CGRG Bibliography of Canadian Geomorphology
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Author : Bolton, M.K.; and Rogers, G.C.
Date : 2002.
Title : Juan de Fuca Plate seismicity at the northern end of the Cascadia Subduction Zone.
Publication : Seismological Society of America 2002, Annual Meeting 17-19 April 2002. Victoria Conference Centre, Victoria, British Columbia
Issue :
Page(s) :
Abstract
Earthquakes occurring within the down-going Juan de Fuca plate, at the northern end of the Cascadia subduction zone occur in two distinct concentrations, with the deepest events extending down to depths of approximately 80 km. The first concentration, in the 25 to 35 km depth range, lies beneath the west coast of Vancouver Island. First motion focal mechanism solutions from this group of earthquakes illustrate a complex stress pattern, indicating no prominent regional tectonic stress. The second concentration, in the 45 to 80 km depth range, lies beneath Georgia Strait and Puget Sound, WA. These earthquakes are deeper than the first concentration as they occur farther from the margin and in a region which coincides with the change in dip of the subducting plate, from approximately 5 to 30 degrees. Most of the earthquakes within the Juan de Fuca plate in the Georgia Strait/Puget Sound area are dominated by normal faulting, with a few strike-slip faulting events. The larger, deeper events indicate predominately normal faulting and down-dip tension axes, as displayed by first motion and moment tensor focal mechanism solutions from the recent Nisqually (February 28, 2001, MW=6.8) and Satsop (June 10, 2001, MW=5.1) earthquakes. This tension is consistent with that expected from such a tectonic regime. Composite focal mechanism solutions for both concentrations of Juan de Fuca earthquakes indicate the complex stress regime. Reliable composite focal mechanisms were obtained for the deepest events and the western events off the coast of Vancouver Island and Washington. The deepest events (~ 70 km) indicate normal faulting with down-dip tension as expected, whereas the western events indicate a dominant strike-slip component. The complexity of the stresses in the remainder of the region prohibited additional reliable composite mechanisms to be obtained.
Bibliography of Canadian Geomorphology