Fundamental mode attenuation coefficients of the vertical components of Rayleigh waves have been obtained for three different tectonic regions of the Iberian Peninsula. The western part of Iberia, which is tectonically most stable, has the lowest attenuation, and the largest quality factor Qa. Average QP at depths from 0 to 80 km is 126 f 84 in the tectonically stable part of western Iberia, and 57 f 22 in the active part of eastern Iberia.
A method for the characterization of a seismically active zone from a distribution of hypocenters is presented. This method is based on principal components analysis, a powerful multivariant statistical technique that is used to find the rupture local ellipsoid (RLE). The ellipsoid is a planar structure with which two variations of the method are developed: the spatial principal components analysis and the spatial‐temporal principal components analysis; using these methods, it is possible to find the dominating tendencies in the fracturing of the seismically active volume as well as the temporal evolution of the process. The methodology developed has been applied to a series of earthquakes that occurred near Antequera, Spain, with the result that the main fracture series trends N70°–80°E. Moreover, the temporal evolution of the system from the most relevant RLE has been characterized.
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.
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