José Badal - Academia.edu (original) (raw)

Papers by José Badal

Communications in Applied Numerical Methods, 1990

The object of this work is to analyse the computational aspects of the finite-element method for ... more The object of this work is to analyse the computational aspects of the finite-element method for the elastic wave equations. The necessary numerical techniques are analysed from the point of view of accuracy, performance and storage requirements when implemented in scalar and vector processors with large storage capacity. The method is implemented on an IBM 3090 with vector facility. For this implementation we consider five different time integration schemes (explicit and implicit central difference, Houbolt, constant average acceleration and Wilson), and in the implicit case, both direct (Gaussian decomposition) and iterative (successive over-relaxation, Jacobi semi-iterative, Jacobi conjugate gradient) sparse linear systems solvers. These solvers are taken from the ITPACK-2C and ESSL libraries using in each case the adequate representation scheme; skyline, row-wise and compressed diagonal. From our results it is concluded that constant average acceleration and explicit central difference are the most adequate integration methods and Jacobi conjugate gradient is the most efficient solver.

Physics of the Earth and Planetary Interiors, 1993

Up to a few years ago, dispersion analyses of surface waves across the Iberian Peninsula and adja... more Up to a few years ago, dispersion analyses of surface waves across the Iberian Peninsula and adjacent zones were based on analog data recorded at the long-period Iberian stations. The installation of the NARS array on Iberian territory for a period of one year, has provided a greater station density than was previously available with the very few permanent long-period seismological stations installed on the peninsula. The NARS array also provided quality digital records, and increased the path coverage for two-station surface wave velocity measurements. Fundamental mode Rayleigh waves recorded at broadband stations belonging to this array have been analyzed to produce phase and group velocity dispersion curves for the period range 10-90 s. With the dataset now available, the elastic structure beneath the Iberian Massif has been investigated in terms of the shear velocity distribution as a function of depth. Time-variable filtering is employed to remove higher mode interference efficiently and to improve isolation of the fundamental mode Rayleigh wave from the seismograms. Multiple filtering is then used to compute group velocities at each station. The interstation Rayleigh wave group velocity can thus be easily calculated. Frequency-domain Wiener deconvolution is used to determine the interstation phase velocity. We perform inversion of velocity dispersion data containing both Rayleigh wave phase velocities and group velocities according to the generalized inversion theory by means of the stochastic inverse operator. The theoretical models for the lower crust and uppermost mantle beneath the Iberian Massif obtained by joint inversion, show a continental lithosphere with a thickness of 81 km. The crustal and subcrustal velocities are greater than in other areas of the Iberian Peninsula. The asthenosphere appears as a layer 100 km thick defined by very low velocities when compared with the rest of the peninsular area. Both the lithosphere and the asthenosphere exhibit a low velocity channel. In the lithosphere a subcrustal low velocity channel has velocity constrained between 4.33 and 4.62 km s~. In the asthenosphere the low velocity channel is constrained between 4.13 and 4.36 km1 * .

Gondwana Research, 2017

The Tibetan plateau is formed by the persistent convergence between the Indian and Eurasian plate... more The Tibetan plateau is formed by the persistent convergence between the Indian and Eurasian plates. The northeastern Tibetan plateau is undergoing young deformation that has been noticed for a long time. We conduct a passive-source seismic profile with 22 stations in NE Tibet in order to investigate the crustal shear-wave velocity structure and its relationship with tectonic processes. In this paper we obtain the Rayleigh-wave phase velocity dispersion data among all station pairs within the period bandwidth of 5-20 s from the method of ambient noise cross-correlations. Phase velocity variations correlate well with surface geological boundaries and tectonic features, for instance, low phase velocity beneath the Songpan-Ganzi block and the Guide basin. We also compute P-wave receiver functions based on the selected teleseismic events with similar ray parameters, and perform the joint inversion of surface wave dispersion data and receiver functions to obtain the 2-D crustal shear-wave velocity structure along the profile. The inversion results show that low shear-wave velocities beneath the Songpan-Ganzi block are widespread in the middle-to-lower crust. In together with high crustal Vp/Vs ratios and high temperature suggested by the P-wave velocities obtained from the active-source seismic study, we suggest that the low velocity zone beneath the Songpan-Ganzi block is probably attributed to partial melting. Across the North Kunlun fault, there is no crustal LVZ found beneath the Kunlun block. This structural difference may have already existed before the collision of the two blocks, or due to limit of the northward extension for the crustal LVZ across the North Kunlun fault.

Physics of the Earth and Planetary Interiors

Continued northeastward compression owing to the colliding Indian subcontinent has led to pronoun... more Continued northeastward compression owing to the colliding Indian subcontinent has led to pronounced surface uplift and significant crustal and mantle deformation in the Sichuan–Yunnan region along the southeastern margin of the Tibetan Plateau. Seismic anisotropy is an effective physical property for characterising crustal and
upper-mantle deformation, as these deformation mechanisms can be investigated by analysing the splitting of compressional-to-shear-wave (P-to-S) converted phases (XKS, which includes the SKS, SKKS, PKS and PKKS phases) at the core–mantle boundary. However, we cannot distinguish any crustal and/or mantle anisotropy
variations owing to the relatively low vertical resolution of XKS splitting. Here we compute the P-wave receiver functions from teleseismic events recorded at 90 permanent and 350 mobile broadband seismic stations that were established by the ChinArray project in the Sichuan–Yunnan region and analyse the P-to-S converted phases at the Moho interface (Pms) to measure the crustal anisotropic parameters. The Pms splitting results are then regarded as the crustal anisotropic parameters, and the anisotropic parameters in the upper mantle beneath 347 stations are extracted from the XKS splitting parameters by removing this crustal anisotropy. The results indicate that an approximately E–W anisotropic fast-wave polarisation direction (FPD) exists in the upper mantle beneath the southeastern margin of the Tibetan Plateau, and that the splitting times range from 0.06 to 1.39 s, with an average splitting time of 0.93 s. The approximately E–W anisotropic FPD in the upper mantle is mainly due to
asthenospheric flow induced by the eastward subduction of the Indian Plate beneath Myanmar. The small splitting times within the southern Sichuan–Yunnan diamond-shaped block (SYDSB) may be attributed to vertical growth of the lithosphere induced by mantle-plume-related magmatic uplift.

