地震活動帯における空白域と地震発生の関係について

Abstract

We investigated relations between seismic gaps in active seismic zones and occurrence of middle-size earthquakes by using of a microearthquake catalog compiled for 25 years by Tottori Observatory which belongs to Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University. Our study sites are active seismic zones of Tottori region, Tottori-Shimane border region and Yamasaki Fault region in the Inner zone of Southwest Japan. We examined preceding seismic activity in and around a focal area of 10 middle-size earthquakes in the active seismic zones.The result is that in most cases a middle-size earthquake(s) occurred in a seismic gap in the active seismic zones, some of which were preceded by small-size earthquakes. To point out present seismic gaps in active seismic zones can, therefore, be a clue of prediction of inland middle-size earthquakes. We investigated spatial distribution of the hypocenters in detail and found out 19 seismic gaps in the active seismic zones.After we pointed out the seismic gaps, earthquakes with magnitude 3.9 and 4.0 occurred in one of the seismic gaps.We intend to keep watch on seismic activity in and around these seismic gaps and try to detect precursory change of the seismic activity before occurrence of middle-size earthquakes.