THE CAPE MENDOCINO, CALIFORNIA, EARTHQUAKES OF APRIL 1992 - SUBDUCTION AT THE TRIPLE JUNCTION

The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demon strated that the North America-Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes fo recast for the Cascadia region. The shock occurred just north of the M endocino Triple Junction and caused strong ground motion and moderate damage in the immediate area. Rupture initiated onshore at a depth of 10.5 kilometers and propagated up-dip and seaward. Slip on steep fault s in the Gorda plate generated two magnitude 6.6 aftershocks on 26 Apr il. The main shock did not produce surface rupture on land but caused coastal uplift and a tsunami. The emerging picture of seismicity and f aulting at the triple junction suggests that the region is likely to c ontinue experiencing significant seismicity.