URBAN GRAVITY STUDY TO DELINEATE FAULTS AND THEIR ROLE IN THE CONTROL OF GROUND WATER FLOW AND AQUIFER RECHARGE IN THE HUECO BOLSON, EL PASO AND CIUDAD JUAREZ REGION

The Hueco Bolson basin acts as the main aquifer for the El Paso and Ciudad Juarez region, a metropolitan area with a population of more than 1.5 million. This sedimentary basin is cut by active Quaternary faults that play a major role for ground water; the faults are present due to the tectonically active Rio Grande Rift. These faults are exposed in some areas outside the city limits but are difficult to trace their extent into more urbanized areas of the cities. We have found that gravity technique is a powerful geophysical tool for locating the density contrast across faults within these urbanized areas. Preliminary analysis of gravity data indicate that the bolson reaches its deepest depths (~4 km of Quaternary fill) near the US-Mexico border and is composed of a number of smaller sub-basins located both north and south of the border. By integrating water well data, well logs and other geophysical data we can determine which of these faults may act as barriers to ground water flow. A better understanding of the structure and stratigraphy of the bolson will also help to determine possible recharge zones for the aquifer. The study will point out faults that act as barriers for ground water. Also by having a better declination of the structure and stratigraphic mechanisms with in the bolson will help to constrain better a possible recharge zone for the aquifer.