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A long-term-average estimate of earthquake likelihoods and the largest earthquake in central Los Angeles

Chris Rollins, & Jean-Philippe Avouac

Published August 7, 2018, SCEC Contribution #8314, 2018 SCEC Annual Meeting Poster #134

Thrust earthquakes present a substantial hazard to Los Angeles, and geodetic data suggest that major thrust faults underlying the city are accruing elastic strain that may be released in future earthquakes. To quantify this hazard, we express this strain accumulation as the buildup rate of a deficit of seismic moment, 1.6 +1.3/-0.5 x 10^17 Nm/yr in total, and assume that on the long-term average, 1) this is also the total rate at which seismic moment is released in earthquakes and 2) those earthquakes obey a log-linear magnitude-frequency distribution up to a maximum magnitude that they do not exceed. We generate a comprehensive suite of long-term-average earthquake rate models satisfying these criteria, vet each model by evaluating how likely it would be to have produced the magnitude-frequency distribution of earthquakes in the 1932-2016 instrumental catalog in Los Angeles, and use these likelihoods to estimate the probability density functions of long-term-average earthquake likelihoods and the maximum earthquake. We estimate a maximum magnitude of Mw=6.8 +1.05/-0.4 or Mw=7.05 +0.95/-0.4 depending on the nature of the assumed magnitude-frequency distribution. The occurrence rates of small and moderate earthquakes in the best-fitting models are similar to the instrumental catalog. We show how these models can be used for probabilistic seismic hazard assessment to estimate, for example, the probability of observing an earthquake of or exceeding a given magnitude within a given timespan.

Rollins, C., & Avouac, J. (2018, 08). A long-term-average estimate of earthquake likelihoods and the largest earthquake in central Los Angeles. Poster Presentation at 2018 SCEC Annual Meeting.

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Tectonic Geodesy