Permeability enhancement related to the 2021 Mw 7.4 Maduo earthquake: Insights from water-level tidal response and multi-depth temperature observations

Abstract

Permeability, which is an important property that controls the transportation processes in the shallow crust, is known to change during large earthquakes. Several studies have independently documented changes in permeability or groundwater motion through water level, streamflow, water temperature, and geochemical observations. In this study, we first compared water level data from three wells located in the Longmenshan Fault zone, where the 2008 Mw 7.9 Wenchuan earthquake occurred. We then analyzed the changes in aquifer permeability associated with the 2021 Mw 7.4 Maduo earthquake, which occurred 640 km away from the study area, using water-level tidal response and multi-depth temperature observations from one of the three wells. Tidal response analysis of water-level data indicated a great increase in the phase shift of the M2 wave from negative to positive, reflecting an enhancement in vertical permeability of the aquifer due to the Maduo earthquake. Multi-depth temperature observations indicated that the co-seismic water temperature increased successively from deeper to shallower depths, indicating the upward migration of the water (at a transient rate of 1.5–2.3 × 10−2 m/s) in observation section. The results indicated that our method is effective for studying changes in the permeability of groundwater motion in an aquifer related to an earthquake.