Large Earthquake Reshapes the Groundwater Flow System: Insight From the Water‐Level Response to Earth Tides and Atmospheric Pressure in a Deep Well.

Quantitative evaluation of earthquake‐induced permeability changes is important for understanding key geological processes, such as advective transport of heat and solute and the generation of elevated fluid pressure. Many studies have independently documented permeability changes in either an aquifer or an aquitard, but the effects of an earthquake on both the aquifer and aquitard of the same aquifer system are still poorly understood. In this study, we use the well water‐level response to earth tides and atmospheric pressure to study the changes in hydraulic properties in an aquifer and an overlying confining layer in Beijing, China, following the 11 March 2011 Tohoku earthquake in Japan. Our results show that both the tidal response amplitude and the phase shift increased and that the phase shift changed from negative to positive after the earthquake. We identified increased permeability in both the aquifer and aquitard by the barometric response function method. The horizontal transmissivity of the aquifer increased by a factor of 6, and the vertical diffusivity of the aquitard doubled. Key Points: Water‐level response to earth tides and atmospheric pressure is used to study earthquake‐induced changes in hydraulic propertiesTidal response and barometric pressure response methods both show permeability changes in the aquifer and aquitardThe transmissivity of the aquifer increased by a factor of 6, and the vertical diffusivity of the aquitard doubled after the earthquake [ABSTRACT FROM AUTHOR]