Physics of the Earth and Planetary Interiors, 2021

The southern part of the Ailaoshan-Red River shear zone (ARRSZ) in southern Yunnan, is an importa... more The southern part of the Ailaoshan-Red River shear zone (ARRSZ) in southern Yunnan, is an important gold-bearing polymetallic metallogenic belt of China. To better understand the metallogenic tectonic setting and the magmatic activity in the area, we deployed a 240-km-long quasi-linear seismic array with numerous short-period stations spaced about 500 m across the ARRSZ. The shear-velocity structure of the upper crust along the survey profile is determined by ambient noise tomography using continuously recorded waveform data. The results show: (1) An upper crust characterized by a laterally varying S-velocity pattern and two high velocity bodies: one located mainly below the Ailaoshan metallogenic belt and the other further east below the Pingbian area, which are separated by a low velocity zone beneath the Red River Fault. (2) The upper crust model provides valuable information on Cenozoic magmatism. The high-velocity body below the Ailaoshan metallogenic zone likely corresponds to...

Earth and Planetary Physics, 2018

Irregular surface flattening, which is based on a boundary conforming grid and the transformation... more Irregular surface flattening, which is based on a boundary conforming grid and the transformation between curvilinear and Cartesian coordinate systems, is a mathematical method that can elegantly handle irregular surfaces, but has been limited to obtaining first arrivals only. By combining a multistage scheme with the fast-sweeping method (FSM, the method to obtain first-arrival traveltime in curvilinear coordinates), the reflected waves from a crustal interface can be traced in a topographic model, in which the reflected wavefront is obtained by reinitializing traveltimes in the interface for upwind branches. A local triangulation is applied to make a connection between velocity and interface nodes. Then a joint inversion of first-arrival and reflection traveltimes for imaging seismic velocity structures in complex terrains is presented. Numerical examples all perform well with different seismic velocity models. The increasing topographic complexity and even use of a high curvature reflector in these models demonstrate the reliability, accuracy and robustness of the new working scheme; checkerboard testing illustrates the method's high resolution. Noise tolerance testing indicates the method's ability to yield practical traveltime tomography. Further development of the multistage scheme will allow other later arrivals to be traced and used in the traveltime inversion.

The purpose of this study is to investigate the shear wave velocity structure in the uppermost li... more The purpose of this study is to investigate the shear wave velocity structure in the uppermost lithosphere in Eastern Spain from a detailed dispersion analysis of Rg waves generated by local earthquakes. Our database includes seismograms generated by 25 local seismic events that were recorded by 7 single-component short-period stations belonging to the Spanish National Seismic Network during the period

Physics of the Earth and Planetary Interiors, 2000

We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group vel... more We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in the 10-100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fundamental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband stations, was identified by applying the frequency time analysis (FTAN) to each epicenter-station path which simultaneously satisfies the two-station method conditions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this procedure, 243 group and phase velocity dispersion curves were processed to obtain tomographic maps by applying the Yanovskaya-Ditmar formulation for periods in the 10-100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully nonlinear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to produce images that have substantially higher lateral resolution compared to images currently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well correlated with the shield-like lithosphere structure in Zagros. A low-velocity zone (LVZ) is not detected in Alborz or the south Caspian basin, which can imply thrusting of the oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh.

Journal of Geodynamics, 1990

Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean ... more Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean Sea using the two-station method applied to seismograph stations located in the coastal regions of Spain and Israel. The average attenuation coefficients vary between 7.36 10-4km-l, at a 16s period, to 0.76 10-4 km 1 at a 70 s period. The associated Rayleigh wave anelastic factors range from 42 to 157. The above results indicate a relatively highly attenuating region. Inversion methods applied to the determined Rayleigh wave attenuation coefficients indicate that a strong and weU-developped shear Q structure seems to be located under the Mediterranean Sea.

Geophysical Journal International, 1990

Coda wave analysis is used to obtain frequency-dependent coda-Q values for different seismic zone... more Coda wave analysis is used to obtain frequency-dependent coda-Q values for different seismic zones of the Iberian area. Seventeen source regions around the Geophysical Observatory of Toledo and some four seismic events per region have been considered in this study. We have used an iterative Fourier analysis technique to see the variation of the frequency along the coda, also taking into account the instrument response. We have applied a suitable criterion to select the predominant frequency every 5 s along the coda. The variation of the frequency with time for each region is averaged with a second-degree polynomial, which is compared to master curves obtained directly from the response of the seismograph system, in order to determine the elastic quality factor Q. It has been observed that the frequency-time curves thus obtained are better explained if Q is considered as an exponential function of the peak frequency. The main result of this work is a set of 1Hz Q values with a clear indication that frequency dependence of Q exists, although the bandwidth from which our conclusions are reached is only 0.5-1 Hz. The coda-Q values obtained for the tectonically most stable areas (north Spain) appear somewhat higher, Q > 300, than those corresponding to the seismic active zones (south Spain), Q <250. Thus, a clear relationship is established between Q values and the two major tectonic provinces in Iberia. These results may be helpful for seismic risk and earthquake engineering purposes.

