SeaMARC II study of a giant submarine slump on the northern Chile continental slope

Abstract

A giant submarine slump, encompassing a 91‐km by 26‐km block, occurring on the continental slope offshore Iquique, Chile, was identified during a SeaMARC II survey. Utilizing SeaMARC II side‐scan imagery, bathymetry, and seismic reflection data, five morphostructural zones of the slump were identified: the fissured zone, scar zone, tensional depression, central block, and front zone. The fissured zone was developed on the crown of the slump; the scar zone is characterized by scars with the crescent‐shaped slip surfaces and throws ranging from 200 m to 50 m. The tensional depression zone is marked by an area voided by mass slumping, while the central block morphology was formed by uplift. The front zone is comprised of both compressional and tensional subzones. The compressional subzone is characterized by a relative topographic low, on the middle slope, whereas the extensional subzone is characterized by a convex pattern of alternated ridges and hollows, which may represent the debris of the slump on the lower slope. The formation of the slump was strongly influenced by the subduction of the Nazca plate beneath the Chile continental margin, which resulted in the subsidence of the continental slope with a resultant increase in the slope gradient and pore‐water pressure in the sedimentary layers. Slump formation was further facilitated by the development of a complex fault system associated with the subduction and by the triggering effect of earthquakes in the area.