Seismically active fracture zones in the continental wedge above the Andean subduction zone in the Arica Elbow region

Abstract

In the continental lithosphere overlying the Wadati-Benioff zone in the Arica Elbow region eleven seismically active fracture zones were delineated on the basis of distribution of earthquake foci. The position and width of the trace, thickness, dip and maximum depth of individual fracture zones were estimated and complemented by tectonic and geological evidence. Existing fault plane solutions were attributed to the pertinent fracture zones and confronted with their orientation, inclination and tectonic function. The analysis shows normal faulting in the eastward dipping fractures, bordering the Andes in the west, and reverse faulting in the westward dipping fractures, limiting the Andes in the east. Fault plane orientations and slip directions indicated by earthquake focal mechanisms were used for the analysis of the state of stress in the fracture zones. The results point to the necessity of presence of fluids for the generation of earthquakes along faults in the western fracture zones. The position, inclination and stress conditions in the westernmost fracture system might influence the shift of active volcanism westwards from the surface projection of the intermediate depth aseismic gap in the Wadati-Benioff zone and cause the channeling of magma through tectonically disintegrated seismically active fracture zones.