USING GPS PLATE VELOCITY DATA TO CONSTRAIN FAULT INTERACTIONS IN EL SALVADOR

Central America lies at the nexus of three plates—Caribbean, Cocos, and North American-- whose boundaries and interactions are poorly constrained. Strike-slip faulting along the El Salvador fault plays an important role in these plate and block interactions and generates large earthquakes in the northern part of Central America. The fault transfers stress from the subduction boundary at the Middle American trench and also influences the movement of the Caribbean plate. Using DEFNODE software for modeling elastic lithospheric block rotations and strains, known continuous GPS velocities were inverted to generate a model for intraplate deformation. The model is based on the slip history of the El Salvador fault and GPS data from adjacent blocks, and does not incorporate data from the entire Cocos plate. The modeling shows that northwestern Honduras is stretching ENE at around 1-3mm/yr, while the forearc sliver between the Middle American trench and the El Salvador fault is moving WNW at 15mm/yr, and the Gulf of Fonseca area is another separate block moving slightly more northerly at 13mm/yr. The modeling process confirmed that the El Salvador fault is almost entirely strike slip and has locking values that decrease down dip. The model results show that the forearc is moving quickly and probably causing many of the earthquakes along the fault, and that the Motagua and Chixoy-Polochic faults to the north are in fact creating a wedge forcing active normal faulting in Honduras. Understanding the details of intraplate deformation in this region is critical for earthquake preparedness. Thus, using GIS, an earthquake and landslide hazards map was created to highlight those areas most likely to be affected by these disasters.