Determination present stress tensor for the north segment of the Andes from focal mechanics major earthquakes

Abstract

The northwestern corner of South America presents a complex geodynamic setting due to the interaction of the Nazca, Caribbean and South American plates with the Andean Block. This interaction has been considered as responsible of the current stress state of the Northern Andes, the tectonic setting and the seismic activity. Inversion of focal mechanisms solutions of major earthquakes, shown a compressive stress state. However, the maximum stress varied along the South American margin from WSW-ENE north of 5° N to W-E south of this latitude. We propose that variation of the máximum stress is due to the partitioning of the convergence vector of the Nazca plate with respect to the orientation the Colombia- Ecuadorian trench. We divided this vector into two components. One parallel to the trench (displacement vector) and the other orthogonal to the trench (deformation vector), which is associated to the seismic activity in the coupling zone. These two vectors are transferred to the continent and favor reactivation of fault systems parallel to the Andes. Therefore, north of 5 ° N left lateral displacement along the faults is expected (North Romeral, Murindo and Salinas Faults), whereas south of this latitude right lateral displacement dominates (South Romeral and Algeciras Faults). Displacement of transpressive systems as Garrapatas, Cucuana and Ibagué faults is also facilitated by this stress regime.