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S U M M A R YIt is well known that orthometric heights can be obtained without levelling by using ellipsoidal and geoidal heights. For engineering purposes, these orthometric heights must be determined with high accuracy. For this reason, the determination of a high-resolution geoid is necessary. In Iberia, since the publication of the most recent geoid (IBERGEO95), a new geopotential model has become available (EIGEN-CG01C, released on 2004 October 29) and a new highresolution digital terrain model (SRTM 90M obtained from the Shuttle Radar Topography Mission) has been developed for the Earth. Logically, these new data represent improvements that must be included in a new geoid of Iberia. With this goal in mind, we have carried out a new gravimetric geoid determination in which these new data are included. The computation of the geoid uses the Stokes integral in convolution form, which has been shown as an efficient method to reach the proposed objective. The terrain correction has been applied to the gridded gravity anomalies to obtain the corresponding reduced anomalies. The indirect effect has also been taken into account. Thus, a new geoid is provided as grid data distributed for Iberia from 35 • to 44 • latitude and -10 • to 4 • longitude (extending to 9 • × 14 • ) in a 361 × 561 regular grid with a mesh size of 1.5 × 1.5 and 202 521 points in the GRS80 reference system. This calculated geoid and previous geoids that exist for this study area (IBERGEO95, EGM96, EGG97 and EIGEN-CG01C) are compared to the geoid undulations corresponding to 16 points of the European Vertical Reference Network (EUVN) on Iberia. The new geoid shows an improvement in precision and reliability, fitting the geoidal heights of these EUVN points with more accuracy than the other previous geoids.

The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999 in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a broadband station located in Egypt (KEG station). The dispersion curves were obtained for periods between 3 and 40 s, by digital filtering with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain a dispersion curve for each source-station path. These dispersion curves were inverted according to generalized inversion theory, to obtain shear wave velocity models for each source-station path, which is the main goal of this study. The shear velocity structure obtained for the Sinai Peninsula is shown through the shear velocity distributions with depth. These results agree well with the geology and other geophysical results, previously obtained from seismic and gravity data. The obtained velocity models suggest the existence of lateral and vertical heterogeneity. The shear velocity increases generally with depth for all paths analyzed in the study area. Nevertheless, in some paths a small low velocity channel in the upper or lower crust occurs. Along these profiles, it is found that the crustal structure of the Sinai Peninsula consists of three principal layers: upper crust with a sedimentary layer and lower crust. The upper crust has a sedimentary cover of 2 km thick with an average S-velocity of 2.53 km/s. This upper crust has a variable thickness ranging from 12 to 18 km, with S-wave velocity ranging from 3.24 to 3.69 km/s. The Moho discontinuity is located at a depth of 30 km,

S U M M A R YThe anelastic attenuation in the Almeria Basin (southeastern Iberian Peninsula) is investigated by using seismic data collected during the summer of 1991. A multiple-lapse time-window analysis is applied to high-frequency seismograms corresponding to 20 shallow seismic events with low magnitudes ( m 12.5) and distances less than 71 km, recorded at six short-period seismographic stations. We have constructed corrected geometrical spreading and normalized energy-distance curves for the region over the frequency bands 1-2,2-4,4-8,8-14 and 14-20 Hz. A theoretical model for body-wave energy propagation in a randomly heterogeneous medium has been employed to interpret the observations. Two parameters describe the medium in this model: the scattering attenuation coefficient qs = kQ3 ' and the intrinsic attenuation coefficient yI = kQ, ', where k is the wavenumber and Qr1 and Q, are the intrinsic and scattering attenuation respectively. This model assumes that scattering is isotropic, including all orders of multiple scattering, and predicting the spatial and temporal energy distribution of seismic energy. A least-squares fitting procedure has been used to find the best estimates of the model parameters. The analysis of the spectral amplitude decay of coda waves has provided coda Q,' values at the same frequency bands. The results obtained show that Q, ', Q2 ' and Q, ' decrease with increasing frequency; for frequencies lower than 3 Hz scattering attenuation is stronger than intrinsic absorption and coda Q, ' takes values between intrinsic and total attenuation, being very close to Qy'. Q;' is more frequency-dependent than Q, ; for frequencies greater than 3 Hz intrinsic absorption is the dominant attenuation effect and Q, and Q3 have significant frequency dependence. In order to correlate the results obtained with the major geological and tectonic features of the region, a geotectonic framework for the area is provided and the predominant frequency decay in coda waves is analysed in order to obtain the coda Q frequency dependence following a power law Qc = Qo( f/fo)", where fo is a reference frequency. In this way we have obtained regionalized values of coda Q at 1 Hz (Qo). Finally, a first-order approach has allowed us to obtain intrinsic and scattering quality factors from the obtained QO and v values, leading us to obtain tentative distributions of Q,, Qs and QO at 1 Hz for the area. The derived intrinsic and scattering quality-factor distributions are in good agreement with the tectonic history and the main geological features of the region. Large scattering and intrinsic attenuation (Qs N 80, QI -100) are found in the sedimentary Neogene and Quaternary basin, while scattering is the dominant effect in the old Palaeozoic rocks of the mountains (Qs -200, QI -1000).Intrinsic Q shows a higher sensitivity to the geological characteristics than scattering Q.

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.