Estimating P- and S-Wave Velocities in Fluid Mud Using Seismic Interferometry

Abstract

Fluid mud plays an important role in navigability in ports and waterways. Characterizing and monitoring the seismic properties of the fluid mud can help understand its geotechnical behavior. Estimation of the wave velocities in fluid mud with high accuracy and repeatability enables investigating the behavior of parameters like the yield stress in a nonintrusive and reliable way. We perform ultrasonic reflection measurements in a laboratory to investigate the wave propagation in a water/fluid-mud layered system. The component of wave propagation in the water layer inevitably brings kinematic dependence on the characteristics of that layer, making the estimation of exact velocities in the fluid mud more challenging. In order to extract the wave velocities only in the fluid-mud layer, we use a reflection geometry imitating field measurement to record the ultrasonic data from sources and receivers in the water layer. We then use seismic interferometry to retrieve ghost reflections from virtual sources and receivers placed directly at the water-mud interface. Using velocity analysis applied to the ghost reflections, we successfully obtain the P-wave and S-wave velocities only inside the fluid-mud layer, and investigate the velocity change during the self-weight consolidation of the fluid mud. Our results indicate that the S-wave velocities of the fluid mud increase with consolidation time, and show that reflection measurements and ghost reflections can be used to monitor the geotechnical behavior of fluid mud.

The utilization of ghost reflections retrieved by seismic interferometry for layer‐specific characterization of the shallow subsurface

“…The retrieved Green function on the left‐hand side of relation (2) comprises pseudo‐physical reflections, as well as ghost reflections. These ghost reflections are retrieved in the time domain from the CC of the primary reflections from two different interfaces due to insufficient destructive interferences (Draganov et al., 2012; Ma et al., 2022). Ghost reflections are similarly retrieved from the correlation of internal multiples with primaries or other internal multiples.…”

“…Ma et al. (2021, 2022) illustrated the application of ghost reflections in estimating the layer‐specific velocity of a fluid–mud layer in a water/fluid–mud system, using ultrasonic experiments. They clearly showed that the retrieved ghost reflections propagate only inside the fluid–mud layer, and the travel paths inside the water layer are eliminated.…”