CGU Annual Meeting

The Canadian Geophysical Union met in Banff, Alberta for its twentieth annual meeting May 14 to 18, 1994. One hundred and seventy six papers were presented in twenty one sessions. There were several new sessions this year including porous media-rock physics, marine geophysics, and global change. A lively presidents plenary session also had a global change theme, with invited presentations from J.E. Faller on "Absolute gravity, a Modem Tool for Monitoring Geophysical Change", D. Dahl-Jensen on "Paleoclimatic "News" From the GRIP ice Core, Centrel Greenland", V. Baker on "Global Paleohydro-Iogical Change", and D.S. Chapman on "Global(?) Warming (7): Climate Change Inferred from Borehole Temperatures".

Wilson Medal to Mike Berry

The Wilson medal is awarded annually by the CGU in recognition of outstanding contributions to geophysics in Canada. The recipient this year is Mike Berry of the Geological Survey of Canada. Mike graduated from the University of Toronto (B.Sc., M.Sc. and Ph.D.) where he worked on diverse geophysical problems with Gordon West, and specialized in Seismology. After working one year with Leon Knopoff, Mike joined the newly created Earth Physics Branch of the department of Energy Mines and Resources, where he was eventually to become director of the Seismology Division.

Mike has made many contributions to crustal seismology as an individual, and his guidance and lobbying within government and scientific circles has indirectly influenced many more. His student work led to the discovery that the mid-continent rift beneath Lake Superior had an extremely deep Moho with unusually high mid crustal velocities. This work strongly influenced the choice of Lake Superior for the 1986 GLIMPCE experiment. His landmark 1973 paper with Karl Fuchs on the crustal structure of the Superior craton and adjacent Grenville province became a model for crustal studies worldwide. It was the first paper in which accurate synthetic seismograms were used for the interpretation of refraction data and it was a key contribution that helped establish the existence of low velocity layers in the crust. In a subsequent paper he proposed that these low velocity layers were the result of water and high pore pressure, an idea that is widely accepted now, but was controversial at the time. Realizing that the complex geometries of crystalline terranes would require much tighter spatial sampling than was the standard, he used 100 m sampling intervals in the 1966-69 Yellowknife project. The quality of this refraction data set was to be unmatched outside the former Soviet Union until the 1980's.

Mike has had a long involvement with continental scale geophysics, first as co-chair of COCRUST, the joint university and government program that covered Canada coast-to-coast with refraction profiles. He was one of the original proponents of LITHOPROBE, promoting and guiding the formative stages of this complex geoscience project, and eventually serving as chair of the Scientific Committee. His most recent appointment is Director General of the Mineral and Continental Geoscience Branch of the Geological Survey of Canada.

Mike Berry is the seventeenth recipient of the Wilson Medal.

Student Paper Competitions

The CGU encourages the participation of students in conferences as an integral part of their education, and recognizes exceptional work with special awards. In addition to the CGU's own best student paper award, Chevron Canada makes an award for the best student paper in Seismology and Shell Canada awards the best poster presentation by a student. Students must be the presenter, and first author, and are judged on content, defense and delivery.

Dave Butler, (with R.J. Knight) of the University of British Columbia, won the CGU award for his presentation on "The Electrical Nature of Subsurface Steam Flow". This work described laboratory investigations of conductivity changes associated with sub-surface steam flood. Results showed that the response was a complicated function of in-situ fluid properties, and the quality of the steam. When salinity variations between saturating fluid and steam source were minimized, the conductivity increased by a factor of about two, due to the decreased viscosity of the saturating fluid, while the arrival of the steam front generally decreased the liquid water saturation, resulting in decreases in conductivity by an order of magnitude. The quality of the steam influences conductivity because if the dimension of the heated zone ahead of the steam front is large, dissolved salts can affect the conductivity right back to the steam front. If the heated zone does not advance ahead of the steam front, then the dilution of salts by the condensing steam can overwhelm the increase of salinity by heat. Tests have also been carried out on oil-saturated sands, where the response is complicated by the flushing of oil ahead of the steam front.

Eric Adeam, of Ecole Polytechnique in Montreal, (with Bernd Milkereit of the Geological Survey of Canada) won the Shell Canada award for best poster presentation for his paper on "Seismic Stratigraphy of an Archean Volcanic Pile". This describes a vibroseis experiment to image depths in the 1 to 1.5 km range in aid of mine planning in the Matagami massive sulphide deposit. Reprocessing of the data, originally collected in 1990 as part of the LITHOPROBE Abitibi-Grenville transect, has shown continuous reflectivity that can be traced to surface and shows good correspondence with two boreholes. Strong reflections are observed when a rhyolite or a basalt is in contact with a gabbro, and weaker reflections are observed at a rhyolite/ basalt contact. A zone of alteration that is genetically linked with the massive sulphides has also been recognized.

Barry Zelt of the University of British Columbia (with R.M. Ellis and R.M. Clowes) won the Chevron Canada outstanding student paper award in seismology for his presentation "Three-dimensional Velocity Structure of the Southwestern Canadian Cordillera from Tomographic Inversion of Wide-Angle Seismic Data". This paper described an interpretation of 3-D wide angle seismic data collected as part of the LITHOPROBE Southern Cordillera program in 1989. A triangular arrangement of shot points and receivers - 330 km on a side was used, with shot points at the ends, and in the middle of each line, as well as at the center of the array, so that, both fan and in-line data were available. The data were modeled by tomographic inversion of travel times calculated on a 3-D finite-difference grid using the Vidale algorithm. Velocity variations throughout the study region were found to be similar to those of the previously interpreted 2-D models. Crustal velocities were not readily correlatable with surface geological features. An apparent southwestward thickening of the crust in the vicinity of the Fraser River fault was found, but velocity-depth trade-offs limit the confidence in this feature.

CGU '95

The next meeting of the CGU will be held at the Banff Centre, from May 22 to May 26, 1995. The call for papers will be issued in October to all CGU members. Others who would like information on the conference should consult the CGU gopher hole at gopher.ucalgary.ca sometime after the middle of October, or contact Rod Blais (blais@ucs.ucalgary.ca), or Patrick Wu (ppwu@acs.ucalgary.ca), to be put on a mailing list. The organizers welcome suggestions for sessions from members and others.