Hi All. The Yountville M5.2 event on 9/3/2000 is the largest earthquake in the North Bay Area since 1969 when two earthquakes, magnitude 5.6 and 5.7, struck Santa Rosa about 80 minutes apart. These earthquakes are associated with the Rodgers Creek fault system.

In fact, these 3 events are the only earthquakes with magnitude greater than 5.0 to hit the region 50-60 mi north of San Francisco Bay since 1906.

However, in the past year there have been several magnitude 4 or greater events in this same region

1) A magnitude 4.7 event near Bolinas on 8/17/99.

2) A magnitude 4.3 near Rohnert Park on 9/22/99.

3) A series of 3 earthquakes, magnitudes 4.0, 4.2, 4.0 near Cloverdale between January 10-18, 2000.

It is not clear whether the increase in seismicity in this region reflects the end of a long period of seismic quiescence. If so, then this would indicate that the levels of stress are perhaps sufficiently high that larger quakes could be expected soon for the region. A similar seismicity pattern was observed in the 50-year period preceding the 1906 earthquake.

However, there is too little data available on which to alter the formal probabilities for the seismic hazard in this region (Earthquake Probability Study for the San Francisco Region). Clearly, had such an argument been put forth after the two earthquakes that rocked Santa Rosa in 1969, the subsequent 30 years of earthquake activity in this region would have proven the argument to be flawed.

Even the current 30 year probability could be flawed if there isn’t a major quake in the next 30 years in the Bay Area. However, I’m not going to hold my breath on the probability of there not being a major quake in the Bay Area in the next 30 years.

Rodgers Creek Fault is still the leading candidate for the next major quake. I have a feeling though that a lot of people are not going to be ready. Take Care…Don in creepy town.