Insights into active deformation in the Gulf of Cadiz from new 3-D seismic and high-resolution bathymetry data

The nature of active deformation in the Gulf of Cadiz is important for developing a better understanding of the interplate tectonics and for revealing the source of the 1755 Great Lisbon earthquake. New, high-resolution 3-D seismic data reveal a classic pull-apart basin that has formed on an east striking fault in the Southern Lobe of the Gulf of Cadiz accretionary wedge. Geometrical relationships between an array of faults and associated basins show evidence for both dextral and sinistral shear sense in the Southern Lobe. Strike-slip faulting within the lobe may provide a link between frontal accretion at the deformation front and extension and gravitational sliding processes occurring further upslope. Inception of the strike-slip faults appears to accommodate deformation driven by spatially variant accretion or gravitational spreading rates, or both. This implies that active deformation on strike-slip faults in the Southern Lobe is unrelated to the proposed modern inception of a transform plate boundary through the Gulf of Cadiz and underscores the importance of detailed bathymetric analysis in understanding tectonic processes.