On the Influence of Slopes, Source, Seabed and Water Column Properties on T Waves: Generation at Shore

Abstract

The term T waves is generally associated with acoustic waves generated by seismic events that subsequently travel horizontally in the ocean at the speed of sound. In this paper, we use a time-domain spectral-element method to perform a parametric study of the inuence of seaoor slope, source position and media properties for a typical (downslope) T-wave generation scenario.We nd that the energy and duration of these waves are particularly sensitive to the environment. In particular, the slopes and physical characteristics of the seabed play a crucial role for both the generation and the conversion of these waves. Likewise, the depth and position of the earthquake relative to the slope is of great importance, with the presence of privileged areas for the generation of T waves, which we map.

Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part II: Modeling of Seismo-Acoustic Wave Propagation

“…This means that only a small amount of the hydroacoustic energy related to the source in the water column is transformed into seismic energy that subsequently propagates toward the coast with some loss due to the presence of sediments. Although this energy transformation is largely favoured by a soft sea bottom and less observed in the case of a hard seabed [27], and despite the fact that the lower the frequency, the more hydroacoustic energy is transformed into the seismic energy [28], this likely cannot lead to huge impact on inland infrastructures.…”

“…In [23], an efficient procedure was derived to compute transmission losses and time dispersion maps for broadband signals and for elastic media as well. In the past decade, the time-domain SEM has been shown to accurately model T-wave generation and propagation in ocean [25], [26], and hence, enable deeper understanding of the seismic-to-hydroacoustic conversion at the sea bottom and the hydroacoustic-to-seismic conversion at the shore [27], [28]. The method has been successfully validated by real experiments [25].…”

Megameter propagation and correlation of T-waves from Kermadec Trench and Islands

“…The interest in studying T-waves started in the 1940s (Linehan, 1940) when they were discovered in seismograms. Nowadays, its study spans areas such as earthquake monitoring, tsunami early detection, and ocean thermometry (see Bottero et al, 2020 for a resume on T-waves areas of interest). T-waves can preserve high-frequency near-field information lost by seismic waves propagating in the crust (Bohnenstiehl et al, 2002) due to the low attenuation of acoustic waves propagating in the ocean.…”

“…In these cases, coupling from earthquake to ocean-acoustic waves can happen in different places (T-wave conversion zone) and hundreds of kilometers away from the hypocenter. T-wave conversion zones are generally linked to areas with large bathymetric gradients such as at slopes in trenches, islands, seamounts, edges of continental shelves, or depressions on the ocean floor (Talandier and Okal, 1979;Okal, 2008;Bottero et al, 2020). The T-wave conversion zone can then be total or partly unknown, adding uncertainty in estimating arrival time and azimuth.…”

“…It is also worth mentioning that T-waves traveling in the ocean (hydroacoustic T-waves) can reach continental slopes and be converted back into seismic waves (seismic T-waves) propagating on land hundreds of kilometers (e.g., Kosuga, 2011;de Groot-Hedlin, 2020). However, the conversion of hydroacoustic to seismic T waves depends mainly on the slope and seabed properties at the shore (Bottero et al, 2020;de Groot-Hedlin, 2020;Stevens et al, 2021).…”