Abstract
S-wave attenuation characteristics were evaluated, taking heterogeneity of the ground (random velocity fluctuation) into account, based on downhole PS logging and suspension PS logging data obtained at a test field composed of horizontal soil layers of Quaternary age. In addition to these evaluations, numerical experiments with detailed velocity structure model based on suspension PS logging data were performed to try to clarify the physical mechanism of attenuation characteristics by comparing the data measured in situ. As a result, it was clarified that the obtained S-wave attenuation characteristic (Quality factor) reflects a strength of heterogeneity of the ground very well. The main part of the attenuation characteristics at frequencies of higher than around 10Hz considered for this study, therefore, may be a scattering attenuation due to the heterogeneity of the ground, and the contribution of an intrinsic attenuation was found to be relatively small. Since the random velocity fluctuations were not taken into account in the velocity structure model for the conventional estimating attenuation method, there is a possibility that the attenuation characteristics have been overestimated. In attenuation estimation, the trade-off between modeling of heterogeneity and estimated attenuation was found.
