Structure and seismogenic activity of the broken foreland to the south of the Chilean-Pampean flat subduction zone: The San Rafael Block

Abstract

Andean broken foreland zones, located to the east of the highest Andes, are associated with populated areas and sedimentary basins with relative economic importance. Understanding their seismogenic potential is crucial for urban development and infrastructure planning. In particular, the San Rafael Block is part of the broken foreland developed to the south of the Chilean-Pampean flat subduction zone. A local seismic network allows analyzing the seismogenic potential of the San Rafael Block. Earthquake distribution suggests a northeast-dipping ramp rooting at the lower crust, cropping out at the western topographic front of the basement uplift. Gravity data confirm the asymmetry of the San Rafael block with a western topographic front associated with the main structure that exhumes the basement. Seismological and gravity data allow proposing a west-verging structure, contrary to previous interpretations based on surficial structural data. The results presented here identify the highest shallow seismogenic potential on the western side of the block, near the El Nihuil dam, and only deep events at the eastern neotectonic front which allegedly hosted historical earthquake occurrences such as the Villa Atuel-Las Malvinas earthquake in 1929.