ASSESSMENT OF ACTIVE TECTONICS IN THE WESTERN MARGIN OF THE SIERRA MADRE ORIENTAL. IMPLICATIONS FOR NEOTECTONIC STRESS REGIME AND SEISMIC HAZARD IN THE CURVATURE OF MONTERREY IN NORTHEASTERN MEXICO

This work presents the evidence of active faults in the western margin of the Sierra Madre Oriental (SMOr) near Galeana, in Northeastern Mexico. For a long time, it has been mentioned that NE Mexico is a tectonically stable region with no seismicity. However, since the installation of permanent seismological stations in 2006, a constant seismic activity with M≤4.5 has been recorded. The eastern limit of the active Mexican Basin and Range Province (BR) in NE Mexico is not well defined and it has been proposed that it is located on the western margin of the SMOr. This contribution presents a geomorphological, geological-structural, and seismological analysis of a basin located on the western margin of the El Potosí anticline on the limits of the states of Coahuila, Nuevo León and Zacatecas.

In this region, a set of Plio-Quaternary normal faults probably associated with the BR-SMOr limit have been proposed based on geological studies. We take as a basis one of these lineaments - fault (?) to study them in detail through fieldwork. The Santo Domingo fault system is located in the eastern edge of Potosí basin. To assess the tectonic activity three geomorphic indices were analyzed: basin asymmetry factor (AF), transverse topographic basin asymmetry (T), and mountain front sinuosity (S). Results suggest the tilting of the basin in the WSW direction. On the other hand, the results of the sinuosity analysis are, perhaps, the ones that offer the least confidence.

The geological-structural analysis carried out along several creeks evidences the existence of faults that cut recent Quaternary alluvial sediments. The structural data collected in the field reveal the existence of a NW-SE fault system located in the proximal part of the mountain front, which coincides with the main fault system proposed in regional studies. In our study, this fault system is redefined from the fieldwork, suggesting that the horizontal stress regime for this area is: S_Hmin azimuth trend 043 ° and S_Hmax azimuth trend 311 °. Therefore, the local neotectonic stress regime is S_V> S_NW > S_NE. The results of this work show that the boundary between the BR - SMOr provinces is located in this area and is still tectonically active. Thus, the results presented here are of great interest to the evaluation of the seismic cycle and the occurrence of earthquakes with 6≤M≤7 in the region.