Hi All. It appears that the Bay Area may have escaped the bullet in the 1989 Loma Prieta quake. The southern San Francisco Bay region of California has a number of oblique dextral reverse faults that verge northeastward from the San Andreas fault experienced triggered slip during the 1989 M7.1 Loma Prieta earthquake. These are the Monte Vista, Shannon, and Berrocal faults. The role of these range-front thrusts in the evolution of the San Andreas fault system and the future seismic hazard that they may pose to the urban Santa Clara Valley are poorly understood. They know they are there, but not exactly where there is.

The most active thrust fault in the Bay Area is the Mt. Diablo thrust fault. This fault has made Mt. Diablo the fastest growing mountain in the Bay Area.

Further to the east is the Great Valley Thrust fault. This fault runs along the western edge of the San Joaquin Valley. There are some who feel that one of the segments in this fault caused the two large quakes in the Vacaville/Winters area in 1892. The recurrence intervals for earthquakes on segments of this fault system are approximately 500-600 years, but this estimate is uncertain. The Great Valley thrust fault consists of 14 segments. There are indications that the 1983 Coalinga quake was caused by segment # 13. There are also some who believe this may have been the expected Parkfield quake as the 1983 quake occurred about 21 miles east of Parkfield.

One of the most dangerous Bay Area thrust faults, because of its location near an urban area, is the Monte Vista fault on the western side of the Santa Clara Valley. However, this fault has a long recurrence interval for large earthquakes - on the order of several thousand years. I was unable to find any information as to how this interval was determined. Take Care…Don in creepy town

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