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

We investigated the characteristics of the seismicity changes prior to the 2000 M = 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 greater than or equal to3.6 during January, 1984 similar to March, 2000. The temporal variation of the number of earthquakes in the epi central zone decreased significantly during 1995 similar to 1996. We applie d another statistical methods, called the RTL algorithm, to the same JMA ea rthquake catalog and found that a seismic quiescence started in 1995 and la sted till the end of 1996. A clear anomalous quiescence zone appeared aroun d the epicenter in 1996. The maximum dimension of this quiescence zone is o ver 200 km, several times larger than the rupture length of the main shock. These consistent results, which were obtained from different approaches, i ndicated 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 pre paration.