Wave Propagation Studies of the Central Mediterranean Sea Using Ocean Bottom Seismometers (Report for Office of Naval Research Contract N00014-77-C-0606. Modification #P00007)

Ocean bottom seismometers (OBS) were deployed in the Mediterranean for two refraction surveys shot with underwater sound signal (SUS) charges. The digital data were analyzed to determine 1) the attenuation features, signal/noise (S/N) characteristics and frequency content of water waves and body waves, and 2) the crustal structure of the test areas. The attenua­ tion of water-wave signals was fairly uniform within the passband of the OBS (10-31 HZ) and was greater in deep water than in shallower water, and body waves were much more strongly attenuated than water waves. The S/N ratios were much larger for the SUS shots detonated at 91 m depth than for those detonated at 244 m depth. The body-wave data indicated the presence of a layer with P-wave velocity of 3.8 km/sec about 0.8 km below mean sea level in one test area. Probably this is a Miocene evaporite sequence.