Tomographic images of the Iberian subcrustal lithosphère and asthenosphere

Abstract

The S wave velocity structure of the lithopheric mantle and asthenosphere beneath Iberia is displayed by means of tomographic images obtained from dispersion data of Rayleigh waves propagating across the Iberian region. We have used long‐period data recorded at the broadband stations of the Network of Autonomously Recording Seismographs (NARS) installed in the Iberian Peninsula on the occasion of the Iberian Lithosphere Heterogeneity and Anisotropy (ILIHA) project. A total of 64 teleseismic events provided by the ILIHA array and 143 seismic paths have been studied. Surface wave dispersion analysis is carried out using various methods: from methods for a correct acquisition of data and subsequent two‐station surface wave velocity measurements to inversion methods for velocity structure and methods for verifying the reliability of the inversion results. The phase and group velocity dispersion curves of the fundamental mode Rayleigh waves are the basic information from which we have obtained several Earth models represented by shear wave velocity distributions with depth. Using these inversion results, we display the most conspicuous features of the velocity stnicture of the Iberian lithosphere‐asthenosphere system and propose a new regional model, the Iberian Lithosphere‐Asthenosphere (ILA) model, for the deep structure of the Iberian Peninsula down to a depth of 200 km. We use a representation technique based on an iterative Laplacian interpolation method for obtaining tomographic images of the subcrustal lithosphere and asthenosphere of Iberia. We find significant lateral velocity variations in the peninsula, though these differences vary with depth interval. A low‐velocity channel in the lithosphere (41–51 km) appears with nonuniform velocity structure. In contrast, at the greatest lithospheric depths (51–81 km), almost the entire peninsula shows a rather uniform velocity structure. The asthenosphere (81–181 km) is clearly a nonhomogeneous gross layer both laterally and with depth. The relatively higher velocities span the shallower depths within the asthenosphere, whereas the lower ones span the deeper part.