Evaluation of subsurface infiltration and displacement in a subsidence-reactivated normal fault in the Aguascalientes Valley, Mexico

In this study, the main hydromechanical characteristics of a portion of the Oriente fault, in the valley of Aguascalientes, Mexico, are analyzed and discussed. This discontinuity corresponds to a normal fault that was originated before the formation of the Aguascalientes graben. However, its recent activity and potential reactivation may be directly linked to the land subsidence currently occurring in the center of the valley. A 1-year campaign to monitor deformation in two transects perpendicular to this fault indicates continuous deformation activity with maximum vertical descending values of 43 mm in the hanging wall. On the other hand, a fieldwork procedure to determine the geologic structure of the fault zone and to establish the infiltration patterns of a selected point in the fault was performed as well. This field test consisted of analyzing the resistivity patterns of profiles across and along the fault, implemented before, during and after pouring groundwater into the fault and monitoring the fluids movement through the fault zone. Results suggest that the fault contains three perpendicular fault branches in a distance of 80 m, portraying a potential domino fault system. The high infiltration capacity of the fault opening allowed the rapid intrusion of water into the subsoil, and the distinguishable changes in electrical resistivity in the profiles parallel to the fault plane suggest that the infiltrating water goes down into the soil through the fault plane or adjacent to it.