Dynamic Poroelastic Response Of Water Level In Well Aquifer To Far-filed Seismic Waves

Estimating the hydralic properties of subsurface aquifers is crucial for proper groundwater resource management,subsurface solute transport assessments,hydraulic fracturing and mining.Traditional methods for obtaining these parameters include laboratory experiments,field tests and model inversions.Laboratory methods mainly analyze the physical properties of the rock or soil samples,which may provide inaccurate parameter values because of the natural heterogeneity and artefacts associated with the specific testing protocol.Field tests are conducted by pumping in a well and then observing water-level responses in the pumped well or in nearby observation wells.Although field testing is common,it can be expensive,and continuous observations of monitoring wells may not be feasible.In contrast,the inversion of the corresponding aquifer parameters by physical models of the water level response to periodic loadings has gradually become practical and cost-effective with the development of various models and the popularity of continuous observation systems.Among the methods for estimating the hydrologic properties of aquifers by model inversion,there are many methods that use well water-level response in combination with the quasi static poroelasticity.However,these approaches have ignored the possible frequency-dependent solid/fluid coupling in the porous aquifer.Therefore,in this study,coseismic water-level variations induced by three great earthquakes(2011Mw9.1 Tohoku,2012 Mw 8.6 Sumatra,and 2018 Mw7.6 Minahassa Peninsula)in six fluid observation wells in Yunnan Province,and the corresponding seismic energy density were calculated and compared with the global data set(Wang and Manga,2010).The Tengchong seismic station containing water level,barometric pressure and seismograph observation datasets is selected,and the dynamic coseismic water-level response is estimated by using dynamic poroelastic theory.In the newly constructed explanatory model,the coseismic water-level response is no longer assumed to be an immediate effect.The ratio of pore pressure and stress may be switched across frequency ranges,and the permeability estimated and validated in different frequency domains by the seismic-wave time series.Finally,the predicted coseismic water levels due to the three great earthquakes are better explained than those using quasi static poroelasticity.The method proposed in this study is useful to evaluate the continuous permeability variations by earthquakes and their aftershocks.