Earthquake-induced persistent and instantaneous groundwater variations caused by volumetric strain of soil in Taiwan from 1999 to 2020

Abstract

Estimating the magnitude of earthquake-induced groundwater level (GWL) based on poroelastic theory is a challenge for researchers. To address this challenge, the present study explores this topic in the context of volumetric strain induced by ground shaking. Specifically, GWL records on the Chi-Chi earthquake in Taiwan, along with other selected events from 2004 to 2020, are analyzed to identify the persistent and instantaneous changes of GWL under distinct geological conditions. The magnitude of the persistent GWL change is highly correlated with peak ground acceleration, and thickness and density of sandy layers. This finding is explained by the magnitude of volumetric strains caused by soil particle rearrangement associated with ground motion intensities and site-specific conditions. Meanwhile, the instantaneous GWL change caused by seismic wave propagation exhibits a highly negative correlation with the vertical ground motion velocity time history because the compression wave induces instantaneous contraction or dilation of the soil. Moreover, the peak instantaneous GWL change correlates well with the peak ground velocity (PGV) in the vertical direction because the compressional (volumetric) strain is theoretically proportional to the PGV of vertical motion.