Geophysical Journal International, 2009

When the signal-to-noise (S/N) ratio is less than −3 dB or even 0 dB, seismic events are generall... more When the signal-to-noise (S/N) ratio is less than −3 dB or even 0 dB, seismic events are generally difficult to identify from a common shot record. To overcome this type of problem we present a method to detect weak seismic signals based on the oscillations described by a chaotic dynamic system in phase space. The basic idea is that a non-linear chaotic oscillator is strongly immune to noise. Such a dynamic system is less influenced by noise, but it is more sensitive to periodic signals, changing from a chaotic state to a large-scale periodic phase state when excited by a weak signal. With the purpose of checking the possible contamination of the signal by noise, we have performed a numerical experiment with an oscillator controlled by the Duffing-Holmes equation, taking a distorted Ricker wavelet sequence as input signal. In doing so, we prove that the oscillator system is able to reach a large-scale periodic phase state in a strong noise environment. In the case of a common shot record with low S/N ratio, the onsets reflected from a same interface are similar to one other and can be put on a single trace with a common reference time and the periodicity of the so-generated signal follows as a consequence of moveout at a particular scanning velocity. This operation, which is called 'horizontal dynamic correction' and leads to a nearly periodic signal, is implemented on synthetic wavelet sequences taking various sampling arrival times and scanning velocities. Thereafter, two tests, both in a noisy ambient of −3.7 dB, are done using a chaotic oscillator: the first demonstrates the capability of the method to really detect a weak seismic signal; the second takes care of the fundamental weakness of the dynamic correction coming from the use of a particular scanning velocity, which is investigated from the effect caused by near-surface lateral velocity variation on the periodicity of the reconstructed seismic signal. Finally, we have developed an application of the method to real data acquired in seismic prospecting and then converted into pseudo-periodic signals, which has allowed us to discriminate fuzzy waveforms as multiples, thus illustrating in practice the performance of our working scheme.

Geophysical Journal International, 1996

A detailed dispersion analysis of Rayleigh waves propagating across the Iberian Peninsula is carr... more A detailed dispersion analysis of Rayleigh waves propagating across the Iberian Peninsula is carried out. The starting data are high-quality long-period data recorded at the broad-band NARS stations installed in the Iberian Peninsula during the ILIHA project. We apply methods to obtain a correct selection of data and subsequent twostation surface-wave velocity measurements. A total of 64 teleseismic events recorded by the NARS array and 143 seismic paths have been studied. Several techniques which provide a significant improvement in the signal-to-noise ratio are employed to remove higher-mode interference efficiently and improve the isolation of the fundamental-mode Rayleigh wave from the seismograms. Thereafter, the interstation Rayleigh wave phase and group velocities are determined. We perform simultaneous inversion of phase-and group-velocity dispersion data by means of the stochastic inverse operator, and test the reliability of the results by computing resolving kernels and also by forward modelling. A regionalization procedure based on the Backus-Gilbert approach for linear inversion of traveltime data is applied. Both the inversion results and the contoured shear-wave velocity panoramas display the main features of the deep structure of Iberia. We find a subcrustal low-velocity channel which extends over practically the whole peninsular area and spans a depth interval of approximately 40-50 km; it exhibits velocities of between 4.30 and 4.50 km s-'. At depths of 66-81 km, we find the highest velocities in the lithosphere, which reach values of 4.85 km s-' in many cases. The low-velocity channel of the asthenosphere spans a large depth interval of approximately 80-180 km; it shows the lowest velocity values computed by us. We find velocities decreasing with depth, which are of the order of 4.25-4.36 km s p l for the first 40 km and of the order of 4.00-4.25 km s-' for the rest. The upper mantle under the asthenosphere exhibits high velocities, which range between 4.62 and 4.82 km sC1 in most cases. The shear-wave velocity structure of the Iberian subcrustal lithosphere and asthenosphere is mapped at 11 depth intervals from 24 to 201 km. At the top of the mantle, relatively low velocities span the Ebro Valley and also the southern third of the peninsula. Low velocities appear in the south-southwest quadrant, and high velocities occur over the Hercynian basement. At greater lithospheric depths, very low velocities extending over the whole peninsula suggest a low-velocity channel of non-uniform lateral structure, where a reduced zone to the west of the Iberian plateau shows relatively high velocities. At the greatest lithospheric depths, the whole Iberian block is fairly homogeneous laterally. The asthenosphere shows a notable lateral heterogeneity as well. We distinguish two parts: the upper asthenosphere, a 40 km thick layer with predominant velocity values of 4.25 km s p l or more; and the lower asthenosphere, a 60 km thick layer with velocity values generally below 4.25 km sf'. The upper asthenosphere seems to be less laterally heterogeneous than the lower asthenosphere. The lower asthenosphere exhibits a more pronounced negative velocity gradient than the upper asthenosphere.

Geophysical Journal International, 1990

Several filtering techniques have been used to remove the effects of multipathing and modal conta... more 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-'. 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.

Geophysical Journal International, 1991

A method based on the coda attenuation law: Q = Q o (f / f o) v leads to the determination of the... more A method based on the coda attenuation law: Q = Q o (f / f o) v leads to the determination of the lateral variation of coda-Q in the southern part of the Iberian Peninsula using seismograms belonging to the seismological network of the Cartuja Observatory, located in Granada. The lateral variation of Qo (Q value corresponding to a reference frequency fo of 1 Hz) and its frequency dependence for the 1 to 5Hz frequency range are, in general, in agreement with coda-Q values for frequencies less than about 1 Hz, previously determined in the region under study. To determine the coda-Q values analytical functions have been used to fit the magnification curves of the vertical component short-period seismographs belonging to the Cartuja network. The problem is solved by using least-squares techniques and non-linear inversion. The determined coda-Q, values and its frequency dependence correlate well with several known geophysical parameters in the southern part of the Iberian Peninsula.

