Focal seismic mechanisms and tectonic stresses in the northern region of the Merida Andes, Venezuela

Improvements in the seismological instrumentation took place in the ninetie s in western Venezuela and the number of available focal mechanisms has inc reased significant. In this work, 17 published focal mechanisms have been c ompiled and 22 new solutions added for events that occurred in the region c omprising the area of the Merida Andes north of the Paramo de Mucubaji, to determine the tectonic stresses. Normal, inverse and strike slip focal mech anisms were found. The inverse mechanisms are mainly associated with the no rthwestern and southeastern foothills and with the Merle Grande-Burro Negro fault system; the strike-slip and normal mechanisms belong to the events l ocated in the zone comprised between the Bocono and Burbusay (Carache) faul ts. The analysis of tectonic stresses indicates that in the latter zone the stress regime is transtensional, whereas in the mountain range foothills i t is compressional. However, the azimuth of the maximum horizontal stresses (S-Hmax) can be considered as approximately constant, because it is restri cted to values between 110 degrees and 135 degrees both in the compressiona l and in the transtensional,zones. An exception is observed northwest of Ag ua Viva, where S-Hmax shows a rotation with respect to the rest of the stud y area.