Linear poroelasticity of groundwater levels from observational records at wells in Hokkaido, Japan

The natural fluctuation of groundwater level depends not only on the stress applied to an aquifer but also on the type of rock that comprises it. Poroelastic parameters, such as strain sensitivity, loading efficiency, and poroelastic bulk moduli, are used to analyze the hydrologic attributes of aquifers. In this study, we use records of groundwater levels from 19 wells to calculate coefficients of poroelastic characteristics. The records allow a comprehensive description of how groundwater levels vary with fluctuations of volumetric strain in the crust's interior. We estimate strain sensitivities in two ways: (a) using the wells' response to tidal strain and (b) using coseismic changes in groundwater level based on historical data. The strain sensitivities estimated by the two different methods have good linear correlation. We also estimate loading efficiency using observational records and calculate bulk moduli from the loading efficiencies and strain sensitivities. The bulk moduli obtained in this manner are roughly consistent with laboratory values.