CORVALLIS, Ore. – The newest studies on the Cascadia Subduction Zone off the coast of the Pacific Northwest have identified a "clustering" of great earthquakes of the type that would cause a major tsunami, yielding a historical record with two distinct implications - one that's good, the other not.
According to scientists at Oregon State University, this subduction zone has just experienced a cluster of four massive earthquakes during the past 1600 years, and if historical trends continue, this cluster could be over and the zone may already have entered a long quiet period of 500 to 1,000 years, which appears to be common following a cluster of earthquake events.
Alternatively, the current cluster of earthquakes may have one or more events left in it – some clusters within the past 10,000 years have had clusters of up to five events – and within a cluster, the average time interval between earthquakes is 300 years. Since the last major Cascadia earthquake occurred in the year 1700, the next event may well be imminent.
"The Cascadia Subduction Zone has the longest recorded data about its earthquakes of any major fault in the world," said Chris Goldfinger, an associate professor of marine geology at OSU and one of the leading experts on this fault zone. "So we know quite a bit about the periodicity of this fault zone and what to expect. But the key point we don't know is whether the current cluster of earthquake activity is over yet, or does it have another event left in it."
http://www.eurekalert.org/pub_releases/2004-12/osu-oe122904.php
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