THE SAN ANDREAS FAULT ZONE IN THE CARRIZO PLAIN, CALIFORNIA: REVIEW OF GEOMORPHOLOGICAL, PALEOSEISMOLOGICAL AND GEOCHRONOLOGICAL ANALYSES

Strike-slip faults have played a significant role in the tectonic development of the Cordilleran region since the Mesozoic time. The San Andreas Fault (SAF) system, the youngest and arguably the most famous of these faults, has provided numerous clues as to how these faults might have formed, matured, and evolved through time. Nearly five decades of paleoseismic investigations carried out along the SAF have contributed to a better but still incomplete understanding of its faulting behavior over multiple earthquake cycles. The majority of these pioneering investigations were performed along the Carrizo section of the SAF, where modeled 95-percentile ranges of the earthquakes prior to the A.D. 1857 earthquake are A.D. 1631-1823, 1580-1640, 1510-1612, 1450-1475, and A.D. 1360-1452. Data indicate that the average time interval between the last six earthquakes that ruptured the SAF in the Carrizo Plain is 88±41 years, less than half the previously calculated recurrence interval estimates. Similarly, offset measurements made using lidar data reveal that slip during the 1857 Fort Tejon earthquake along the Carrizo section was 5-6 m, significantly lower than the previously reported 8-10 m. Consequent investigations have alluded to caveats in using geomorphological features as offset markers for slip and slip rate calculations and demonstrated the usefulness and significance of single grain post-IR IRSL dating of fluvial and alluvial sediments in the Carrizo Plain. New slip rate studies confirm that geodetic and geologic slip rates along the Carrizo section are similar, suggesting that the Carrizo section of the SAF likely behaves in a slip-predictable manner. In this talk, I will summarize all available paleoseismic data from the Carrizo section of the SAF, discuss its limitations, and describe ongoing projects aimed at testing this fundamental question of fault behavior for the southern SAF.