Estimating aquifer volumetric strain caused by the 2008Wenchuan earthquake from tidal effect of groundwater

Water level in many wells will change in response to an earthquake．One can use the coseismic water level change and its response to tide effect to calculate the volumetric strain in aquifer induced by the earthquake．We tried to study the changes in volumetric strain induced by great earthquakes in large scale．The two and a half years of original groundwater level data，recorded in the five wells located in different tectonic settings，were firstly corrected by removing both the trend and barometric pressure effect．Then harmonic analysis was used to calculate the tidal factor for each well-aquifer system，and further the volumetric strains of these five well-aquifer systems were calculated based on the tidal factors and groundwater level changes in response to the Wenchuan earthquake．The result shows that the volumetric strain in aquifers caused by the earthquake may reach 10-7．The attenuation of volumetric strain induced by the earthquake is complicated，and it may be determined by the distribution of active faults, structure of crustal media, as well as the earthquake epicentral distance．