Seismic quiescence prior to the 2000 M=6.8 Nemuro Peninsula earthquake

Abstract

We investigated the characteristics of the seismicity changes prior to the 2000M=6.8 Nemuro Peninsula earthquake by using the earthquake catalog of Japan Meteorological Agency (JMA). The JMA catalog is complete for all the events with M≥3.6 during January, 1984-March, 2000. The temporal variation of the number of earthquakes in the epicentral zone decreased significantly during 1995-1996. We applied another statistical method, called the RTL algorithm, to the same JMA earthquake catalog and found that a seismic quiescence started in 1995 and lasted till the end of 1996. A clear anomalous quiescence zone appeared around the epicenter in 1996. The maximum dimension of this quiescence zone is over 200km, several times larger than the rupture length of the main shock. These consistent results, which were obtained from different approaches, indicated that the seismic quiescence that occurred 3 years before the main shock reflected the preparation of the earthquake. Therefore, investigation of seismicity changes prior to the Nemuro Peninsula earthquake may provide useful information for understanding the physical nature of earthquake preparation.