CGRG Bibliography of Canadian Geomorphology
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Author : Bent, A.L.; and Perry, H.K.C.
Date : 2000.
Title : Depths of earthquakes in Eastern Canada from regional data.
Publication : 96th Annual Meeting of the Seismological Society of America, 9-12 April, Scripps Institution of Oceanography/University of California, San Diego, California.
Issue :
Page(s) :
Abstract
While the Canadian National Seismograph Network (CNSN) provides adequate coverage for reliable epicenter determinations, in most regions of Canada earthquake depth cannot be determined by routine location procedures. As depth has implications for seismotectonics and seismic hazard, it is an important parameter to constrain. Standard practice has been to fix the depths of most earthquakes at the mid-crustal depth of 18 km. We have developed a method for rapid depth determination of small and moderate earthquakes using stacked regional data. Seismograms recorded at distances of between 250 and 500 km are normalized with respect to amplitude, stacked and filtered (2-6 Hz). We evaluate the window between Pn and Sn. The offset of the largest peak relative to Pn is measured. It is assumed that the peak (Pmax) corresponds to sPn. The method was calibrated using earthquakes in the Charlevoix Seismic Zone where the CNSN is dense enough to provide reliable depth estimates. In most cases the depth determined by Pmax-Pn was within 2 km of the network depth The Pmax-Pn relation was applied to earthquakes in the western Quebec and lower St. Lawrence seismic zones. The mean number of seismograms stacked was eight. The average depth of earthquakes in the western Quebec seismic zone is 13 km with a range from 6 to 30 km. Earthquakes in the lower St. Lawrence appear to be deeper on average (23 km). We were able to determine depths for most of the earthquakes studied but occasionally the method could not be applied because there was no prominent secondary arrival or there were two arrivals of roughly equal amplitude, or Pn was not clear enough for a reliable offset to be determined. Pmax was generally clearer for larger earthquakes and after our tests with earthquakes in the Charlevoix region, we restricted our analysis to events of magnitude 3.0 or greater.
Bibliography of Canadian Geomorphology