SEISMOGENIC LAYER OF THE CRUST IN THE INNER ZONE OF SOUTHWEST JAPAN

Hypocenters of earthquakes determined from the data recorded by Kamitakara, Hokuriku, Abuyama and Tottori Observatories, Kyoto University during 1976-1991 are collected to define the distribution of the thickness of the seismogenic layer of the crust in the inner zone of southwest Japan. Total of 63, 961 well-located earthquakes are selected and used to determine the cutoff depths in the crust. As a result, the thickness of the seismogenic layer varies 5-25 km from place to place and is closely related to the thermal structure of the crust. Further, active faults and large inland earthquakes are likely to occur at the steepchange in the cutoff depth. Thus, the thickness of the seismogenic layer is important to examine the rheological characteristics of the crust and eventually to reveal the relationship beteen the crustal heterogeneity and large inland earthquakes.