Friday Seminar (Feb. 8th, 2019) by Project Assis. Prof. T. Kumazawa (Center for Geophysical Observation and Instrumentation)The epidemic type aftershock sequences (ETAS) model is useful for statistical analysis of time sequences of earthquake occurrences. The conditional intensity function of the point process model is defined for the occurrence rate of an earthquake in the immediate future, and it is indispensable for providing probability forecast of earthquakes in a given future period. Also, it provides the standard seismicity model that is useful for detecting anomalies from a series of earthquake occurrences. Then remodeling of the intensity function can improve the earthquake forecasting. In this presentation, I focus on the analysis by the ETAS model and its variations, especially the non-stationary ETAS model which provides inversion solution of nonstationary changes in seismicity. I will introduce examples of model applications to the seismic activity in the Izu region, and to some seismic activity in recent years.
For the swarm activity in the Izu district, we investigated the predictability of the swarm earthquake associated with magma intrusion in the volcanic zone. It is reported that the volumetric strain change associated with the magma ascending in the eastern part of the Izu district shows a high correlation with the number of earthquakes, but we found that the temporal change of the background seismicity rate of the ETAS model shows a higher correlation. We then found that the background seismicity rate can be well predicted as a function of preceding volumetric strain changes coupled with the onset location of earthquake swarm event, and demonstrated predictions retrospectively for the numbers of earthquakes in major swarm events in the Izu region.