Hydrological modeling of groundwater disturbances to observed gravity: Theory and application to Asama Volcano, Central Japan

摘要

The gravity disturbance caused by groundwater is derived based on hydrological physics by solving nonlinear hydrological diffusion equations for three-dimensional and temporal groundwater distributions. The gravity disturbance is then estimated by the spatial integral of the groundwater distributions. This approach aims to resolve the problems of previous methods for the correction of groundwater disturbances in gravity data, such as instrumental drift of relative gravimeters, empirical estimation of gravity assuming a linear gravity response to precipitation, and the use of lower-dimensional water transfer models. The disturbance estimated using the proposed model is consistent with the observed gravity change at Asama Volcano in Central Japan during the rainy summer of 2006. The model reproduces the rapid increase and subsequent gradual decrease in gravity following rainfall events. The water mass within 150 m of the gravimeter is shown to dominate the observed gravity change during precipitation. It is also demonstrated that the use of adequately representative soil parameters is essential in order to accurately estimate the groundwater distributions and consequent gravity variations. This study shows that correcting for hydrological disturbances requires a more sophisticated model of water movements, particularly during heavy rainfall.