Evidences of seismic flysch outline in the Gulf of Trieste

The Gulf of Trieste is a shallow epicontinental basin that is part of the northern Adriatic Sea. During the last decade, the National Institute of Oceanography and Experimental Geophysics (OGS) carried out three geophysical surveys in the Gulf of Trieste, collecting 630 km of Multichannel Seismic reflection profiles. Part of this dataset was used in the present work to build a tomographic velocitydepth model in the eastern portion of the gulf. This model gives information on the main surfaces and units (i.e., quaternary sediments, turbiditic flysch and carbonates) up to a depth of about 1600 m below sea level. Two main tomographic methods were applied in this work, allowing to build interval velocity models for both reflected and refracted seismic waves and to produce a detailed depth seismic section of the geological structures in the study area. In particular, the average vertical and horizontal P-wave velocities at the top of the flysch unit are about 2900 m/s and 3700 m/s, respectively, denoting a pronounced anisotropic effect. The large discrepancy between the two tomographic velocity values is here justified using the generalized Backus theory, and therefore interpreted as the anisotropic effect due to the laminated internal structure of the flysch unit.