3D-ETAS model with depth-dependent trigger potential

In the past decades, the Epidemic Type Aftershock Sequence (ETAS) model has been widely used for describing the occurrence and clustering of earthquakes in space and time. Because of large depth uncertainties in the past, this model is two-dimensional and uses only epicentral information. Current earthquake catalogs provide high-precision depth values that contain valuable information. Thus, we extend the spatiotemporal ETAS model to 3D versions exploiting the full hypocentral information of earthquake catalogs by incorporating a depth-dependent kernel into the trigger function. To explore its most appropriate parametric form, we first examine different triggering functions for the depth difference of the aftershock-mainshock pairs identified by the Nearest-Neighbor (NN) method, showing that a magnitude-dependent power-law kernel fits best the earthquakes data in Southern California. Therefore, in order to incorporate the earthquakes' depth information in the ETAS model, we extend the established 2D spatial power-law kernel by using hypocentral instead of epicentral distances. Furthermore, in our extended 3D-ETAS model, we consider space-dependent background activity, where we additionally allow for depth-dependent aftershock productivity. A first application to data from Southern California shows a good performance of the 3D model. 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.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)