Earth and Planetary Science Letters, 2015

In an attempt to characterize the subsurface structure that is related to fossil mantle plume act... more In an attempt to characterize the subsurface structure that is related to fossil mantle plume activity, a comprehensive geophysical investigation was conducted in the Emeishan Large Igneous Province (ELIP). The nature and geometry of the crust were examined within the scheme of the domal structure of ELIP, which comprises the Inner, Intermediate and Outer zones, which are defined on the basis of the biostratigraphy of pre-volcanic sediments. The bulk crustal properties within the Inner Zone are characterized by high density, high P-wave velocity, high Vp/Vs ratios and large crustal thickness. A visible continuous seismic converter is present in the upper part of the crust in the whole Intermediate Zone and the eastern part of the Inner Zone, but it is absent in the Inner Zone, where another seismic converter is observed in the lower part of the crust. The geometric configuration of these converters is attributable to the addition of mantle-derived melts to the pre-existing crust and subsequent interaction between them. The crustal geometry, which is delineated by the migrated image of receiver functions from the passive seismic experiment, and the crustal 3 properties collectively suggest that a mafic layer of 15-20 km thickness and 150-180 km width exists at the base of the crust in the Inner Zone. Such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust. The salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity, if the pre-volcanic domal uplift is generated by the Permian Emeishan mantle plume. This arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data. This study therefore characterizes and provides evidence for a plume-modified crust in a large igneous province.

Journal of Computational Physics

The mass-lumped method avoids the cost of inverting the mass matrix and simultaneously maintains ... more The mass-lumped method avoids the cost of inverting the mass matrix and simultaneously maintains spatial accuracy by adopting additional interior integration points, known as cubature points. To date, such points are only known analytically in tensor domains, such as quadrilateral or hexahedral elements. Thus, the diagonal-mass-matrix spectral element method (SEM) in non-tensor domains always relies on numerically computed interpolation points or quadrature points. However, only the cubature points for degrees 1 to 6 are known, which is the reason that we have developed a p-norm-based optimization algorithm to obtain higher-order cubature points. In this way, we obtain and tabulate new cubature points with all positive integration weights for degrees 7 to 9. The dispersion analysis illustrates that the dispersion relation determined from the new optimized cubature points is comparable to that of the mass and stiffness matrices obtained by exact integration. Simultaneously, the Lebesgue constant for the new optimized cubature points indicates its surprisingly good interpolation properties. As a result, such points provide both good interpolation properties and integration accuracy. The Courant-Friedrichs-Lewy (CFL) numbers are tabulated for the conventional Fekete-based triangular spectral element (TSEM), the TSEM with exact integration, and the optimized cubature-based TSEM (OTSEM). A complementary study demonstrates the spectral convergence of the OTSEM. A numerical example conducted on a half-space model demonstrates that the OTSEM improves the accuracy by approximately one order of magnitude compared to the conventional Fekete-based TSEM. In particular, the accuracy of the 7th-order OTSEM is even higher than that of the 14th-order Fekete-based TSEM. Furthermore, the OTSEM produces a result that can compete in accuracy with the quadrilateral SEM (QSEM). The high accuracy of the OTSEM is also tested with a non-flat topography model. In terms of computational efficiency, the OTSEM is more efficient than the Fekete-based TSEM, although it is slightly costlier than the QSEM when a comparable numerical accuracy is required.

Bulletin of the Seismological Society of America, 2002

The human losses after strong earthquakes that occurred in the world during the twentieth century... more The human losses after strong earthquakes that occurred in the world during the twentieth century have been analyzed, and a quantitative model for a preliminary assessment of casualties is proposed. It consists of a correlation between the number of casualties and the earthquake magnitude as a function of population density. We tackle the distribution of the total number of casualties within areas of different macroseismic intensity. Prognostic estimations of the expected number of killed or injured people caused by a supposed strong earthquake in Andalucia (Spain), using the model based on worldwide data, are suggested. Prognostic estimations based on specific data about the Kanto–Tokai (Japan) region are likewise given and compared with the number of casualties due to the 1995 Kobe (Japan) earthquake. In relation to the expected number of victims in areas affected by strong seismic impacts, we compute the casualty rate as the number of people killed divided into the inhabitants of a region and show its variation for different population density groups in the case of two extreme earthquake magnitudes.

Abstract Visualisation of seismic and tomographic results is a crucial point to properly understa... more Abstract Visualisation of seismic and tomographic results is a crucial point to properly understand the models provided by seismic methods. We consider several geostatistical methods (inverse distance weighting, point kriging and mathematical wavelets) to map surface wave tomography in a sparsely sampled study area, and to compare their accuracy and efficiency with proper raypath methodologies (inversion and projection onto convex sets). A large set of synthetic data is used to estimate seismic velocities before application to real data. The contour maps of prediction errors indicate that spatial prediction and inversion perform similarly.

When applying a methodology for obtaining the 3-D shear-wave velocity structure of a medium from ... more When applying a methodology for obtaining the 3-D shear-wave velocity structure of a medium from surface wave dispersion data, the problem must be considered with caution since one inverts path-averaged velocities and the use of any inversion method entails some drawbacks such as lack of uniqueness, unwarranted stability and constraints affecting the data. Several imaging techniques aimed at volumetric modeling

Journal of Geodynamics, 1990

Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean ... more Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean Sea using the two-station method applied to seismograph stations located in the coastal regions of Spain and Israel. The average attenuation coefficients vary between 7.36 10-4km-l, at a 16s period, to 0.76 10-4 km 1 at a 70 s period. The associated Rayleigh wave anelastic factors range from 42 to 157. The above results indicate a relatively highly attenuating region. Inversion methods applied to the determined Rayleigh wave attenuation coefficients indicate that a strong and weU-developped shear Q structure seems to be located under the Mediterranean Sea.

