Evain, M., Galve, A., Charvis, P., Laigle, M., Kopp, Heidrun , Weinzierl, Wolfgang , Hirn, A., Flueh, Ernst R. and Gallart, J. and Thales Scientific Party (2013) Structure of the Lesser Antilles subduction forearc and backstop from 3D seismic refraction tomography. Tectonophysics, 603 . pp. 55-67. DOI 10.1016/j.tecto.2011.09.021.

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Abstract

In 2007 the Sismantilles II experiment was conducted to constrain structure and seismicity in the central
Lesser Antilles subduction zone. The seismic refraction data recorded by a network of 27 OBSs over an
area of 65 km×95 km provide new insights on the crustal structure of the forearc offshore Martinique
and Dominica islands. The tomographic inversion of first arrival travel times provides a 3D P-wave velocity
model down to 15 km.
Basement velocity gradients depict that the forearc is made up of two distinct units: A high velocity gradient
domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward
named the outer forearc. Whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a
whole to the south, short wavelength deformations of the outer forearc basement are observed, beneath a 3
to 6 km thick sedimentary pile, in relation with the subduction of the Tiburon Ridge and associated seafloor
reliefs.
North, offshore Dominica Island, the outer forearc is 70 km wide. It extends as far as 180 km to the east of the
volcanic front where it acts as a backstop on which the accretionary wedge developed. Its width decreases
strongly to the south to terminate offshore Martinique where the inner forearc acts as the backstop.
The inner forearc is likely the extension at depth of theMesozoicmagmatic crust outcropping to the north in La
Désirade Island and along the scarp of the Karukera Spur.
The outer forearc could be either the eastern prolongation of the inner forearc, but the crust was thinned and
fractured during the past tectonic history of the area or by recent subduction processes, or an oceanic terrane
more recently accreted to the island arc.

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