WAVE-FORM INVERSION OF SEISMIC VELOCITIES AND ATTENUATION FROM LOW-FREQUENCY WAVES IN CYLINDRICAL-BARS

A new technique for laboratory measurement of seismic wave velocities and attenuation in the frequency range of 10-150 kHz consists of measu ring extensional waveforms using two cylindrical bars of the same mate rial but unequal length. Based on the dispersion equation of the bar a nd rough estimates of compressional and shear velocities of the bar ma terial, the waveform measured within the shorter bar is theoretically continued to the length of the longer bar to match with the waveform m easured there. An inversion is then performed to minimize the phase di fference between the two waveforms. The velocities are obtained when t he phase difference reaches a minimum, at which the two waveforms atta in the optimum phase match. After the phase match, a further inversion is performed to minimize the amplitude difference between the two wav eforms to derive the extensional wave attenuation within the bar. By t his inversion procedure, wave velocities and attenuation can be jointl y determined at frequencies much lower than those of the ultrasonic me asurements. By using the technique, compressional and shear velocities and extensional attenuation values in a lucite material and in dry Si erra White granite were measured. The results from the present techniq ue are consistent with the results from other techniques (resonant bar and ultrasonic), if the effect of intrinsic attenuation is accounted for.