Open Intervals, Clusters and Supercycles: 1100 years of Moment Release in the Southern San Andreas Fault System: Are we Ready for the Century of Earthquakes?

Thomas K. Rockwell

Submitted September 20, 2016, SCEC Contribution #6367, 2016 SCEC Annual Meeting Talk on 9/12 10:30 (PDF)

Compilation of paleoseismic data from several dozen trench sites in the southern San Andreas fault system, along with geomorphic observations of displacement in recent earthquakes, allows for sequencing of the past 1100 years of large earthquakes for the southern 160 km of the main plate boundary. At least four generalizations are clear: 1) M7 and larger earthquakes account for most of the moment release in the southern San Andreas fault system over the past 1100 years; 2) large earthquakes on individual faults are quasi-periodic but display a relatively high coefficient of variation in recurrence time, similar to most long California paleoseismic records, and which may be a reflection of Coulomb stress interactions; 3) moment release has temporally varied during the past 1100 years but within potentially predictable bounds; and 4) the southern San Andreas fault system is currently moment deficit when compared to the previous millennium of moment release. Comparison of the timing of earthquakes with the timing of past high-stands of Lake Cahuilla supports the idea that lake fillings influenced and may have modulated the timing of southernmost San Andreas fault earthquakes. If so, then the long (300 year) open interval on the southern San Andreas fault may be in part explained by the absence of a complete lake filling episode in the past 300 years. Together, the record suggests that the southern San Andreas fault is late in the cycle but not necessarily “overdue”, and that a systems level approach may be more accurate in long-term earthquake forecasting than estimates made from individual faults. If the past is the key to the future, then the next century is likely to see far more large earthquake activity on the southern San Andreas fault system than was observed in the past one to two centuries.

Key Words
Southern San Andreas fault system, paleoseismology, open intervals, forecasting large earthquakes

Citation
Rockwell, T. K. (2016, 09). Open Intervals, Clusters and Supercycles: 1100 years of Moment Release in the Southern San Andreas Fault System: Are we Ready for the Century of Earthquakes?. Oral Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology