Seismotectonic and gravimetric analysis of the central Neuquen Basin

Abstract

Understanding the seismotectonics in the foreland region of orogenic belts is crucial for several reasons. Firstly, it allows us to infer stress conditions and structural controls in distant orogenic areas. Secondly, because these regions are often densely populated, it becomes essential to assess the associated risks, hazards, and vulnerabilities. In this study, we investigate intraplate seismicity in the foreland region of the Neuquén Basin in the southern Central Andes. Our data were obtained from a local broadband seismic network and high-resolution gravimetric enhancement methods. We analysed three distinct sets of earthquakes associated with major subsurface structural features. We found that seismic events near the Añelo locality may be linked to anthropogenic causes, underscoring the importance of identifying active structures and understanding regional tectonics. The seismicity is mostly aligned with Mesozoic transfer zones, as well as a large laccolithic magmatic intrusion. Focal mechanisms and enhanced gravimetric methods further elucidate previously unidentified structural features related to seismicity and gravity gradients. Reactivation directions coincide with reported Andean E-W maximum stress orientations. To the south of Añelo, seismicity and gravity gradient patterns suggest lineaments within the Huincul System. Notably, NE-SW trending lineaments between 71º W and 70º W align with seismicity possibly associated with the Agrio fold and thrust belt, and the projection of the Valdivia Fracture Zone. At 70º W, E-W trending lineaments correspond to seismic activity near the Chihuidos anticline and Cortaderas lineament. At 69º W, a shorter NE-SW lineament coincides with clustered seismicity, the Añelo anticline, and an eastward shift of the deformation front. Lastly, ESE-WNW trending lineaments at 68º W indicate structural rotations consistent with the complex Mesozoic Huincul System framework. From these results, we propose that the Huincul System exerts strong control over the structural character and seismotectonics of the central foreland region of the Neuquén Basin. This comprehensive analysis underscores the utility of integrating diverse geophysical methods for understanding intraplate seismicity and structural dynamics in foreland basin settings.