An extension of the Aki (1969) coda model takes into account the instrument and Earth Q-filter effects on the dispersion of the coda. The coda dispersion and coda shapes are easily derived and plotted as a function of t* = t/Q. Observed data can be overlaid on master curves to directly estimate shear-wave Q and to normalize for earthquake moment to estimate the attenuation coefficient of γ. The method works well when the earthquakes studied have corner frequencies greater than the combined peak response of the instrument and Earth Q-filters. Comparing results from central California and the southeastern United States, there is a slight indication that the excitation of the coda is inversely proportional to Q.

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