Anelastic Rayleigh Wave Attenuation In the Iberian Peninsula

Cañas, J. A.; Miguel, F. De; Vidal, F.; Alguacil, Gerardo

doi:10.1111/j.1365-246x.1988.tb00476.x

Cited by 24 publications

(18 citation statements)

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“…The above Q values are in agreement with the attenuation obtained from crustal phases (Canas et al 1987), which is higher in the southern part of Iberia than in any other region. These authors give for Q an average value of 198 f 2 5 for southern Iberian and of 331 f 13 for the northeastern part of the Peninsula, similar to the values we have obtained.…”

Section: Discussionsupporting

confidence: 90%

“…Herraiz & Mezcua (1984) and Pujades (1987) have supplied the first set Qf Q data from coda wave analysis. Canas et al (1987) and Pujades et al (1990) have shown some regional variations for crustal coda-Q in this continental area, the lowest Q value being related to the southern part of Spain, and the highest one to the most stable central and western parts of the Peninsula. Very recently, Pujades et al (1990) have studied the problem of the frequency dependence law of the anelastic attenuation factor Q and have proposed a new interpretation for the frequency dependence.…”

Section: Introductionmentioning

confidence: 95%

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Seismic attenuation in Iberia using the coda-Qmethod

Payo

Badal

Cañas

et al. 1990

Geophysical Journal International

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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.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 95%

Seismic attenuation in Iberia using the coda-Qmethod

Payo

Badal

Cañas

et al. 1990

Geophysical Journal International

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“…Preliminary studies concerning the anelastic structure and based on wavetrains recorded at analogical WWSSN stations can be found in CANAS et al (1988CANAS et al ( , 1991, PAYO et al (1990) and PUJADES et al (1990). More recently, CASELLES et al (1997) and LANA et al (1999) have achieved regionalised models of Q À1 b structure for the Iberian Peninsula.…”

Section: Introductionmentioning

confidence: 99%

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

Martínez

Lana

Caselles

et al. 2005

Pure appl. geophys.

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The elastic and anelastic structure of the lithosphere and asthenosphere of the Iberian Peninsula is derived by means of tomographic techniques applied to local phase and group velocities and local attenuation coefficients of Rayleigh wave fundamental mode. The database consists of surface wavetrains recorded at the broadband stations located in the Iberian Peninsula on the occasion of the ILIHA project. Path-averaged phase and group velocities and attenuation coefficients were previously obtained by standard filtering techniques of surface wavetrains and, subsequently, local dispersion curves were computed according to the Yanovskaya-Ditmar formulation. First, a principal component analysis (PCA) and the average linkage (AL) clustering algorithm are applied to these local values in order to classify the Iberian Peninsula in several rather homogeneous domains from the viewpoint of the similarity of the corresponding local dispersion curves, without previous seismotectonic constraints. Second, averaged phase and group velocities and attenuation coefficients representing each homogeneous region are used to derive the respective elastic and anelastic models of the lithosphere and asthenosphere. This purpose is achieved by using the uncoupled causal inversion of phase and group velocities and attenuation coefficients. The main features of the homogeneous regions are discussed by taking as reference the Hercynic, Alpine and Neogene domains of the Iberian Peninsula, and two questions affecting the reliability of the elastic-anelastic models are revised. First, the coherence of the shear-velocity and Q À1 b models obtained by causal uncoupled inversion for each region is analysed. Second, the influence of the causal phase and group velocities on the shear-velocity models is evaluated by comparing elastic and anelastic models derived from causal uncoupled inversion with those deduced from non-causal inversion.

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“…Moreover, the presence of high conductive features at the middle-lower levels of the crust (e.g., Santos et al, 2002), may locally affect the splitting pattern beneath these stations. Another feature worth bearing in mind is that the lithospheric Q values under the Iberian Peninsula (Canas et al, 1988) are lower than those observed in other large continental areas like North America, South America, the Indian shield, and the Himalayas (Hwang and Mitchell, 1987). In addition, Calvert et al (2000) detected a low Pn velocity (7.6e7.8 km/s) and significant Sn attenuation in the uppermost mantle beneath the Betics in southern Spain, in sharp contrast to the relatively normal Pn velocity (8.0e8.1 km/s) and efficient Sn imaged beneath the Alboran Sea.…”

Section: Discussionmentioning

confidence: 99%

A seismological evidence for the northwestward movement of Africa with respect to Iberia from shear-wave splitting

Salah

2012

Geoscience Frontiers

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Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting. Waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study. Although the station coverage is not uniform in the Iberian Peninsula and northwest Africa, significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains. Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia; being consistent with the absolute plate motion in the region. In the northern part of the Iberian Peninsula, fast velocity directions are oriented nearly EeW; coincident with previous results. Few stations located slightly north of the plate boundary and to the southeast of Iberia show EeW to NE-SW fast velocity directions, which may be related to the Alpine Orogeny and the extension direction in Iberia. Delay times vary significantly between 0.2 and 1.9 s for individual measurements, reflecting a highly anisotropic structure beneath the recording stations. The relative motion between Africa and Iberia represents the main reason for the observed NW-SE orientations of the fast velocity directions. However, different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region. Many geophysical observations such as the low Pn velocity, lower lithospheric

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Anelastic Rayleigh Wave Attenuation In the Iberian Peninsula

Cited by 24 publications

References 24 publications

Seismic attenuation in Iberia using the coda-Qmethod

Seismic attenuation in Iberia using the coda-Qmethod

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

A seismological evidence for the northwestward movement of Africa with respect to Iberia from shear-wave splitting

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