## 30 Year Forecast for the Current California Earthquake Drought

Ruben Li Wu, Gisselle Mondragon, Terri Tang, Laura Davey, Vanessa Y. Carpio, Amabel F. Teca, Malka A. Lazerson, Jerlyn L. Swiatlowski, Kevin R. Milner, Scott Callaghan, & Thomas H. JordanSubmitted August 1, 2019, SCEC Contribution #9312, 2019 SCEC Annual Meeting Poster #309

Since 1906, California’s San Andreas Fault System has not produced a M7.0+ earthquake in over 100 years. After over a century of dormancy, the San Andreas Fault is approaching its recurrence rupture interval of 140 years (Wald et al., 2019). In light of this absence of large earthquakes, we investigated different types of earthquake droughts, the likelihood of our current seismic drought ending in the next 30 years, and a forecast of the seismic rate after the drought has ended. In order to measure and compare the statistical likelihood of major earthquake ruptures in California, we defined an earthquake drought four different ways: (1) no M7.5+ earthquakes in the entire state of California in a 100 year period, (2) no M7.0+ earthquakes over a 100 year period sections of the San Andreas Fault system, which includes, the San Andreas Fault, the San Jacinto Fault, the Hayward Fault, and the Elsinore Fault, (3) no M6.5+ earthquakes over a 100 year period at five paleoseismic sites used by Biasi and Sharer (2019) and (4) no M6.5+ earthquakes over a 100 year period on 30 paleoseismic sites extracted from UCERF3 (Unified California Earthquake Rupture Forecast version 3). We used RSQSim (Rate State earthQuake Simulator), a physics based earthquake simulator, on the Blue Waters supercomputer to generate 2 million year catalog of simulated earthquakes. We calculated probabilities regarding earthquake behavior based on the time-independent Poisson distribution model in order to find the overall probability of a M7.5+ earthquake occurring over any 30-year period. We then compared this time-independent model to a time-dependent model to see the differences in probability between the earthquake occurrences. Using a catalog of 2 million years, the probability of being in a drought of 100 years or more on the San Andreas Fault system (Definition 2) is 2%. Furthermore, the probability of a M7.0+ drought ending event occurring for the same definition such that a 100 year drought has passed is 91%. Therefore, California, regardless of which definition used, is in a very unlikely drought and is very likely to see the drought end soon. Considering these probabilities, we hope that this motivates both the public and policy makers to prepare for the drought that is most probably going to end soon.

**Citation**

Li Wu, R., Mondragon, G., Tang, T., Davey, L., Carpio, V. Y., Teca, A. F., Lazerson, M. A., Swiatlowski, J. L., Milner, K. R., Callaghan, S., & Jordan, T. H. (2019, 08). 30 Year Forecast for the Current California Earthquake Drought. Poster Presentation at 2019 SCEC Annual Meeting.

**Related Projects & Working Groups**

Communication, Education, and Outreach (CEO)