This project is a five-year collaborative geodetic study of the large-scale neotectonics of northern Central America, where the western end of the Caribbean plate abuts both the Middle America subduction zone and Motagua-Polochic strike-slip fault system. The scientific objectives are as follows: (1) Estimate the magnitude and distribution of frictional coupling along the Cocos-Caribbean subduction interface, (2) Measure the rate of strike-slip motion at one or more points across the Motagua-Polochic fault system, (3) Measure extension across the Central American "basin-and-range" south of the Motagua-Polochic fault system, (4) Measure how quickly strain accumulates across faults in the Central American volcanic arc that accommodate dextral forearc shear in response to oblique subduction, (5) Test whether significant regional uplift occurs, possibly in response to the hypothesized detachment of the slab subducting beneath this region, and (6) Improve kinematic models of the Caribbean plate geodetic reference frame. Work on the first objective is contributing to an emerging understanding of the fundamental role of aseismic processes in accommodating subduction. Progress on objectives 2-5 is advancing the present poor understanding of the neotectonics and seismic hazards at the western, trailing edge of the Caribbean plate. Work on the final objective benefits multiple NSF-sponsored GPS studies of deformation around the complexly deforming margins of the Caribbean plate. These objectives are being accomplished through modeling of velocities determined from annual or more frequent occupations of 50-100 GPS sites distributed throughout Honduras, Guatemala, and El Salvador and velocities at seven continuous GPS sites that are already operating in these countries. Modeling is done using three-dimensional finite element code that allows for a tectonically realistic representation of the study area, including laterally- and vertically-varying material properties representative of an ocean-continent subduction boundary. All measurements are made by local scientists, except for the initial network reconnaissance and installation, which were a collaborative effort.
The project is structured to benefit significantly the research careers of Honduran, Guatemalan, and Salvadoran scientists with whom are collaborating. The budget includes annual operating funds, GPS receivers, and travel funds for Honduran seismologist and Guatemalan seismologists, and possibly an earth scientist from El Salvador. Ultimately, progress on the goals above will improve estimates of the likely frequency of significant earthquakes along a variety of faults that present a seismic hazard in this extensive region.
