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.

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