A research team from University of Wisconsin and California State University Stanislaus, in collaboration with scientists from El Salvador, Guatemala, Honduras, France, Mexico, and Spain are carrying out an integrated study of faulting and the earthquake cycle in northern Central America, at the deforming western end of the Caribbean plate. The major emphasis is to better measure and model deformation around a continental triple junction in southern Guatemala, where the Motagua and Polochic fault system terminates the Caribbean-North America plate boundary. Existing and new data from 110 campaign and continuous GPS sites in El Salvador, Guatemala, Honduras, and southern Mexico will be compiled and analyzed to create the first consistent regional-scale GPS velocity field for the western Caribbean. The new velocity field will be used to study four important topics, including: 1) how deformation is accommodated around the continental triple junction; 2) the motion and internal deformation of the Central America forearc sliver; 3) the manner in which the Jalpatagua fault and other volcanic arc faults in Guatemala accommodate this movement and interact with the magmatic arc; and 4) how extension is accommodated between the sinistral Motagua-Polochic fault system and the dextral Jalpatagua fault and the influence on subduction coupling and upper plate deformation of a 50 degree change in the dip of the subducting Cocos plate. Complementary outcrop, gravity, paleomagnetic, radiometric, and geochemical data will be collected in Guatemala and Honduras to provide a geological framework for interpreting and modeling the GPS velocity field. Forward and inverse modeling that integrates the available geodetic and structural observations and suitable earthquake constraints will be used to better understand the factors that dictate deformation in the region and optimize estimates of block rotations, fault coupling and locking depths, and strain rates and directions within quasi-rigid blocks.
Estimates of interseismic strain rates and long-term fault slip rates that will result from this work will inform risk analysis in El Salvador, Honduras, and Guatemala, where destructive earthquakes have occurred in the past 35 years. The study complements publicly funded studies of natural hazards in neighboring countries (i.e. Mexico, Nicaragua, Costa Rica) and together will substantially advance understanding of these hazards in much of Central America and southern Mexico. Training workshops to be held in Guatemala and El Salvador will target one or more techniques and will constitute a mini-forum for presenting project results and educating students, scientists, and the broader public in the host countries.
