Estimation of barometric responses of groundwater levels at observation stations of the Geological Survey of Japan, AIST in and around the Kinki district.

Abstract

AIST has been measuring the groundwater level of wells in order to detect crustal movements. We analyzed the barometric responses of the groundwater levels to understand the hydraulic characteristics of the well and stratum. These information are useful to exactly evaluate detection capability of the crustal movements. The groundwater levels have been measured at 26 wells of 21 observation stations in and around the Kinki district mainly since 1996. We describe the three phenomena, which affect the barometric responses of the groundwater levels, and the characteristics of frequency dependence caused by each phenomenon. We calculated the frequency dependence of the barometric response of the groundwater level for each AIST observation well. The characteristics of frequency dependence of the barometric responses fall into several standard patterns. From the characteristics at each well, we estimated what phenomena affected the groundwater level. There are some wells of which the groundwater levels were largely affected by rainfall and the barometric responses could not be well estimated. We also compared the tidal response with the barometric response at each well. At some wells, the barometric responses of the groundwater levels were not consistent with the tidal responses of the groundwater levels. The possible causes of the inconsistency were discussed.