ON THE MEASUREMENT OF ANELASTIC ATTENUATION USING AMPLITUDES OF LOW-FREQUENCY SURFACE-WAVES

A method is presented for the measurement of attenuation of long-perio d Rayleigh waves which minimizes two effects: that of biases owing to uncertainties in the source moment tensor and that of focusing owing t o propagation in a laterally heterogeneous elastic Earth. In this mann er, by measuring attenuation over minor arcs, odd terms of lateral het erogeneity in Q can be resolved. Global average Q estimates are in goo d agreement with the Preliminary Reference Earth Model (PREM) in the p eriod range 180-285 s. At periods shorter than 180 s, our estimates of Q are lower than predicted by PREM. Maps of lateral variations in Q-1 show a general correspondence of high Q to high shear velocity and lo w Q to low shear velocity. In particular, the shift to the west, at in creasing period, of the locus of the minimum in the Pacific Ocean is a lso observed in the Q-1 maps.