Using groundwater level variation triggered by earthquake to evaluate the hydraulic property of aquitard

Aquitard plays an important role in a lot of fields. However, the hydraulic properties of aquitard are not easy to obtain because the monitoring wells are usually installed in aquifers for groundwater resources management. This study adopts a physical model to fit the postseismic variations of groundwater level triggered by the Chichi Earthquake and evaluates the hydraulic properties of aquitards in Jhoushuei River Alluvial Fan. The monitoring wells have different responses to the Chichi Earthquake and thus only eight of the wells have the appropriate fitting results. The investigation results showed that the estimated values of hydraulic diffusivity are 7.91 × 10^-3̃1.88 × 10^-1 m²/s in the eight wells. The evaluated values of hydraulic conductivity of the aquitards are 3.03 × 10^-8 ̃ 2.06 × 10^-6 m/s, suggesting a silty medium of the aquitards. The results locate in the range of those obtained in previous studies. The discrepancy might be due to the different monitoring wells adopted for analyses. The estimated results are combined with those in previous studies to show the distribution of hydraulic conductivity in the first two aquitrads in Jhoushuei River Alluvial Fan. The patterns are different for aquitards one and two. The discrepancies might be due to the different sedimentary environments or the adopted monitoring wells. The technique proposed in this study provides a method to evaluate the hydraulic properties of aquitards. The results can be used in hydrogeological analyses, contaminant transport modeling, and subsidence evaluation.