UACE2017 Proceedings: 3-D modeling of the generation and propagation of acoustic T-waves at seafloor spreading ridges

• Session:
  Three-dimensional sound propagation models and effects
• Paper:
  3-D modeling of the generation and propagation of acoustic T-waves at seafloor spreading ridges
• Author(s):
  Jean Lecoulant, Jean-Yves Royer, Claude Guennou, Laurent Guillon
• Abstract:
  Seafloor spreading ridges are generally isolated in the middle of the oceans and remote from seismometers deployed on land. As a result, their low-level seismic activity and near-field phenomena related to earthquakes are poorly known. Using hydrophones recording the hydroacoustic waves generated by undersea earthquakes, known as T-waves, is an alternative way to monitor this seismic activity of the ridges. The rapid attenuation of seismic waves in the Earth crust is overcome by the excellent acoustic properties of the ocean. To better understand the interaction of a seismic event with the seafloor and the resulting generation of the T-wave acoustic phase, we use a 3D spectral finite-element code – SPECFEM3D – that jointly models the propagation of seismic waves in a solid medium (the Earth crust) and of the acoustic waves in the fluid medium (the ocean). Using simplified configurations, we investigate the dependency of T-wave generation on the focal mechanism and on the topography of the sea-bottom. The focal mechanism determines the radiation pattern of P- and S-waves in the crust, whose conversion into T-waves at the sea-bottom have not the same efficiency. The time-function used to model the earthquake source also influences the duration and frequency content of the signal that will propagate in the water column. The near-field modeling of the generation of T-waves helps in defining the most appropriate and efficient form of time-function. The seafloor topography, hence the size and shape of the conversion zone, determines the presence of T-waves and the amplitude, shape and duration of the signal. Our first results confirm the importance of 3D-effects in the generation and propagation of T-waves, which must be taken into account to fully describe and understand T-waves recorded by networks of hydrophones monitoring seafloor spreading ridges.
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Contact details

• Contact person:
  Mr Jean Lecoulant
• e-mail:
  
• Affiliation:
  Laboratoire Géosciences Océan - CNRS UMR 6538
• Country:
  France