We present a method for estimating seismic attenuation based on frequency shift data. In most natural materials, seismic attenuation increases with frequency. The high-frequency components of the seismic signal are attenuated more rapidly than the low-frequency components as waves propagate. As a result, the centroid of the signal's spectrum experiences a downshift during propagation. Under the assumption of a frequencyindependent Q model, this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically. The frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In comparison to some other methods of estimating attenuation, our frequency shift method is relatively insensitive to geometric spreading, reflection and transmission effects, source and receiver coupling and radiation patterns, and instrument responses. Tests of crosswell attenuation tomography on 1-D and 2-D geological structures are presented.

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[1] Differential Acoustic Resonance Spectroscopy (DARS) has been developed to investigate the acoustic properties of samples in the kilohertz frequency range. This new laboratory measurement technique examines the change in resonant frequencies of a cavity perturbed by the introduction of a small test sample. The resonant frequency shift between the empty and sample-loaded cavity is used to estimate the acoustic properties of the loaded sample. This paper presents a DARS perturbation formula that combines a theoretical derivation with numerical simulation and laboratory measurements. Furthermore, a semi-empirical calibration technique is proposed to estimate the acoustic properties of a test sample. This research demonstrates the potential of the DARS measurement technique for estimating the acoustic properties of acoustically small and/or irregularly shaped samples.

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