SEISMIC ATTENUATION VALUES OBTAINED FROM INSTANTANEOUS-FREQUENCY MATCHING AND SPECTRAL RATIOS

In this paper, attenuation values are obtained from seismic data using instantaneous frequency matching and spectral ratios. To obtain differential t* values using instantaneous-frequency matching, a near offset reference pulse is attenuated until the resulting instantaneous frequency matches the observed value at the receiver. Prior to matching, filtering can be applied to each trace in order to reduce the effects of noise on the calculated instantaneous frequencies. In the second method, the spectral ratio between a receiver pulse and a reference pulse is used to obtain differential t* values. To obtain an unbiased estimate, a variable spectral bandwidth is used depending on the noise level of the data. The two methods are tested using synthetic traces and then applied to crustal refraction data from the 1986 PASSCAL Ouachita experiment. Results show that the differential t* values obtained using filtered, instantaneous frequency matching are consistent with and have less scatter than those obtained from spectral ratios with a variable bandwidth.