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Project Summary

Data on the rupture history of the SAF form the basis of numerous models of fault behavior and seismic hazard. Models of fault behavior range from simple, deterministic systems such as the time-predictable and slip predictable models of Shimazaki and Nakata (1980), to complex, non-linear, and/or chaotic systems that can be described as a group, but cannot be individually predicted (Liu, 2003). The high slip rate, short recurrence interval, great length and accessibility of the SAF make it the best target in the U.S. (and perhaps the world) for observational testing of fault behavior models. Paleoseismic data are essential for such testing, because they are the only type of observations that span multiple earthquake cycles.

The Carrizo Plain is one of the best places to study the rupture history of the SAF
because it has a proven paleoseismic record with excellent slip rate and slip per event measurements, and the potential to significantly enlarge the data set by increasing the length of the earthquake record. The Carrizo Plain has been one of the most productive sections of the SAF for paleoseismic research, yielding multiple slip rates from different time intervals at Wallace Creek in agreement with geodetic measurements; slip per event measurements for the last 6 ruptures; and well-constrained dates of the last 5 major earthquakes at the Bidart Fan and Phelan Creeks . The Bidart Fan site in the Carrizo Plain has the potential to produce a multi-cycle rupture history spanning at least 3000 years, with a minimum of 10 surface ruptures. We propose to exploit this record in the characterization of the rupture history of the south-central San Andreas Fault. The record will be especially valuable because it can be combined with existing slip rates, slip per event data, and future measurements of slip per event at the Van Matre Ranch (VMR) site and the nearby Wallace Creek offset site of Sieh, Liu, and associates. Our proposed research at the Bidart Fan should allow us to double the temporal record of surface ruptures in the Carrizo Plain and provide a third major paleoseismic site on the San Andreas fault for developing and testing models of fault behavior.

Bottom line: The proposed research will provide additional insights on the magnitude and dates of past earthquakes in the Carrizo Plain and thereby help to assess the potential magnitude, location, and date of future damaging earthquakes.

NSF Proposal