Magnitude-5 Shock Strikes the Bartlett Springs Fault

Ross Stein, Temblor

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The right-lateral strike-slip quake was felt in Ukiah, Yuba City, and Clear Lake. The quake struck at 18 km depth, near or on the discontinuous Bartlett Springs Fault is 120 km long, so it could conceivably rupture in a Mw=7.5 earthquake. Given a long-term fault slip rate of 1-2 mm/yr and Such a quake, with about 3 m of slip, would have a rough inter-event time of several thousand years.


Taylor and Swan (1986) and Swan and Taylor (1991) interpreted a Bartlett Springs Fault trench excavation to expose at least three prehistoric earthquakes, the most recent event occurring 300-1,000 years ago. To be seen in a trench, a rupture usually needs to be larger than M=7, and yesterday’s quake struck along its most active section. So although fortunately remote, this fault is potentially dangerous.


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Data from USGS, Northern California Seismic Network, and

Swan, F.H., and Taylor, C.L., 1991, Geologic and geomorphic evidence suggesting spatial and temporal clustering of paleoseismic events along the Bartlett Springs fault zone, northern California: Seismological Research Letters, v. 62, no. 1, p. 11.

Taylor, C.L., and Swan, F.H., 1986, Geological assessment of the seismic potential of the Bartlett Springs shear zone for Scott Dam, Lake County, California: Final report by Geomatrix Consultants for Pacific Gas and Electric Company, 51 p.