抄録
We excavated a trench across the Kawakami fault, one of the segments of the Median Tectonic Line Fault Zone in southwest Japan. Three faults appeared on the trench walls. The sense of apparent displacement across the fault zone is down to the north, consistent with the fault scarps around the trench site. The sediments exposed on the trench walls contain evidence for three episodes of surface-rupturing earthquakes. The most recent seismic event, event I, on the Kawakami fault occurred after AD 1405. The penultimate seismic event, event II, occurred sometime during 790 BC-AD 65. Another seismic event, event III, occurred sometime during c.a. 29,000 yBP-560 BC. The timing of these seismic events is consistent with that revealed by previous trenching studies. The ages of the most recent and penultimate events are better constrained in this study. By combining this study with previous study results, the timing of paleoseismic events on the Kawakami fault is summarized as follows. The most recent seismic event, event 1, occurred between AD 1405 and AD 1780. The timing of the event is consistent with the 1596 Keicho-earthquake. The penultimate seismic event, event 2, occurred during AD 25-AD 1000. Other events occurred during 790 BC-AD 65 and during c.a. 29,000 yBP. -560 BC. Given that the 1596 Keicho-earthquake is the latest faulting event of the Kawakami fault, the average recurrence intervals are inferred to be 765-1193 years.
