HR: 1340h
AN: S23B-0241    [Abstracts]
TI: Fault Segmentation and its Implication to the Evaluation of Future Earthquakes from Active Faults in Japan
AU: * Awata, Y
EM: awata-y@aist.go.jp
AF: Active Fault Research Center, Geological Survey of Japan, AIST, AIST Central 7, Higashi 1-1-1, Tsuchiura, 305-8567 Japan
AU: Yoshioka, T
EM: yashioka-t@aist.go.jp
AF: Active Fault Research Center, Geological Survey of Japan, AIST, AIST Central 7, Higashi 1-1-1, Tsuchiura, 305-8567 Japan
AB: Segmentation of active faults is essential for the evaluation both of past and future faulting using geologic data from paleoseismological sites. A behavioral segment is defined as the smallest segment of fault having a characteristic history of faulting. More over, we have to estimate the earthquake segments that can be consist of multiple faulting along a system of behavioral segments. Active fault strands in Japan are segmented into behavioral segments based on fault discontinuity of 2-3 km and larger (Active Fault Res. Group, GSJ, 2000), large bend of fault strand and paleoseismicity. 431 behavioral segments, >= 10 km in length and >= 0.1 m/ky in long-term slip-rate, are identified from a database of active faults in Japan, that is constructed at AFRC, GSJ/AIST. The length of the segments is averaged 21 km and approximately 70 km in maximum. Only 8 segments are exceed 45 km in length. These lengths are very similar to those of historical surface ruptures not only in Japan since 1891 Nobi earthquake, but also in other regions having different tectonic setting. According to the scaling law between fault length and amount of displacement of behavioral segment, a maximum length of ca. 70 km can estimate a slip of ca. 14 m. This amount of slip is as large as world largest slip occurred during the 1931 Fuyun earthquake of M 8, 1999 Chichi earthquake of M 7.4 and the 2001 Central Kunlun earthquake of M 7.9 in East Asia. Recent geological and seismological studies on large earthquakes have revealed that multiple-rupturing is very common during large earthquakes. Therefore, evaluation of simultaneous faulting along a system of active faults is indispensable for the estimation of earthquake size. A Matsuda's (1990) idea of "seismogenic faults", that is divided or grouped based on the geometric discontinuity of 5 km, may useful for the best estimation of earthquake segment. The Japanese behavioral segments are grouped into "seismogenic faults", each consists of about 2 segment in average and 15 in maximum. That average number of behavioral segment in a single earthquake segment best estimated is similar to that number of the Japanese historical earthquakes. The longest ?gseismogenic fault?h, the Median Tectonic Line Active Fault System of 350 km-long, was probably ruptured during the 16th century, in a series of large earthquakes, and the second longest Itoigawa-Shizuoka Tectonic Line Active Fault System of 145 km-long was also ruptured between the 8th and 9th centuries. These historical and paleoseimological events support the usefulness of the "seismogenic faults"-idea for the best estimation of earthquake segment.
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005