GPS constraints on seismic hazard in the Pacific Northwest

Meghan Miller

Professor of Geology
Dean of the College of the Sciences
Central Washington University, Ellensburg, WA

Application of the Global Positioning System technology over the last decade has led to greater understanding of the active deformation of the North America plate margin in the Pacific Northwest. Using GPS, fault-related deformation of the earth's surface can be observed both as annual velocities of GPS stations relative to the stable interior of the continent and as discrete offsets during deformation events such as earthquakes or short periods of accelerated fault creep. Seismic hazard comes from three kinds of faults: Very large magnitude earthquakes occur along the converging plate boundary itself, and are thought to be similar to the devastating 2004 earthquake and tsunami in Indonesia. Smaller faults that lie within the North America plate in the Seattle region also generate earthquakes, probably in excess of magnitude 7, but these events are relatively infrequent. The most typical historical deformation events within western Washington and southern British Columbia are Mw > 6.0 earthquakes within the subducting Juan de Fuca plate and frequent, apparently periodic silent earthquakes along the megathrust transition zone. The frequent deformation events and large infrequent earthquakes must be understood as an integrated system of seismic strain release, in order to fully characterize potential seismic hazard and risk.

Meghan Miller