Surface Displacement and Groundwater Level Changes Associated with the 24 May 2006 Mw 5.4 Morelia Fault Earthquake, Mexicali Valley, Baja California, Mexico

Abstract

On 24 May 2006, a moderate-size ( M w 5.4) earthquake occurred in the Mexicali Valley, Mexico. The event created 5 km of surface rupture. Associated deformation was recorded by geotechnical instruments, leveling profile, and synthetic aperture radar interferometry. A coseismic steplike groundwater level change was detected at seven wells. The surface rupture consisted of up to 30 cm of primarily normal displacement. 20–25 cm of vertical offset was recorded by a crackmeter and 20 cm on leveling line. We created Envisat C-band interferograms spanning the 24 May 2006 earthquake to image the coseismic displacement. Although the coherence of the interferometric images is low, the images clearly show a spatial displacement field centered on the known surface rupture that is consistent with the expected sense of motion. The interferograms and leveling line also include subsidence related to geothermal production. This anthropogenic subsidence component was estimated using a pre-event interferogram. Source parameters for the earthquake were estimated using forward modeling of both surface deformation data and static volume strain change (inferred from coseismic changes in groundwater level). Modeling was based on finite rectangular fault embedded in an elastic media. The preferred fault model has a strike, rake, and dip of (48°, -89°, 45°) and has a length of 5.2 km, width of 6.7 km, and 34 cm of uniform slip. The geodetic moment, based on the modeled fault parameters, is ![Graphic][1] . The model matched the observed surface deformation, expected groundwater changes, and teleseismic moment reasonably well. [1]: /embed/inline-graphic-1.gif