Fault kinematics in northern Central America and coupling along the subduction interface of the Cocos Plate, from GPS data in Chiapas (Mexico), Guatemala and El Salvador

Abstract

International audienceNew GPS measurements in Chiapas (Mexico), Guatemala and El Salvador are used to constrain the fault kinematics in the North America (NA), Caribbean (CA) and Cocos (CO) plates triple junction area. The regional GPS velocity field is first analysed in terms of strain partitioning across the major volcano-tectonic structures, using elastic half-space modelling, then inverted through a block model. We show the dominant role of the Motagua Fault with respect to the Polochic Fault in the accommodation of the present-day deformation associated with the NA and CA relative motion. The NA/CA motion decreases from 18-22 mm yr−1 in eastern Guatemala to 14-20 mm yr−1 in central Guatemala (assuming a uniform locking depth of 14-28 km), down to a few millimetres per year in western Guatemala. As a consequence, the western tip of the CA Plate deforms internally, with ≃9 mm yr−1 of east-west extension (≃5 mm yr−1 across the Guatemala city graben alone). Up to 15 mm yr−1 of dextral motion can be accommodated across the volcanic arc in El Salvador and southeastern Guatemala. The arc seems to mark the northern boundary of an independent forearc sliver (AR), pinned to the NA plate. The inversion of the velocity field shows that a four-block (NA, CA, CO and AR) model, that combines relative block rotations with elastic deformation at the block boundaries, can account for most of the GPS observations and constrain the overall kinematics of the active structures. This regional modelling also evidences lateral variations of coupling at the CO subduction interface, with a fairly high-coupling (≃0.6) offshore Chiapas and low-coupling (≃0.25) offshore Guatemala and El Salvador

The 2017 Mw 8.2 Chiapas, Mexico, Earthquake: Energetic Slab Detachment

“…The location relative to the trench is similar to that for the 1931 Oaxaca earthquake, which is down-dip of a locked portion of the megathrust (Singh et al, 1985). We infer that the seaward portion of the megathrust up-dip from where the 2017 rupture plane intersects it is partially locked, based on the occurrence of minor thrusting activity in this region and the regional geodetic inference of slip deficit (Franco et al, 2012). However, the lack of historic large megathrust ruptures in the relatively narrow strip of megathrust slip deficit raises the possibility that the coupling is either very heterogeneous due to the bathymetric structure of the subducting ridge, reducing the size of ruptures in the region, or the buoyancy is such that the region is undergoing high-stress creep rather than stick-slip motion.…”

“…There is more interplate thrusting along the megathrust along Oaxaca to the northwest, and offshore of the southernmost Chiapas coast east of 94°W. This region is also tectonically complicated by the northwestward extent of the Caribbean plate and the oblique trend of the Caribbean-North American plate boundary through central Guatemala and offshore over the region of the 2017 rupture (e.g., Franco et al, 2012). The Caribbean plate appears to be leaving a forearc block behind as it moves eastward, complicating the upper plate deformation pattern.…”

“…The Caribbean plate appears to be leaving a forearc block behind as it moves eastward, complicating the upper plate deformation pattern. Franco et al (2012) allow for this and infer fairly high interplate coupling, >0.6, offshore of Chiapas as far west as 95.5°W, spanning the region above the 2017 rupture zone, in contrast to relatively low coupling to the southeast offshore Guatemala and El Salvador.…”

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

“…Recent models agree on the fact that the dextral Jalpatagua Fault (Fig. 2) coupled with extension along the grabens of Guatemala represents the limit between the forearc sliver and the Caribbean Plate (e.g., Lyon-Caen et al, 2006;Andreani et al, 2008a;Authemayou et al, 2011;Franco et al, 2012). However, there is no clear consensus on the boundary between the forearc sliver and the North American Plate.…”

Tsunami hazard assessment in El Salvador, Central America, from seismic sources through flooding numerical models.

“…The complete rupture of the subduction interface from Nicaragua to Chiapas seems unlikely given the low coupling of the subduction (Pacheco et al, 1993;Franco et al, 2012) and the lack of historical records of major events in the last six centuries (Fernández, 2002) for a subduction rate of about 70 mm yr −1 (DeMets et al, 2010). We define as a segment rupture the 1992 Nicaragua event of magnitude M W = 7.7 and we divided the rest of the subduction interface into three parts.…”