664 km on 6 lines in Central Atlantic Ocean, VEMA Fracture Zone

Gravity; Seismic reflection

Multi-channel seismic reflection systems; seismic refraction systems; gravimeters; satellite positioning systems

During summer 1992 OGS, in cooperation with the Istituto di Geologia Marina (CNR), conducted a seismic survey of the Central Atlantic Ocean. The aim of the survey was the investigation of two fracture zones; potential sites for drilling as part of the ODP program. The second site investigated was the VEMA fracture zone. Vema is a transform fault which displaces the Mid Atlantic Ridge by about 320 km. The main scientific objective was the detection of the thickness and the acoustic characteristics of the limestone 'caps' present on the southern part of the fault. The seismic data have been collected with the following sampling parameters: Coverage = 3000 % Sample Rate = 2 ms Shot Interval = 50 m Streamer Length = 3000 m Streamer Depth = 12 m Group Interval = 25 m Number of Groups = 120 Record Length = 17-20 sec Air-Guns: - Total Volume = 80-23 l - Pressure = 140 bar - Depth = 6-3 m

National Institute of Oceanography and Applied Geophysics - OGS, Division of Geophysics
Borgo Grotta Gigante 42/c
Sgonico (Trieste),

34010
Italy