A non-linear regression technique (Gauss-Newton method) is used to fit the single-scattering model of coda wave generation to experimental data. Comparisons between these results and those obtained applying the technique used in seismological practice (logarithmic linearization of the model equation and least-squares fit) are made. Data used are: a) a synthetic coda generated by white Gaussian noise modulated with an attenuation factor, exp(-kt), and a geometrical spreading factor; b) seismograms provided by two seismic series that occurred in the Abruzzo (Italy) and Antequera (Southern Spain) regions.
The study from synthetic data shows that when the signal-to-noise ratio of the final part of the coda is greater or equal to 5, there are no significant differences in the values of Q_c inferred by both techniques. When the signal-to-noise ratio is less than 5, we observed that the log-log technique produces a systematic overestimation of the values of Q_c. Results obtained with real seismograms show that the log-log technique overestimates the Q_c values when compared with the Gauss-Newton method, when the whole coda is used. When a long coda is used, the Q_c dependence on frequency estimated using log-log is different in some cases from the one obtained with the Gauss-Newton technique. The Q_c dependence on the lapse-time is less pronounced when the Gauss-Newton technique is used. This effect is more evident when different coda durations are obtained fixing the start-time of coda analysis, and increasing the end-time of the same coda. This pattern is also observed for the Abruzzo (Italy) and Antequera (Spain) series; when the log-log technique is used, a lapse-time dependence is observed, but, when the Gauss-Newton technique is used, this dependence is less significant.

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We investigate the feasibility of using microtremor measurements in short and long period ranges for the prediction of frequency-dependent amplification effects due to local site geology in the Granada basin and Granada city (Southern Spain). Following a seismic reflection profile crossing the Granada basin, microtremor measurements were recorded at 12 different sites. Peaks centered at 0.7 s (1.5 Hz) and 3-4 s are observed in the microtremor spectra. The 0.7 s peak is interpreted in terms of microtremors and the second one in terms of ocean-generated microseisms. The former is present at all sites on Pliocene and Quaternary sedimens while the 3-4 s peak is present at all sites regardless of the surface geology, although with differences in the spectral amplitude. In order to investigate the possible influence of geologic parameters on long period motion, the maximum spectral amplitude value in the range 1 to 5 s was estimated at all sites in Granada basin. A good linear relation between the maximum spectral amplitude value and surface geology and depth to underground basement was found. However, for short period range (T<1 s), only the surface geology has any relation with the maximum spectral amplitude value. For Granada city, differences in the microtremor spectra were found to depend on the local geology. In the downtown area, situated on alluvial clay and sand from the Quaternary age, differences of up to 10 times with respect to the hill zones (located on compact conglomerates of Pliocene age) are observed. Results from coda-Q analysis from local earthquakes in the Granada basin show overestimations of Q_c, for lapse times of 70 s, of up to 4 times at stations situated on sediment when compared to those obtained on bedrock for the 1.5 Hz frequency and to a lesser extent for 3 Hz. This overestimation is explained in terms of seismic-wave amplification in the Granada basin.

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Least squares prediction of the spatial distribution of the rates of vertical crustal movements in the Tokai district, Central Japan, was performed with the aid of an empirically deduced local covariance function referring to data obtained during the period from 1979 to 1985, and the results are illustrated with contour lines.
Although least squares prediction which is related to least squares collocation was originally developed to obtain the distribution of gravity anomalies, it had not been widely applied in the study of crustal deformation. This was partially due to some difficulties in obtaining an empirical covariance function of crustal deformation. In order to apply least squares collocation for the study of vertical crustal movements in the Tokai district, we tried first to deduce a covariance function of Gaussian type. From the rates of vertical crustal movements at 67 stations in the Tokai district obtained during the period from 1979 to 1985, we estimated C_s(0)=8.0[(mm/a)²], k=0.035, C_r(0)=3.0[(mm/a)²] in the Gaussian function of the form C(d)=C_s(0)exp(-k²d²), where d is the distance between two stations and C_r(0) is the variance of observational errors at d=0. We applied this function to estimate the distribution of the rates of vertical crustal movements. Predicted contour lines of the rates of vertical crustal movements derived from 197 data signals showed almost the same pattern as those from 67 signals in the case of an area of approximately 200×350 km² in the Tokai district. Uncertainty in the parameter k had certainly some influence on the contour lines, but this effect is not so definitive. On the contrary, prediction without filtering sometimes produced results distinguished from the those obtained with filtering. Generally we recommend to perform prediction with filtering. As for the tectonic implication from the present results, we emphasize that a paired motion of subsidence at Omaezaki and uplift at Akaishi is more clearly concluded to exist than the one by the other methods.

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A non double-couple earthquake was found in an oceanic crust of the Philippine Sea plate subducting into the mantle in the Kanto district, central Japan. Its magnitude and focal depth are 4.6 and 57 km, respectively. This subducting oceanic crust consists of low-density gabbro or basalt at depths shallower than about 60 km, while it consists of high-density eclogite to which gabbro transformed at depths deeper than about 60 km. The non double-couple earthquake occurred at this density boundary in the oceanic crust. Since the first motion of seismic P waves is predominantly dilatational and shows volume contraction, we consider that this event was probably caused by a sudden phase transformation from gabbro to eclogite. Its predominant frequency implies that this phase transformation occurred instantaneously in the metastability field. Since this event emanated not only compressional waves but also shear waves, we conclude that the sudden volume contraction triggered a double-couple earthquake immediately. This interpretation is supported by the aftershock distribution and the P-wave first-motion distribution of an eyeball type, which has only one cone on the focal sphere.

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