Active Triclinic Transtension in a Volcanic Arc: A Case of the El Salvador Fault Zone in Central America

Abstract

The El Salvador Fault Zone (ESFZ) is part of the Central American Volcanic Arc and accommodates the oblique separation movement between the forearc sliver and the Chortis block (Caribbean Plate). In this work, a triclinic transtension model was applied to geological (fault-slip inversion, shape of volcanic calderas), seismic (focal mechanisms) and geodetic (GPS displacements) data to evaluate the characteristics of the last stages of the kinematic evolution of the arc. The El Salvador Fault Zone constitutes a large band of transtensional deformation whose direction varies between N90°E and N110°E. Its dip is about 70° S because it comes from the reactivation of a previous extensional stage. A protocol consisting of three successive steps was followed to compare the predictions of the model with the natural data. The results show a simple shear direction plunging between 20° and 50° W (triclinic flow) and a kinematic vorticity number that is mostly higher than 0.81 (simple-shearing-dominated flow). The direction of shortening of the coaxial component would be located according to the dip of the deformation band. It was concluded that this type of analytical model could be very useful in the kinematic study of active volcanic arcs, even though only information on small deformation increments is available.

2D FEM Numerical Prediction of Local Seismic Effects at San Salvador Municipality (El Salvador) Induced by 2001 Earthquakes

“…El Salvador country is located in the Central American Volcanic Arc (CAVA), which extends from Guatemala to Costa Rica along the active Pacific margin and ends to the north in a diffuse triple junction among the Cocos, Caribbean, and North American plates (Figure 1) [33][34][35][36]. The CAVA accommodates the fault system in El Salvador region, named El Salvador Fault Zone (ESFZ), that crosses the country from east to west [39] connecting with the Jalpatagua Fault [37,40,41]. The ESFZ is 150 km long and 20 km wide of distributed strike-slip faulting.…”

“…The ESFZ is 150 km long and 20 km wide of distributed strike-slip faulting. The ESFZ is divided into five sectors (see the inset in Figure 1), which are named, from west to east: Western Segment, San Vicente Segment, Lempa Segment, Berlin Segment, and San Miguel Segment [39].…”

“…The second source of seismicity is characterized by upper crustal earthquakes that are prevalently of tectonic origin [42,43] (and are generated in the "volcanic chain" area) The CAVA accommodates the fault system in El Salvador region, named El Salvador Fault Zone (ESFZ), that crosses the country from east to west [39] connecting with the Jalpatagua Fault [37,40,41]. The ESFZ is 150 km long and 20 km wide of distributed strikeslip faulting.…”