Upper mantle compressional velocity structure beneath the West Mediterranean Basin

P waveforms of regional crustal earthquakes have been modeled to obtain an upper mantle compressional velocity model for the West Mediterranean Basin. Data come from long-period stations of the World-Wide Standardized Seismograph Network and broadband stations located in the Iberian Peninsula. Synthetic waveforms have first been computed for published velocity models corresponding to different tectonic provinces and obtained with analogous techniques. A model that strongly improves the fits to the data is then derived. The proposed model is characterized by a 100-km-thick lid overlaying a not very pronounced low-velocity zone and a 3% discontinuity at 368 km where an increase of the velocity gradient also occurs. These features could be explained either as a deflection of the olivine-to-spinel phase transition, regionally detected at about 395 km, resulting from the lower temperature produced by the subduction of the African plate, or as being due to the presence below 300 km depth of a layer of silicate melt, producing a strong reflection from its bottom, and a more usual depth for the olivine-spinel transition. In both cases the occurrence of relatively low velocities beneath 300 km is interpreted as being caused by the presence of melt associated with the northward dipping subduction of the African plate.

[1]  G. Nolet,et al.  P and S deep velocity structure of the Hellenic area obtained by robust nonlinear inversion of travel times , 1997 .

[2]  R. Jeanloz.  Earth dons a different mantle , 1995, Nature.

[3]  Guust Nolet,et al.  Seismic heterogeneity in the upper mantle , 1994 .

[4]  C. Bina,et al.  Frequency dependence of the visibility and depths of mantle seismic discontinuities , 1994 .

[5]  G. Nolet,et al.  Low S velocities under the Tornquist‐Teisseyre zone: Evidence for water injection into the transition zone by subduction , 1994 .

[6]  M. J. R. Wortel,et al.  Regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle: The Mediterranean region , 1994 .

[7]  G. Nolet,et al.  Shear‐wave velocity variations in the upper mantle beneath central Europe , 1994 .

[8]  P. Shearer.  Global mapping of upper mantle reflectors from long-period SS precursors , 1993 .

[9]  J. Vidale,et al.  Sharpness of upper-mantle discontinuities determined from high-frequency reflections , 1993, Nature.

[10]  D. Helmberger,et al.  Upper mantle compressional velocity structure beneath the northwest Atlantic Ocean , 1993 .

[11]  Robert D. van der Hilst,et al.  Travel-time tomography of the European-Mediterranean mantle down to 1400 km , 1993 .

[12]  W. Spakman,et al.  The P-wave velocity structure of the mantle below the Iberian Peninsula: evidence for subducted lithosphere below southern Spain , 1993 .

[13]  Rob Westaway,et al.  Seismic moment summation for historical earthquakes in Italy: Tectonic implications , 1992 .

[14]  A. Thompson.  Water in the Earth's upper mantle , 1992, Nature.

[15]  L. Stixrude,et al.  Petrology, elasticity, and composition of the mantle transition zone , 1992 .

[16]  R. Madariaga,et al.  Intermediate and deep earthquakes in Spain , 1991 .

[17]  T. Jordan,et al.  Mantle layering from ScS reverberations: 3. The upper mantle , 1991 .

[18]  Guust Nolet,et al.  Tomographic imaging of subducted lithosphere below northwest Pacific island arcs , 1991, Nature.

[19]  T. Ahrens,et al.  The equation of state of a molten komatiite: 1 Shock wave compression to 36 GPa , 1991 .

[20]  H. Mao,et al.  Experimental determination of element partitioning and calculation of phase relations in the MgO‐FeO‐SiO2 system at high pressure and high temperature , 1991 .

[21]  J. Plomerová,et al.  The deep lithosphere in the Alps: a model inferred from P residuals , 1990 .

[22]  D. Helmberger,et al.  Upper mantle P velocity structure of the Canadian Shield , 1989 .

[23]  J. Trampert,et al.  Large-scale P-velocity structures in the Euro-Mediterranean area , 1989 .

[24]  T. Katsura,et al.  The system Mg2SiO4‐Fe2SiO4 at high pressures and temperatures: Precise determination of stabilities of olivine, modified spinel, and spinel , 1989 .

[25]  M. Cocco,et al.  Evidence for the variation of stress drop between normal and thrust faulting earthquakes in Italy , 1989 .

[26]  Roel Snieder,et al.  Large-scale waveform inversions of surface waves for lateral heterogeneity , 1988 .

[27]  Hanneke Paulssen,et al.  Evidence for a sharp 670‐km discontinuity as inferred from P‐to‐S converted waves , 1988 .

[28]  Nathalie Wajeman.  Detection of underside P reflections at mantle discontinuities by stacking broadband data , 1988 .

[29]  Ichiro Nakanishi,et al.  Reflections of P′P′ from upper mantle discontinuities beneath the Mid-Atlantic Ridge , 1988 .

[30]  James Jackson,et al.  Active tectonics of the Adriatic Region , 1987 .

