Journal of Natural Disaster Science
Journal of Natural Disaster Science, Volume 19, Number 1, 1997, pp.9f.
SEISMIC RISK ASSESSMENT OF ACTIVE FAULT SYSTEMS IN THE WESTERN CHUGOKU DISTRICT OF SOUTHWEST JAPAN
(Received 15 August, 1997 and in revised form 2 April, 1998)
Abstract
The two NE-SW-trending active fault systems, Lake Ohara-W. Yauneyama and Iwakuni-Kamine in the western Chugoku district, are zones composed of active and geologic faults based on the distributions of lineaments, geologic faults, and active faults. The 1997 M6.1 Yamaguchi-ken-hokubu earthquake (M: Japan Meteorological Agency scale) was generated in the central part of the Lake Ohara-W. Yauneyama fault system. The average moment-release rate of the seismic moments of this fault system is estimated as 0.0046 x 10^19 Nm/yr from the magnitudes of destructive inland earthquakes. In contrast, the average moment-release rate of the Iwakuni-Kamine fault system is estimated lo range from 0.00154 to 0.00476 x 10^19 Nm/yr based on the average slip-rate of its constituent active faults. The amount of seismic moments is given from the calculated average moment-release rate multiplied by the elapsed period from the latest earthquake event to the present. The magnitude of the probable earthquake that would occur along an active fault system in 1997, described as the magnitude potential of the probable earthquake, is derived from the amount of seismic moments. The magnitude potential calculated until 1997 exceeded M6.5 for the two fault systems. The moments released by the M6.l Yamaguchi-ken-hokubu earthquake were estimated as 0.085 x 10^19 Nm, whereas the moments released by the earthquake in the Lake Ohara-W. Yauneyama fault system having the 1997 magnitude potential M6.5 are estimated as 0.28 x 10^19 Nm. The moments released by the Yamaguchi-ken-hokubu earthquake are only 30% those of an earthquake with a probable magnitude potential of 6.5, indicative that most of the moments for producing a large earthquake remained stored after the generation of the Yamaguchi-ken-hokubu earthquake.
Key words
active fault system, seismic moment, inland earthquake, risk assessment