Structural and tectonic characterization of the Valley of Mexico: an analysis from the shear wave splitting technique
摘要
A seismic anisotropy study based on the shear wave splitting technique is conducted in the Valley of Mexico, analyzing 814 seismic events occurred between 1996 and 2023. This analysis provides insight into the region’s tectonic and structural behaviors, as well as the main causes controlling seismic anisotropy. The study reveals a geologically complex setting, with notable spatial and depth-dependent variations across distinct structural regions. Fast polarizations were identified along NW–SE, N–S, E–W, ENE–WSW, and NE–W trends, with anisotropy strength ranging from 0.17 to 21.16 ms km−1, and individual values reaching up to 61 ms km−1. Approximately 52.1% of the mean fast polarization directions correlate with local geological structures. In the central, central–western, and northern sectors of México City, 78.5% of MDP values align with NE–SW and ENE–WSW regional regimes. This percentage decreases in other areas, indicating the combined influence of regional and local stress regimes. The dominant regional anisotropic pattern extends to depths shallower than 15 km. Superimposed on this are localized anisotropic features with NW–SE, N–S, and E–W trends, indicating additional structural controls or ‘dual’ dominant regimes. Anisotropic layers cover much of the Valley, with anisotropy percentages ranging from 2.0 to 9.0%. The highest values are concentrated in the central and central–western sectors, suggesting zones of structural weakness that may facilitate deformation and connectivity with larger fault systems. Anisotropy strength increases with decreasing depths, from 2.5 ms km−1 at 10–12 km to 27.59 ms km−1 in the uppermost 0–2 km layer, indicating pervasive shallow crustal anisotropy. These high anisotropy concentrations may reflect the presence of compliant, self-organized critical systems, contributing to stress-induced and temporal varying anisotropy.