Overexploitation of groundwater resources in the faulted basin of Querétaro,
Mexico: A 3D deformation and stress analysis
G. H. Ochoa-Gonzalez
Instituto Tecnologico y de Estudios Superiores de Occidente (ITESO), Jalisco, Mexico
D. Carreon-Freyre, M. Cerca
Laboratorio de Mecánica de Geosistemas, Centro de Geociencias,
Universidad Nacional Autónoma de México (UNAM), Queretaro C.P., México
A. Franceschini, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
The City of Querétaro is located on a continental basin filled since the Oligocene with lacustrine and alluvial
sediments, pyroclastic deposits, and interbedded fractured basalts. The graben structure of the basin was formed
by two major North-South trending normal faults, among which the thicknesses of the filling materials vary
many tens of meters in close distances. Hence, important differences of hydraulic and mechanical properties
characterize the various geologic units. Groundwater has been strongly withdrawn over the last three decades in
the study area, with a decline of the piezometric level exceeding 100 m. Because of the high variability of the
geologic deposits, the piezometric decrease and consequently the effective stress increase are characterized by a
large spatial variability. Piezometric variations are also due to faults that strongly impact on groundwater flow
dynamics. The deformation and effective stress variability has caused large differential subsidence causing
ground fracturing that has damaged the urban infrastructure of the City of Querétaro. This complex geological
setting has been properly accounted into a three-dimensional (3D) flow and geomechanical modeling approach
to quantify the displacement, deformation, and stress fields caused by water withdrawal. The static geologic
model was accurately defined using geological logs from extraction wells, field mapping of faults, fractures, and
the integration of major structures reported in previous geophysical works. The model has been calibrated using
observed groundwater levels and land settlement records. The simulations have spanned the period from 1970 to
2011. The modeling results highlight that the areas where large differential subsidence and horizontal
displacements developed correspond to the portions of the city where ground fractures are observed. Normal and
shear components of the stress field changes accumulate along the discontinuity surfaces at depth, providing
evidence that large piezometric declines can be a key factor triggering the fault reactivation. The spatial
relationship between major withdrawals, discontinuities of the geologic structure, and accumulation of large stress
and strain fields clearly emerged from the outcomes of the 3D geomechanical model.