Communications in Applied Numerical Methods, 1990

The object of this work is to analyse the computational aspects of the finite-element method for ... more The object of this work is to analyse the computational aspects of the finite-element method for the elastic wave equations. The necessary numerical techniques are analysed from the point of view of accuracy, performance and storage requirements when implemented in scalar and vector processors with large storage capacity. The method is implemented on an IBM 3090 with vector facility. For this implementation we consider five different time integration schemes (explicit and implicit central difference, Houbolt, constant average acceleration and Wilson), and in the implicit case, both direct (Gaussian decomposition) and iterative (successive over-relaxation, Jacobi semi-iterative, Jacobi conjugate gradient) sparse linear systems solvers. These solvers are taken from the ITPACK-2C and ESSL libraries using in each case the adequate representation scheme; skyline, row-wise and compressed diagonal. From our results it is concluded that constant average acceleration and explicit central difference are the most adequate integration methods and Jacobi conjugate gradient is the most efficient solver.

Physics of the Earth and Planetary Interiors, 1993

Up to a few years ago, dispersion analyses of surface waves across the Iberian Peninsula and adja... more Up to a few years ago, dispersion analyses of surface waves across the Iberian Peninsula and adjacent zones were based on analog data recorded at the long-period Iberian stations. The installation of the NARS array on Iberian territory for a period of one year, has provided a greater station density than was previously available with the very few permanent long-period seismological stations installed on the peninsula. The NARS array also provided quality digital records, and increased the path coverage for two-station surface wave velocity measurements. Fundamental mode Rayleigh waves recorded at broadband stations belonging to this array have been analyzed to produce phase and group velocity dispersion curves for the period range 10-90 s. With the dataset now available, the elastic structure beneath the Iberian Massif has been investigated in terms of the shear velocity distribution as a function of depth. Time-variable filtering is employed to remove higher mode interference efficiently and to improve isolation of the fundamental mode Rayleigh wave from the seismograms. Multiple filtering is then used to compute group velocities at each station. The interstation Rayleigh wave group velocity can thus be easily calculated. Frequency-domain Wiener deconvolution is used to determine the interstation phase velocity. We perform inversion of velocity dispersion data containing both Rayleigh wave phase velocities and group velocities according to the generalized inversion theory by means of the stochastic inverse operator. The theoretical models for the lower crust and uppermost mantle beneath the Iberian Massif obtained by joint inversion, show a continental lithosphere with a thickness of 81 km. The crustal and subcrustal velocities are greater than in other areas of the Iberian Peninsula. The asthenosphere appears as a layer 100 km thick defined by very low velocities when compared with the rest of the peninsular area. Both the lithosphere and the asthenosphere exhibit a low velocity channel. In the lithosphere a subcrustal low velocity channel has velocity constrained between 4.33 and 4.62 km s~. In the asthenosphere the low velocity channel is constrained between 4.13 and 4.36 km1 * .

Gondwana Research, 2017

The Tibetan plateau is formed by the persistent convergence between the Indian and Eurasian plate... more The Tibetan plateau is formed by the persistent convergence between the Indian and Eurasian plates. The northeastern Tibetan plateau is undergoing young deformation that has been noticed for a long time. We conduct a passive-source seismic profile with 22 stations in NE Tibet in order to investigate the crustal shear-wave velocity structure and its relationship with tectonic processes. In this paper we obtain the Rayleigh-wave phase velocity dispersion data among all station pairs within the period bandwidth of 5-20 s from the method of ambient noise cross-correlations. Phase velocity variations correlate well with surface geological boundaries and tectonic features, for instance, low phase velocity beneath the Songpan-Ganzi block and the Guide basin. We also compute P-wave receiver functions based on the selected teleseismic events with similar ray parameters, and perform the joint inversion of surface wave dispersion data and receiver functions to obtain the 2-D crustal shear-wave velocity structure along the profile. The inversion results show that low shear-wave velocities beneath the Songpan-Ganzi block are widespread in the middle-to-lower crust. In together with high crustal Vp/Vs ratios and high temperature suggested by the P-wave velocities obtained from the active-source seismic study, we suggest that the low velocity zone beneath the Songpan-Ganzi block is probably attributed to partial melting. Across the North Kunlun fault, there is no crustal LVZ found beneath the Kunlun block. This structural difference may have already existed before the collision of the two blocks, or due to limit of the northward extension for the crustal LVZ across the North Kunlun fault.

Physics of the Earth and Planetary Interiors

Continued northeastward compression owing to the colliding Indian subcontinent has led to pronoun... more Continued northeastward compression owing to the colliding Indian subcontinent has led to pronounced surface uplift and significant crustal and mantle deformation in the Sichuan–Yunnan region along the southeastern margin of the Tibetan Plateau. Seismic anisotropy is an effective physical property for characterising crustal and
upper-mantle deformation, as these deformation mechanisms can be investigated by analysing the splitting of compressional-to-shear-wave (P-to-S) converted phases (XKS, which includes the SKS, SKKS, PKS and PKKS phases) at the core–mantle boundary. However, we cannot distinguish any crustal and/or mantle anisotropy
variations owing to the relatively low vertical resolution of XKS splitting. Here we compute the P-wave receiver functions from teleseismic events recorded at 90 permanent and 350 mobile broadband seismic stations that were established by the ChinArray project in the Sichuan–Yunnan region and analyse the P-to-S converted phases at the Moho interface (Pms) to measure the crustal anisotropic parameters. The Pms splitting results are then regarded as the crustal anisotropic parameters, and the anisotropic parameters in the upper mantle beneath 347 stations are extracted from the XKS splitting parameters by removing this crustal anisotropy. The results indicate that an approximately E–W anisotropic fast-wave polarisation direction (FPD) exists in the upper mantle beneath the southeastern margin of the Tibetan Plateau, and that the splitting times range from 0.06 to 1.39 s, with an average splitting time of 0.93 s. The approximately E–W anisotropic FPD in the upper mantle is mainly due to
asthenospheric flow induced by the eastward subduction of the Indian Plate beneath Myanmar. The small splitting times within the southern Sichuan–Yunnan diamond-shaped block (SYDSB) may be attributed to vertical growth of the lithosphere induced by mantle-plume-related magmatic uplift.

