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TitleA seismic survey in the Canadian Shield, II: Refraction studies based on timed blasts
AuthorHodgson, J H
SourcePublications of the Dominion Observatory vol. 16, no. 6, 1953, 15 pages, (Open Access)
PublisherCanada Department of Mines and Technical Surveys
Mediapaper; on-line; digital
RelatedThis publication is related to Hodgson, J H; (1953). A seismic survey in the Canadian Shield, I: refraction studies based on rockbursts at Kirkland Lake, Ontario, Publications of the Dominion Observatory vol. 16 no. 5
File formatpdf
ProvinceQuebec; Ontario
NTS31K/SW; 31L/NW; 31L/SE; 41I/SE
AreaLa Cave; Rolphton; Sudbury; Temiskaming
Subjectsgeophysics; structural geology; tectonics; crustal studies; epicentres; p waves; refraction studies; rockbursts; s waves; seismic interpretations; seismic velocities; seismic surveys; Canadian Shield; Huronian Basin
Illustrationsphotographs; graphs; tables
Natural Resources Canada Library - Ottawa (Earth Sciences)
Released1953 01 01; 2018 10 09
AbstractDuring the rock burst studies described in Part I of this series, blasts timed at their source were recorded at one or more of the stations of the profile.
One group of blasts, at La Cave and at Rolphton, were timed automatically by the stations maintained at those points. These blasts frequently recorded at the other station of the pair, and sometimes at Ottawa. Timing and location were not as precise as in other sections of this work, but it was possible to determine mean velocities for P1 and S1 of 6.29 ± 0.04 km/sec. and 3.44 ± 0.03 km/sec. respectively. The uncertainties listed are Probable Errors of the means.
A second group of blasts, occurring at, La Cave and at Temiskaming, were precisely located and were timed with the greatest possible accuracy. They were recorded at stations lying northwestward toward Kirkland Lake, and the series thus provided a reverse profile. P1 and S1 velocities obtained, with probable errors, were 6.19 ± 0.07 km/sec. and 3.54 ± 0.07 km / sec. A very strong phase, both in the P and S group, suggested the existence of a second layer, but this interpretation proved to be inconsistent with the evidence of other secondary arrivals.
The final group of blasts provided data on the variation of velocity with rock type. The source was near Sudbury and as the blasts were recorded at eight different stations of the rockburst profile a variation of 47° of azimuth was obtained. This provided many different sections across the Huronian basin. Mean velocities, and their Probable Errors, for P1 and S1 were 6.189 ± 0.023 and 3.551 ± 0.007 km/sec.
The mean for all determinations, including that made with the aid of rockbursts, together with the Probable Error of the mean, proved to be: for P1 6.234 ± 0.012 km/sec., and for S1 3.544 ± 0.011 km/sec. Secondary arrivals, in general, satisfied the single-layer travel time curves developed for the rockburst profile, although in this case also there were variations from the curves such as might have been due to variations in rock type and variations in crustal thickness.