Seismic and hydro-acoustic waves emitted by submarine landslides at laboratory scale for the detection and assessment of associated hazards

Landslides and the potential tsunamis they generate represent one of the major natural hazards. Their detection and simulation currently remain an open problem, made extremely difficult by the lack of field data on the dynamics of these flows, data that are nevertheless necessary to validate the models developed. In this context, the seismic and hydro-acoustic waves generated by submarine landslides represent a unique study tool, carrying precious information on the characteristics of the flow (mass, velocity, mechanical behaviour, etc.) at distances of up to hundreds of km from the source. However, it is very difficult to analyse these waves because of the complexity of the generation mechanisms and the strong influence of wave propagation. In this context, laboratory experiments provide an unparalleled opportunity to study processes in a simplified way, by separating effects such as the presence or absence of water, topography, initial conditions, etc. The Institut Langevin, IPGP and EOST have joined forces, notably as part of the SLIDEQUAKES ERC, to study the generation of elastic waves during dry granular flows. The work carried out on dry granular flows has clearly revealed spectral and temporal signatures that have been validated by numerical approaches and interpreted using analytical models, involving various parameters such as granular temperature, density, velocity profile, etc. These laboratory measurements were combined with discrete element simulations to gain access to internal variables that could not be measured in the laboratory. The results obtained have made it possible to clarify the physical origin of the empirical laws observed at field scale and to propose new ways of interpreting seismic waves in terms of flow characteristics. We propose here to change the paradigm by studying acoustic emission from granular flows, but this time immersed. Over the last thirty years, work on granular flows has led to a quantum leap in the understanding and description of the behaviour of granular media. However, apart from a single preliminary study carried out in 2012, the acoustic emission associated with these flows remains a largely unexplored topic at the interface between granular physics and physical acoustics. This work is all the more important as they are analogous to submarine landslides, for which very little data exist but which can generate potentially devastating tsunamis. Using the waves emitted by these landslides to detect them and constrain their behaviour would be an exceptional advance for assessing the associated risks. The use of hydroacoustic waves for this purpose is virtually non-existent, despite the fact that these waves propagate very far and carry the signature of landslide velocity.

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