Potential geologic hazards on the eastern Gulf ofCadiz slope (SW Spain)

摘要

Gelogic hazards resulting from sedimentary,oceanographic and tectonic processes affect more than one third ofthe offshore Gulf of Caidiz, and are identified by interpreting high-resolution seismic profiles and sonographs. Hazards ofsedimentary origin include the occurrence of slope instabilityprocesses in the form of single or multiple slumps occupying up to147km2 mainly concentrated in the steeper, upper slope area.Besides the presence of steep slopes, the triggering of submarinelandslides is probably due to seismic activity and favoured by thepresence of biogenic gas within the sediment. Gassy sediments andassociated seafloor pockmarks cover more than 240 km2 in theupper slope. Hazards from oceanopraphic processes result fromthe complex system of bottom currents created by the interactionof the strong Mediterranean Undercurrent and the rough seafloorphysiography. The local intensification of bottom currents isresponsible for erosive processes along more than 1900 km2 in theupper slope and in the canyons eroded in the central area of theslope, undermining slopes and causing instability. The strongbottom currents also create a mobile seafloor containing bedformsin an area of the Gulf that extends more than 2500km2, mostly inthe continental slope terraces. Hazards of tectonic origin areimportant because the Gulf of Cadiz straddles two major tectonicregions, the Azores-Gibraltar fracture zone and the Betic range,which results in diapir uplift over an area of more than 1000km2,and in active seismicity with earthquakes of moderate magnitude.Also, tsunamis produced by strong earthquakes occur in the Gulfof Cadiz, and are related to the tectonic activity along the Azores-Gibraltar fracture zone.