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We present new seismic data from the Gulf of Lion located east of the Pyrenees on the continental shelf of the Mediterranean Sea. The deep penetration LISA (Ligurian–Sardinia Sea) seismic lines, the shots of the LISA cruise recorded on land, and the high definition ELF seismic sections allow us to present a complete picture of the tectonics in this area from the surface to the Moho level, and also to document late Miocene–early Pliocene extensional tectonics in the area. Previous studies show a prominent thinning of the crust observed from the Pyrenees towards the Gulf of Lion. The Moho depth varies from 48 km beneath the Axial Range crust (thickened during the Pyrenean Eocene Orogeny) to 21 km below the Catalan Basin in the Gulf of Lion. This crustal thinning occurred mainly during the early Miocene extension of the Mediterranean Sea. Balanced reconstructed geological sections derived from reflection and refraction seismic data allow us to evaluate the stretching factors at the crustal level. A maximum extension of 25 km is computed for the Catalan Basin area. This extension is related to detachments that penetrate the crust as deep as 11 km to the base of the brittle crust. These intra basement detachments have been confused in the past with the Paleozoic acoustic basement. The detachments show a clear listric shape and the geometry of horst and grabens can be explained by a hanging wall and footwall configuration with isostatic rebound of the footwall. The uplift in the Eastern Pyrenees (Alberes and Canigou Massifs), on the other hand, is related to the late Miocene–early Pliocene extension we mapped in the area. These elevated features, probably formed by isostatic rebound, are surrounded by deep basins such as the Roussillon and El Emporda depressions. A 1.7 km uplift during the late Miocene–early Pliocene is computed in the offshore part of the Alberes Massif. The cause of this Late Miocene–early Pliocene extension is not well explained although an uplift related to the Messinian desiccation or a thermal anomaly in the mantle have been proposed. The relationship between the Eastern Pyrenees and the Gulf of Lion is governed by NE–SW transfer faults. These faults represent the southwestern limits of the Gulf of Lion basins. Although much seismicity is recorded in the Eastern Pyrenees, we do not see evidence of present tectonics in the Gulf of Lion as the extensional faults were active only until the early Pliocene. Therefore, the present stress is probably compressional, as shown by the focal mechanisms of the earthquakes, although the trends of compressional vectors are divergent in Spain and France.

Within the framework of the joint FAUST (French Australian Seismic: Transect) program, the Australian research vessel Rig-Seismic recorded a series of multichannel seismic profiles between the New Hebrides Arc and the Australian Margin. The very high quality of these profiles allows the examination of the continental or oceanic basement over the whole area surveyed. In basins beneath the eastern margin of the northern Lord Howe Rise and the New Caledonia Basin, where the crust is thinner, the Moho discontinuity is present at about 8.5 seconds two-way time (TWT) (about 12–13 km) on the profiles processed onboard. The data collected suggest that the sedimentary section within the basins includes syn-rift Cretaceous sediments that are not yet definitively identified. The Upper Eocene-Middle Oligocene subduction of the Australian plate beneath the Pacific plate is highlighted by thrust faults concentrated along the Lord Howe, Norfolk and Fairway Ridges. This episode probably corresponds to the period of convergent tectonism associated with the Upper Eocene obduction of the New Caledonian ophiolites.

Summary Stacking methods applied to wide arrays of long period stations provide a powerful tool to investigate the physical properties of the upper mantle by means of higher modes. In this paper, the UC-diagram technique of Cara (1976) is applied to a subset of records first used by Nolet (1975, 1976) to determine the dispersion of higher Rayleigh modes in western Europe. For the fundamental and first higher modes, the phase velocities found in the present study are very similar to those first obtained by Nolet (1976) but the second made exhibits slightly higher velocities in the period range 35–55 s. As a consequence, the low density channel proposed by Nolet (1977) under western Europe is no longer necessary to explain the higher mode data and further investigation will be necessary to obtain more details in the density distribution with depth. A new set of higher Love mode phase velocities has been also obtained in western Europe. As it has already been observed for the fundamental mode in several parts of the world, the phase velocities found here for the first and second higher modes are too large compared to those predicted by the models fitting the Rayleigh mode data. It is very difficult to interpret both the Love and Raylcigh wave data in terms of isotropic S velocity distribution and an anisotropy of the elastic parameters of the upper mantle is probable under western Europe. Another wide continental region, northern Eurasia, is investigated from higher Rayleigh mode phase velocities measured for the path between northern Japan and western European stations. A nearly constant 4.5–4.6 km s−1S velocity is required by these data in the uppermost 200 km of the upper mantle. Unlike the higher mode data obtained for the central and eastern United States by Cara (1978) or for western Europe in this paper, no wide low velocity channel is necessary to explain the higher mode data in this large arca.