Depth-Dependent Aftershock Trigger Potential Revealed by 3D-ETAS Modeling

Current earthquake catalogs provide high-precision depth values that contain valuable information. Thus, we extend the spatiotemporal Epidemic Type Aftershock Sequence model to 3D by considering hypocentral instead of epicentral distances. To explore the most appropriate parametric form of the spatial kernel, we first examine different triggering functions for the depth difference of the aftershock-mainshock pairs identified by the Nearest-Neighbor method, showing that a magnitude-dependent power-law kernel fits best the earthquakes data in Southern California. Therefore, we incorporate the corresponding kernel into the 3D-ETAS model with space-dependent background activity, where we additionally allow for depth-dependent aftershock productivity. The application to Southern California shows that the model fits the data well. We also find that the aftershock productivity strongly depends on depth, similar to the seismic moment released by the mainshocks, which may be related to depth-dependent seismic coupling.