A Statistical Method for Associating Earthquakes with Their Source Faults in Southern California

Walker S. Evans, Andreas Plesch, John H. Shaw, Natesh L. Pillai, Ellen Yu, Men-Andrin Meier, & Egill Hauksson

Published January 14, 2020, SCEC Contribution #9057

We present a new statistical method for associating earthquakes with their source faults in the Southern California Earthquake Center’s 3D Community Fault Models (CFMs) (Plesch et al., 2007) in near-real-time and for historical earthquakes. The method uses the hypocenter location, focal mechanism orientation, and earthquake sequencing to produce the probability of association between a given earthquake and each fault in the CFM or no CFM fault at all. We used a set of known associations (the Known Sets) as training/testing data and demonstrated that our models perform effectively on this known data and therefore could be expected to perform well on other earthquakes with similar characteristics. We also give evidence that they could be expected to perform well across the catalogue of southern California earthquakes (Hauksson et al., 2012). To produce near-real-time associations for future southern California earthquakes, the models have been implemented as an R script and linked to the Southern California Earthquake Center’s systems to automatically produce fault associations for earthquakes as they occur. To produce historical associations, we apply the method to the most recent CFM version (5.2), yielding modeled historical associations for all events of ≥ M 3.0 in the catalogue of southern California earthquakes from 1981-2016. Over 80% of these events and 99% of moment within the geography covered by the CFM had a primary association with a CFM fault. The models can help identify clusters of small earthquakes that may be foreshocks of larger events on major faults. The method will also assist in communicating objective information about the faults that source earthquakes to the scientific community and general public. In the event of a damaging southern-California earthquake, the near-real-time model will provide valuable information regarding the similarity of the current event to forecast scenarios, potentially aiding in earthquake response.

Citation
Evans, W. S., Plesch, A., Shaw, J. H., Pillai, N. L., Yu, E., Meier, M., & Hauksson, E. (2020). A Statistical Method for Associating Earthquakes with Their Source Faults in Southern California. Bulletin of the Seismological Society of America, 110(1), 213-225. doi: 10.1785/0120190115.

Related Projects & Working Groups
CFM, USR