Resumen: There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and
tsunami hazard assessments [e.g., ten Brink and Lin, 2004; ten Brink et al., 2004; Grindlay
et al, 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary.
Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies. The cruise collected multibeam bathymetry, gravity, magnetic, high-resolution seismic, deep seismic sounding, and multichannel seismic reflection data, which are currently being processed and interpreted (Table 1). In early November 2005, 10 ocean-bottom seismometers (OBS) that had been deployed northeast of Puerto Rico and the Virgin Islands (Figure 1) during the cruise were recovered. These OBS recorded data during the cruise and the local seismicity between April and October 2005.
Palabras clave: Caribbean, Active tectonics, Marine geophysics
Resumen: One recent project, Caribbean–North American Plate Boundary Analysis: From Beata Ridge (Dominican Republic) to Anegada
Passage (Lesser Antilles) (CARIBENORTE), has conducted onshore and offshore surveys in the Dominican Republic
region to study subduction,
strike- slip, and collision processes in this area. This survey included a cruise aboard the Spanish R/V Hespérides in April 2009 and simultaneous fieldwork onshore. The CARIBE NORTE project complements the study of the northeastern Caribbean plate
boundary carried out during the Structure and Geodynamics of the Northeastern Boundary of the Caribbean Plate: Puerto
Rico (GEOPRICO- DO) project in 2005 [Carbó et al., 2005].
Resumen: The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate
geometry difficult. In addition, the compressive deformational features observed
in the upper crust and sandbox kinematic modeling do not
necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate’s interior
beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction
process yield a regional mass deficit beneath the island arc
independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N–S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8 to 30 reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin.
Resumen: Multibeam bathymetry data acquired during the 2005 Spanish R/V Hespérides cruise and reprocessed
multichannel seismic profiles provide the basis for the analysis of the morphology and deformation in the
central Muertos Trough and Muertos thrust belt. The Muertos Trough is an elongated basin developed where
the Venezuelan
Basin crust is thrusted under the Muertos fold-and-thrust belt. Structural variations along the
Muertos Trough are suggested to be a consequence of the overburden of the asymmetrical thrust belt and by
the variable nature of the Venezuelan Basin crust along the margin. The insular slope can be divided into
three east–west trending slope provinces with high lateral variability which correspond to different accretion
stages: 1) The lower slope is composed of an active sequence of imbricate thrust slices and closed fold axes,
which form short and narrow accretionary ridges and elongated slope basins; 2) The middle slope shows a
less active imbricate structure resulting in lower superficial deformation and bigger slope basins; 3) The
upper slope comprises the talus region and extended terraces burying an island arc basement and an inactive
imbricate structure. The talus region is characterized by a dense drainage network that transports turbidite
flows from the islands and their surrounding carbonate platform areas to the slope basins and sometimes to
the trough. In the survey area the accommodation of the ongoing east–west differential motion between the
Hispaniola and the Puerto Rico–Virgin Islands blocks takes place by means of diffuse deformation. The asymmetrical development of the thrust belt is not related to the geological conditions in the foreland, but rather may be caused by variations in the geometry and movement of the backstop. The map-view curves of the thrust belt and the symmetry of the recesses suggest a main north–south convergence along the Muertos margin. The western end of the Investigator Fault Zone comprises a broad band of active normal faults which result in high instability of the upper insular slope.
