Hi All. Just thought you would like to know that in the past Northern California has been pretty active in the quake department. Did you that from 1911 to 1995 there have been 25 quakes above 6.0 just off the coast of Eureka and in the surrounding area. The largest was a M>7.3 on 01/31/1922.

Also there were two M>6.1 quakes off the coast of Monterey Bay. They both occurred on 10/22/1926 about 9 miles apart. They appeared to have occurred on the San Gregorio fault, which is considered by some to be a sleeper in the pack. Not much is known about the history of this fault.

The last large quake in the Bay Area was on 07/01/1911. It was a M>6.6 just east of San Jose. Since 1979, three earthquakes of Richter magnitude 5.8 or greater have occurred in the east San Francisco Bay area. The first of these was the August 1979 Coyote Lake earthquake, the second occurred in January 1980 some 16 km (10 miles) northwest of Livermore, and the third was the 1984 Morgan Hill earthquake. This is a marked increase over the rate of seismicity in this area since the great magnitude 8.3 San Francisco earthquake of 1906.

Since the 1849 gold rush when earthquake reporting became relatively complete, 23 earthquakes of M 5.8 or greater have occurred within 100 km of San Francisco Bay. The largest earthquakes were the M 6.8 earthquake of 1868 that ruptured the Hayward fault over a length of 50 km (30 miles) centered near Hayward, and the M 8.3 San Francisco earthquake of 1906 that ruptured the San Andreas fault for some 400 km (250 miles) from near Monterey Bay to the Mendocino coast. No earthquakes of M> 5.8 occurred near San Francisco Bay between 1926 and 1979. The largest earthquake to occur in the area between 1926 and 1979 was the M 5.7 Santa Rosa earthquake of 1959. The seismicity was lower during this period than during the last century, reflecting the massive release of stress in the M 8.3 San Francisco earthquake of 1906. Take Care…Don in creepy town

Reference

Tousson R. Toppozada, Seismologist

California Division of Mines and Geology

ANSS Catalog