Earthquake-induced permeability and hydrochemical variation in an aquifer–aquitard system

Abstract

Groundwater level, permeability, and chemical components can be affected by earthquakes; however, there are few comprehensive investigations utilizing long-term continuous hydrological monitoring data covering multiple strong earthquakes. In this study, a continuous 2-year dataset of groundwater levels and chemical composition (Ca²⁺, Mg²⁺, HCO₃⁻) from well #32 in the Xichang area of Sichuan Province, China, was used to analyze changes in earthquake-induced hydrological processes within an aquifer–aquitard system. Co-seismic changes in groundwater level and ion concentrations were associated with the Yangbi M_W 6.1 and Luding M_W 6.6 earthquakes. Horizontal and vertical permeability, estimated using the tidal response model, decreased during both earthquakes, possibly owing to dynamic strain resulting from seismic waves. In addition, there were significant correlations between vertical permeability and ion concentrations, with ion fluctuations during earthquake periods possibly associated with reduced mixing of different groundwater sources owing to the decrease in permeability. The results of this study provide new insight into the role of earthquakes in dynamic hydrological processes.