LABORATORY TESTS OF EXCITATION AND ATTENUATION OF CODA WAVES USING 2-D MODELS OF SCATTERING MEDIA

Effects of the scattering and intrinsic Q measured for direct waves on the decay of seismic coda with time and the level of the coda excitation were investigated by laboratory experiments. Seismograms with long codas were produced using an ultrasonic technique and sufficiently large 2-D models of scattering media. The results are: (1) the level of coda excitation is high when scattering attenuation is large, whereas it is low when scattering attenuation is small; (2) the observed coda decay depends only on the intrinsic Q of media models as predicted by the energy transfer theory of Shang and Gao; and (3) the scattering Q-1 value has a peak around kd = 2-3 (k is the wave number and d is the scatterer size) and decreases steeply on both sides of the peak.