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  • 1
    Publication Date: 2018-05-31
    Description: Recent advances in seafloor and subsurface imaging allow accurately mapping and characterizing the kinematic pattern and the style of deformation of submarine faults with unprecedented detail to better assess seismic and tsunami hazards in coastal areas. The Alboran Sea is a Neogene basin generated by crustal extension associated with the subduction in the Gibraltar Arc. At present, several fault systems absorb part of the strain related to the NW-SE convergence (4-5.5 mm/yr) between the African and Eurasian plates. Consequently, the Alboran Sea shows a significant seismic activity. New high-resolution bathymetric and seismic data reveal the presence of poorly known pervasive fault systems in the central part of the Alboran Sea, the Averroes Fault (AF) and the North Averroes Faults (NAFs). These are secondary fault systems located between two large active faults, the Carboneras and Yusuf/Alboran Ridge faults, and represent a hitherto unrecognized seismogenic potential. The WNW-ESE trending AF and NAFs, which may have evolved since the Lower Pliocene (4.57 Ma), are subvertical right-lateral strike-slip active faults since: a) are offsetting the Quaternary sedimentary units and deforming the seafloor; and b) produce a right-lateral displacement of the northwestern margin of the Alboran Channel and across the Adra Ridge North. Given that the AF and NAFs have formed in a continental crust and that are located in a zone surrounded by some of the main active faults in the Alboran Sea, we postulate that these fault systems have been developed into a distributed dextral strike-slip shear zone with the local bulk shear striking approximately N90º. Considering their surface length they could generate earthquakes with magnitudes (Mw) between 6.3 and 7.2, but reaching 7.6 when AF and Yusuf Fault are linked. The high resolution bathymetry map has allowed us measuring lateral offsets produced by the AF and NAFs. Assuming that these displacements have been accumulated during the last 4.57 Ma, the calculated lateral slip rate for AF is approximately1.5 mm/yr and range between 0.2 and 0.4 mm/yr for the NAFs. Our results evidence the importance of the kinematic and seismogenic characterization of secondary fault systems to better comprehend earthquake and tsunami hazards.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
    Publication Date: 2018-12-14
    Description: Highlights • Northern Hispaniola Margin is studied with new high-resolution bathymetry and vintage seismic data. • Northern Hispaniola Deformed Belt forms an active N-verging fold-and-thrust imbricate system. • Gravity failures are frequent features in the Northern Hispaniola Margin and Bahamas Banks slope. • Oblique collision accelerates the Bahamas Carbonate Province collapse and retreat. • New observations help the assessment of tsunami hazards in the Northern Caribbean region. Abstract The northern margin of Hispaniola records the oblique collision/underthrusting of the Bahamas Carbonate Province with the island-arc. Due to the collision, northern Hispaniola has suffered several natural disasters caused by major earthquakes and tsunamis, such as the historic earthquake of 1842, the tsunami caused by earthquake-driven slumping in 1918 in the Mona Passage, the seismic crisis of 1943–1953 with five events of M 〉 7.0 or the seismic crisis of 2003 with a main shock of M6.3 and a large aftershock of M5.3. Using new swath multibeam bathymetry data and vintage single- and multi-channel seismic profiles, we have performed a regional scale analysis and interpretation of the shallow surface and active processes along the northern margin of the Dominican Republic. We have identified three morphostructural provinces: a) the Bahamas Banks, b) the Hispaniola Trench and c) the Insular Margin, which are divided into two tectonic domains, the Collision Domain and Underthrusting Domain. The southern slope of the Bahamas Carbonate Province shows a very irregular morphology produced by active erosive processes and normal dip-slip faulting, evidence of an extensional tectonic regime and margin collapse. This collapse is of major extent in the Oblique Collision Domain where there are erosive and fault escarpments with higher dip-slip fault throws. The Hispaniola Trench, is formed by the Caicos and Hispaniola basins in the underthrusting domain, and by the Santisima Trinidad and Navidad basins in the Oblique Collision Domain. They have a flat seafloor with a sedimentary filling of variable thickness consisting of horizontal or sub-horizontal turbiditic levels. The turbiditic fill mostly proceeds from the island arc through wide channels and canyons, which transports sediment from the shelf and upper slope. The Insular Margin comprises the Insular Shelf and the Insular Slope. The active processes are generated on the Insular Slope where the Northern Hispaniola Deformed Belt is developed. This Deformed Belt shows a very irregular morphology, with a WNW-ESE trending N verging imbricate thrust-and fold system. This system is the result of the adjustment of the oblique collision/underthrusting between the North American plate and the Caribbean plate. In the Oblique Underthrusting Domain the along-strike development of the imbricate system is highly variable forming salients and recesses. This variability is due to along-strike changes in the sediment thickness of the Hispaniola Trench, as well as to the variable topography of the underthrusting Bahamas Carbonate Province. In the Oblique Collision Domain, the morphology of the Insular Slope and the development of the Deformed Belt deeply change. The imbricate system is barely inferred and lies upslope. These changes are due to the active collision of Bahamas Carbonate Province with the Insular Margin where the spurs are indented against the Insular Margin. Throughout the entire area studied, gravitational instabilities have been observed, especially on the Insular Margin and to a lesser extent on the southern slope of the Bahamas Carbonate Province. These instabilities are a direct consequence of the active underthrusting/collision process. We have mapped large individual slumps north of Puerto Plata in the Oblique Underthrusting Domain and zones of major slumps in the Oblique Collision Domain. These evidences of active processes must be considered as near-field sources in future studies on the assessment of tsunami hazards in the region.
    Type: Article , PeerReviewed
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