Abstract
Crustal strain has been observed using borehole-type multi-component strainmeters at Tsuruga and Imazu stations in the northern part of the Kinki district, Japan. We investigated 12.5 years of strain data recorded at these stations starting from 1996. Seasonal strain changes observed at Imazu correlate well with the changes in ground water level observed there. Seasonal strain changes observed at Tsuruga are well described by the output of a tank model with daily precipitation as input. Strain changes corresponding to the initial stabilization of the strainmeters are modeled by exponential functions. After seasonal and exponential strain changes are removed, the strain history shows excursions around 2000 and 2005. These cannot be explained by temporal changes in strainmeter sensitivity or long-term variations of precipitation. We calculated expected strain changes at the two stations caused by the slow slip events in the Tokai district from 2000 to 2005 and found that calculated principal axes of strain are consistent with observations, although the amounts of observed strain are about ten times larger than calculated ones.
