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| | Abstract | | Data from walkaway vertical seismic profile (VSP) from the Nankai Trough exploratory well, offshore Tokai, central Japan, are used to estimate S-wave attenuation in methane hydrate (MH)-bearing sediments at seismic frequencies. We apply three different attenuation estimation methods: spectral ratio method, centroid frequency shift method, and the combination of the modified median frequency shift method and seismic interferometry. Numerous authors have shown that the existence of methane hydrates grown in the pore spaces of porous materials results in significant increases in elastic wave velocity due to the cementing effect. So far, although existing studies show that high S-wave attenuation has been observed in the sonic frequency range in the MH-bearing sediments, few measurements and little data processing with regard to S-wave attenuation at seismic frequencies have been carried out. In order to develop a reasonable mechanism for seismic attenuation in MH-bearing sediments, it is important to obtain S-wave attenuation data at various frequencies. |
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