CGRG Bibliography of Canadian Geomorphology
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Author : Dragert, H.; Mazzotti, S.; and Wang, K .
Date : 2002.
Title : Aseismic slip on the northern Cascadia Subduction Zone: impacts on seismic hazard estimates.
Publication : American Geophysical Union 2002 Fall Meeting, Moscone Center, San Francisco, California, 6-10 December 2002.
Issue :
Page(s) :
Abstract
Based on data from the few longer operating continuous GPS sites in southwestern British Columbia and northwestern Washington State, aseismic slip appears to occur repeatedly on the deeper interface of the Cascadia Subduction Zone (CSZ) underlying the eastern Olympics and southern Vancouver Is. The spatial and temporal character of the slip events observed so far have implications for regional seismic hazard estimates. During the period between slips, stress accumulates over an interface region wider than the normal locked/transition zone of the CSZ. However, it appears that there is little long-term stress accumulation on the deeper interface and the potential rupture zone for the next megathrust earthquake remains predominantly offshore. Because of its location downdip of the locked plate interface, a deep aseismic slip produces a small, discrete Coulomb stress increment of the order of 0.01 MPa which moves the locked zone closer to rupture, potentially acting as a trigger for a future great thrust earthquake. The spatial correlation of the boundary of the slip zone with the location of large in-slab earthquakes also suggests a common structural cause or a possible stress interaction. The silent slips and in-slab earthquakes may both be related to a common process of slab dehydration. However, the observed slip events create a Coulomb shadow for normal earthquakes on steeply dipping faults within the descending slab downdip from the slip zone. The region of slip also underlies the areas of high crustal seismicity of Puget Sound and Georgia Strait, but estimates of Coulomb stress changes on crustal faults due to deep slip are extremely sensitive to geometry, thus obscuring patterns of possible crustal stress interactions. To date, no temporal correlations have been found between rates of crustal seismicity and the occurrence of aseismic slip.
Bibliography of Canadian Geomorphology