Highlights: 27• We explored submarine portions of fault systems bounding the Gonâve microplate 28• Structures are a series of delineated left--lateral strike--slip fault segments 29• The distinct segments 50 to 100 km--long cut across pre--existing structures 30• A 16.5km total strike--slip displacement on the northern system estimated since 1.8 Ma 38Haiti and Jamaica (EPGFZ) and 300--km between Dominican Republic and Cuba (SOFZ). The primary 39 plate--boundary structures are a series of strike--slip fault segments associated with pressure ridges, 40restraining bends, step--over, and dogleg offsets indicating very active tectonics. Several distinct 41 segments 50 to 100 km--long cut across pre--existing structures inherited from former tectonic 42 regimes or bypass recent morphologies formed under the current strike--slip regime. Along the most 43 recent trace of the SOFZ, we measured a strike--slip offset of 16.5 km that indicates steady activity for 44 the past ~1.8 Ma if its current GPS--derived motion of 9.8 ±2 mm/yr has remained stable during the 45 entire Quaternary. 47 48 -Introduction 49 50Following the 2010 Mw 7.0 Haiti earthquake, an international effort was initiated to investigate the 51 corresponding fault system and to constrain both the individual fault slip rates and their seismic 52 history. Such an effort depends critically on knowledge of the detailed geometry of the fault system 53 delineating the northern boundary of the Caribbean domain (Fig. 1). The Caribbean plate is currently 54 moving eastward relative to North America and the plate motion is accommodated along a complex, 55200 km--wide deformed zone, the Northern Caribbean plate Boundary (NCarB). The NCarB is a 56 seismogenic zone extending over 3000 km along the northern edge of the Caribbean Sea ( Fig. 1) and 57 a deforming region that includes two large strike--slip fault systems, the Septentrional--Oriente fault 58 zone (SOFZ) in the north and the Enriquillo--Plantain--Garden fault zone (EPGFZ) in the south (Mann et 59 al., 1991; Calais and De Lépinay, 1995). The SOFZ extends from the Mid Cayman spreading center, 60 initiated 50 Ma ago (Leroy et al., 2000), runs along the Southern coast of Cuba to cut across the 61 northern Hispaniola (Calais and Mercier de Lépinay, 1989; Mann et al., 1998). The EPGFZ, the 62 prolongation to the east of Jamaica of the Walton fault, cuts across the Southern Peninsula in Haiti 63and dies out eastwards in the vicinity of the Muertos trough south of Hispaniola, delimiting the 64Gonâve microplate (DeMets and Wiggins--Grandison, 2007) (Fig. 1). Between the two strike--slip 65 systems, the middle to late Eocene East Cayman margin is described offshore Jamaica (Leroy et al., 66 1996) and the early Miocene to Present collisional wedge of Haiti, well--described onshore (Pubellier 67 et al., 2000), continues offshore in the Gonâve Gulf ( Figs. 1 and 2). 68Destructive earthquakes are reported along the NCarB both onshore and offshore (Ali et al., 2008; 69 96 -Geometry and segmentation o...

Haiti, located at the northern Caribbean plate boundary, records a geological history of terrane accretion from Cretaceous island arc formations to the Eocene to Recent oblique collision with the Bahamas platform. Little is presently known about the underlying crustal structure of the island. We analyze P-waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in Haiti to determine the crustal structure of western Hispaniola. We compute teleseismic receiver functions using the Extended-Time Multi-Taper method and determine crustal thickness and bulk composition (V p /V s ) using the H-к stacking method. Three distinctive and fault-bounded crustal domains, defined by their characteristic Moho depth distributions and bulk crustal V p /V s , are imaged across Haiti. We relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the Caribbean plate and are presently being deformed in a localized fold and thrust belt. In the northern domain, made up of volcanic arc facies, the crust has a thickness of~23 km and Vp/Vs of 1.75 ± 0.1 typical of average continental crust. The crust in the southern domain is part of the Caribbean Large Igneous Province (Caribbean LIP), and is~22 km thick with Vp/Vs of 1.80 ± 0.03 consistent with plume-related rocks of late Cretaceous age. Significantly thicker, the crust in central Haiti has values of Moho depths averaging~41 km and with Vp/Vs of 1.80 ± 0.05. We propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or LIP material. We produce a crustal profile along a N-S transect across Haiti accounting for the surface geology, shallow structural history, and new seismological constraints provided by variations of crustal thickness and bulk composition.