Physics of the Earth and Planetary Interiors, 2021

The southern part of the Ailaoshan-Red River shear zone (ARRSZ) in southern Yunnan, is an importa... more The southern part of the Ailaoshan-Red River shear zone (ARRSZ) in southern Yunnan, is an important gold-bearing polymetallic metallogenic belt of China. To better understand the metallogenic tectonic setting and the magmatic activity in the area, we deployed a 240-km-long quasi-linear seismic array with numerous short-period stations spaced about 500 m across the ARRSZ. The shear-velocity structure of the upper crust along the survey profile is determined by ambient noise tomography using continuously recorded waveform data. The results show: (1) An upper crust characterized by a laterally varying S-velocity pattern and two high velocity bodies: one located mainly below the Ailaoshan metallogenic belt and the other further east below the Pingbian area, which are separated by a low velocity zone beneath the Red River Fault. (2) The upper crust model provides valuable information on Cenozoic magmatism. The high-velocity body below the Ailaoshan metallogenic zone likely corresponds to...

Earth and Planetary Physics, 2018

Irregular surface flattening, which is based on a boundary conforming grid and the transformation... more Irregular surface flattening, which is based on a boundary conforming grid and the transformation between curvilinear and Cartesian coordinate systems, is a mathematical method that can elegantly handle irregular surfaces, but has been limited to obtaining first arrivals only. By combining a multistage scheme with the fast-sweeping method (FSM, the method to obtain first-arrival traveltime in curvilinear coordinates), the reflected waves from a crustal interface can be traced in a topographic model, in which the reflected wavefront is obtained by reinitializing traveltimes in the interface for upwind branches. A local triangulation is applied to make a connection between velocity and interface nodes. Then a joint inversion of first-arrival and reflection traveltimes for imaging seismic velocity structures in complex terrains is presented. Numerical examples all perform well with different seismic velocity models. The increasing topographic complexity and even use of a high curvature reflector in these models demonstrate the reliability, accuracy and robustness of the new working scheme; checkerboard testing illustrates the method's high resolution. Noise tolerance testing indicates the method's ability to yield practical traveltime tomography. Further development of the multistage scheme will allow other later arrivals to be traced and used in the traveltime inversion.

The purpose of this study is to investigate the shear wave velocity structure in the uppermost li... more The purpose of this study is to investigate the shear wave velocity structure in the uppermost lithosphere in Eastern Spain from a detailed dispersion analysis of Rg waves generated by local earthquakes. Our database includes seismograms generated by 25 local seismic events that were recorded by 7 single-component short-period stations belonging to the Spanish National Seismic Network during the period

Physics of the Earth and Planetary Interiors, 2000

We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group vel... more We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in the 10-100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fundamental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband stations, was identified by applying the frequency time analysis (FTAN) to each epicenter-station path which simultaneously satisfies the two-station method conditions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this procedure, 243 group and phase velocity dispersion curves were processed to obtain tomographic maps by applying the Yanovskaya-Ditmar formulation for periods in the 10-100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully nonlinear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to produce images that have substantially higher lateral resolution compared to images currently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well correlated with the shield-like lithosphere structure in Zagros. A low-velocity zone (LVZ) is not detected in Alborz or the south Caspian basin, which can imply thrusting of the oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh.

Journal of Geodynamics, 1990

Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean ... more Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean Sea using the two-station method applied to seismograph stations located in the coastal regions of Spain and Israel. The average attenuation coefficients vary between 7.36 10-4km-l, at a 16s period, to 0.76 10-4 km 1 at a 70 s period. The associated Rayleigh wave anelastic factors range from 42 to 157. The above results indicate a relatively highly attenuating region. Inversion methods applied to the determined Rayleigh wave attenuation coefficients indicate that a strong and weU-developped shear Q structure seems to be located under the Mediterranean Sea.

Geophysical Journal International, 1990

Coda wave analysis is used to obtain frequency-dependent coda-Q values for different seismic zone... more Coda wave analysis is used to obtain frequency-dependent coda-Q values for different seismic zones of the Iberian area. Seventeen source regions around the Geophysical Observatory of Toledo and some four seismic events per region have been considered in this study. We have used an iterative Fourier analysis technique to see the variation of the frequency along the coda, also taking into account the instrument response. We have applied a suitable criterion to select the predominant frequency every 5 s along the coda. The variation of the frequency with time for each region is averaged with a second-degree polynomial, which is compared to master curves obtained directly from the response of the seismograph system, in order to determine the elastic quality factor Q. It has been observed that the frequency-time curves thus obtained are better explained if Q is considered as an exponential function of the peak frequency. The main result of this work is a set of 1Hz Q values with a clear indication that frequency dependence of Q exists, although the bandwidth from which our conclusions are reached is only 0.5-1 Hz. The coda-Q values obtained for the tectonically most stable areas (north Spain) appear somewhat higher, Q > 300, than those corresponding to the seismic active zones (south Spain), Q <250. Thus, a clear relationship is established between Q values and the two major tectonic provinces in Iberia. These results may be helpful for seismic risk and earthquake engineering purposes.

