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Crustal structure from a seismic refraction profile across southern British Columbia

University of British Columbia

A partially reversed seismic refraction profile utilizing mine blasts as sources was recorded across southern British Columbia from Sparwood to the Highland Valley. The westwardly directed profile consisted of 32 short period seismograms covering 440 km, while the reversed line extended 330 km with 41 seismograms. The FM field tapes were digitized, filtered, and combined into vertical component record sections. Instrument and shot amplitude corrections were applied in order to display the true relative amplitude variation along the profile. As well as geometrical techniques, least squares delay-time methods and disc ray theory synthetic seismograms were used to interpret the data. Where the profile crosses the Rocky Mountain Trench and the Okanagan Valley, the seismic data show arrival time and amplitude anomalies in the approximately 6.0 km/s upper crustal refraction arrivals. An intermediate crustal layer of velocity 7.05 km/s, depth 29 km, and thickness 9 km is defined by second arrival data recorded 100 to 200 km west of the Kaiser shot point. There is poorer evidence, based on data between 80 and 180 km from the Highland Valley shot point, for a layer with a velocity of 7.35 km/s, a depth of 15 to 24 km, and a thickness of 6 to 10 km. The M-discontinuity generally dips to the east from an approximate depth of 33 km near the Highland Valley, to about 42 km just to the west of the Kaiser shot point. The upper mantle velocity is 7.8 km/s between the Okanagan Valley and Kootenay Lake. Delay time interpretations suggest that a 165 km wavelength anomaly in average crustal velocity and/or depth to the mantle occurs in the Eastern Metamorphic Belt. The anomaly is probably associated with a deep transition zone between the Arrow Lakes and Kootenay Lake. The results of the present study are applicable primarily to the eastern Interior Plateaux and the Eastern Metamorphic Belt south of 51°N.

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2010-02-16

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http://hdl.handle.net/2429/20297

Geophysics

University of British Columbia

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