Seismic Imaging of the Eastern Algerian Margin off Jijel from Wide-angle and Seismic Reflection Data

Abstract

This study presents the results of a deep seismic survey across the north Algerian margin, based on the combination of 2D multi-channel and wide-angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a North-South line extending 180 km off Jijel into the Algerian offshore basin, and 25 land stations deployed along a 100 km-long line, cutting through the Lesser Kabylia and the Tellian thrust-belt. The final model obtained using forward modeling of the wide-angle data and pre-stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin. The sedimentary layers in the Algerian basin are 3.75 km thick to the north and up to 4.5 to 5 km thick at the foot of the margin. They are characterized by seismic velocities from 1.9 km/s to 3.8 km/s. Messinian salt formations are about 1 km thick the study area, and are modeled and imaged using a velocity between 3.7 km/s to 3.8 km/s. The crust in the deep sea basin is about 4.5 km thick and of oceanic origin, presenting two distinct layers with a high gradient upper crust (4.7 km/s - 6.1 km) and a low gradient lower crust (6.2 km/s - 7.1 km/s). The upper mantle velocity is constrained to 7.9 km/s. The ocean-continent transition zone is very narrow between 15 km to 20 km wide. The continental crust reaches 25 km depth as imaged from the most landward station and thins to 5 km over a less than 70 km distance. The continental crust presents steep and asymmetric upper and lower crust geometry, possibly due to either asymmetric rifting of the margin, an underplated body, or flow of lower crustal material towards the ocean basin. Present-time deformation, as imaged from 3 additional seismic profiles, is characterized by an interplay of gravity-driven mobile-salt creep and active thrusting at the foot of the tectonically inverted Algerian margin. (Go to www.searchanddiscovery.com to see figures.)

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015