Estimation of sediment shear speed using interface waves in the New England Mudpatch

Stoneley and Scholte interface waves were generated in the New England Mud Patch in May 2022 by the Interface Wave Sediment Profiler (iWaSP). The iWaSP is a piezoelectric bender beam transducer which vibrates the seabed about 70 m below the sea surface. The range between the iWaSP and the receiving Ocean Bottom Recorders (OBX) with 3-axis geophones and hydrophone was about 40 m. The speed of these interface waves is approximately 90% of the shear wave speed in the higher-speed elastic medium. Arrivals were detected on the geophones with speeds ranging from 39 to 133 m/s for a mud thickness of about 6 m. However, the top 50 to 60 cm is much softer than the underlying mud and we term that the “surface layer.” We hypothesize that these interface waves propagated on the surface-layer-mud (Scholte) and the mud-sand interfaces (Stoneley). This work shows detections of Scholte and Stoneley waves and their arrival times provide estimates of the shear speeds of the layers. Modeling of these waves was performed using finite element modeling in COMSOL. Finally, an updated shear speed model for New England Mudpatch sediments is presented. [Work supported by ONR.]