Crustal structure of the northern Andean Precordillera, Argentina, based on seismological and gravity data

Abstract

This paper aims to better comprehend the crustal structure of the Precordillera and the Iglesia Valley. Located in the northern sector of the Pampean flat-slab (San Juan, Argentina), this region was the epicenter of the historical 1894, M > 7 earthquake (intensity IX on the modified Mercalli scale) and thus considered as a region of particularly high seismic hazard. The structure and deformation style associated with such events remain poorly understood. In this study, we analyze 4 months of regional seismic records from national and international stations in order to characterize a sequence of 74 crustal events that followed the occurrence of an intermediate magnitude (MW = 4.8 and ML = 5.2) earthquake on October 28th, 2019 for which we constrain the source parameters using regional moment tensor inversion. The analysis also includes the determination of 11 focal mechanisms from P-wave polarities and P–S waves amplitude ratios. Most of the focal mechanisms indicate reverse motion solutions. Seismological results are then integrated with other geophysics (gravity and seismic reflection profiles) as well as geological data, to build a 3D structural model that allows a better understanding of the crustal deformation mechanisms of the study area. Our results suggest that the seismic deformation is mostly concentrated in the basement of the Western Precordillera, at the transition with the Frontal Cordillera. This deformation seems respond to compressional stresses. The proposed model provides evidence of ongoing seismic activity related to the interaction between the thick-skinned deformation of the Frontal Cordillera with the thin-skinned fold and thrust belt of the Western Precordillera.