No. 918

Title:

Detection of anomalous seismicity as a stress change sensor

Author(s):

Ogata, Yosihiko (The Institute of Statistical Mathematics)

Key words:

Coulomb failure stress change; ETAS model; Seismicity quiescence and activation.

Abstract:

Anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the 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 dataset of origin-times and magnitudes of recent earthquakes or aftershocks in various regions 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. The results lead us to a summarized observation that even small sizes of the CFS increment of the order of several millibars, can trigger such activation or lowering of microseismicity, which is also supported by the seismicity rate-change equation of Dieterich [1994]. Thus, we expect that deviation of aftershock and general seismic activity relative to the modeled rates is sensitive enough to detect a slight stress-change.