Geophysical Journal International, 2009

When the signal-to-noise (S/N) ratio is less than −3 dB or even 0 dB, seismic events are generall... more When the signal-to-noise (S/N) ratio is less than −3 dB or even 0 dB, seismic events are generally difficult to identify from a common shot record. To overcome this type of problem we present a method to detect weak seismic signals based on the oscillations described by a chaotic dynamic system in phase space. The basic idea is that a non-linear chaotic oscillator is strongly immune to noise. Such a dynamic system is less influenced by noise, but it is more sensitive to periodic signals, changing from a chaotic state to a large-scale periodic phase state when excited by a weak signal. With the purpose of checking the possible contamination of the signal by noise, we have performed a numerical experiment with an oscillator controlled by the Duffing-Holmes equation, taking a distorted Ricker wavelet sequence as input signal. In doing so, we prove that the oscillator system is able to reach a large-scale periodic phase state in a strong noise environment. In the case of a common shot record with low S/N ratio, the onsets reflected from a same interface are similar to one other and can be put on a single trace with a common reference time and the periodicity of the so-generated signal follows as a consequence of moveout at a particular scanning velocity. This operation, which is called 'horizontal dynamic correction' and leads to a nearly periodic signal, is implemented on synthetic wavelet sequences taking various sampling arrival times and scanning velocities. Thereafter, two tests, both in a noisy ambient of −3.7 dB, are done using a chaotic oscillator: the first demonstrates the capability of the method to really detect a weak seismic signal; the second takes care of the fundamental weakness of the dynamic correction coming from the use of a particular scanning velocity, which is investigated from the effect caused by near-surface lateral velocity variation on the periodicity of the reconstructed seismic signal. Finally, we have developed an application of the method to real data acquired in seismic prospecting and then converted into pseudo-periodic signals, which has allowed us to discriminate fuzzy waveforms as multiples, thus illustrating in practice the performance of our working scheme.

Geophysical Journal International, 1996

A detailed dispersion analysis of Rayleigh waves propagating across the Iberian Peninsula is carr... more A detailed dispersion analysis of Rayleigh waves propagating across the Iberian Peninsula is carried out. The starting data are high-quality long-period data recorded at the broad-band NARS stations installed in the Iberian Peninsula during the ILIHA project. We apply methods to obtain a correct selection of data and subsequent twostation surface-wave velocity measurements. A total of 64 teleseismic events recorded by the NARS array and 143 seismic paths have been studied. Several techniques which provide a significant improvement in the signal-to-noise ratio are employed to remove higher-mode interference efficiently and improve the isolation of the fundamental-mode Rayleigh wave from the seismograms. Thereafter, the interstation Rayleigh wave phase and group velocities are determined. We perform simultaneous inversion of phase-and group-velocity dispersion data by means of the stochastic inverse operator, and test the reliability of the results by computing resolving kernels and also by forward modelling. A regionalization procedure based on the Backus-Gilbert approach for linear inversion of traveltime data is applied. Both the inversion results and the contoured shear-wave velocity panoramas display the main features of the deep structure of Iberia. We find a subcrustal low-velocity channel which extends over practically the whole peninsular area and spans a depth interval of approximately 40-50 km; it exhibits velocities of between 4.30 and 4.50 km s-'. At depths of 66-81 km, we find the highest velocities in the lithosphere, which reach values of 4.85 km s-' in many cases. The low-velocity channel of the asthenosphere spans a large depth interval of approximately 80-180 km; it shows the lowest velocity values computed by us. We find velocities decreasing with depth, which are of the order of 4.25-4.36 km s p l for the first 40 km and of the order of 4.00-4.25 km s-' for the rest. The upper mantle under the asthenosphere exhibits high velocities, which range between 4.62 and 4.82 km sC1 in most cases. The shear-wave velocity structure of the Iberian subcrustal lithosphere and asthenosphere is mapped at 11 depth intervals from 24 to 201 km. At the top of the mantle, relatively low velocities span the Ebro Valley and also the southern third of the peninsula. Low velocities appear in the south-southwest quadrant, and high velocities occur over the Hercynian basement. At greater lithospheric depths, very low velocities extending over the whole peninsula suggest a low-velocity channel of non-uniform lateral structure, where a reduced zone to the west of the Iberian plateau shows relatively high velocities. At the greatest lithospheric depths, the whole Iberian block is fairly homogeneous laterally. The asthenosphere shows a notable lateral heterogeneity as well. We distinguish two parts: the upper asthenosphere, a 40 km thick layer with predominant velocity values of 4.25 km s p l or more; and the lower asthenosphere, a 60 km thick layer with velocity values generally below 4.25 km sf'. The upper asthenosphere seems to be less laterally heterogeneous than the lower asthenosphere. The lower asthenosphere exhibits a more pronounced negative velocity gradient than the upper asthenosphere.

Geophysical Journal International, 1990

Several filtering techniques have been used to remove the effects of multipathing and modal conta... more 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-'. 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.

Geophysical Journal International, 1991

A method based on the coda attenuation law: Q = Q o (f / f o) v leads to the determination of the... more A method based on the coda attenuation law: Q = Q o (f / f o) v leads to the determination of the lateral variation of coda-Q in the southern part of the Iberian Peninsula using seismograms belonging to the seismological network of the Cartuja Observatory, located in Granada. The lateral variation of Qo (Q value corresponding to a reference frequency fo of 1 Hz) and its frequency dependence for the 1 to 5Hz frequency range are, in general, in agreement with coda-Q values for frequencies less than about 1 Hz, previously determined in the region under study. To determine the coda-Q values analytical functions have been used to fit the magnification curves of the vertical component short-period seismographs belonging to the Cartuja network. The problem is solved by using least-squares techniques and non-linear inversion. The determined coda-Q, values and its frequency dependence correlate well with several known geophysical parameters in the southern part of the Iberian Peninsula.

