CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Cassidy, J.F.; Schmitt, S.; and Bent, A.
Date : 2002.
Title : The 1953-1957 MacKenzie Mountains earthquake sequence.
Publication : Seismological Society of America 2002, Annual Meeting 17-19 April 2002. Victoria Conference Centre, Victoria, British Columbia
Issue :
Page(s) :
Abstract
The northern Canadian Cordillera is a region of intense, yet poorly understood seismicity. Between 1953 and 1957 a series of five moderate-to-large earthquakes (M=5.5-6.5) struck the northern MacKenzie Mountains. These are the largest earthquakes ever recorded in the immediate area, although earthquakes as large as 6.5-6.9 have occurred in a similar tectonic environment, both a few hundred km's to the northwest, and to the southeast. With renewed interest in seismic hazards in this region, we have examined this previously unstudied earthquake sequence to better define the epicentres, focal depths, and magnitudes, and to determine the focal mechanisms. The 1953 and 1955 earthquakes,which occurred in a sparsely populated region, were felt (up to intensity V) to distances of 230-280 km. The magnitudes (Ms) of these events have been determined at 6.3 and 6.5, respectively. Epicentres have been re-determined using teleseismic path corrections obtained from well-recorded modern earthquakes (M=4.5-5) in this region, and by waveform comparison techniques. The relocated epicentres are distributed in a ESE-WNW direction over a distance of about 45 km. The first earthquakes in the sequence are located to the ESE and later events migrate to the WNW. The 1955 mainshock and largest aftershock are separated by about 20 km, with the aftershock being located to the NNE of the mainshock. The 1957 (M=5.3) earthquake is located a similar distance and direction from the 1956 (M=5.6) earthquake, suggesting that it may be an aftershock of that event. Focal mechanisms and depths were determined using body wave modelling. All depths ranged between 9 and 15 km, and focal mechanisms show thrust faulting along either a plane dipping at 30-40 degrees to the NNE, or a plane dipping at 50-60 degrees to the SSW. The orientation of the WNW-ESE striking nodal planes is consistent with the distribution of epicentres and the regional geology. The NNE-SSW striking, shallow-dipping P-axes are consistent with the regional stress field. It is likely that these earthquakes are caused by stresses transmitted from the plate boundary more than 700 km to the west, activating favourably oriented thrust faults in the northeastern Canadian Cordillera.
Bibliography of Canadian Geomorphology