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Rupture propagation through the Big Bend of the San Andreas Fault: a dynamic modeling case study of the Great Earthquake of 1857

Julian C. Lozos

Published August 15, 2017, SCEC Contribution #7816, 2017 SCEC Annual Meeting Poster #158

The great San Andreas Fault (SAF) earthquake of 9 January 1857, estimated at M7.9, was one of California’s largest historic earthquakes. Its ~360 km rupture trace follows the Carrizo and Mojave segments of the SAF, including the ~30° compressional Big Bend in the fault. If 1857 were a characteristic rupture, the hazard implications for southern California would be dire, especially given the inferred ~150 year recurrence interval for this section of the fault. However, recent paleoseismic studies in this region suggest that 1857-type events occur less frequently than single-segment Carrizo or Mojave ruptures, and that the hinge of the Big Bend is a barrier to through-going rupture.
Here, I use 3D dynamic rupture modeling to attempt to reproduce the rupture length and surface slip distribution of the 1857 earthquake, to determine which physical conditions allow rupture to negotiate the Big Bend of the SAF in a single event. These models incorporate the nonplanar geometry of the SAF, surrounding material properties from the SCEC CVM, and a regional stress field from seismicity literature. Under a variety of different interpretations of a regional stress field, I am unable to produce model events that both match the observed surface slip on the Carrizo and Mojave segments of the SAF and include rupture through the hinge of the Big Bend. I suggest that accumulated stresses at the bend hinge from multiple Carrizo-only and Mojave-only ruptures may be required to allow rupture through the bend — a concept consistent with paleoseismic observations. This study may contribute to understanding the cyclicity of hazard associated with the southern-central SAF.

Key Words
San Andreas Fault, 1857 earthquake, Ft. Tejon earthquake, Big Bend, dynamic rupture modeling,

Lozos, J. C. (2017, 08). Rupture propagation through the Big Bend of the San Andreas Fault: a dynamic modeling case study of the Great Earthquake of 1857. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)