Influence of Scattering on Seismic Waves: Physical Mechanisms Contributing to Attenuation in the Crust
Scientific rept. no. 2, 1 Aug 1986-31 Jan 1987
MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
Pagination or Media Count:
The mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data, coda waves and strong motion attenuation measurements in the northeastern United States and Canada and theoretical models. The relative contributions to attenuation of anelasticity of crustal rocks constant Q, fluid flow and scattering are evaluated. Scattering is found to be strong with albedo of Bo - 0.9 and scattering extinction length of about 17 km. The intrinsic attenuation in the crust can be explained by a high constant Q 500 or sub 0 2000 and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks. A fluid-flow attenuation model gives a frequency dependence Q approx Q sub 0 f to the 5th power similar to those determined from the analysis of coda waves of regional seismograms.