CRUSTAL AND VELOCITY STRUCTURE OF THE VALENCIA TROUGH (WESTERN MEDITERRANEAN) .2. DETAILED INTERPRETATION OF 5 EXPANDED SPREAD PROFILES

A dense grid of single-ship and two-ship multichannel seismic profiles has been used to study the crustal structure of the Valencia trough (western Mediterranean). Five full ESPs (Expanded Spread Profiles) and one half ESP (ESP 2) with a total shot-receiver range up to 100 km were shot as part of the survey. The interpretation of 5 ESPs is discussed here in detail. These ESPs were analyzed by matching travel-time and amplitude variations in both χ-t and τ-p domains. The final travel-time fit of the synthetic to real data is good enough to be confident that seismic phases have been correctly identified. The ESPs show clear seismic arrivals up to ranges of 100 km. Middle and lower crustal arrivals and wide-angle Moho reflections can be seen in all profiles. The ESPs are located on the Catalan continental shelf and the Mallorca margin (ESPs 6, 5, 3) and in the trough (ESPs 2, 4, 7). In the northeast part of the trough (ESP 2), the crustal velocity structure is of the oceanic type, where typical velocities of oceanic layers 2 and 3 are recognised. In the centre of the trough, the results from ESP 4, based only on travel-time modelling, indicate that a thinned continental crust (~ 14 km thick) underlies that part of the trough, thickening towards the southwest where the crust is 16 km thick beneath ESP 7. In the Catalan and Balearic margins, the total crustal thicknesses are about 20 and 23 km, respectively. The upper and middle crusts are characterised by velocities ranging from 5.9-6.0 to 6.4 km/s, whereas in the lower crust velocities vary from 6.4 to 7.0 km/s. An anomalous low uppermost-mantle velocity is found beneath the basin that ranges from 7.6 km/s in the Catalan margin to 8.0 km/s in the southeast part of the trough. © 1992