Different Sensitivities of Earthquake-Induced Water Level Responses and the Influencing Factors in Fault Zones: Insights from the Dachuan-Shuangshi Fault

The earthquake-induced water level responses in the fault zone may be distinctly different, even when the underground wells are very close. How to qualitatively and quantitatively analyze the differences and controlling factors of the groundwater response to earthquakes in the fracture zone is a hot topic in seismic hydrogeology. This study utilizes three adjacent groundwater monitoring wells, located across distinct structural domains of the Dachuan-Shuangshi Fault, to systematically investigate the different sensitivities of earthquake-induced water level responses and their main influencing factors. The statistical results reveal that monitoring wells located on opposing fault blocks demonstrate higher co-seismic sensitivity compared to the well situated within the fault fracture zone. The water level co-seismic responses are governed by multiple controlling factors, rather than being dominated by individual parameters. Therefore, we employed random forest to quantitatively assess the importance of influencing factors related to hydraulic parameters, aquifer confinement, fault architecture, tidal characteristics, and barometric efficiency. The results showed that hydraulic properties and aquifer confinement are the primary factors influencing the differential sensitivity of water level co-seismic responses. In contrast, the influence of barometric efficiency on water level co-seismic responses is relatively minor. These findings provide critical insights into the understanding of the mechanism and characteristics of seismic hydrological responses in fault zones and provide support for optimizing the placement of groundwater monitoring in seismotectonic environments.