Coast Geological Society

 “Timing, Extent and Size of Pre-historic Earthquakes Along the Northern San Jacinto Fault Zone” 

In southern California, most of the relative movement between the North American and Pacific plates is concentrated along the southern San Andreas and the San Jacinto fault zones. To evaluate how these two main faults interact and how plate boundary slip is divided between them, we have been working along the northern San Jacinto fault making slip-rate measurements, slip-per-event measurements, and collecting paleoseismic data. In the past few years, we have been obtained new slip-rate and slip-per-event data from several deflected and offset stream channels. We have also been able to identify and trench a new paloeseismic site that is located within a small sag formed between two fault strands along the north side of Mystic Lake in the San Jacinto Valley. I will compare our new data with similar data from the central San Jacinto fault and the San Andreas fault, and discuss the implications for rupture patterns and the possibility of ruptures jumping from one fault to the other.

 Bio:

 Nate Onderdonk is an Assistant Professor in the Dept. of Geological Sciences at Long Beach State University. He earned a BS in Physics from Principia College and an MS and PhD in Geology from UC Santa Barbara. He spent two years as a post-doc at the University of Oslo, Norway studying arctic geology in western Norway, Spitsbergen, and eastern Greenland. His research spans a range of topics in the fields of tectonics and geomorphology and currently includes tectonic rotation in California, the San Jacinto fault zone, and hydrothermal seeps in the Imperial Valley.