Analysis and interpretation of earthquake-related groundwater response and ground deformation: a case study of May 2006 seismic sequence in the Mexicali Valley, Baja California, Mexico

Abstract

Anomalous groundwater level and temperature changes are compared with ground deformation recorded before and after an earthquake of MW 5.4 and its foreshocks and aftershocks that occurred during 22–28 May 2006 in the Mexicali Valley, Baja California, Mexico. The coseismic groundwater level changes could be attributed to static volumetric strain changes caused by the mainshock, except for one well, where the groundwater level change may have been affected also by a triggered slip event at a nearby fault. Some of the coseismic temperature changes were attributed to increased convection and mixing of groundwater by seismic shaking. Modeling of groundwater level records allowed the estimation of hydraulic diffusivity. The observed ground tilt and groundwater level anomalies in the area close to the source fault before and after the mainshock and before the aftershocks occurrence are explainable by the dilatancy–diffusion theory, or possibly by assuming the occurrence of a slow slip events and/or fault permeability changes.