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The 1911 M~6.6 Calaveras earthquake:
Focal mechanism and relationship to static and dynamic Coulomb stress changes imparted by the 1906 San Francisco earthquake,
submitted to Bull. Seismol. Soc. Amer., 2007.
Doser, Diane I., Kim B. Olsen, Fred F. Pollitz, Ross S. Stein, and Shinji Toda
[Printable article (1.8 Mb)]

Non-technical summary: We have used all extant seismograms of the 1 July 1911 Calaveras earthquake to re-analyze this enigmatic earthquake. We find that the event was most likely a right-lateral strike-slip Calaveras fault earthquake, larger than but otherwise resembling the 1984 M=6.1 Morgan Hill earthquake in roughly the same location. We could recover, however, no unambiguous displacement or strain data to corroborate the seismic analysis. The occurrence of a right-lateral strike-slip event in 1911 is inconsistent with the calculated -0.4 to -3.0 bar stress decrease imparted by the 1906 rupture, and 5 years of post-1906 crustal relaxation does little to reload the Calaveras fault. We also calculated the peak dynamic Coulomb stress imparted by the 1906 rupture, and find that the 1911 shock struck where the dynamic stress increased by 1-6 bars (see accompanying figure, showing three different dynamic models for the 1906 event). Despite this positive association between the dynamic stress and the 1911 earthquake, there is no correlation of 1906 aftershock frequency or magnitude with the peak dynamic stress, perhaps because the sample is small and the aftershocks are poorly located. Just 20 km to the south of the 1911 epicenter, surface creep of the Calaveras at Hollister paused for about 17 years after 1906, about the expected delay for the calculated static stress drop imparted by the 1906 earthquake when San Andreas postseismic creep and relaxation are included. Thus, the 1911 Calaveras earthquake may have been promoted by the transient dynamic stresses, while Calaveras creep was inhibited by the static stress changes.