Seismically-induced Groundwater Flow into Confining Clays: an Experimental and Numerical Study

This study investigates seismically-induced hydraulic responses in an aquifer system focusing on the hydraulic interaction between a model aquifer and confining clays following shaking as experienced during seismic events. These responses are being investigated by both experimental and numerical methods. In contrast to the conventional assumption assuming a clay layer as a hydraulic barrier to seismically-induced hydrological responses in an aquifer, this study highlights that the excess pore pressure in the aquifer generated by shaking may facilitate water flow crossing the overlying clay layer. This hypothesis is supported by experimental results that show measurable surface settling, excess pore pressure and step-like wellbore water level increase following shaking-induced sand consolidation, and notably, upward flow of water from an aquifer into the clay layer indicated by sustained water level drops in the well after shaking experiments. Numerical simulations further reveal that perturbations influence water flow from the aquifer to the clay layer, modifying pressure distribution within both layers. Key factors such as aquifer flow regime, hydraulic conductivity of the aquifer and clay layer, and their effects on flow dynamics are addressed by numerical modeling. This study provides insights into hydraulic responses and contributes to risk assessments in the context of seismic perturbations.