Open AccessA seismic refraction experiment in the Tyrrhenian Sea
Author(s) -
Duschenes J.,
Sinha M. C.,
Louden K. E.
Publication year - 1986
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1986.tb05175.x
Subject(s) - geology , crust , oceanic crust , continental crust , seafloor spreading , seismology , seismic refraction , oceanic basin , abyssal plain , transition zone , geophysics , structural basin , subduction , tectonics , paleontology
Summary. We present the results of two 100 km long reversed seismic refraction lines shot in the Tyrrhenian Sea, using explosive sources and ocean‐bottom receivers. The results have been interpreted using ray‐tracing through laterally varying structures. The more easterly line, T2, was shot in the central part of the Tyrrhenian abyssal plain, in a water depth of 3.5 km. The crust here is shown to be oceanic in character, but to exhibit significant lateral heterogeneity. The upper part of the crust (layer 2) contains a steep velocity gradient from about 4 to over 6 km s −1 at a depth of typically 2 km. The lower part of the crust (layer 3) contains a smaller velocity gradient, from 6.6 to 6.9 km s −1 at the base of the crust. Total crustal thickness is between 6 and 8 km. The other line, T1, carried out in the Cornaglia Basin in 2.7 km of water, reveals a more complicated velocity structure. We conclude that its southern half is underlain by oceanic crust, similar to that observed at T2. However, its northern half appears to be underlain by crust of similar thickness, but in which seismic velocities increase slowly with depth from 4.9 km s −1 immediately below the superficial sediments to 6.3 km s −1 at the Moho. We interpret this latter structure as thinned continental crust. Surprisingly neither the seafloor topography nor the depth to Moho reflect the transition from oceanic to continental crust. We infer from these results that although the southern and eastern parts of the Tyrrhenian basin were formed primarily by seafloor spreading, much of the basin north of about 40°N and probably including some areas with water depths in excess of 3 km, is underlain by thinned continental crust. The evolution of the northern part of the Tyrrhenian basin must therefore have occurred chiefly through a process of continental extension, which in some areas has reduced crustal thickness to as little as 6–8 km. South of 40°N, however, extension results in the generation of young oceanic lithosphere, which now underlies most of the deepest parts of the basin.