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Nowcasting Earthquakes in Southern California with Machine Learning:Bursts, Swarms and Aftershocks May Reveal the Regional Tectonic Stress
  • John B. Rundle,
  • Andrea Donnellan
John B. Rundle
University of California - Davis

Corresponding Author:[email protected]

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Andrea Donnellan
Jet Propulsion Laboratory
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Seismic bursts in Southern California are sequences of small earthquakes strongly clustered in space and time, and include seismic swarms and aftershock sequences. A readily observable property of these events, the radius of gyration (), allows us connect the bursts to the temporal occurrence of the largest ³7 earthquakes in California since 1984. In the Southern California earthquake catalog, we identify hundreds of these potentially coherent space-time structures in a region defined by a circle of radius 600 km around Los Angeles. We compute for each cluster, then filter them to identify those bursts with large numbers of events closely clustered in space, which we call “compact” bursts. Our basic assumption is that these compact bursts reflect the dynamics associated with large earthquakes. Once we have filtered the burst catalog, we apply an exponential moving average to construct a time series for the Southern California region. We observe that the of these bursts systematically decreases prior to large earthquakes, in a process that we might term “radial localization.” The then rapidly increases during an aftershock sequence, and a new cycle of “radial localization” then begins. These time series display cycles of recharge and discharge reminiscent of seismic stress accumulation and release in the elastic rebound process. The complex burst dynamics we observe are evidently a property of the region as a whole, rather than being associated with individual faults. This new method allows us to improve earthquake nowcasting in a seismically active region.