Mechanism of Different Coseismic Water-Level Changes in Wells with Similar Epicentral Distances of Intermediate Field

Abstract

Water-level changes at different monitoring stations are observed during the Wenchuan earthquake ( M S 8.0) in the Chinese mainland. In the intermediate field, we observed coseismic water-level changes of different amplitude in wells with similar epicentral distances. In order to study the mechanism of those coseismic water-level changes, we calculated the static strain change with the Okada dislocation model (Okada, 1992; Lin and Stein, 2004; Toda et al. , 2005). By comparing the calculated coseismic water-level change based on the poroelastic theory with the observed water-level change, we can judge whether the poroelastic theory can be applied to the aquifer of the well. From our research, we find the poroelastic theory can be applied to the area with epicentral distance≲1.5 fault rupture length. Bearing this in mind, we find that when the water-level change of those wells can be explained by the poroelastic theory and that the difference of the water-level change in wells with similar epicentral distances is mostly related to the difference of Skempton’s coefficient B . Otherwise, the water-level change may be induced by the transition of the seismic waves because it is usually larger than the one induced by the undrained dilatation and consolidation, and changes more gradually.