Application of Interferometry Synthetic Aperture Radar (InSAR) in the study of the subsidence of Mexico City and its relationship with the abatement of the static level of groundwater.

Abstract

<p>Mexico City has suffered for many years from the phenomenon of land subsidence because the city is located within the limits of the old Lake Texcoco. The lithological materials that constitute the lake area are deposits, mainly clayey, of low consolidation, that compose the upper aquitard of the city, from which volumes of water have been extracted that have caused the clayey materials to rearrange causing the subsidence of the land, thus leading to visible affectations in buildings and communication routes. The subsidence of the city is not presented homogeneously as there are regions of the city that present greater settlement than others, since previous studies have shown that studying the phenomenon regionally leaves more doubts than certainties due to the complexity of the sedimentary material of the lake plain since this deposit is mainly composed of clays of various origins, in addition to being interbedded with volcanic materials.</p> <p>This study aims to identify areas within the city, with similar characteristics that allow us to understand the behavior of land subsidence and its relationship with the reduction of the static groundwater level. To do this, data on the vertical displacement of the terrain were obtained using the InSAR technique and associated with the drawdown values ​​of the static level to verify if there is a direct relationship between the extraction of groundwater and the descent of the terrain. It was considered that in the old Lake of Texcoco, there was a presence of salty and sweet waters, which would be decisive in forming different clay minerals in the lake plain. For this reason, it was decided to divide the city according to the environment that governed the site when Lake Texcoco existed. Four study areas were proposed: Lake Texcoco area, which is located northeast of the city where brackish waters predominated; the Northeast area of ​​the town, where the ancient city of Tenochtitlán was located and where fresh waters dominated; the Xochimilco Lake Zone, which had fresh waters and a higher elevation than the Tenochtitlán zone; and the Lake Chalco Zone, which presents characteristics similar to those of Lake Xochimilco.</p> <p>The results of the study show that zoning the lake plain into 4 regions allows for a linear relationship of the variables of vertical displacement of the terrain and dejection (decrease) of the static level of groundwater, showing that there is a direct relationship between both variables, contrary to what recent studies showed since when studying the phenomenon regionally, the results showed little or no linear relationship between land settlement and the drop in the static level.</p>