Inhomogeneous spatio-temporal epidemic-type aftershock sequence model incorporating seismicity-triggering slow slip events

Clarifying the relationship between regular earthquakes and slow fault slip is essential for understanding the mechanisms behind seismic activity. We hypothesize that the background seismic activity is partially triggered by interplate slow-slip events (SSEs). Consequently, we present an extension of the spatio-temporal epidemic-type aftershock sequence (ETAS) model, which incorporates background seismicity as a piecewise constant function over time based on recent advances in the inference of space-time inhomogeneous point processes. In this study, Global Navigation Satellite System (GNSS) data is employed to identify the occurrence periods of SSEs, thereby delineating the intervals during which changes in background seismicity may occur. Due to the technical complexity of performing inference with an inhomogeneous ETAS model, this work employs a maximum likelihood inference method using the Expectation-Maximization (EM) algorithm. This approach also enables the inference of the branching process for aftershocks, allowing for the estimation of earthquake genealogy. This study elucidates how the background seismicity increases during the periods of SSEs in Guerrero, Mexico and Boso Peninsula, Japan, which allows for a more comprehensive understanding of seismic activity and the relationship between slow and fast earthquakes.