Fault length, multi-fault rupture, and relations to earthquakes in California

Fault length is used to estimate the rupture length of future earthquakes. However, fault length is often poorly defined, and rupture often breaks beyond the mapped faults. Furthermore, multiple faults often rupture together in a single earthquake. In this work I quantify how to use fault length to infer future rupture length. I used observations of previous ruptures breaking multiple faults to estimate the probability of multiple faults rupturing in a single event. Then I mapped linear trends in the relocated microseismicity for southern California, and used satellite images to investigate the locations of unmapped faults. I added these features to the fault map and infer locations where future multi-fault rupture may occur, or regions where faults may lengthen beyond the currently mapped fault trace. I used all of this information to determine the moment rate and cumulative earthquake rate of several faults systems in California. First, I find the cumulative earthquake rate for several individual faults summed together. Then I find the cumulative earthquake rate for the same faults combined together into one length. I found that the maximum magnitude increases when the separate faults are considered a combined fault system. However, the combined fault lengths decrease the number of magnitude 5-7 earthquakes when compared to the summed rate. In general a combined fault length allows more moment to be released in infrequent but larger magnitude earthquakes (7-8), but requires fewer smaller magnitude earthquakes (5-7).