1586年天正地震の震源断層推定の試み

——液状化履歴地点における液状化可能性の検討から——

抄録

The Chubu and the Kinki regions in central Japan were widely and seriously damaged by the 1586 Tensho earthquake. The detail of this event is not well understood because reliable descriptions in historical documents for Tensho era are few. Previous researches have provided wide variety of arguments about location of source fault and magnitude of this event, which yield several differing interpretations. In this study, we focus on ground liquefaction which has been not intensively investigated yet for this event. The four areas under consideration involve liquefaction sites discovered in the ruins or inferred from the reliable descriptions. These are the Tonami Plain, Toyama Plain, Nobi Plain and north-east coast of Lake Biwa. We attempt to estimate source fault of this event by evaluating the possibility of liquefaction to seismic ground motion assuming hypothetical source faults. Hypothetical source faults are along the Shokawa fault group, southern part of the Atera fault group and the Yoro-Kuwana-Yokkaichi faults. The possibility of liquefaction is evaluated by P_L value which is calculated using predicted seismic intensity and borehole data (including N-value and soil data). Predicted seismic intensity is calculated using Estimation Tools for Earthquake Ground Motion by empirical attenuation relations of J-SHIS. Borehole data from 296 boring sites in public database is used. As a result, P_L value is large in all these areas in case of occurrence a single earthquake of M_j 7.9 on the Shokawa fault group. It means that the event likely cause liquefaction and can explain liquefaction in all these areas.