Nowcasting Earthquakes in Southern California with Machine Learning: Bursts, Swarms and Aftershocks May Be Related to Levels of Regional Tectonic Stress

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 (RG), allows us connect the bursts to the temporal occurrence of the largest M 7 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 RG 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.