Quantitative description of induced seismic activity before and after the 2011 Tohoku‐Oki earthquake by nonstationary ETAS models

The epidemic‐type aftershock sequence (ETAS) model is extended for application to nonstationary seismic activity, including transient swarm activity or seismicity anomalies, in a seismogenic region. The time‐dependent rates of both background seismicity and aftershock productivity in the ETAS model are optimally estimated from hypocenter data. These rates can provide quantitative evidence for abrupt or gradual changes in shear stress and/or fault strength due to aseismic transient causes such as triggering by remote earthquakes, slow slips, or fluid intrusions within the region. This extended model is applied to data sets from several seismic events including swarms that were induced by the M9.0 Tohoku‐Oki earthquake of 2011.