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Haiti - FLASH : Active tectonic faults highlighted in PAP 14/02/2016 12:39:03 Despite its magnitude, the earthquake of 12 January 2010, has left no trace of surface breaks making difficult its seismotectonic interpretation. The consensus that had prevailed until then, about this earthquake was that he had not broken the great fault-Enriquillo Plantain-Garden (EPGF), but one or more blind faults to the North of the latter. The active structures in the area of the epicenter being hitherto little known, the authors sought to identify them and characterize through the use of aerial images, high resolution topographic, bathymetric maps and geological observations. A set of active overlapping, of orientation Northwest-Southeast and with a inclination to the south, were able to be mapped in the Bay of Port-au-Prince and in the Cul de Sac where is the city of Port-au-Prince. One of them, the overlapping of Lamentin through the densely populated city of Carrefour and extends offshore to the west, in the bay, where it controls the morphology of the fringing reef. In the East, the overlap of Lamentin connects to the large strike-slip fault of Enriquillo Plantain-Garden. The many earthquakes recorded after the main shock of 12 January clearly emphasize these two structures and show that they are connect in depth. The authors propose that these two faults have broken on 12 January 2010. This new scenario perfectly describes the surface deformations recorded by geodetic data (GPS and radar interferometry) and the corals of microatolls type. The modeling of geodetic data suggests that the rupture was probably initiated along the overlap of Lamentin then spread along the fault Enriquillo-Plantain-Garden. Under this scenario, the strongest sliding along the overlap of Lamentin took place deep near its connection with the fault Enriquillo-Plantain-Garden, with for effect a drastic fall of the compressive stress that is applied perpendicular to the latter, thus promoting its breakdown. The 2010 earthquake caused by rupture coupled of these two flaws could be an exceptional event in relation to earthquakes more "classic" that have left traces in the landscape along the fault of Enriquillo-Plantain-Garden by accumulating including shifts of river of a few meters. This new model implies that part of the stresses accumulated over recent decades along the fault Enriquillo-Plantain-Garden have been properly released during the earthquake, but in return, they have been increased at both ends of the rupture zone and particularly in Port-au-Prince. The existence of overlapping actifs in the city of Port-au-Prince and its suburbs also involves a significant seismic hazard to characterize more in detail in order to be considered in the future development plans of the territory. HL/ HaitiLibre
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