Tectonic Summary
Magnitude 7.2 OFF THE COAST OF NORTHERN CALIFORNIA
Wednesday, June 15, 2005 at 02:50:53 UTC
Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver
This earthquake occurred in a deformed section of the southernmost Juan de Fuca plate that is commonly called the Gorda plate. The epicenter lies to the west of the Cascadia Subduction Zone. Light shaking from this earthquake was widely felt along the northern California - southern Oregon coastline.
Preliminary analysis of the quake indicates that it resulted from slip on a NE striking, left-lateral, strike-slip fault; this type of mechanism has been documented for other earthquakes having locations in the interior of the Gorda plate. This earthquake did not produce a damaging tsunami, although, a small ~3 centimeter tsunami wave was observed on sensitive tide gauges. Earthquakes with strike-slip mechanisms are less likely to produce large tsunamis because they cause relatively little vertical ground displacement.
Earthquakes are common in the Gorda plate, which is subjected to north-south compression due to the north-west moving Pacific Plate that collides with the southern boundary of the Gorda Plate along the east-west Mendocino Fracture Zone. This quake occurred approximately 67 miles west of the epicenter of the November 8, 1980 7.2M earthquake. There have been 3 other quakes of magnitude M>6 that have occurred with 50 miles radius of the epicenter of this quake (August 16, 17 1991 and July 24 1996).
