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 diffe rential t values using instantaneous-frequency matching, a near offse t reference pulse is attenuated until the resulting instantaneous freq uency matches the observed value at the receiver. Prior to matching, f iltering can be applied to each trace in order to reduce the effects o f noise on the calculated instantaneous frequencies. In the second met hod, the spectral ratio between a receiver pulse and a reference pulse is used to obtain differential t values. To obtain an unbiased estim ate, a variable spectral bandwidth is used depending on the noise leve l of the data. The two methods are tested using synthetic traces and t hen applied to crustal refraction data from the 1986 PASSCAL Ouachita experiment. Results show that the differential t values obtained usin g filtered, instantaneous frequency matching are consistent with and h ave less scatter than those obtained from spectral ratios with a varia ble bandwidth.