No abstract

No abstract

Several attenuation studies have established a frequency dependence law of the anelastic attenuation factor Q in the form Q = Qo(f/fo)v for the approximate 1-10 Hz frequency range. We propose a method that leads to the determination of Q,, which is a function of the reference frequency fo, and the real exponent v with a single station. To carry out the problem we determine a set of master curves as a function of Y. We discuss the method, and the different features of the master curves, when it is applied to the complicated regions of the Iberian Peninsula and to several instruments with different responses. Using this new method and the seismographic stations available in the Iberian Peninsula we have mapped iso-Qo lines, at a reference frequency of 1 Hz, applying inversion methods. The Q, values determined for Iberia vary between about 100 and about 600. Values close to 100 correspond to the southern part of Iberia. In general, Q, values increase from south to north with values about 600 near the NW part of Iberia. The Pyrenees Mountains and adjacent areas present Q, values between about 200 and about 350. These results suggest a strong Qo lateral variation in Iberia. A considerable frequency dependence of coda-Q has also been determined. The v values vary between 0.3 and 0.8. The Q, values obtained in the Iberian Peninsula show very good agreement with several Q, values obtained in other regions of the world. Comparison betweenthe iso-Q, lines and other geophysical parameters, like regional variations of P,, velocities, heat flow, isoseismal intensity distribution and crustal thickness, indicates that lower Q, values are associated with higher isoseismal intensity attenuation, higher heat flow, lower P,, velocities and thinner crust.

In this paper, the response of different synthetic models to geoelectrical multi-electrode surveys is studied. The models considered are related to two main problems, which are very common in geophysical research regarding hydrogeology and engineering. The first class of models represents buried walls, similar archaeological remains or remains of buried foundations; the other class corresponds to a sea-water intrusion of a fresh water aquifer, which is generally studied in hydrogeophysics. A set of 2D simulations, starting from the synthetic models, was carried out to compare the behaviour of the different arrays when acquiring measurements of electrical resistivity tomography. For each model, the apparent resistivity data-and relative pseudo-sections-were calculated for common electrode arrays (Wenner, dipole-dipole, Wenner-Schlumberger). Furthermore, a 'non-classical' configuration (i.e. the linear grid) was also tested. The synthetic data, after adding different levels of Gaussian noise, were inverted using RES2DINV software; then the interpretative models were compared with the initial synthetic models using different parameters to estimate the quality of the matching. Finally, the comparison between the results obtained using the various arrays is presented. Furthermore, the effectiveness of the various arrays is evaluated for each problem, also taking into account some other characteristics of the arrays, including the associated practical advantages in time consumption and noise level. Results on synthetic data were also confirmed by two field tests: one at an archaeological site survey and one at a coastal aquifer study.

No abstract