Earth and Planetary Science Letters, 2015

In an attempt to characterize the subsurface structure that is related to fossil mantle plume act... more In an attempt to characterize the subsurface structure that is related to fossil mantle plume activity, a comprehensive geophysical investigation was conducted in the Emeishan Large Igneous Province (ELIP). The nature and geometry of the crust were examined within the scheme of the domal structure of ELIP, which comprises the Inner, Intermediate and Outer zones, which are defined on the basis of the biostratigraphy of pre-volcanic sediments. The bulk crustal properties within the Inner Zone are characterized by high density, high P-wave velocity, high Vp/Vs ratios and large crustal thickness. A visible continuous seismic converter is present in the upper part of the crust in the whole Intermediate Zone and the eastern part of the Inner Zone, but it is absent in the Inner Zone, where another seismic converter is observed in the lower part of the crust. The geometric configuration of these converters is attributable to the addition of mantle-derived melts to the pre-existing crust and subsequent interaction between them. The crustal geometry, which is delineated by the migrated image of receiver functions from the passive seismic experiment, and the crustal 3 properties collectively suggest that a mafic layer of 15-20 km thickness and 150-180 km width exists at the base of the crust in the Inner Zone. Such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust. The salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity, if the pre-volcanic domal uplift is generated by the Permian Emeishan mantle plume. This arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data. This study therefore characterizes and provides evidence for a plume-modified crust in a large igneous province.

Journal of Computational Physics

The mass-lumped method avoids the cost of inverting the mass matrix and simultaneously maintains ... more The mass-lumped method avoids the cost of inverting the mass matrix and simultaneously maintains spatial accuracy by adopting additional interior integration points, known as cubature points. To date, such points are only known analytically in tensor domains, such as quadrilateral or hexahedral elements. Thus, the diagonal-mass-matrix spectral element method (SEM) in non-tensor domains always relies on numerically computed interpolation points or quadrature points. However, only the cubature points for degrees 1 to 6 are known, which is the reason that we have developed a p-norm-based optimization algorithm to obtain higher-order cubature points. In this way, we obtain and tabulate new cubature points with all positive integration weights for degrees 7 to 9. The dispersion analysis illustrates that the dispersion relation determined from the new optimized cubature points is comparable to that of the mass and stiffness matrices obtained by exact integration. Simultaneously, the Lebesgue constant for the new optimized cubature points indicates its surprisingly good interpolation properties. As a result, such points provide both good interpolation properties and integration accuracy. The Courant-Friedrichs-Lewy (CFL) numbers are tabulated for the conventional Fekete-based triangular spectral element (TSEM), the TSEM with exact integration, and the optimized cubature-based TSEM (OTSEM). A complementary study demonstrates the spectral convergence of the OTSEM. A numerical example conducted on a half-space model demonstrates that the OTSEM improves the accuracy by approximately one order of magnitude compared to the conventional Fekete-based TSEM. In particular, the accuracy of the 7th-order OTSEM is even higher than that of the 14th-order Fekete-based TSEM. Furthermore, the OTSEM produces a result that can compete in accuracy with the quadrilateral SEM (QSEM). The high accuracy of the OTSEM is also tested with a non-flat topography model. In terms of computational efficiency, the OTSEM is more efficient than the Fekete-based TSEM, although it is slightly costlier than the QSEM when a comparable numerical accuracy is required.

Bulletin of the Seismological Society of America, 2002

The human losses after strong earthquakes that occurred in the world during the twentieth century... more The human losses after strong earthquakes that occurred in the world during the twentieth century have been analyzed, and a quantitative model for a preliminary assessment of casualties is proposed. It consists of a correlation between the number of casualties and the earthquake magnitude as a function of population density. We tackle the distribution of the total number of casualties within areas of different macroseismic intensity. Prognostic estimations of the expected number of killed or injured people caused by a supposed strong earthquake in Andalucia (Spain), using the model based on worldwide data, are suggested. Prognostic estimations based on specific data about the Kanto–Tokai (Japan) region are likewise given and compared with the number of casualties due to the 1995 Kobe (Japan) earthquake. In relation to the expected number of victims in areas affected by strong seismic impacts, we compute the casualty rate as the number of people killed divided into the inhabitants of a region and show its variation for different population density groups in the case of two extreme earthquake magnitudes.

Abstract Visualisation of seismic and tomographic results is a crucial point to properly understa... more Abstract Visualisation of seismic and tomographic results is a crucial point to properly understand the models provided by seismic methods. We consider several geostatistical methods (inverse distance weighting, point kriging and mathematical wavelets) to map surface wave tomography in a sparsely sampled study area, and to compare their accuracy and efficiency with proper raypath methodologies (inversion and projection onto convex sets). A large set of synthetic data is used to estimate seismic velocities before application to real data. The contour maps of prediction errors indicate that spatial prediction and inversion perform similarly.

When applying a methodology for obtaining the 3-D shear-wave velocity structure of a medium from ... more When applying a methodology for obtaining the 3-D shear-wave velocity structure of a medium from surface wave dispersion data, the problem must be considered with caution since one inverts path-averaged velocities and the use of any inversion method entails some drawbacks such as lack of uniqueness, unwarranted stability and constraints affecting the data. Several imaging techniques aimed at volumetric modeling

Journal of Geodynamics, 1990

Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean ... more Fundamental-mode Rayleigh wave attenuation coefficients have been obtained for the Mediterranean Sea using the two-station method applied to seismograph stations located in the coastal regions of Spain and Israel. The average attenuation coefficients vary between 7.36 10-4km-l, at a 16s period, to 0.76 10-4 km 1 at a 70 s period. The associated Rayleigh wave anelastic factors range from 42 to 157. The above results indicate a relatively highly attenuating region. Inversion methods applied to the determined Rayleigh wave attenuation coefficients indicate that a strong and weU-developped shear Q structure seems to be located under the Mediterranean Sea.