ALBERT

Description: In July 2003 cruise SO173-1 was conducted with RV Sonne to collect various types of marine seismic data off Costa Rica and Nicaragua for the Collaborative Research Project SFB 574. Two very high-resolution deep-tow multichannel seismic surveys were carried out to study mound structures and fluid escape features on the continental margin of Middle America. Whereas the first survey revisited Mound Culebra off Costa Rica (see Bialas et al.), a new deep-tow seismic reconaissance survey investigated an area of approximately 700 km² size on the continental slope off Nicaragua. Water depths ranged between 1000 and 2300 m. According to a previously recorded multibeam bathymetry several mound structures of unknown height and size were expected in this area.Both bathymetry and preliminary brute stacks of the deep-tow seismic profiles show that the continental margin off Nicaragua is dominated by deeply incised canyons and numerous mounds as well as slides on the lower continental slope. The two most prominent mounds are located on the uppermost continental slope. The largest one rises about 300 m above the sea floor. The deep-tow seismic sections show well stratified sedimentary layers of about 250 - 300 m thickness. They are based by a band of strong reflections, which seem to form the recent base of the deeply incised canyons. At some locations the channel incision has stopped some meters above and at other locations has cut into the high reflectivity band, but none of the channels cut through this reflection band. Underneath occurs a less reflective zone, in which a BSR is visible in most parts of the survey area. This BSR varies in strength along all profile lines. Beneath some mound structures the BSR appears to be continuous, beneath other mound structures it vanishes. Final data processing has to proof, if the BSR can be traced underneath these mounds, too.