Present-day crustal deformation along the El Salvador Fault Zone from ZFESNet GPS network

Abstract

This paper presents the results and conclusions obtained from new GPS data compiled along the El Salvador Fault Zone (ESFZ). We calculated a GPS-derived horizontal velocity field representing the present-day crustal deformation rates in the ESFZ based on the analysis of 30 GPS campaign stations of the ZFESNet network, measured over a 4.5 year period from 2007 to 2012. The velocity field and subsequent strain rate analysis clearly indicate dextral strike-slip tectonics with extensional component throughout the ESFZ. Our results suggest that the boundary between the Salvadoran forearc and Caribbean blocks is a deformation zone which varies along the fault zone. We estimate that the movement between the two blocks is at least ~12 mm yr-1. From west to east, this movement is variably distributed between faults or segments of the ESFZ. We propose a kinematic model with three main blocks; the Western, Central and Eastern blocks delimited by major faults. For the first time, we were able to provide a quantitative measure of the present-day horizontal geodetic slip rate of the main segments of ESFZ, ranging from ~2 mm yr-1 in the east segment to ~8 mm yr-1 , in the west and central segments. This study contributes new kinematic and slip rate

GPS constraints on deformation in northern Central America from 1999 to 2017, Part 2: Block rotations and fault slip rates, fault locking and distributed deformation

“…10a). The fastest measured rates agree well with previous 12-16 mm yr −1 estimates of the sliver motion (DeMets 2001;Lyon-Caen et al 2006;Correa-Mora et al 2009;LaFemina et al 2009;Alvarado et al 2011;Kobayashi et al 2014;Staller et al 2016).…”

“…Locking depths that are estimated for the volcanic arc faults in El Salvador are typically 2.5 to 5 km (Fig. 7a), consistent with 4-9 km locking depths estimated by Staller et al (2016) from 1-D modelling of a subset of these observations. A 1-D forward elastic half-space model in which locking is assumed to extend downwards to a depth of 15 km systematically misfits the velocities of sites in a transect of central El Salvador (dashed grey line in Fig.…”

“…For our two-part study, we compiled all available legacy and new GPS data from El Salvador, Guatemala, Honduras, parts of Nicaragua and the Mexican state of Chiapas. These included all the raw GPS data that were used to derive previous velocity fields, which span the period 1999 to 2012 (Lyon-Caen et al 2006;Turner et al 2007;Correa-Mora et al 2009;LaFemina et al 2009;Rodriguez et al 2009;Alvarado et al 2011;Franco et al 2012;Staller et al 2016). New observations from our own field efforts come from the following sources: (1) Seven continuous GPS stations that we installed in southern Guatemala and western El Salvador in 2012 and 2014.…”

CCAF-DB: the Caribbean and Central American active fault database

“…The location and nature of faults continuing into Nicaragua are also unclear, though given the abundant seismicity, deformation is certainly present. Geodetic studies (e.g., Turner et al, 2007;Styron, 2008;Alvarado et al, 2011) indicate that the northwestern Nicaraguan fault translates ∼ 15-20 mm a −1 with respect to the stable Caribbean plate. This is the fastest arc-parallel motion observed in Central America.…”

“…These focal mechanisms have been interpreted to reflect sinistral "bookshelf" faulting on structures orthogonal to the arc (LaFemina et al, 2002), but this interpretation is not supported by the alignment of lowermagnitude seismicity and no evidence for these faults is present away from the southwestern terminus of the Marabios range, on the margins of the Managua graben, which is widely interpreted as a releasing stepover in the system (as described below). GPS geodetic data are also best explained by a dextral fault underneath the arc (Styron, 2008). Confusingly, there is very little geomorphic evidence for dextral shear in the forearc or backarc; the most convincing is the presence of low hills near El Congo that are interpreted as a small restraining stepover in between the Marabios range and Cosigüina Volcano (Funk et al, 2009).…”