GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua

Abstract

S U M M A R YWe invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long-term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3-D finite element model is used to approximate the geometries of the subduction interface and strike-slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14-16 mm yr −1 and has coupling of 85-100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550-km-long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 ± 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the M w 7.3 1982 and M w 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the observed trench-parallel forearc motion.

Structural evolution of the El Salvador Fault Zone: an evolving fault system within a volcanic arc.

“…This latter model is supported by recent GPS measurements at 21 sites in El Salvador and southern Honduras. All stations in the forearc move 14 ± 2 mm/yr to the west-northwest, parallel to the trench without any vertical displacement, consistent with weak or no coupling of the subduction interface (Correa-Mora et al, 2009), suggesting that stress partitioning does not occur.…”

“…For example, the large scarp (80 metres high) bounding the northern border of the Lempa basin and the scarp of the San Vicente segment, north of the San Vicente volcano, are too high to be created just as a component of the transtensional strike-slip movement. Formation of large vertical scarps due to normal faulting would require very large Quaternary slip, not coherent with neither measured GPS velocities nor slip rates obtained from paleoseismic analysis (Correa-Mora et al, 2009;Alvarado et al, 2011;Canora et al, 2012). A plausible explanation for these large vertical scarps and the presence of the longitudinal depression named "Median trough of El Salvador" (Williams and Meyer-Abich, 1955;Carr, 1976), is that the tectonic regime prior to the current transtension was purely extensional and a graben structure was present in the area.…”

“…To date, studies on the ESFZ have mainly addressed aspects of fault structure at a local scale (Corti et al, 2005), tectonic modelling of the area and current GPS velocities (DeMets, 2001 andCorrea-Mora et al, 2009). In this study, we analyse in detail the ESFZ geomorphology and structure by using field-based observations and digital terrain model (DTM), aerial photographs and Quickbird images interpretation.…”

Geomorphic analysis of transient landscapes in the Sierra Madre de Chiapas and Maya Mountains (northern Central America): implications for the North American–Caribbean–Cocos plate boundary

“…2), and the Guayape Fault in Honduras. However, more recent works suggest that dextral slip along the Central American volcanic arc is in fact related to a slip partitioning along the trench (e.g., DeMets, 2001;Turner et al, 2007;Correa-Mora et al, 2009). Using GPS data (Fig.…”

The unrest of the San Miguel volcano (El Salvador, Central America): installation of the monitoring network and observed volcano-tectonic ground deformation

“…This fault is locally called the "El Salvador fault zone (ESFZ)". The forearc sliver shows a regional movement relative to the Caribbean plate towards the northwest, with an average speed of about 15 ± 2 mm per year (Correa-Mora et al, 2009;Alvarado et al, 2011).…”