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.

Love and Rayleigh Wave Tomography of the Qinghai-Tibet Plateau and Surrounding Areas

“…The surface waves observed on records of earthquakes are predominantly fundamental mode Rayleigh-and Love-waves and their group velocities along their respective great-circle propagation paths are mainly controlled by variations in the velocity structure of the crust and mantle. Therefore, in view of the dispersive character of the elastic medium, a detailed group velocity dispersion analysis of the waves recorded from earthquakes leads to a good resolution for depth-layered properties, and may be of great interest for the determination of regional seismic velocity structure and exploration of the contrasting geology between neighbouring geological formations (CORCHETE et al, 1995;BADAL et al, 1996;BONNER and HERRIN, 1999;MARTÍNEZ et al, 2000;FREDERIKSEN et al, 2001;MISHRA et al, 2005;MITRA et al, 2006). Surface wave velocity tomography (YANOVSKAYA et al, 2000;HUANG et al, 2003;YANOVSKAYA and KOZHEVNIKOV, 2003) is a useful tool for this purpose and for monitoring nuclear explosions with discriminants (PASYANOS and WALTER, 2001).…”

Ambient noise surface wave tomography of the Iberian Peninsula: Implications for shallow seismic structure

“…The deployment during 1988 -1989 of the broadband NARS stations as part of the ILIHA experiment [Paulssen, 1990] provided a significant impulse to surface wave studies in the Iberian Peninsula. Using two-station dispersion measurements, Corchete et al [1995] obtained shearwave images of the lithosphere and asthenosphere beneath the Iberian Peninsula. The shallow structure has also been studied using short period (1 -6 seconds) Rg Rayleigh waves from small earthquakes and explosions for different regions of Iberia (e.g., Chourak et al [2005] for the Betics).…”

Shear-wave velocity structure of the south-eastern part of the Iberian Peninsula from Rayleigh wave analysis

“…Previous studies, which cover all Iberian area also performed with longperiod Rayleigh waves, never attained a minimum depth less than 24 km (Badal et al 1990(Badal et al , 1992. Nevertheless, further studies performed also with Rayleigh waves in the Iberian area, attained to increase the maximum depth of the S-wave velocity models down to 200 km (Corchete et al 1995;Badal et al 1996). On the other hand, several S-wave velocity models of the Iberian area have been obtained for shallow depths (from 0 to 4 or 5 km of depth) from shortperiod Rayleigh waves (Sarrate et al 1993;Navarro et al 1997;Chourak et al 2003).…”