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.

et al.. The northern Caribbean plate boundary in the Jamaica Passage: structure and seismic stratigraphy. Tectonophysics, Elsevier, 2016, 675, pp

International audienceTranspressive deformation at the northern Caribbean plate boundary is accommodated mostly by two major strikeslipfaults, but the amount and location of accommodation of the compressional component of deformation is still debated.We collected marine geophysical data including multi-beam bathymetry and multichannel seismic reflection profiles alongthis plate boundary around Hispaniola, in the Jamaica Passage and in the Gulf of Gonâve. The data set allows us to imagethe offshore active strike-slip faults as well as the compressional structures. We confirm that the Enriquillo-Plantain-GardenFault Zone (EPGFZ) in the Jamaica Passage has a primary strike-slip motion, as indicated by active left-lateral strike-sliprelatedstructures, i.e.: restraining bend, asymmetrical basin, en echelon pressures ridges and horsetail splay. Based ontopographic cross-sections across the EPGFZ, we image a very limited compressional component, if any, for at least thewestern part of the Jamaica Passage. Toward the east of the Jamaica Passage, the fault trace becomes more complex and weidentify adjacent compressional structures. In the Gulf of Gonâve, distributed folding and thrust faulting of the most recentsediments indicate active pervasive compressional tectonics. Estimates of shortening in the Jamaica Passage and in the Gulfof Gonâve indicate an increase of the compressional component of deformation towards the east, which nonetheless remainsvery small compared to that inferred from block modelling based on GPS measurement

Oblique convergence of the Caribbean and North American plates has partitioned strain across a major transpressional fault system that bisects the island of Hispaniola. The devastating M W 7.0, 2010 earthquake that struck southern Haiti, rupturing an unknown fault, highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation. Here we assess seismic activity and fault structures across Haiti using data from 33 broadband seismic stations deployed for 16 months. We use traveltime tomography to obtain relocated hypocenters and models of V p and V p /V s crustal structure. Earthquake locations reveal two clusters of seismic activity. The first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture. The second cluster shows shallow activity north of Lake Enriquillo (Dominican Republic), interpreted to have occurred on a north-dipping thrust fault. Crustal seismic velocities show a narrow low-velocity region with an increased V p /V s ratio (1.80-1.85) dipping underneath the Massif de la Selle, which coincides with a southward-dipping zone of hypocenters to a depth of 20 km beneath southern Haiti. Our observations of seismicity and crustal structure in southern Haiti suggests a transition in the Enriquillo fault system from a near vertical strike-slip fault along the Southern Peninsula to a southward-dipping oblique-slip fault along the southern border of the Cul-de-Sac-Enriquillo basin. This result, consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the Enriquillo fault system, is an important constraint in our understanding of regional seismic hazard.

The boundary between the Caribbean and North American plates in the Hispaniola region is the northwestern termination of the North American plate subduction evolving from westward subduction in the Lesser Antilles to southward subduction in the Greater Antilles and oblique collision against the Bahamas platform in Cuba. We analyze P waveforms recorded by 27 broadband seismic temporary stations deployed during the Trans-Haiti project. Seismicity recorded by the temporary network from June 2013 to June 2014 is used to locate the earthquakes. A total of 514 events were identified with magnitudes ranging from 1 to 4.5. Twenty-six moment tensors were calculated by full waveform inversion using the ISOLA software. The analysis of the new moment tensors for the Haiti upper lithosphere indicates that normal, thrust and strike-slip faulting are present but with a majority of thrust faulting. The mean P and T axes for the moment tensors indicated that the current compressional deformation is mainly N-S to NNE-SSW. Moreover, a dozen intermediate-depth earthquakes (>70 km) are located under Haiti, with one event in the south of the island reaching 260 km depth. The seismic data of the Haiti network, over a one-year time period, tend to confirm the existence of a lithospheric slab inherited from southward subduction under the Greater Antilles. The scarcity of the intermediate-depth seismic events in this area may be the effect of the lack of a dense seismic network or may indicate that we image the western slab edge.

International audienceWe determine the lateral variations in seismic velocity of the lithospheric mantle beneath the Gulf of Aden and its margins by inversion of Pn (upper mantle high-fre- quency compressional P wave) traveltimes. Data for this study were collected by sev- eral temporary seismic networks and from the global catalogue. A least-squares tomo- graphic algorithm is used to solve for veloc- ity variations in the mantle lithosphere. In order to separate shallow and deeper struc- tures, we use separate inversions for shorter and longer ray path data. High Pn velocities (8.2-8.4 km/s) are observed in the uppermost mantle beneath Yemen that may be related to the presence of magmatic underplating of the volcanic margins of Aden and the Red Sea. Zones of low velocity (7.7 km/s) are present in the shallow upper mantle beneath Sana'a, Aden, Afar, and along the Gulf of Aden that are likely related to melt transport through the lithosphere feeding active volcanism. Deeper within the upper mantle, beneath the Oman margin, a low-velocity zone (7.8 km/s) suggests a deep zone of melt accumulation. Our results provide evidence that the asthe- nosphere undergoes channelized flow from the Afar hotspot toward the east along the Aden and Sheba Ridges

Haiti, on the island of Hispaniola, is situated across the North American-Caribbean plate boundary at the transition point between oblique subduction in the east and a transform plate boundary in the west. Here we use shear wave splitting measurements from S waves of local (0-50 km) and intermediate depth (50-150 km) earthquakes as well as SK(K)S phases from teleseismic earthquakes to ascertain good spatial and vertical resolution of the azimuthal anisotropic structure. This allows us to place new constraints on the pattern of deformation in the crust and mantle beneath this transitional region. SK(K)S results are dominated by plate boundary parallel (E-W) fast directions with~1.9 s delay times, indicating subslab trench parallel mantle flow is continuing westward along the plate boundary. Intermediate depth earthquakes originating within the subducting North American plate show a mean fast polarization direction of 065°and delay time of 0.46 s, subparallel to the relative plate motion between the Caribbean and North American plates (070°). We suggest a basal shear zone within the lower ductile crust and upper lithospheric mantle as being a potential major source of anisotropy above the subducting slab. Upper crustal anisotropy is isolated using shear wave splitting measurements on local seismicity, which show consistent delay times on the order of 0.2 s. The fast polarization directions indicate that the crustal anisotropy is controlled by the fault networks in close proximity to the major strike-slip faults, which bisect the north and south of Haiti, and by the regional stress field where faulting is less pervasive.