New measurements of compressional wave attenuation in deep ocean sediments

Abstract

In many situations of low frequency acoustic propagation in the ocean, the acoustic properties of the bottom are an important factor. One quantity of which few measurements have been made or reported is the compressional wave attenuation profile. This paper reports attenuation measurements based upon measurements from explosive sources which encountered the ocean bottom several times. It was found that compressional wave attenuation coefficients at 100 m depth are approximately 0.015 dB/m-kHz in terrigenous turbiditc sediments and 0.03 dB/m-kHz in calcareous sediments. These values are as low as, and lower than, the smallest previously reported estimates.

Acoustics of marine sediment under compaction: Binary grain-size model and viscoelastic extension of Biot’s theory

“…Compressional-and shear-wave attenuation in near-surface sediments Figure 9 shows predictions from the model for the attenuation coefficient in the near-surface regime of the compressional waves in sample MFG with varying montmorillonite content ͑solid lines͒ and in sandy sediment with 8% of clay ͑heavy dashed line͒ as a function of frequency, together with data ranges from the literature. 11,42 and, illucidating the significance of the model extensions presented here, the corresponding curves resulting from the original Biot theory. In the lower frequency range, it can be clearly seen that the significance of the VCM consists of creating a background attenuation proportional close to the first power of frequency.…”

Deep seafloor arrivals: An unexplained set of arrivals in long-range ocean acoustic propagation

“…In this case the model is about 12 km thick. The seafloor consisted of ͑i͒ a 20 m thick layer of homogeneous sediment with Vp = 1.6 km/ s and attenuation of 0.01 dB/ m at 70 Hz ͓all attenuation values are from Hamilton ͑1976͒, although better values for sediments have been recommended in more recent papers ͑Bowles, 1997; Kibblewhite, 1989;Mitchell and Focke, 1980͔͒, ͑ii͒ a 2 km thick layer of basalt with a gradient in P-wave speed from 4.0 to 6.8 km/ s and attenuation of 0.0025 dB/ m, ͑iii͒ a 4 km thick layer of gabbro with a gradient in P-wave speed from 6.8 to 8.1 km/ s and attenuation of 0.0025 dB/ m, and ͑iv͒ a homogeneous half-space for the mantle at 8.1 km/ s and attenuation of 0.0025 dB/ m. Density in the sediments ͑mostly pelagic clay͒ is given by: density ͑g / cc͒ = 1.35 + ͑1.80− 1.35͒ / 300ϫ depth ͑m͒ ͑Hamilton, 1976͒. For the igneous rocks density is related to compressional sound speed by: density ͑g / cc͒ = 1.91+ 0.158Vp ͑km/ s͒ ͑Swift et al, 1998͒.…”

Numerical evaluation of pile vibration and noise emission during offshore pile driving

“…The dependency of the attenuation on the depth is discussed by Hamilton [20][21][22] and by Mitchell and Focke [23]. Mitchell and Focke [23] divide the sediment into soil with low, medium and high attenuation.…”

“…Mitchell and Focke [23] divide the sediment into soil with low, medium and high attenuation. Depending on this nature the compressional attenuation can increase or decrease within the first 100 m depth.…”