ABSTRACT: Contributions to earthquake hazard characterization in Canada from precision GPS data.

CGRG Bibliography of Canadian Geomorphology
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Abstract

In the active seismic regions of Canada, the hazard posed by the recurrence of potentially devastating (M >7) earthquakes is not well defined due to the brevity of the instrumental and historical records, the lack of clear paleoseismic evidence for past large events, and the inexact nature of extrapolating the rate of occurrence of frequent small events to the occurrence of rare large events. This serious shortcoming of probabilistic seismic hazard estimation can be addressed through high-precision GPS measurements which can monitor crustal motions and regional crustal strain associated with the build-up of stress before a large earthquake. In southwestern British Columbia, over a decade of observations of motions of GPS sites of the Western Canada Deformation Array (WCDA) and GPS campaign sites have led to improved models of the locked plate interface on the Cascadia Subduction Zone and better estimates of the landward extent for the next megathrust (M~9) rupture. Regional strain rates based on continuous GPS data from the WCDA and PANGA (Pacific Northwest Geodetic Array) show that the recurrence interval for M7 crustal earthquakes is of the order of 400 years, not several decades as once estimated. Continuous GPS data from these arrays have also led to the discovery of "silent slip" or "slow earthquakes" on the deeper plate interface which do not generate impulsive seismic waves but relieve stress over periods of one to two weeks. For southern Vancouver Island and northwestern Washington State, these slip events appear to occur regularly at ~14 month intervals and have now been found to be associated with distinct, non-earthquake tremors, coining the name "Episodic Tremor and Slip" (ETS) for this newly discovered phenomenon. The repeated relief of small amounts of stress in the ETS zone provides an additional definition of the down-dip limit of megathrust rupture, and the onset of ETS activity could mark times of higher probability for the occurrence of thrust rupture in the Cascadia subduction zone. It is expected that the occurrence of large earthquakes in other active seismic regions in Canada (lower St. Lawrence & Ottawa Valley, Queen Charlotte Islands, the Yukon) coul

Bibliography of Canadian Geomorphology