Hi All. Just recently I made a request for as much data as I could get concerning the Rodgers Creek fault and a map showing the location of the fault. I received more then I could ever have hoped for. As most of you know Petra has a fault very near her backyard. As a matter of fact she has two faults located very near her backyard. This is the Rodgers Creek fault and the Tolay fault. The Tolay is much closer then the Rodgers Creek fault. As a matter of fact it’s close enough (this should make her happy) that she could be sitting on it. It follows Petaluma Creek and is segmented into two parts.

The most recent geologic investigations of two sites along the Rodgers Creek fault in the Glen Ellen quadrangle by the U.S. Geological Survey have resulted in preliminary determinations of slip rate, earthquake recurrence, and magnitude (Budding and others, 1991; Schwartz, 1992). They estimate a slip rate of 6.4 to 10.4 mm/yr and about 2m of slip per event, a magnitude of M7, and a recurrence of 131 to 370 years last three events in late Holocene time. This work is not yet complete but has already caused the Working Group on California Earthquakes (1990) to estimate a 22% probability on the Rodgers Creek fault in the next 30 years. This 22% has been recently changed to 32%.

The seismicity of the Rodgers Creek fault has been recently studied by Wong (1991) who shows the southern half to be seismically quiet. Microseismicity extends along the northern half of the fault and continues northward connecting complexly with the Healdsburg and Maacama faults in a right stepover. The M5.9 earthquake of 1969, located just north of Santa Rosa, is the only historic earthquake known to have occurred on the Rodgers Creek fault. Study was made before the Rohnert Park quake. Several early earthquakes of moderate size occurred in the general vicinity of the Rodgers Creek fault, but none have been documented by surface faulting.

The approximate location of the fault in Santa Rosa is indicated by a scarp and large
closed depression (now modified) northeast of the town center and by gravity anomalies to the south.

To the north of the mapped area, the fault becomes progressively less active based on the lack of well-defined geomorphic features. Most likely the deformations is somewhat distributed as the fault attempts to connect with the active Maacama fault to the north.

The south end of the Rodgers Creek fault is also poorly defined as it approaches the large right stepover to the Hayward fault.

From Taylor Mountain to Sonoma Mountain large-scale lateral spreading and landslides extensively obscure the active surface trace of the fault. Take Care…Don in creepy town.