At high frequency, the time scale is very short and acceleration becomes important. There must be a pressure difference in the main pores to drive fluid acceleration, which as a side effect is capable of inducing a reverse squirt in the throat connecting two pores. Based on such a mechanism, we develop a novel model of an S wave in fluid-saturated rock, which yields phase velocity (V-s) and the quality factor (Q(s)) as functions of frequency. Applications of the new model to Berea sandstone and Boise sandstone yield throat permeability. The second porosity represented by throats appears to be 5% of the total porosity. Nonetheless, Q(s) is predicted as 10(6) at a frequency of 10 Hz, far higher than seismic Q(s) measured in the field. This may be because groundwater has softened the skeleton of sedimentary rocks and/or because internal reflections at multiple lithological interfaces attenuate seismic waves.

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