No. 992

Title:

Seismic and geodetic anomalies preceding the rupture around the focal region : The Niigata-Ken-Chuetsu Earthquake of October 23, 2004, central Japan

Author(s):

Ogata, Yosihiko (The Institute of Statistical Mathematics)

Key words:

Baseline distance; Coulomb Failure Stress increments; ETAS model; GPS; Seismicity activation and quiescence.

Abstract:

The ordinary short-term occurrence rate of earthquakes in a region is predicted using the Epidemic Type Aftershock Sequence (ETAS) model of triggering seismicity. Any anomalous seismic activity, such as quiescence and activation, can be quantified by identifying significant deviation from the predicted rate. Such anomalies are revealed to have occurred during the three year period leading up to the 2004 Chuetsu Earthquake of M6.8 (Mw6.6), central Japan. The quiescence and activation took place in the region of negative and positive increments of the Coulomb Failure Stress, respectively, that were transferred from possible aseismic slips on the focal fault plane. Such slips are further supported by transient crustal movement around the rupture source. Time series records of the baseline distances between the permanent GPS stations deviated from the predicted trends, with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the Chuetsu Earthquake. The cumulated preceding slip is estimated to be roughly equivalent to Mw5.9.