Interpreting the Sub-crustal Reflectivity beneath the Iberian Massif

  1. I. Palomeras 1
  2. P. Ayarza 1
  3. J. Andrés 2
  4. J. Díaz 2
  5. J. Alcalde 2
  6. A. Alvarez-Valero 1
  7. J. Gómez-Barreiro 1
  8. R. Carbonell 2
  1. 1 Universidad de Salamanca

    Universidad de Salamanca

    Salamanca, España


  2. 2 Institut de Ciències de la Terra Jaume Almera-CSIC
Geotemas (Madrid)

ISSN: 1576-5172

Year of publication: 2021

Issue Title: X Congreso Geológico de España

Issue: 18

Pages: 555-558

Type: Article

More publications in: Geotemas (Madrid)


Since the late 80s, the Iberian Massif has been sampled by different controlled and natural source seismic expe- riments. The ILIHA-DSS, IBERSEIS-WA and ALCUDIA-WA wide-angle reflection/refraction surveys acquired in south and western Iberia have offsets and energy large enough to illuminate the uppermost mantle and reveal some deep reflected energy. Sub-Moho reflections can be also observed in vertical incidence (ALCUDIA-NI) and seismic interferometry (CIM- DEF) transects beneath the Central Iberian Zone. All datasets indicate that the energy reflects off an interface with a positive velocity contrast at a depth that concurs with that assumed for the Hales discontinuity that is the phase transition from spinel to garnet lherzolite. The coda and amplitude of this event suggest that it can correspond to a ~10 km thick heterogeneous layer where the spinel and garnet ratio varies. To test this hypothesis we used a 2D second order finite-difference acoustic full wave-field scheme on a P-wave velocity model with a layer consisting of randomly distributed bodies, thinner than ¼ of the wavelength of the seismic waves featuring a ΔVp=±0.1 km/s at the considered depth range. Resulting synthetic shot gathers reproduce well the observed amplitudes and codas as the constructive interference caused by the layering produces a tuning effect in this gradient heterogeneous zone.