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Ground-rupturing earthquakes on the northern Big Bend of the San Andreas Fault, California, 800AD to Present
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Paleoseismic data on the timing of ground-rupturing earthquakes constrain the recurrence behavior of active faults and can provide insight on the rupture history of a fault if earthquakes dated at neighboring sites overlap in age and are considered correlative. This study presents the evidence and ages for 11 earthquakes that occurred along the Big Bend section of the southern San Andreas Fault at the Frazier Mountain paleoseismic site. The most recent earthquake to rupture the site was the M(w)7.7-7.9 Fort Tejon earthquake of 1857. We use over 30 trench excavations to document the structural and sedimentological evolution of a small pull-apart basin that has been repeatedly faulted and folded by ground-rupturing earthquakes. A sedimentation rate of 0.4cm/yr and abundant organic material for radiocarbon dating contribute to a record that is considered complete since 800A.D. and includes 10 paleoearthquakes. Earthquakes have ruptured this location on average every similar to 100years over the last 1200years, but individual intervals range from similar to 22 to 186years. The coefficient of variation of the length of time between earthquakes (0.7) indicates quasiperiodic behavior, similar to other sites along the southern San Andreas Fault. Comparison with the earthquake chronology at neighboring sites along the fault indicates that only one other 1857-size earthquake could have occurred since 1350A.D., and since 800A.D., the Big Bend and Mojave sections have ruptured together at most 50% of the time in M(w)7.3 earthquakes.
|Journal of Geophysical Research. Solid Earth
|In Copyright (All Rights Reserved)
|An edited version of this paper was published by AGU. Copyright 2017 American Geophysical Union.