Earth Planets Space, Vol. 56 (No. 12), pp. e45-e48, 2004E-LETTER
Fumiaki Kimata1, Rikio Miyajima1, Masayuki Murase1, Dudy Darwaman1, Takeo Ito1, Yusaku Ohata1, Meilano Irwan1, Kazutomo Takano1, Fauzan Ibrahim1, Etsuro Koyama2, Hiroshi Tsuji2, Teturo Takayama3, Kazuya Uchida4, Jun Okada5, David Solim6, and Herri Anderson6
1Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan
2Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan
3Disaster Prevention Research Institute, Kyoto University, Uji 611-0011, Japan
4Graduate Schoo1 of Science, Kyushu University, Hukuoka 812-8581, Japan
5Graduate Schoo1 of Science, HokkaidoUniversity, Sapporo 060-0810, Japan
6Department of Geodesy, Institute of Technology Bandung 40132, Indonesia
(Received August 7, 2004; Revised December 10, 2004; Accepted December 27, 2004)
Repeated precise leveling in the earthquake swarm area of Ontake, central Japan has revealed uplift of 3-6 mm in proximity to the epicentral region of the most active earthquake cluster in 2002-2004. Although the uplift is small, the vertical displacement is significant even considering leveling error. This uplift is associated with increases in 3He/4He ratios and CO2 d13C values at a mineral spring in the region, indicating an upper mantle contribution. A region of low resistivity at a depth of 2 km beneath the uplift area has also been inferred, suggesting that the observed uplift is related to changes in a shallow seismogenic layer due to increased hydrothermal input from the earthquake swarm area.
Key words: Ground uplift, precise leveling, Ontake earthquake swarm, shallow seismogenic layer, low resistivity layer, 3He/4He ratio, d13C, CO2.