"Poop Shot," Early Seismic Explosion, Lethbridge, 1936.
Geological exploration by seismic survey involves detonating explosives in shallow drill holes. As the resulting shock waves reverberate off successive layers of rock, their velocity (low in sedimentary rock and high in hard rock) is measured by geophones or "Jugs" laid out on the surface by "Jug hustlers." The time and intensity of the shock waves are measured back at the recording truck (in the distance, to the right) by the reflection seismogram on tape, giving the exploration geophysicist a graphic picture of the geological structures which is fairly accurate to depths of 4,500 metres. More recently environmental concerns have dictated the use of much smaller charges than those in the picture. In some cases vibrating units (vibroseis) on the surface produce similar effects, as do electrical pulses or compressed gas explosions in deep-sea seismic exploration.
The principle of the seismograph, which was originally applied to measure vibrations caused by earthquakes, found significant use in the exploration geology of Western Canada. As a tool of the broader science of geophysics, which employs other means such as magnetometers, gravimeters and core-drilling to explore sub-surface geology, seismography became the most widely used in the Alberta field. In 1930, Highwood and Sarcee Petroleums and Nordon Oil were the first to use seismic search techniques in the Turner Valley field and, later, throughout southern Alberta and Saskatchewan. Their success was limited, however, in the highly complex faults and fields of the foothills country.
The field crew employed in the Lethbridge area by Carter Oil was one of less than a dozen that operated throughout Alberta in the thirties. In the post-war era, however, seismic exploration played a significant role in the discovery of the Leduc-Woodbend field in 1947, and the number of seismic crews jumped to 142 in 1952. As exploration moved farther north the number declined in the mid-fifties to less than a hundred in Alberta. More recently, seismic survey parties, which set off minor explosions in the wake of their large Flextrac Nodwell and Bombardier snow vehicles, have become familiar sights on the arctic tundra.
Courtesy: Glenbow-Alberta Institute, Carter Oil Company (PB 533-2)
