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| | Abstract | | The presence of shear wave attenuation anisotropy in the hydrate bearing sediments can provide new information about the distribution of hydrates in the pore spaces. However, few measurements of attenuation anisotropy from sonic logging waveform data have been conducted. In this study, I have estimated shear attenuation anisotropy from upper and lower dipole waveforms based on the modified median frequency shift method described in Suzuki and Matsushima (2013). Although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method, the median frequency shift methods strongly depend on reference data under lower signal-to-noise ratios. The modified median frequency shift method does not depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation. This paper has demonstrated that the modified median frequency shift method provides more stable and reliable attenuation results. The final shear attenuation results from both upper and lower dipole data indicate that there is no significant shear wave attenuation anisotropy in methane hydrate bearing sediments. |
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