CODA-Q DISTRIBUTION IN THE CANARY-ISLANDS

The Canary Archipelago, near the African plate between 27 degrees and 30 degrees N and 13 degrees and 19 degrees W, is included in the oldes t region(> 135 m.y.) of the eastern Atlantic Ocean. The tectonic seism icity is moderate, with low magnitudes, and it is almost totally relat ed to an active fault located between the islands of Tenerife and Gran Canaria. The purpose of this paper is to provide a clear idea of the anelasticity of coda waves in the region. In order to compute master d ispersion curves as a function of the quality factor, Q, we have appli ed inversion methods to obtain analytical magnification curves for all the seismographic stations used. f(p)-t data, corresponding to the co da wave dispersion of 52 local and regional seismic events recorded at 6 seismographic stations, have been obtained. The fit of the data to the master curves determined yields estimates of coda-Q values and the ir frequency dependence. Most of the Q(0) values determined, at 1 Hz, vary between 100 and 300, showing a strong frequency dependence in the range 0.2-2 Hz. The characteristic nu value (degree of frequency depe ndence of Q) in the region, given by the law Q = Q(0) f(nu) is nu = 0. 9. By applying regionalization techniques an iso-Q(0), map, for a refe rence frequency of 1 Hz, has been obtained for the Canary Archipelago. This map shows important lateral variations in Q(0), reflecting the t ectonics and the volcanism of the region. The lowest Q(0) values are f ound along the trend of the fault and beneath the islands.