[S08-P] Poster

[S08-P-02] Temporal clustering and occurrence probability of large earthquakes on active faults in Japan

^○Hisao Kondo^{1, 3}, Kazuhiro Iwakiri^{2, 3}, Hirota Tani³, Kenji Satake⁴ (1.Geological Survey of Japan, AIST, Tsukuba, Japan, 2.Japan Meteorological Agency, Tokyo, Japan, 3.Earthquake and Disaster-Reduction Division, MEXT, Tokyo, Japan, 4.ERI, The University of Tokyo, Japan)

The 2016 Kumamoto earthquake (Mj 7.3) caused devastating damages and more than 180 casualties. It occurred in an active fault zone and surface ruptures appeared mostly along the previously mapped active faults (HERP, 2016). Meanwhile, the occurrence of large (greater than Mj 6.8) earthquakes on minor active faults has been more frequent in recent years. We here re-examined the frequency and probabilities of large earthquakes on active faults in the last 125 years, based on the historical catalogue of damaging earthquakes in Japan and previous reports. In total, 28 large damaging crustal earthquakes occurred in the last 125 years, and 22 of them (80 %) are related with mapped active faults, and 6 (20 %) are not. The 22 earthquakes in 125 years yield the average recurrence interval of 5.7 years. Using the individual recurrence intervals, 4.6+/-3.7 years is obtained for all damaging earthquakes and 6.0+/-5.5 years for those on active faults. The frequency distribution of recurrence intervals shows a bimodal distribution consisting of two groups. The average recurrence interval in the shorter group is 2.9+/-1.5 years. The longest interval is 17 years before the 1995 Kobe earthquake. It is thus apparent that the occurrence of the damaging earthquakes exhibits the temporal clustering and long quiescence periods. The temporal clustering is related with the occurrence of mega-thrust earthquakes such as the 2011 Tohoku earthquake, the 1944 Tonankai and 1946 Nankai earthquakes. Under the assumption of Poisson process, we obtained 72%, 92%, 100% probabilities within the next 5, 10 and 30 years for all damaging large earthquakes, and 62%, 86%, 99.7% for active fault earthquakes, respectively. If the present day is within a clustering period, the probability increases up to 68-97% within the next 5 years. To forecast them more accurately, the earthquake probability based on the BPT model for individual active faults and time-dependent seismic hazard assessment are necessary.