Processing and Inversion of Long-Period Surface-Wave Data Collected in the Iberian Peninsula

Abstract

SUMMARY Several filtering techniques have been used to remove the effects of multipathing and modal contamination, and to isolate the fundamental mode from Rayleigh wavetrains. Group velocity data are obtained by means of the multiple‐filter technique. A time‐variable filter has allowed the influence of noise as well as the interference produced by higher modes to be removed. Multiple filtering is then used again to compute group velocities at each station. the interstation group velocity for the fundamental mode Rayleigh wave is estimated according to the velocities at two stations. Frequency‐domain Wiener deconvolution is used to compute the phase velocity between two stations. the well‐known three‐station method is applied to correct the distances travelled by the waves across the array and therefore to determine interstation phase and group velocities in a more accurate manner. On the other hand, lateral refraction at the Atlantic continental edge of the Peninsula is also studied. Phase velocities are corrected for the anelastic effect. Inversion of the interstation Rayleigh wave phase velocities is then made in accordance with generalized inversion theory to obtain theoretical 2‐D layered earth models. In this paper, these methods are applied to Rayleigh waves generated by teleseismic events propagating across the Iberian Peninsula and recorded at WWSSN stations. As a consequence, new and principal features for the Iberian lithosphere‐asthenosphere system are obtained. A very interesting feature of the the Iberian lithosphere was found‐a low‐velocity layer directly under the Moho, between 39 and 64 km depth, with shear velocities ranging from 4.12 to 4.37 km s‐1. the Iberian asthenosphere, which lies between 100 and 180km depth, is not an homogeneous layer and shows a negative velocity gradient from top to bottom together with a sudden increase in shear velocity beneath the low‐velocity zone.

Shallow Seismic Velocity Structure of the Betic Cordillera (Southern Spain) from Modelling of Rayleigh Wave Dispersion

“…A combination of multiple filtering and time variable filtering ensures the extraction of the fundamental mode Rayleigh wave from the observed (unfiltered) seismic signal with the less amount of noise (Badal et al, 1990(Badal et al, , 1992. Rg-wave group velocity measurements were performed by means of a detailed dispersion analysis based on the filtering of wave trains according to a methodology used previously (Badal et al, 1990(Badal et al, , 1992(Badal et al, , 1996. We used moving-window analysis of the signal to obtain approximate group times and then we carried out a correction of the waveform using a time-variable filter (Cara, 1973) in order to measure with the least possible bias the dispersion of the wave train.…”

“…In the period range of study, multipathing effects may influence the Rg wave content due to the sensitivity of the Rg waves to lateral heterogeneities in the medium. A combination of multiple filtering and time variable filtering ensures the extraction of the fundamental mode Rayleigh wave from the observed (unfiltered) seismic signal with the less amount of noise (Badal et al, 1990(Badal et al, , 1992. Rg-wave group velocity measurements were performed by means of a detailed dispersion analysis based on the filtering of wave trains according to a methodology used previously (Badal et al, 1990(Badal et al, , 1992(Badal et al, , 1996.…”

“…Moreover, mapping upper crustal shear-wave velocities is a very important topic, not only for accurate earthquake location and geological interpretation, but also for deriving deterministic models of strong ground motion (synthetic seismograms). The main goals are to compute group velocities for fundamental-mode Rg waves by means of digital filtering (Badal et al, 1990(Badal et al, , 1992 and to invert the dispersion measurements via generalized inversion (Badal et al, 1996) in order to infer shear-wave velocity models for depths of up to 5 km. Later, with the help of an imaging method already used with success in previous works (Corchete et al, 1995;Sabadell et al, 1997;Sero´n et al, 1999Sero´n et al, , 2001, we produce 3-D visualizations of the study region through horizontal and vertical cross-sections.…”

Elastic-anelastic Regional Structures for the Iberian Peninsula Obtained from a Rayleigh Wave Tomography and a Causal Uncoupled Inversion

“…BADAL et al (1990BADAL et al ( , 1992, with long-period data, and PAYO et al (1992), with short-period data, continued this kind of study with data sets belonging to the Iberian WWSSN stations. BADAL et al (1993BADAL et al ( , 1996 used data belonging to broadband stations of the ILIHA project to obtain shear-velocity structures and LANA et al (1997) deduced regionalised shear-velocity structures for the Iberian Peninsula according to the PCA and AL algorithms.…”

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

“…A pioneer study performed by Badal et al (1993) determined the deep (32-182 km) S-wave velocity structure for the southern part of Iberia, from long-period 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).…”