48 Tectónica de las Américas: Sesión en español

North, Central, and South America have a complex and active tectonic activity. We invite contributions that will help expand our knowledge of the geology, stratigraphy, sedimentology, geochemistry, geophysical characteristics and tectonic history of this region.

Sunday, 19 October 2025
1:30 PM - 5:30 PM
HBGCC, 217B

Contreras Shear Zone to the south of the Sierra de las Cruces. Implications for seismic activity west of Mexico City

Paper number: 48-6
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

The Sierra de las Cruces (SC) is a mountain range located on the western edge of the Basin of Mexico, within the eastern sector of the Trans-Mexican Volcanic Belt. This range has a preferential NNW-SSE trend and is composed primarily of Pliocene-Pleistocene stratovolcanoes and domes of dacitic and andesitic composition. Although the SC is cut by a complex set of faults and seismic activity has recently occurred along its eastern slope, the kinematics, geometry, arrangement, and deformation history of these faults remain unknown. In this work, we analyse the NE-SW-trending faults, with particular emphasis on the so-called Contreras Shear Zone. Our results reveal the existence of three fault families, characterized by NNW-SSE, E-W, and NE-SW orientations. The ~E-W faults have normal kinematics, whereas the NNW-SSE and NE-SW faults have oblique kinematics with a dominant normal component. Normalized Correlation Count (NCC) analyses indicate that faults in the SC have a clustered arrangement, likely related to the inheritance and/or reactivation of previous structures. The Contreras shear zone presents a NE-SW trend, with an exposed length of 35 km and a width of 10 km. This shear zone is formed by a tectonic pillar bordered by oblique faults, with a major contribution from the normal component and a left-lateral displacement. In the NE part of the shear zone, a set of fractures is exposed with NE-SW, WNW-ESE, and ~E-W orientations, associated with the inheritance of previous structures. The principal stress directions in this shear zone have a strike and dip of 175/60, 078/04, and 345/29 for σ1, σ2, and σ3, respectively. The frequency-size relationship of NE-SW faults follows a power law function with an exponent of -1.61. We suggest that the NE-SW faults are the product of reactivation and/or inheritance from previous structures in a three-dimensional deformational condition. Furthermore, the inversion of fractures and the angular relationships between suggest that the Contreras shear zone accommodates deformation in a transpression regime in its central sector. The NE-SW shear zone can be projected to the current seismic zone in the southwest of Mexico City, with hypocenters located at 1-3 km. It is likely that this shear zone is the responsible for these swarms that have affected this region of the city.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412938

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