HR: 1330h
AN: S52F-0177    [PDF]
TI: Quantitative Evaluation of Inland Seismic Activity in Japan using GIS -Part 2-
AU: * Itaba, S
EM: itaba@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRI, Kyoto Univ., Gokasyo, Uji, Kyoto, 611-0011 Japan
AU: Watanabe, K
EM: watkun@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRI, Kyoto Univ., Gokasyo, Uji, Kyoto, 611-0011 Japan
AU: Nishida, R
EM: nishidar@cv.tottori-u.ac.jp
AF: Tottori Univ., 4-101 Koyama-cho-minami, Tottori, 680-8552 Japan
AU: Noguchi, T
EM: noguchi@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRI, Kyoto Univ., Gokasyo, Uji, Kyoto, 611-0011 Japan
AU: Mori, J
EM: mori@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRI, Kyoto Univ., Gokasyo, Uji, Kyoto, 611-0011 Japan
AB: It is important for earthquake evaluations to quantitatively estimate the seismic activity; however, this evaluation has been seldom performed, and usually only subjective evaluations are done. On the other hand, the assessment of earthquake activity on active faults is a general public requirement today. We proposed a GIS (Geographic Information System) - method to quantitatively evaluate seismic activity (Nishida et al, 1999). And use it to evaluate the activity of inland active faults in Japan. In this investigation, we tried to evaluate the activity of the 98 major active faults listed by The Headquarters for Earthquake Research Promotion using the catalog of shallow inland earthquakes compiled by JMA from Oct. 1997 to May 2002. This method uses GIS to create buffered zones around the fault traces. A buffered zone is a region within a distance between Ri and Ri+1 from the fault. Then, the earthquakes included in each buffered zone can be tabulated. The seismic activity of the zone is expressed by using three parameters, namely, number of events, accumulated fault surfaces and released energy. Dividing total amount of these quantities by the area of the corresponding zone, the density of seismic activity can be obtained for each buffered zone. Considering the relation between the seismic activity densities and the distance from the fault trace, an effective distance can be estimated, in which the seismic activity is influenced by the existence of the fault. By adopting this definition of the effective distance, we can examine the seismic activity of each fault. For some faults, the seismic activity decreases in proportion to distance from the fault, but not for others. The inland seismic activity of southwest Japan is generally higher than that of northeast Japan. There may be two reasons. First, the main pattern of fault movement in Northeast Japan is dip-slip, and that in Southwest Japan is strike slip. Dip slip faults need more tectonic energy to move than strike slip ones. Second, there may be a difference of coupling factors. In order to remove the influence of the dip of a fault, the angle of inclination of a fault was assumed, along with the position in depth, and a position compensation for the fault was performed. Consequently, in many dip slip type faults, the effective distance of the activity, turns out to be the peak of the activity density that exists near a fault. The relation of the activity and the time from the last large (M is greater than 6.5) earthquake is also considered. Although a large amount of time may have passed since the latest large earthquake, the activity of some faults is very high. This may indicate a pre-seismic stage after a time of low seismic activity. From our results, it is thought that seismic activity characteristic to a fault can be extracted by using this technique.
UR: http://www.rcep.dpri.kyoto-u.ac.jp/~itaba
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting