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 oldest region(> 135 m.y.) of the eastern Atlantic Ocean. The tectonic seismicity is moderate, with low magnitudes, and it is almost totally related 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 dispersion curves as a function of the quality factor, Q, we have applied inversion methods to obtain analytical magnification curves for all the seismographic stations used. f(p)-t data, corresponding to the coda 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 their 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 dependence 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 reference frequency of 1 Hz, has been obtained for the Canary Archipelago. This map shows important lateral variations in Q(0), reflecting the tectonics and the volcanism of the region. The lowest Q(0) values are found along the trend of the fault and beneath the islands.