Hi All. I have posted regarding the Pinole fault in the past, but with the recent information that I have obtained I thought a revisit to the Pinole fault might be in order.

Recent geophysical surveys in San Pablo Bay involving conventional and very high resolution (VHR) seismic imaging have suggested that the Rodgers Creek fault may be linked with the Pinole fault, (a thrust fault) therefore increasing its potential rupture length by 10-15 km (Anima et al., 1992). In addition, a structure, thought to be the offshore continuation of the Pinole fault, shows repeated movement during Holocene time (Williams et al., 1993; Williams and Ingram, 1994; Williams et al., 1994). Previous studies (summarized in Bedrossian, 1980) have indicated that the onshore part of the Pinole fault is inactive. The recent geophysical survey results now call into question this assumed inactivity. Age-dating of sediments offset in San Pablo Bay shows that the Pinole fault has a recurrence interval of about 900 years; a recurrence rate that is about a factor-of-five smaller than either the Hayward or the Rodgers Creek faults (Williams and Ingram, 1994).

The Pinole fault in the northeastern San Francisco Bay area, formerly believed to be inactive, has had a history of repeated movement during the last 10,000 years. The Pinole fault may be a potential linking structure between the active Hayward and Rodgers Creek faults, thereby significantly increasing the potential rupture length and, hence, the maximum earthquake which may be generated by these faults. This investigation involves detailed mapping and analysis of the landforms along the Pinole fault in order to better understand its activity and prehistoric earthquake behavior.

Having been told to view the Maacama fault as an extension of the Rodgers Creek fault I thought I would take a look at the locations of the two faults and how they relate to one another. I found that the Maacama fault starts from a location just north of Santa Rosa. The Rodgers Creek fault ends near Healdsburg so the faults are side by side for a short distance. The distance separating them is about 5 miles.

Looking at a worst-case scenario it could be possible that the Maacama, Rodgers Creek, Pinole and the Hayward fault could rupture as a single unit. The magnitude of the quake would be higher then it would be if just one fault ruptured, but not much higher. However the length of the rupture would mean that a greater area would be involved. I don’t know what the odds are for a rupture of this nature, but doubt that something like this could happen. If this did happen it would most certainly surpass the destruction caused by the 1906 San Francisco and the 1989 Loma Prieta quakes combined. Something to think about the next time there is a quake in the Bay Area. Take Care…Don in creepy town

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