Sediment accretion, subduction, and dewatering at the base of the trench slope off Costa Rica: A seismic reflection view of the décollement
Article first published online: 20 SEP 2012
Copyright 1986 by the American Geophysical Union.
Journal of Geophysical Research: Solid Earth (1978–2012)
Volume 91, Issue B2, pages 2019–2028, 10 February 1986
How to Cite
1986), Sediment accretion, subduction, and dewatering at the base of the trench slope off Costa Rica: A seismic reflection view of the décollement, J. Geophys. Res., 91(B2), 2019–2028, doi:10.1029/JB091iB02p02019., and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 11 SEP 1985
- Manuscript Received: 19 MAR 1985
Sea Beam bathymetric and water gun seismic reflection data off the west coast of Costa Rica image the base of the trench slope, its underlying structure, and the behavior of a décollement surface in the presence of relief on the subducting plate. A low-angle, landward-dipping reflection marks the master décollement, above which only about 80 m of a 350 m oceanic sedimentary section is offscraped and accreted to the lower trench slope. A small horst block at least 9 km long, 1.5 km wide, and 300 m high is being obliquely subducted beneath the landward trench slope. On five seismic lines the décollement rises over the horst and then descends into the next incoming graben as the fault zone maintains a specific stratigraphic level. The undulating geometry of the décollement implies that the subducting grabens are not sites for sediment entrapment and subduction and that the horsts are not causing tectonic erosion of the landward trench wall. Substantial dewatering within the subducting sediments is documented within about 4 km of the deformation front. The dewatering may favor development of bedding-parallel zones of low shear strength within the subducting sediments and the master décollement may seek one of these zones.