[31]  H. Paulssen.  Lateral heterogeneity of Europe's upper mantle as inferred from modelling of broad-band body waves , 1987 .

[32]  B. Wood,et al.  Olivine‐spinel transitions: Experimental and thermodynamic constraints and implications for the nature of the 400‐km seismic discontinuity , 1987 .

[33]  D. L. Anderson,et al.  Transition region of the Earth's upper mantle , 1986, Nature.

[34]  Jean-Claude Sibuet,et al.  Geological evolution of the tethys belt from the atlantic to the pamirs since the LIAS , 1986 .

[35]  S. Mueller,et al.  The Western Mediterranean Region as an upper-mantle transition zone between two lithospheric plates , 1985 .

[36]  S. Roecker.  Velocity structure in the Izu-Bonin seismic zone and the depth of the olivine-spinel phase transition in the slab , 1985 .

[37]  D. Helmberger,et al.  Upper mantle shear structure beneath the northwest Atlantic Ocean , 1984 .

[38]  Don L. Anderson,et al.  Composition of the upper mantle: Geophysical tests of two petrological models , 1984 .

[39]  James J. Simpson,et al.  A simple model of the 1982‐83 Californian "El Nino" , 1984 .

[40]  M. Toksöz,et al.  On melting of the subducted oceanic crust: effects of subduction induced mantle flow , 1983 .

[41]  F. Ferrucci,et al.  A 550 km long moho traverse in the Tyrrhenian Sea from O.B.S. recorded PN waves , 1983 .

[42]  Don L. Anderson,et al.  Travel times and station corrections for P waves at teleseismic distances , 1983 .

[43]  P. Wyllie.  Subduction products according to experimental prediction , 1982 .

[44]  R. Scarpa.  Travel-time residuals and three-dimensional velocity structure of Italy , 1982 .

[45]  L. Burdick.  A comparison of the upper mantle structure beneath North America and Europe , 1981 .

[46]  C. Frohlich,et al.  The P velocity within the Tonga Benioff Zone determined from traced rays and observations , 1981 .

[47]  Barbara Romanowicz,et al.  A study of large‐scale lateral variations of P velocity in the upper mantle beneath western Europe , 1980 .

[48]  G. Panza,et al.  The gross features of the lithosphere-asthenosphere system in Europe from seismic surface waves and body waves , 1980 .

[49]  G. Nolet,et al.  New inferences from higher mode data in western Europe and northern Eurasia , 1980 .

[50]  G. Calcagnile,et al.  P-Wave Velocities in the Upper Mantle Beneath Fennoscandia and Western Russia , 1976 .

[51]  S. Solomon,et al.  Elevation of the olivine-spinel transition in subducted lithosphere: Seismic evidence , 1975 .

[52]  A. E. Ringwood,et al.  The petrological evolution of island arc systems , 1974, Journal of the Geological Society.

[53]  A. Bottari,et al.  Some results for the middle western Mediterranean basin from the study of Pn waves , 1974 .

[54]  K. Kaila,et al.  Upper mantle shear-wave velocity structure in the Japan region , 1974, Bulletin of the Seismological Society of America.

[55]  D. Helmberger.  Long-period body-wave propagation from 4° to 13° , 1972, Bulletin of the Seismological Society of America.

[56]  K. Kaila,et al.  Upper mantle P-wave velocity structure in the Japan region from travel-time studies of deep earthquakes using a new analytical method , 1971, Bulletin of the Seismological Society of America.

[57]  G. Payo.  Crustal structure of the Mediterranean Sea Part II. Phase velocity and travel times , 1969 .

[58]  Michael J. Berry,et al.  Structure of the upper mantle under the western Mediterranean basin , 1967 .

[59]  G. Payo.  Crustal structure of the Mediterranean sea by surface waves. Part I: Group velocity , 1967 .

[60]  Walter I. Futterman,et al.  Dispersive body waves , 1962 .

[61]  I. Lehmann.  S and the Structure of the Upper Mantle , 1961 .

[62]  W. McDonough,et al.  Mineralogy and composition of the upper mantle , 1998 .

[63]  S. Sipkin,et al.  Seismic evidence for silicate melt atop the 410-km mantle discontinuity , 1994, Nature.

[64]  C. Agee,et al.  Olivine flotation in mantle melt , 1993 .

[65]  J. Dewey,et al.  Kinematics of the western Mediterranean , 1989, Geological Society, London, Special Publications.

[66]  I. Nakanishi.  A search for topography of the mantle discontinuities from precursors to P'P'. , 1989 .

[67]  M. H. Worthington,et al.  The travel time of P seismic waves in Europe and Western Russia , 1977 .

[68]  I. Lehmann.  Velocities of longitudinal waves in the upper part of the earth's mantle , 1959 .

[69]  Ș.,et al.  Seismic Velocities in Mantle Minerals and the Mineralogy of the Upper Mantle , 2022 .