Spatial Variation of Aquifer Permeability in the North China Plain from Large Magnitude Earthquake Signals

Permeability changes induced by earthquakes have been studied widely. However, basic questions still remain: what are the spatial differences in permeability changes induced by far-field earthquakes? Is there an inevitable relationship between seismic energy density, epicenter azimuth and permeability change? We try to answer the above questions by examining records of 11 years of groundwater hydrographs of 7 wells in the North China plain at large distance from the epicenters of 221 earthquakes during the period 2008 ~ 2018. The results shows permeability changes varied between the different wells, with the permeability variation of the JN well most sensitively responding to seismic events, while the least sensitive wells being SH, JZ and LK. We found that the azimuths of seismic waves can greatly influence the changes in permeability, i.e. mainly concentrated between 25 and 295°. The seismic density energy (SDE) value larger than approximately 10^–9 J/m³ is likely to induce a change in permeability in the NCP aquifer materials. It is found that SDE is not a predictor of permeability change at a given well, by calculating the seismic energy density which did not cause permeability change. While the permeability change ratio before and after the earthquake can be considered as the ability of permeability respond to the dynamic stress and it shows a weak correlation with depth of aquifer. Thus, Factors that probably affect permeability responses changes would have implications for crustal geomechanics.