Abstract
Two adjacent wells-Mangshi (MS) and Lijiang (LJ), are located in the southeast margin of the Tibet Plateau The 2015 Mw 7.8 Nepal earthquake induced different far field (>1000 km) co-seismic water level responses that range from 0.16 to 0.76m We confirm that the seismic wave influences the water level greatly in a high-frequency band (f > 8 cpd) by coherence analysis Furthermore we use the tidal-response variations (M2 tide) to explain this hydrological response The results show that the co-seismic water level response to the distant earthquake may be explained by aquifer permeability or transmissivity enhancements caused by the passage of seismic waves through the mobilization of the colloidal particles Horizontal groundwater flow can be induced in a confined aquifer system as in the MS well While in the LJ well vertical groundwater flow can be further induced by a switch to semiconfined aquifers which may be caused by preexisting vertical fractures The post-seismic tidal-response relax which also means a healing of the aquifer after great earthquakes.
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