Characterization of surficial mudflat sediments using shear wave elastography, core-logging, and microscopy...

Area of Science:

• Geophysics
• Acoustics
• Sedimentology

Background:

• Surficial sediments exhibit complex heterogeneity due to physical, biological, and chemical processes.
• This heterogeneity significantly impacts elastic wave transmission and scattering.
• Non-invasive techniques are needed to characterize these delicate surficial layers.

Purpose of the Study:

• To apply shear wave elastography (SWE) for high-resolution imaging of shear speed heterogeneity in surficial sediments.
• To correlate elastic properties with microstructural characteristics.
• To investigate the relationship between sediment structure and wave propagation.

Main Methods:

• Samples collected from New Hampshire mudflats.
• Acoustic radiation force generated shear waves (50-200 Hz).
• High-frame-rate ultrasound imaged shear wave propagation, creating 2D shear speed maps.
• Microscopy techniques analyzed sediment microstructure.

Main Results:

• SWE identified millimeter-scale stiff inclusions (up to 16 m/s) within a softer matrix (~2 m/s).
• Spatial spectral analysis showed shear speed strengths between -42 and -38 dB re 1 m.
• Positive shear speed gradients correlated with decreased pore connectivity and increased grain connectivity with depth.

Conclusions:

• Shear wave elastography is effective for characterizing fine-scale heterogeneity in surficial sediments.
• Sediment microstructure, particularly grain contacts and organo-clay content, influences elastic wave properties.
• Findings support a grain shearing model for lubricated, compliant contacts.