Aftershock distribution and seismic velocity structure in and around the focal area of the 2004 Niigata-Chuetsu earthquake using double-difference tomography, and its relationship with the earthquake generation process

HR: 14:05h
AN: S53A-03 [Abstracts]
TI: Aftershock distribution and seismic velocity structure in and around the focal area of the 2004 Niigata-Chuetsu earthquake using double-difference tomography, and its relationship with the earthquake generation process
AU: * Okada, T
EM: okada@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Umino, N
EM: umino@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Matsuzawa, T
EM: matuzawa@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Nakajima, J
EM: nakajima@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Uchida, N
EM: uchida@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Nakayama, T
EM: nakayama@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Hirahara, S
EM: hirahara@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Sato, T
EM: sato@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Hori, S
EM: hori@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Kono, T
EM: kono@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Yabe, Y
EM: yabe@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Ariyoshi, K
EM: ariyoshi@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Gamage, S
EM: sng@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Shimizu, J
EM: shimizu@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Suganomata, J
EM: suga@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Kita, S
EM: kita@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Yui, S
EM: yui@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Arao, M
EM: kt.arao@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Hondo, S
EM: s.hondo@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Mizukami, T
EM: mizu@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Tsushima, H
EM: tsushima@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Yaginuma, T
EM: yagi@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Hasegawa, A
EM: hasegawa@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku Univ., 6-6 Aramaki-Aza-Aoba, Aoba-ward, Sendai, 9810966 Japan
AU: Asano, Y
EM: asano@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1,Tennodai, Tsukuba, 3060066 Japan
AU: Zhang, H
EM: hjzhang@ice.geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706 United States
AU: Thurber, C H
EM: clifft@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706 United States
AB: A destructive large earthquake sequence (2004 Niigata-Chuetsu earthquake, magnitude 6.9) occurred in the central part (Chuetsu district) of Niigata Prefecture, central Japan on Oct. 23, 2004. We deployed a dense temporary seismic network composed of 54 stations for aftershock observation just above and around the focal area of the earthquake for about a month. Using arrival time data from the temporary seismic network and surrounding permanent stations, we obtained the precise aftershock distribution and 3D seismic velocity structure in and around the rupture zones of the main shock and its four major (M=>6) aftershocks by double-difference tomography. The results show three major aftershock alignments. Two of them are almost parallel and dipping toward the WNW. The shallow and deep aftershock alignments correspond with the fault plane of the main shock and that of the largest aftershock, respectively. The third alignment is almost perpendicular to the WNW-ward dipping planes and perhaps corresponds with the fault plane of the M6 aftershock on Oct. 27. A significant feature of the obtained velocity structure is that the hanging wall (western part of the focal area) has lower velocity and the footwall (eastern part of the focal area) has higher velocity. This observation suggests that the 2004 Niigata-Chuetsu earthquake sequence occurred along faults that acted as normal faults in the Miocene and reactivated as reverse faults under the current compressional stress regime. The main velocity boundary seems to migrate to the west at a location near the central part of the focal area, where the main shock rupture initiated. Some parts of the fault planes were imaged as low velocity zones. This complex crustal structure may be one of possible causes of the complicated character of the 2004 Niigata-Chuetsu earthquake sequence.
UR: http://www.aob.geophys.tohoku.ac.jp/
DE: 7209 Earthquake dynamics and mechanics
DE: 7230 Seismicity and seismotectonics
DE: 8015 Local crustal structure
DE: 8180 Tomography
SC: Seismology [S]
MN: 2005 Joint Assembly