Seismic imaging of the crust and upper mantle beneath Haiti and the Caribbean Sea

Abstract

Haiti straddles the North American-Caribbean plate boundary, which accommodates oblique convergence between the two plates at a rate of 19 mm/yr. As a result, strain is partitioned acrosstwo major fault zones that transect Haiti in the north and south. The devastating 2010 MW 7.0 earthquake served to highlight our limited understanding of regional fault segmentation and itslink to plate boundary deformation. The Trans-Haiti project represented the first regional deployment of seismic stations across Haiti, recording continuous seismic data for 16 months from 2013 to 2014. 1,055 local earthquake were detected and located using a new 1-D velocity model. 437 of these earthquakes were then re-located in a tomographic inversion, retrieving the first 2-D seismic velocity model of Haiti’s crust. Hypocentre locations and low-velocity zones imaged a clear change in the structure of the Enriquillo-Plantain Garden fault zone (EPGF) in southern Haiti, transitioning from a vertical strike-slip fault in the west, to a series of south dipping oblique-slip faults across central Haiti. This was consistent with seismic anisotropy, which showed the maximum compressional stress to be orientated NNE-SSW, sub-parallel to the plate convergence direction andperpendicular to the strike of the compressional faults. In addition, anisotropic fabrics observed inthe lower crust and upper mantle highlight the coupling between the convergence across the plateboundary and the style of faulting observed in Haiti. Using data from permanent stations acrossPuerto Rico, Hispaniola (Haiti and the Dominican Republic), Jamaica and Cuba, S-to-P receiverfunctions were used to constrain crustal and lithospheric thicknesses regionally across the plateboundary. While crustal thickness was consistent at 28-34 km across the islands, these receiverfunctions highlighted a thickened lithosphere of 135 km beneath the Caribbean Large IgneousProvince (CLIP). The northern boundary of the CLIP lies in southern Haiti, beneath the expression of southward-dipping compressional faults. I suggest that this change in lithospheric thicknessmay be another factor which contributes to the observed faulting, and the transition from E-W strike-slip to NW-SE oblique-slip faults observed across southern Haiti.

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ORCID for Derek Keir: orcid.org/0000-0001-8787-8446

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