Estimating Aquifer Parameters From Barometric-pressure Effect Of Groundwater Before And After Wenchuan Earthquake

Various abnormal changes occurred in groundwater before, during and afterearthquakes had been documented for a long time. Large-scale co-seismicgroundwater level changes were observed in China following the2008greatWenchuan earthquake. This provide us precious data to study these phenomena.Barometric effect, which is one of the common phenomenon existed in groundwaterfluctuation, is closely related with the structure of well-bore and the aquiferparameters. The tiny changes of stress and strain state of rock in the crust, can bereflected by the balance of hydrostatic pressure in the dynamical water level of well.Therefore, it provides us a method to estimate the aquifer parameter.According to the previous studies, the static barometric coefficient in theborehole of water level depends upon the storage and porosity of the aquifer. In orderto explore the relationship between barometric effect and aquifer parameters,mathematical model of barometric effect in confined well is built up and gives theanalytical solution. Then, case studies in Nanxi, Chaohu and Qionglai which locatedin Sichuan and Anhui province are selected to test the method. The transmissivity andspecific storage of the three well-aquifer system are attained. The result shows thatthis method is feasible under some conditions. What’s more, the results shows thattransmissivity, specific storage and porosity in three wells are all changed incomparing with their values before the Wenchuan earthquake. From this, the aquiferparameters or tectonic setting change caused by the earthquake maybe the majormechanism of the co-seismic water level changes. However, further study is neededbetween the aquifer parameter changes and water levels recover after the earthquake.