Research papersSensitivity of hydraulic properties to dynamic strain within a fault damage zone

- Coseismic water level shows different behaviors within and outside a fault zone.
- Earthquake changed hydraulic properties within a fault damage zone.
- Hydraulic properties within a fault damage zone are more sensitive.

Seismically induced water level changes were observed in seven wells in the south part of the Tanlu fault zone, eastern China. Three wells are located within damage zone of the Tanlu major fault zone, and four wells are relatively far from the fault. The three wells located within the fault damage zone showed strong sustained water level changes in response to the passage of seismic waves, while the four wells outside the fault zone showed oscillational behaviors during the passage of seismic waves. We utilized tidal factor and phase shift as a proxy for hydraulic property and found that, at the three wells within the fault damage zone, hydraulic properties (permeability and poroelastic properties) changed after multiple large earthquakes, in contrast, at the four wells outside the fault damage zone, hydraulic properties remained unchanged before and after each earthquake. Contrasting the hydraulic response behaviors and properties within and outside the fault damage zone, we suggest that hydraulic properties within a fault damage zone are more sensitive and vulnerable than that away from the fault damage zone. The sensitivity and vulnerability may be correlated to seismically induced dynamic strains loading on damaged rocks, which can effectively change permeability and poroelastic properties of a groundwater system.