Short- and long-term effects of GPS measured crustal deformation rates along the south central Andes

In this study we present the contemporary crustal deformation field along the central and southern Andes (17-42 - S) estimated from four Global Positioning Sys- tem (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 conver- gence 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 overrid- ing South American plates. We have also detected a strong post-seismic deformation sig- nal in the vicinity of the 1995 Mw8.0 Antofagasta (22-26 - S) and 1960 Mw9.5 Chile (38- 43 - 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 high- lights the post-seismic, as well as more long-term deformation eects. For example, we find a strong evidence for the continuing crustal shortening across the back-arc, reach- ing its maximum (4 mm/yr) in the very north of our study area. In addition, between latitudes 29-34 - 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.