Hi All. Evidence shows that the northern Hayward fault was the site of a major earthquake sometime between the mid-1600s and the arrival of Spanish colonists in 1776. Fitting the history of activity along that fault, it would be due for a quake right now.

"Pressure builds up regularly until the pressure is released like snapping an elastic band when the earthquake happens, which looks like happens every 330 years on the Rodgers Creek fault," said William "Terry" Wright, geology professor at Sonoma State University. "Rodgers Creek is considered to be a very active fault. We're right in the time of an earthquake."

With 9 to 10 millimeters of movement believed to have occurred along the fault in the last 1,000 years, scientists have created a time scale, known as a recurrence interval, that suggests a somewhat major earthquake along that fault line about once every 300 years.

On the northern Hayward Fault, the researchers identified three major clusters of identical repeating small quakes along the northern fault zone, representing centers of slippage up to 7 millimeters per year at from 4 to 10 kilometers depth.

When data from all sources was collated, a remarkably detailed picture of the Hayward Fault emerged. Shallow creep falls off markedly where the fault dives under San Francisco Bay at Point Pinole; creep is at a maximum at El Cerrito, with indications of rapid slippage continuing to great depths; surface creep diminishes south of Berkeley, over the locked portion of the fault that broke in 1868.

The model suggests that no locking occurs from Berkeley north to Point Pinole and that this freely creeping stretch of the fault is not likely to be the site of origin for a major quake. Prospects for the southern Hayward Fault, however, and for the Rodgers Creek fault, north of the Bay, are less sanguine.

It is the southern portion of the Rodgers Creek Fault that has the potential of a major quake. Digs across the fault don’t show any movement in the recent past. As it was pointed out this doesn’t mean very much as the digs could be in the wrong place.

The recent earthquake maps I have show four earthquakes that could be associated with the southern portion of the Rodgers Creek fault. Two of the quakes were recorded between 1910-1971 by the UCB and two by USGS 1969-1973. The quakes ranged from 1.0M to 2.9M. There are also four quakes that could be associated with the southern portion of the Tolay Fault. These were recorded by the UCB between 1910-1971.

Of course there could be more quakes in that area, but at present I don’t have any knowledge of them. I’m going to make that my next priority. Take Care…Don in creepy town.