ESTIMATION OF FUTURE DESTRUCTIVE EARTHQUAKES FROM ACTIVE FAULTS ON LAND IN JAPAN

Abstract

Most of active faults (=Quaternary faults) known on land in Japan are ranked to class A(1<S≤10mm/year), class B(0.1<S≤1mm/year) or class C(0.01<S≤0.1mm/year), according to a long-term average slip rate (S) during late Quaternary. A map of active faults which was recently compiled in scale of 1:4, 000, 000 describes locations of most faults of class A and class B. Statistics of recent historic on-land destructive earthquakes in Japan imply that the class C faults are much greater in number than the higher classes faults and that one third of future destructive earthquakes greater than magnitude 6.5 would occur from faults shown in the map. Probable magnitude and recurrence time of earthquakes from active faults on land in Japan are calculated based on a long-term slip rate (S), length of fault (Lt) and length of time (t) elapsed without earthquakes up to the present. Recurrence time (R) of destructive earthquakes from an active fault on land is shown to be about 1, 000 years or longer. Active faults with a elapse ratio E(=t/R)≥0.5 are marked in the active fault map as 'precaution faults.'