Earth Planets Space, Vol. 57 (No. 5), pp. 447-452, 2005LETTER
Naoko Kato1, Tomoo Echigo2, Hiroshi Sato1, Masaaki Tateishi3, Sumiko Ogino1, Shin'ichi Sakai1, Shigeru Toda4, Shin Koshiya5, Tanio Ito6, Tsuyoshi Toyoshima7, Toshifumi Imaizumi8, Hajime Kato9, and Shintaro Abe10
1Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
2Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan
3Department of Geology and Earth Material Science, Niigata University, Niigata 950-2181, Japan
4Aichi University of Education, Kariya 448-8542, Japan
5Department of civil and Environmental Engineering, Iwate University, Morioka 020-8551, Japan
6Department of Earth Sciences, Chiba University, Chiba 263-8522, Japan
7Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
8Department of GeoEnvironmental Science, Tohoku Univ., Sendai 980-8578, Japan
9Faculty of Education and Human Sciences, Yamanashi University, Kofu 400-8510, Japan
10Central Research Institute of Electric Power Industry, Abiko 270-1194, Japan
(Received February 15, 2005; Revised April 20, 2005; Accepted April 20, 2005)
The Mid-Niigata Prefecture earthquake in 2004 (MJMA 6.8) generated surface ruptures along the eastern rim of the Uonuma Hills. To elucidate the structural linkage between the surface ruptures and the source fault at depth, the high-resolution seismic reflection profile across the surface ruptures and nearby active faults, and the data of aftershock distribution are examined. The 5.2-km-long, high-resolution, depth-converted seismic section reveals an emergent thrust beneath the surface ruptures. A two-dimensional model of the fault geometry has been constructed based on the aftershock distribution and the shallow reflection profile. The development of the main geologic structure are well explained by forward modeling using a balanced cross-section method. In detail, the fault system generated the main shock dips at a steep angle (60°) below 5 km depth and more shallowly (30°) near the surface.
Key words: 2004 Mid-Niigata Prefecture earthquake, seismic reflection profile, fault model, subsurface structure, surface rupture, active fault-and-fold, balanced-cross section, central Japan.