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

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

Deep structural setting of the North Caribbean plate boundary in eastern Guatemala

Two-dimensional inverse gravity modeling is presented to help determine the deep structural framework of the left-lateral Polochic-Motagua fault systems; They represent a major segment of the North American-Cari-bbean plate boundary. These seismically active tectonic lineaments, crossing broadly E-W Guatemala, are super¬imposed over a narrow suture where slices of ophiolitic assemblages crop out. Within the principal displacement zone of the fault systems, pull-apart basins and restraining zones (push-up) were formed. A fault population analysis along the strike of both fault systems in the Izabal and Motagua valleys, combined with satellite-de¬rived data, have allowed determining the gross geometry and kinematics of the transform systems. Geological information and commercial seismic data were used to constrain the shallow geometry and structure of the plate boundary across a 60-km-long cross-section located to the east of Lago Izabal, the largest pull-apart basin formed along the Polochic transform system, and across the Motagua valley. The inverse gravity model fits the complete Bouguer anomaly map of the area and explains most of the observed long-wavelength anomalies, as well as the local anomalies associated with intracrustal and shallow crustal geological bodies. The main features derived from the integrated geophysical-geological approach are the geometry and depth of sedimentary basins associ¬ated with the transform systems, and the root of the ophiolitic bodies in the suture zone

Deep structural setting of the North American-Caribbean plate boundary in eastern Guatemala.

Se presenta un modelo bidimensional de gravedad para determinar la estructura en profundidad del sistema de fallas lateral–izquierda de Motagua–Polochic, que son parte del límite de las placas América del Norte y del Caribe. Estos elementos tectónicos, sismicamente activos, atraviesan oeste–este la región de Guatemala y se sobreponen a una línea de sutura donde afloran cuerpos ophiolíticos. En las principales zonas de desplazamiento de las fallas se han desarrollado cuencas de pull–apart y regiones de restricción (push–up). El análisis estructural de algunas de estas fallas, situadas a lo largo del valle Izabal y del valle Motagua, en combinación con los datos obtenidos del satélite, ha permitido determinar la cinemática y el patrón de estos sistemas. La geometría y la estructura superficial del límite de las placas han sido determinadas a partir de datos geológicos y perfiles sísmicos resultantes de estudios efectuados a lo largo de una línea de 60 km de longitud al este del Lago Izabal, perpendicular al límite de placas y que interesa el valle Motagua. El Lago Izabal es la mayor cuenca de pull–apart que se ha formado a lo largo del sistema cizallante de Polochic. Los datos obtenidos con el modelo de gravedad confirman las principales características del mapa de anomalías de Bouguer de la zona y explica la mayor parte de las anomalías de amplia longitud de onda, así como aquellas de tipo local asociadas a los cuerpos geológicos de la corteza superficial y sub–superficial. La determinación de la geometría, la profundidad de las cuencas sedimentarias asociadas al sistema cizallante, así como la profundidad de los cuerpos ophiolíticos de la zona de sutura, son los principales resultados derivados de la implementación del estudio geológico y geofísico. doi: https://doi.org/10.22201/igeof.00167169p.2009.48.3.2

Variance in Fibronectin Binding and fnb Locus Polymorphisms in Staphylococcus aureus: Identification of Antigenic Variation in a Fibronectin Binding Protein Adhesin of the Epidemic CMRSA-1 Strain of Methicillin-Resistant S. aureus

The fnbA and fnbB genes of Staphylococcus aureus 8325-4 encode fibronectin (Fn) binding proteins FnBPA and FnBPB, which promote adherence to host tissues. Each adhesin contains three copies of a repeated D motif that binds Fn and is a target for vaccine development. In this study, we assess variability within the Fn-binding domain of the FnBP adhesins and evaluate factors that promote variance in Fn binding among clinical isolates. Based on variation in the number of fnb genes or the number of D motifs, we identified five polymorphism groups. S. aureus 8325-4 and 91% of methicillin-resistant S. aureus (MRSA) isolates belong to polymorphism group I, with two fnb genes and three copies of the D motif. Polymorphism group II contained one fnb gene with only two D motifs and was associated with the epidemic CMRSA-4 strain, which exhibited high protease activity and low Fn binding. Polymorphism group III was unique to the epidemic CMRSA-1 strain, defined by the presence of a fourth D motif that exhibited antigenic variation within a conserved sequence that is essential for Fn binding. However, the sequence of the D motifs was otherwise highly conserved among the other polymorphism groups. Variation in Fn binding among MRSA isolates was inversely related to protease activity but not to the number of fnb genes or the number of D motifs. Therefore, the fnb locus is polymorphic in a small number of strains, but this does not contribute to variation in Fn binding. The antigenic variation that was observed only in the epidemic CMRSA-1 strain may have evolved in response to a host immune response encountered during successive cycles of colonization, transmission, and infection in the nosocomial environment