raybending at interfaces. It is, however, very sensitive to errors in input parameters.


Graduate Student Applications Up

The number of applications for Graduate School received by the Department of Geology & Geophysics has risen dramatically - 100 people applied for September, 30 of whom have applied to the Geophysics program. Many of the applicants have excellent qualifications, and we are looking forward to an influx of new and talented students in the Fall.

Personnel

Dr. Jim Brown, one of the directors of CREWES, will be taking a leave of absence from the University of Calgary for the next two years. Jim will be working with PGS Reservoir in Oslo, Norway. PGS is a CREWES Sponsor, and Jim will continue to work on issues related to CREWES research and to be in close communication with the Project. He plans to work on the use of P-S waves in reservoir characterization, especially in a marine environment. This will involve developing methods to detect lithological variation, such as Vp/Vs profiles, and to locate evidence of anisotropy due to fracturing. We all wish Jim the best of luck - "lykke til!"

Michael Slawinski successfully defended his Ph.D. thesis this month. Under the supervision of Jim Brown, Michael worked on "Reflection/Refraction laws, raytracing and traveltime inversion in weakly anisotropic media". A summary of this work is shown in this newsletter; the complete dissertation will be distributed at the Sponsors Meeting in October. Michael will begin work at PanCanadian Petroleum in June, but in the meantime, he plans to travel to the Yukon to climb Mt. Logan (the highest mountain in Canada at 6050 m) with his brother Raphael. Good show, Michael! Congratulations to Dr. Don Lawton, who was awarded a CSEG Meritorious Service Award. Don accepted his award at the March CSEG Annual Meeting and Luncheon. Perhaps now he can take a few minutes off to relax!


Making Contact...

The CREWES Project
Dept. of Geology & Geophysics
University of Calgary
2500 University Dr. N.W.
Calgary, Alberta
T2N 1N4 CANADA

Fax: (403)284-0074
Email: crewes@geo.ucalgary.ca
WWW (World Wide Web):
http://www.crewes.ucalgary.ca/

Administrative Secretary:
Louise Forgues: 220-8279
Editor: Sue Miller

Directors:
Dr. Robert Stewart: 220-3265
Dr. Jim Brown: 220-7484
Dr. Don Lawton: 220-5718

Research Staff:
Dr. John Bancroft: 220-5026
Malcolm Bertram: 220-3267
Henry Bland: 220-8461
Darren Foltinek: 220-6137
Eric Gallant: 220-3259
Stan Gorek: 220-4292
Dr. Gary Margrave: 220-4606
Sue Miller: 220-7462
Grace Yang: 220-8969
Qi Zhang: 220-3264

Graduate Students
Jill Belisle:220-3271
Siriporn Chaisri: 220-3083
Wai-Kin Chan: 220-8093
Maria Donati: 220-6444
Jocelyn Dufour: 220-8266
Ken Fang: 220-8093
Robert Ferguson: 220-3271
Helen Isaac: 220-8396
Glenn Larson: 220-3458
Xinxiang Li: 220-6749
Nicolas Martin: 220-3083
Darryl Parry: 220-3032
Chanpen Silawongsawat: 220-3083
Zandong Sun: 220-6444
Dan Vetrici: 220-3269
Shaowu Wang: 220-5027
Hans Westbroek: 220-6596