@article{953cdf6c04bd4e7d9bb603c99ed81e5a,
title = "Aftershock distribution and 3D seismic velocity structure in and around the focal area of the 2004 mid Niigata prefecture earthquake obtained by applying double-difference tomography to dense temporary seismic network data",
abstract = "A destructive large earthquake (the 2004 mid Niigata prefecture earthquake) sequence occurred in the central part (Chuetsu district) of Niigata prefecture, central Japan on October 23, 2004. We have deployed a 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 travel time data from the temporary seismic network and surrounding routine stations, we obtained precise aftershock distribution and 3D seismic velocity structure in and around the fault planes of the earthquake and four major (M ≥ 6) aftershocks by double-difference tomography. The results clearly show three major aftershock alignments. Two of them are almost parallel and dipping toward the WNW. The shallow and deep aftershock alignments correspond to the fault plane of the mainshock and that of the largest aftershock (M6.4), respectively. The third alignment is almost perpendicular to the WNW-ward dipping planes and perhaps corresponds to the fault plane of the M6 aftershock on October 27. General 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. Major velocity boundary seems to shift westward in comparison to in northern and southern parts at a location near the central part of the focal area, where the main shock rupture started. Some parts of the fault planes were imaged as low velocity zones. This complex crustal structure would be one of possible causes of the multi-fault rupture of the 2004 mid Niigata prefecture earthquake sequence.",
keywords = "Aftershock, Double difference tomography, Fault plane, Seismic velocity structure",
author = "T. Okada and N. Umino and T. Matsuzawa and J. Nakajima and N. Uchida and T. Nakayama and S. Hirahara and T. Sato and S. Hori and T. Kono and Y. Yabe and K. Ariyoshi and S. Gamage and J. Shimizu and J. Suganomata and S. Kita and S. Yui and M. Arao and S. Hondo and T. Mizukami and H. Tsushima and T. Yaginuma and A. Hasegawa and Y. Asano and H. Zhang and C. Thurber",
note = "Funding Information: Acknowledgments. We would like to express our condolences with people in the focal area of the 2004 mid Niigata prefecture earthquake on the disasters caused by the event. We are grateful for all the help by the organizations, municipalities, and people in the focal area of the present earthquake at the deployment. We borrowed some instruments from Kyoto Univ., Hirosaki Univ. and Yamagata Univ. Dr. Y. Iio of Kyoto Univ., Dr. M. Kosuga and Dr. K. Watanabe of Hirosaki Univ., and Prof. A. Hasemi of Yamagata Univ. kindly prepared and offered the instruments just after the occurrence of the main shock. We used data from Univ. of Tokyo, JMA, Hi-net, F-net, NIED. Discussions with Emeritus Prof. Y. Kono, Dr. R. Honda, Dr. Y. Hiramatsu of Kanazawa Univ., Dr. H. Kim of Kyoto Univ., and Dr. Y. Yagi of BRI were valuable. We would like to thank Prof. N. Hirata, Dr. Y. G. Li and Dr. S. Kodaira for helpful comments. This work was conducted under the support of Grant-in-Aid for Special Purposes (No. 16800054), MEXT, Japan. This work was also conducted as part of the 21st COE program, {\textquoteleft}Advanced Science and Technology Center for the Dynamic Earth{\textquoteright}, at Tohoku University. This work was also partially supported by MEXT.KAKENHI (16740247) and JSPS.KAKENHI (15204037), Japan.",
year = "2005",
doi = "10.1186/BF03351830",
language = "English",
volume = "57",
pages = "435--440",
journal = "Earth, Planets and Space",
issn = "1343-8832",
publisher = "Terra Scientific Publishing Company",
number = "5",
}