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.