ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2aUW3. Modeling the near-bottom seafloor.

Robert D. Stoll

Lamont-Doherty Earth Observatory of Columbia Univ., Palisades, NY 10964

In mine counter measures work and other seafloor engineering applications, there are two distinctly different classes of sediment properties that play important roles in object detection and sonar performance---those that determine if an object will sink into the bottom or stay fully or partially exposed and those that control the penetration of high-frequency sonar signals into the bottom. The ability of the seafloor to support an object depends largely on shearing strength which is a nonlinear, large-strain property associated with plastic deformation and complete disruption of the in-situ structure. In contrast, the complex velocity (speed and attenuation) of low-amplitude geoacoustic signals is a small-strain property that can be treated to a good approximation using linear theories. Both classes of response and their interaction are discussed using insights gained from the Biot--Gassmann theory. This theory allows extrapolation from low- to high-frequency response and examination of the effects of various parameters such as gas content and low overburden pressure. In particular the effect of recently measured high attenuation and velocity gradients is discussed and a correlation between shear strength and shear-wave velocity is shown. [Work supported by NRL, CBBLSRP.]