|Notable Earthquake of the Week|
|Cape Mendocino M 7.1, M 6.6, and M 6.7 Earthquakes|
The sequence began at 11:06 a.m. on April 25 with a powerful M 7.1 mainshock centered beneath the mountains a couple miles northwest of Petrolia at a depth of 10 km. It had a thrust style fault motion similar to that of the Northridge earthquake in 1994. Severe shaking interrupted a Saturday morning parade at Ferndale, shattering plate-glass windows and tumbling bricks and masonry onto the sidewalk and street.
Strong aftershocks measuring M 6.6 and M 6.7 occurred at 12:41 a.m. and 4:18 a.m. the following morning about 14 miles off the coast. These quakes were centered in the Gorda plate and had left-lateral strike-slip fault motions.
The three quakes shook homes from their foundations, threw chimneys to the ground, and broke underground utility lines. Numerous landslides occurred in the mountainous regions and extensive ground cracking and soil failures happened in the low lying areas near the coast. (See a Shaking Intensity Map by HSU)
Then President Bush declared the communities of Ferndale, Fortune, Honeydew, Petrolia, Rio Del, and Scotia as disaster zones. Although several hundred people were injured and over $60 million in damages were incurred, no fatalities were recorded.
Images from a photo set provided by the California Governor's Office of Emergency Services, Oakland, California
Recent Earthquakes on California's North Coast; Humboldt Earthquake Education Center, Humboldt State University.
Petrolia Earthquake Sequence, Tinker, M.A., and Beck, S.L. (1995). Inversion of regional surface-wave spectra for source parameters of aftershocks from teh 1992 Petrolia Earthquake quence, Bulletin of the Seismological Society of America, pp 705-715.
The Cape Mendocino Earthquakes of April 25-26, 1992; John Martin and Associates [excellent summary!]
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