Numerical Relationship between Surface Deformation and a Change of Groundwater Table before and after an Earthquake
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NUMERICAL RELATIONSHIP BETWEEN SURFACE DEFORMATION AND A CHANGE OF GROUNDWATER TABLE BEFORE AND AFTER AN EARTHQUAKE
Yoshihiko AKAO Inst. Technology, Shimizu corp., 3-4-17, Etchujima, Koto-ku, Tokyo, 135, JAPAN
ABSTRACT The purpose of this study is to estimate the effect of earthquakes upon a groundwater flow around a repositories for high-level radioactive wastes. Estimation of a groundwater flow change before and after an earthquake or a volcanic eruption is one of the issues for a longterm safety assessment of the repositories. However, almost any systematic investigation about the causality between a groundwater flow change and an earthquake or an eruption was not found, and as well no estimation formula has been published. We succeeded to obtain a primitive relationship between a groundwater change and an earthquake in this study. Our study consists of three stages. First, several survey reports which describe field observation results of groundwater anomalies caused by earthquakes or eruptions have been collected. The necessary data have been read from the literature and systematically arranged. Second, source mechanisms of the corresponding earthquakes were inspected and static displacements at the well positions were calculated by the dislocation theory in the seismology. Third, parametric studies among the parameters of groundwater anomalies and earthquakes were carried out to find a numerical relationship between a couple of them. Then, a preliminary relationship between water table change in a well and static displacement at the well position was found. We can conclude that temporary change of water table seems to depend on the norm of displacement vector. In this relationship, the maximum value of water table change would be approximately one hundred times of the displacement. INTRODUCTION The estimation of groundwater flow from underground repositories to ground surfaces is dominant issue in safety assessment of geological disposal of radioactive wastes. Especially, we should pay a sufficient attention for natural disaster events i.e., earthquakes or volcanic eruptions. For a long human history, however, we have often suffered unexpectedly severe damages from these events. It is quite important to evaluate maximum impact on groundwater flow from a future event. In this paper, we investigate a relationship between parameters of groundwater anomalies and tectonic deformations associated with earthquakes. Several examinations on correlation between one of earthquake mechanical parameters and water table change were carried out. Then, a preliminary relationship between water table change in a well and static deformation at the point was found. So far, we did not have any knowledge as to variance of groundwater table before and after an earthquake. Now we get a quite useful tool for a design of underground structures. Furthermore, this relationship is thought be applicable on a volcanic eruption in principle as well as an earthquake. DATA SURVEY IN LITERATURE We collect several survey reports [1]-151 which
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