HR: 0800h
AN: S31A-1035    [Abstracts]
TI: Seismic reflection profiling between the Tone canal and eastern Saitama city in the Kanto plain, central Japan
AU: * Yamaguchi, K
EM: yamaguchi-k@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Kano, N
EM: n,kano@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Ito, S
EM: s.ito@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Ohtaki, T
EM: t-ohtaki@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Yokota, T
EM: yokota-t@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Yokokura, T
EM: taka.yokokura@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AU: Tanaka, A
EM: akiko-tanaka@aist.go.jp
AF: Natl Inst of AIST, 1-1-1 C7 Higashi Tsukuba, Ibaraki, 3058567 Japan
AB: Thick sedimentary layers down to the basement top affect the strong ground motions generated by earthquakes. Underground surveys are necessary to obtain the fundamental knowledge of active structures and earthquake hazard mitigation especially in thick sedimentary plains. The AIST carried out seismic reflection surveys almost in the middle of the Kanto plain, the metropolitan area and the largest plain of Japan. The survey lines are totally about 20km long between the Tone canal and eastern Saitama city. We used a 4-ton mini-vibrator or a 17-ton vibrator in the eastern and central parts (Yoshikawa line, 14km) and two 17-ton vibrators in the western part (Saitama line, 6km) as seismic source. Intentionally, a 3.5km part is left for future survey between the central part and the western part because of densely population. The data quality is poorer in the westernmost part of the Saitama line than in other part. This is perhaps due to energy attenuation in the surface sediments. A conventional data processing was applied to the seismic data. In the Yoshikawa line, the basement top is 1.1s deep in two way time at the eastern edge and gradually deepens westward to 1.6s at the western edge. In the Saitama line, the basement top is not clearly defined due to multiple reflectors and poorer data quality, but it is considered deeper than 2.1s. The basement depths in the seismic sections are almost compatible with those of well data near the seismic lines. The difference of depth is at least 0.5s (about 500m) in the gap between the two lines. Layers upper than the basement are horizontal or dip westward more gently than the basement top in both lines. On the basis of above results, a fault or inclined top of the basement is inferred in the gap and it has been inactive since the formation of upper sediments.
DE: 7223 Seismic hazard assessment and prediction
DE: 8015 Local crustal structure
SC: Seismology [S]
MN: 2004 AGU Fall Meeting