Subsidence and liquefaction analysis in Mexicali, Mexico, during the Cucapa earthquake (April 4, 2010) using Envisat/Asar and Spot images.

An earthquake, 7.2° moment magnitude, occurred on April 4, 2010. Its epicenter was located in southern Cucapa Range, Northern Baja California Peninsula, Mexico, in the confluence of a set of active tectonic faults. Two additional hazards after the earthquake affected population: subsidence and liquefaction. Farmer communities and agriculture lands located in southern Mexicali City were flooded due to the liquefaction phenomenon. Great volumes of fine sediments and water sprouted in different points, flooding agricultural lands and some small communities. The fault displacement during the earthquake damaged roads and buildings. Land subsidence was observed in some areas. More than 35,000 inhabitants and 60,000 ha of agricultural lands were affected. To analyze the consequences of such an earthquake, two multi-spectral and two panchromatic Spot images (before and after the earthquake) were acquired by means of the National Commission of Water, the Mexican Government Water Agency. In addition to these optical images, three interferometric pairs from Envisat/Asar radar sensor were acquired on the grounds of the project C1P6926 with the European Space Agency (ESA). A red, green, blue (RGB) false color composite of the multi-spectral images, before and after the earthquake, shows the inundated areas caused by the liquefaction phenomenon. The two panchromatic images form a stereoscopic pair. These images were integrated into multi-spectral images to derive the texture relief caused by the liquefaction phenomenon. An interferometric analysis was applied to the three interferometric pairs. The coherence images and the digital elevation model (DEM) were calculated as well. The interferometry, the amplitude and the DEM were overlaid. This overlay shows subsidence occurrence in the area of study due to the earthquake. From results and field data, it was possible to identify subsidence-affected areas as well as flooded areas due to the liquefaction phenomenon. [ABSTRACT FROM AUTHOR]