Spectrum Response of LJ Well to Various Stresses During Non-seismic and Seismic Periods

Abstract

The well water level in a deep well has significant frequency dependence on various crustal stresses, which can provide an effective pathway for determining the well-aquifer properties and investigating the response mechanism of groundwater. However, due to the limitations and complexity of the field conditions, there is a lack of on-site stress–strain data for rocks. Therefore, it is difficult to directly and quantitatively interpret the transfer response between the strain–stress and the well water level. The observation item data for the LJ well in China are relatively complete, including rainfall, barometric pressure, volumetric strain and deep water level data. By calculating the spectral period, spectral density, coherence function and transfer function of various physical variables, the spectrum response characteristics of the well-aquifer system to various stresses can be effectively obtained. When the crust is in a relatively stable state, the semidiurnal and diurnal waves are dominant. Moreover, the transfer functions of the well water level’s response to the theoretical semidiurnal and diurnal Earth tides and the barometric pressure are basically consistent with the correlation analysis results. In addition, when earthquakes occur, the signals of the volumetric strain and the well water level can more effectively highlight the relatively intermediate- and high-frequency information. The transfer function between the well water level and the volumetric strain is nearly an order of magnitude smaller than that in the stable state, indicating that the hydrogeological conditions of the LJ well-aquifer change instantaneously when subjected to seismic waves. All the above conclusions show that the correlation and transfer function based on spectral analysis is a feasible and advantageous method of determining the correlation of various physical variables. These results provide a foundation for further research on the hydrogeological characteristics of aquifers.