UC Berkeley

Coseismic groundwater-level changes induced by earthquakes have been reported for thousands of years. The M8.0 Wenchuan earthquake caused coseismic groundwater-level responses across the Chinese mainland. Three types of changes were recorded in 197 monitoring wells: coseismic oscillations ranging in amplitude from 0.004 to 1.1m, immediate coseismic step changes ranging from 0.0039 to 9.188 m, and more gradual postseismic changes ranging from 0.014 to 1.087 m. Hydrogeological and tectonic settings are dominant factors in determining the coseismic response. Wells located near the boundaries of active blocks can have large coseismic responses even when the epicenter distance is large. Both the sign and amplitude of water-level changes are random at the continental scale. Poroelastic response to the coseismic static strain cannot explain most of the coseismic changes. Permeability changes caused by stress changes may explain the large variability of the coseismic response amplitude.