Sensitivity of the response of well-aquifer systems to different periodic loadings: A comparison of two wells in Huize, China

摘要

Groundwater well can be used as a seismograph or as strainmeter, since the well water level is sensitive to seismic waves and other crustal strains through mechanical coupling between rock and groundwater. The use of the groundwater level in monitoring tectonic strain, however, is hindered by the enigmatic response discrepancy among wells (different responses may be recorded by even closely clustered wells). Therefore, understanding the factors that control the sensitivity of well-aquifer systems in response to different periodic loadings is important. In this paper, we analyzed two closely located wells that show no response to seismic waves and respond differently to earth tides and barometric pressure. We discuss these wells' sensitivity of response to periodic loadings by using the spectrum, barometric response function, tidal response, and slug test methods. Our results show that the different response characteristics are due to the differences in permeability and confinement of the well-aquifer systems. Well-aquifer systems with a low permeability cannot record coseismic responses, even if they can record clear tidal and barometric signals. In addition, periodic loading signals in shallow aquifers will be easily masked by the interference from the surface, for example rainfall or pumping, which diminishes the signal-to-noise ratio of the tectonic activity. Thus, the hydrogeological and tectonic settings are the two key factors that should be considered in choosing a suitable monitoring well location for tectonic strain monitoring.