Objective
For hydrocarbon exploration a new refraction seismic measuring system based on ocean bottom seismographs (obs) should be developed together with fast data processing and evaluation techniques and tested in a rather complex area offshore western greece.
In the obs recorded seismic sections the first and later arrivals could clearly be identified up to epicentral distances of 60 km. The selections showed strong wide angle reflections from the cristalline basement. By evaluating these wide angle reflections and the first arrivals the sedimentary structures beyond the top of the above mentioned limestones (acoustic basement in normal incidence reflection seismic sections) down to the cristalline basement in depths of 6-7 km could be deliniated. This shows that additional measurements with the obs based technique can be a great help in investigating sedimentary structures, where normal incidence reflection seismics fail to penetrate interfaces with high acoustic impedance contrasts.
In an area offshore w. Greece up to 30 obs were deployed every 3 km on 3 profiles of 40 - 60 km length. On the lines 12.5 km shots were fired in regular intervals of 400 m. The analogue recorded geophone and hydrophone traces were digitized, filtered,
deconvolved and plotted into seismogram sections. The data evaluation was subsequently performed using (1) a combined delay time and ray tracing procedure, (2) a more sophisticated ray tracing technique, deployed interactively and (3) a ray method for computation of amplitudes and synthetic seismograms.
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DEM - Demonstration contractsCoordinator
200 Hamburg
Germany