Short and long-term effects of GPS measured crustal deformation rates along the South-Central Andes

Abstract

In this study we present the contemporary crustal deformation field along the central and southern Andes (17-42\deg S) estimated from four Global Positioning System (GPS) campaigns conducted in 1994-97. We find that the majority of the observed crustal deformation field is relatively homogenous: roughly parallel to the plate convergence direction with decreasing velocities away from the trench. We attribute this type of deformation pattern to the inter-seismic phase of an earthquake deformation cycle caused by 100\% locking of the thrust interface between the subducting Nazca and the overriding South American plates. We have also detected a strong post-seismic deformation signal in the vicinity of the 1995 M$_w$8.0 Antofagasta (22-26\deg S) and 1960 M$_w$9.5 Chile (38-43\deg S) earthquakes. This type of deformation can be described as short-term in nature compared to geological timescales. The above conclusions are based on the results of the 3-D Andean Elastic Dislocation Model (AEDM). By subtracting the AEDM predicted deformation rates from the observations we obtained a residual velocity field, that highlights the post-seismic, as well as more long-term deformation effects. For example, we find a strong evidence for the continuing crustal shortening across the back-arc, reaching its maximum (4 mm/yr) in the very north of our study area. In addition, between latitudes 29-34\deg S, there is an indication of E-W oriented extension within the fore-arc, in accordance with the recent geologic findings for the N-S oriented normal faulting.