Optimal Transmission of Interface Vibration Wavelets—A Simulation of Seabed Seismic Responses

Abstract

Seismic interface waves generated by seabed impacts are believed to have biological importance. Previous work on the effects of ocean piling and dredging studied water motion adjacent to the seabed, using sediment measurements as reviewed in the literature. This new modelling work has idealised the sediment data to a simple model with few parameters, and has shown how this leads to filtration of the applied energy to propagate simple seismic vibration wavelets. These special wavelets remain compact with high peak levels of the associated water particle velocity as they ripple outward, and provide a means of assessing the worst-case environmental impact. The form of this wavelet morphs from a hump shape to a dip and back, via intermediate forms which are here described in mathematical terms based on the Ricker form. Whilst the model structure is idealised it is much closer to reality than the Rayleigh and Scholte half-space models, but with only two more parameters required. The resultant wavelet peaks are propagated with values given by the optimal limit case of cylindrical spreading (ignoring absorption) which results in a relatively widespread impact.

An overview of fish bioacoustics and the impacts of anthropogenic sounds on fishes

“…Passage of sound and vibration into the substrate, which can be caused by sources such as pile driving, dredging and seismic surveys, may result in waves propagating through the substrate, both as compression waves and interface waves (Popper & Hawkins, ). The interface waves are often referred to as ground roll (Hazelwood et al, ). These waves travel slower than the speed of sound and can have strong particle motion components.…”

Finding a home in the noise: cross-modal impact of anthropogenic vibration on animal search behaviour

“…Whilst the strikes on the substrate in the present study had an acoustic component, there is no evidence to suggest pressure detection in marine crustaceans to date (Popper et al, 2001), and the measurement of water-borne particle motion is still hindered by a lack of readily-available sensors (Popper and Hawkins, 2018). Although the vast majority of invertebrates are either solely or partially benthic or have benthic life-stages, seabed vibration is not routinely measured (Popper and Hawkins, 2018; Roberts and Elliott, 2017) despite sensitivities to this energy (Roberts et al, 2016), and recent modelling of particle motion waves travelling in the sediment surface (Hazelwood et al, 2018). Indeed, there are only a handful of papers (Day et al, 2016, 2017; Miller, 2015; Roberts et al, 2016, 2017) which include vibration measurement or modelling relating to animal exposure.…”

“…Water-borne acoustic energy propagates from sources, consisting of a pressure change, and an associated back and forth movement of molecules known as particle motion (Popper and Hawkins, 2017, 2018). Substrate-borne vibrational waves may also propagate through the seabed, particularly when sources directly contact the sediment (Hazelwood et al, 2018; Roberts and Elliott, 2017). Impulsive noise, which involves sudden high pressure and particle motion changes, is of particular interest, since it may increase the likelihood of sensory damage.…”

Noise Waveforms within Seabed Vibrations and Their Associated Evanescent Sound Fields

“…As pointed out by Shearer [14] and Achenbach [15], dispersion does not occur in either of the half-space models of Rayleigh or Scholte. We used a more realistic half-space model from our earlier work [16] with gradually increasing material stiffness with depth. This is seen to support vibration wave modes that travel at different speeds.…”

“…Our choice of parameters was based on Hamilton's data, mainly lying within the considerable variation he described. The initial fit by Hazelwood and Macey in 2016 [18] was simplified for the 2018 paper [16] to a linear increase of V s with depth d. The function V s (d) then has a gradient, g r .…”