Abstract
On 14 June 2008, the Iwate-Miyagi inland earthquake (MJ7.2) occurred along a NNE-SSW-trending reverse fault at the boundary between Iwate and Miyagi Prefectures, resulting in heavy damage and loss of human life. After the earthquake, the present author undertook a hearing investigation of pre- and coseismic changes in hot spring activity in and around the epicentral region. Coseismic changes in the discharge rate and color of hot spring water were more commonly observed in the hanging wall of the fault than in the footwall. A preseismic increase in water temperature (of up to 5°C) was recorded at the Matsurube, Shinyu, and Yuhama spas, located near the epicentral region. Increases in discharge rate were recorded at the Kawatabi spa and part of the Narugo spa, which are located at the southern end of the aftershock area. These preseismic changes were clearly observed, yet a tilt meter and GPS unit set very close to the epicenter did not detect any precursor events. These observations provide important information regarding preseismic deformation of the earth’s crust and strategies for earthquake prediction.
