We extend a model for seismic attenuation that includes scattering and intrinsic components, Q-1 = Q(s)-1 + Q(i)-1, over five decades in experimental wavelength. Core images and downhole logs from Ocean Drilling Program Hole 735B near the Atlantis II Fracture Zone in the Indian Ocean were used to construct vertical profiles of heterogeneity and to compute a spectrum of Q(s)-1 using a multiple scattering model. Measurements of velocity dispersion suggest that Q(i)-1 is small compared to the measured attenuation Q-1. Measurements of Q-1 made at this site by laboratory, sonic log and VSP experiments are compared to the computed Q(s)-1 spectrum. Peaks in the Q(s)-1 spectrum occur at six major correlation lengths scales (0.006 m, 0.02 m, 0.16 m, 0.63 m, 8.0 m, and 25.0 m) which can be attributed to formation heterogeneity. Compared to typical seismic estimates of Q-1 in oceanic Layer 3, the measurements in Hole 735B are high, but can be explained by large Q(s)-1 values in shallow, fractured ocean crust. Based on this comparison, we conclude that the proximity of the experimental wavelength in band-limited studies to the length scale of heterogeneity is critical in the measurement of Q-1.
Pn308Times Cited:8Cited References Count:21