Earth Planets Space, Vol. 60 (No. 10), pp. 1005-1010, 2008LETTER
Tomoaki Yamada1, Kimihiro Mochizuki1, Masanao Shinohara1, Toshihiko Kanazawa1, Asako Kuwano1, Kazuo Nakahigashi1, Ryota Hino2, Kenji Uehira3, Takeo Yagi1, Naoto Takeda1, and Shinichi Hashimoto1
1Earthquake Research Institute, University of Tokyo, Tokyo 113-0032,
2Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
3Institute of Seismology and Volcanology, Kyushu University, Shimabara 855-0843, Japan
(Received June 30, 2007; Revised February 3, 2008; Accepted February 25, 2008; Online published November 7, 2008)
The Noto Hanto earthquake in 2007 (Mj 6.9) occurred on March 25, 2007 near the west coast of the Noto peninsula, Honshu, Japan. To study the aftershock activity under the sea, we deployed pop-up type ocean bottom seismometers (OBSs) from April 5 to May 8, 2007. We combined data from ten ocean bottom and four onshore seismic stations located around the rupture area of the earthquake and determined the preliminary distribution of the aftershocks. Most of the offshore aftershocks are located in a depth range between 2 and 10 km, and no earthquakes are observed in the lower crust. Hypocenters of deep events occurring at depths greater than 5 km are confined to an area northeastward from the largest aftershock in offshore region. Most of the aftershocks aligned along a high angle and southeast dipping plane, which is consistent with the geometry of the active faults revealed by previous seismic reflection surveys.
Key words: The 2007 Noto Hanto earthquake, OBS, aftershock distribution.