Seismic attenuation tomography and its application to rock mass evaluation

Abstract

We developed two methods of ray-based seismic attenuation tomography. One is amplitude attenuation tomography, which uses amplitude attenuation of the first arrival P-wave. As amplitude is easily influenced by various factors other than viscosity, we removed the effects of velocity structure on wave amplitude, such as transmission loss and diffraction, in the analysis. Decrease of wave frequency during propagation is estimated to obtain the Q-value directly. The other method is pulse broadening tomography, which uses broadening of rise-time or pulse-width of the first arrival P-wave. This method is based on the rise-time principle, which describes pulse broadening with travel time in viscous media. In this method, attenuation information can be obtained by using time data only. The combined use of velocity and attenuation characteristics can be a powerful tool to characterize an in situ rock mass. Therefore we integrated the seismic travel time tomography and the seismic attenuation tomography to a series procedure, and applied it to field data obtained in a mine. The result of travel time tomography agrees with the rock condition estimated by the geological observation at the sites. Faults and fractured zones were detected by the attenuation tomography.