Seismo-lineaments and potentially seismogenic faults in the overriding plate of the Nazca-South American subduction zone (S Peru)

Abstract

The Peruvian subduction zone is prone to destructive megathrust earthquakes that rupture plate interface, often associated with devastating tsunamis, and usually smaller crustal earthquakes in the overriding plate that, due to the shallow focal depth and proximity to the human settlements, can be equally hazardous. However, these latter ones are generally less studied and often not included in the seismic hazard assessments. Thus, in this study, we used the Seismo-Lineament Analysis Method (SLAM) to explore potentially active structures on the overriding plate above the Nazca subduction zone in the Southern Peruvian Andes, which according to the current crustal seismicity, might have hosted ruptures in the past. Moreover, we computed their possible seismogenic potential, assuming the worst-case scenario, and discussed the tectonic implications and likely sources of stress that might trigger earthquakes along these faults. For that, we combined the focal mechanism data and obtained seismo-lineaments with the results of the morpho-tectonic analysis of the digital elevation models and satellite images.The principally W- to NW-striking seismo-lineaments identified in the study area that could represent the surface expressions of potentially seismogenic faults, in general, agree with the previously reported shallow crustal active fault systems in the Southern Peruvian Andes. The applied scaling relationships suggest a seismic potential for earthquakes of maximum moment magnitudes up to 7.3–7.4 for the recorded structures. Collected data indicates an extensional regime in the upper crust of the South American plate above the Nazca subduction, with the horizontal extension perpendicular to the trench axis. The reactivation of identified structures can be related to the following sources of stress: 1) strain partitioning in the oblique subduction zone, 2) crustal seismicity induced by megathrust earthquakes, 3) extension in the most upper part of the uplifting area above the subducting slab, and 4) volcanic activity.Our findings highlight the usefulness of the SLAM technique as a tool to recognize prone areas for potential seismogenic faults that should be studied in greater detail using paleoseismological, geomorphological, geodetic, and geophysical methods. These also show the importance of crustal faults in the overall seismic hazard assessments.