The Biot poroelastic theory is used to model ultrasonic (1 MHz) compressional wave velocity (Vp) and specific attenuation (Qp−1) for carbonate sediment sequences from three Deep Sea Drilling Project (DSDP) sites 288, 289, and 316 on the Ontong–Java Plateau in the western Pacific ocean. The sediments are assumed to be represented by a granular frame containing tortuous capillary tubes of a constant radius. Experimental data for the variation of shear velocity Vs and bulk density ρ with depth are used as input parameters for the model. Assumptions of the frame Poisson’s ratio σb, grain bulk modulus Kg, and tortuosity α are necessary. The low-frequency asymptote of the Biot theory is adequate in modeling the variation of Vp with depth for sites 288 and 289. Modeled velocities agree to within 8% of experimental. The sensitivity of the modeled velocities to the uncertainty in the input parameters is investigated. The equations of motion are partially differentiated with respect to each parameter and the resulting equations are used in conjunction with each parameter’s uncertainty or error. The uncertainty in the modeled velocities is on average 11% and is mostly dependent upon the uncertainties in Kg and σb. The assumption of constant σb for the chalk-limestone sequences from sites 288 and 289 is then tested. It is found to remain constant at a value of 0.2 for the chalk, and decreases to approximately 0.1 for the transition to limestone. Modeled values for Qp−1 are found to be sensitive to σb and ρ, in addition to the pore space parameters, and are considerably smaller than the experimental observations from sites 288, 289, and 316.

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Results from a series of laboratory geotechnical and acoustical tests on carbonate sediments from the Western Indian Ocean are presented. With these data, empirical relationships for variations in porosity (Φ) and compressional and shear wave velocity (V p and V 5 ), with effective stress (σ'), were established. With an σ' vs. depth (z) profile, nontemperature-corrected empirical equations for V^ and V s vs. z were then obtained. These data cover cover only the upper 100 m of sediments. An empirical equation for the variation of shear modulus (G) with z is then established. This is shown to be dominated by the variation of V s with z.The importance of these equations in developing geoacoustical models of the seafloor, which accurately represent in-situ conditions, is assessed. A check of internal consistency was made: values of V p were calculated with V 5 vs. σ' and Φ vs. σ' equations in Gassmann's theory, and comparisons are made with V^ vs. σ' empirical predictions. Uncertainty bounds were calculated for the Gassmann V p predictions, and it was found that empirical V p predictions were close to the upper limits of the Gassmann V^ predictions. We therefore concluded that a partial verification of the internal consistency of the empirical equations was demonstrated.

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