This award will provide partial support to Prof. Thomas Gardner of The Pennsylvania State University for a sabbatical stay in Costa Rica to calculate uplift rates determined from fluvial terrace sequences along the northwestern portion of Costa Rica and to relate that data to the plate tectonic model for subduction of the adjacent aseismic Cocos Ridge. The research should provide critical data on crustal uplift rates resulting from "normal" subduction in northwestern Costa Rica during the time of subduction of the Cocos Ridge in southeastern Costa Rica. The proposed site provides the ideal location for determining the needed tectonic data because the Quatenary plate tectonic history of the region is well known. The subduction of buoyant, ocean lithosphere in the form of oceanic plateaus, aseismic ridges, or very young lithosphere may be responsible for anomalous tectonic activity along convergent plate boundaries. While the latter activity may be broadly understood, its specific causes and quantifications remain largely unaddressed. The Pacific coast of Costa Rica represents an unsurpassed site for a study of one specific case among these phenomena: the vertical motions of the crust in proximity to a subducting oceanic lithosphere that contains an aseismic ridge. This study, which is part of a larger study supported by the NSF, will involve scientists from the Instituto Geografico Nacional, the Universidad de Costa Rica, and the Instituto Costarricense de Electricidad. In particular, Prof. Ana Chinchilla of the Universidad de Costa Rica will formally participate in the field work. By closely involving scientists from Costa Rica in the research, this award serves to advance the objectives of the Science in Developing Countries Program.
