A Geodesy- and Seismicity-Based Local Earthquake Likelihood Model for Central Los Angeles

We estimate time-independent earthquake likelihoods in central Los Angeles using a model of interseismic strain accumulation and the 1932–2017 seismic catalog. We assume that on the long-term average, earthquakes and aseismic deformation collectively release seismic moment at a rate balancing interseismic loading, mainshocks obey the Gutenberg-Richter law (a log linear magnitude-frequency distribution [MFD]) up to a maximum magnitude and a Poisson process, and aftershock sequences obey the Gutenberg-Richter and “Båth” laws. We model a comprehensive suite of these long-term systems, assess how likely each system would be to have produced the MFD of the instrumental catalog, and use these likelihoods to probabilistically estimate the long-term MFD. We estimate M_max = 6.8 + 1.05/−0.4 (every ~300 years) or M_max = 7.05 + 0.95/−0.4 assuming a truncated or tapered Gutenberg-Richter MFD, respectively. Our results imply that, for example, the (median) likelihood of one or more M_w ≥ 6.5 mainshocks is 0.2% in 1 year, 2% in 10 years, and 18–21% in 100 years.