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Context of the Project:  Earthquakes in the Pacific Northwest

In the 1996 and 1997 Regional Meeting of the Geologic Society of America (GSA) geologists shared evidence supporting a hypothesis that the Pacific Northwest has experienced high magnitude (8-9) earthquakes on a (roughly calculated) 300 year re-occurrence interval. Based on sands remaining from a tsunami event found in coastal deposits along the Oregon and Washington coasts, initial estimates of the most recent event is about 1700. Japanese tsunami records actually date such an event on January 1, 1700 at 9:36 am (or some amazingly specific time). The coastal impact revealed a pattern unlike that of the other great subduction zone earthquakes (Alaska, 1964; Chile, 1960).
        An event of such magnitude may have occurred at the North American-Juan de Fuca plate boundary. However, historical records show only one event right on that subduction zone (1992 Petrolia earthquake 7.1 magnitude).  The quakes of this region are mostly in the upper (North American) plate, while some occur in the lower (Juan de Fuca) plate. There is debate as to whether this "seismic gap" is the result of aseismic convergence or the more ominous possibility of a strain building, locked plate boundary.  From Cape Mendecino California to Vancouver B. C. city, state and provincial governments are acting to minimize seismic induced damage. That endeavor starts with assessment and resource allocation.