The upper-mantle structure of the Western Mediterranean Region, i.e.
the Western Mediterranean basins with the surrounding land areas,
has been investigated by means of surface-wave analysis. Phase velocities
of teleseismic Rayleigh waves have been obtained from the records
of a specially designed long-period seismic station network. The
dispersion data have been regionalized employing a computerized procedure
and have then been inverted by means of the so-called ?hedgehog?
method.
The upper mantle shows pronounced lateral heterogeneities which are
correlated with the tectonic activity of the region. Some deep anomalous
features are revealed such as the ?soft? continent-like structure
of the lithosphere under the Alboran Sea, the absence of lithospheric
roots below the mountain range of the High Atlas, the continental
platform-like upper mantle along the northern margin of Africa. While
the upper mantle under the Provençal and the Algerian basins shows
oceanic or back-arc basin-like structure, the Balearic Promontory
and particularly the Valencia Trough are shown to possess upper mantle
structure with characteristics close to those of a continental rift
system. We therefore suggest that the boundary?at the level of the
upper mantle?between the African and the European plates, should
rather be viewed as a broad transition zone involving the upper mantle
of the entire Western Mediterranean region across which the plate
interaction takes place.