On compressional wave attenuation in muddy marine sediments

Area of Science:

• Geophysics
• Acoustics
• Sedimentology

Background:

• Compressional wave attenuation is a key parameter for understanding acoustic propagation in marine sediments.
• Fine-grained sediments, such as those found in the New England Mud Patch, exhibit complex acoustic properties.
• Previous methods for measuring attenuation in situ have limitations in complex sediment structures.

Purpose of the Study:

• To measure in situ compressional wave attenuation in fine-grained sediments.
• To investigate the influence of sediment structure, specifically sand-mud transition intervals, on acoustic attenuation.
• To develop a predictive model for compressional wave attenuation in muddy continental shelf environments.

Main Methods:

• Application of a novel method measuring in situ compressional wave attenuation using spectral decay of reflection coefficient Bragg resonances.
• In situ measurements were conducted in the New England Mud Patch on mud layers of varying thickness (10.3 m and 3.2 m).
• Analysis focused on the impact of a sand-mud transition interval on measured attenuation values.

Main Results:

• Layer-averaged compressional wave attenuation was measured at 0.04 dB/m/kHz in a 10.3 m mud layer.
• Attenuation was found to be twice as large in a site with a 3.2 m mud thickness.
• Both measurements were significantly influenced by a ~1 m sand-mud transition interval at the base of the mud layer.

Conclusions:

• The spatial dependence of compressional wave attenuation in muddy sediments can be predicted by accounting for the sand-mud transition interval.
• Simple scaling methods incorporating the transition interval can improve attenuation predictions.
• The findings suggest that this predictive scaling approach is applicable to muddy continental shelf environments globally.