Detection of anomalous seismicity as a stress change sensor

摘要

Anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the epidemic-type aftershock sequence (ETAS) model that represents the normal occurrence rate of earthquakes in a region indicating the empirical triggering effect by the previous events. The model is fitted to a data set of origin times and magnitudes of earthquakes or aftershocks during May–August 2003 in and around northern Japan. The detected quiescence and activation relative to the predicted seismicity rate are consistent with the coseismic changes of Coulomb failure stress (CFS) in the corresponding regions, transferred from certain strong earthquakes. Few results in this paper agree with the claim that there should be a threshold value of ΔCFS capable of affecting seismic changes. Thus we expect that significant deviation of actual activity from the predicted rates is sensitive enough to detect a slight stress change. Furthermore, I offer a similar interpretation of the detected seismicity lowering relative to the modeled rates preceding the strong earthquakes, assuming some aseismic slips.