Reconciling Geodesy and Geology at Subduction Plate Boundaries
The interseismic, GPS derived velocity field in Central America has been interpreted in terms of two major processes: elastic strain accumulation due to locking on the shallow (less than 50 km down-dip depth) part of the dipping plate boundary and trench-parallel translation of the forearc due to oblique subduction. Our new velocity field also indicates significant strain partitioning in southern Costa Rica where tectonic shortening and uplift of a young mountain belt takes place. To a first approximation, the former may be regarded as a purely elastic process, generating no net deformation of overriding plate lithosphere, while the latter two processes are capable of generating considerable long-term lateral displacement of forearc terrains and upper plate shortening. We present a model of these processes assuming elastic half space rheology, and draw inferences from the model results regarding the driving forces for both trench-parallel forearc motion and shortening. We then compare our results with estimates of upper plate deformation based on geologic mapping and structural analysis.