2025_programme: Vertical-mode and horizontal-ray modeling of T waves from the 2020 Beirut-port explosion

• Day: June 16, Monday
    Location / Time: A. TERPSIHORI at 14:50-15:10
• Last minutes changes: -
• Session: 04. Comprehensive Nuclear-Test-Ban Treaty Monitoring, and its Civil and Scientific Applications
  Organiser(s): Georgios Haralabus, Mario Zampolli, Tiago Oliveira, Mark Prior
  Chairperson(s): Georgios Haralabus, Tiago Oliveira
• Lecture: Vertical-mode and horizontal-ray modeling of T waves from the 2020 Beirut-port explosion
  Paper ID: 2282
  Author(s): Jean Lecoulant, Abdel-Ouahab Boudraa
  Presenter: Jean Lecoulant
  Abstract: On 2020, August 4st, a devastating chemical explosion occurred at Beirut port. It generated seismic, hydroacoustic and infrasonic waves that were measured hundreds of kilometers away from the source. The hydroacoustic waves, known as T waves, were measured by 13 ocean bottom seismometer (OBS) localized in the Eastern Mediterranean. The OBS provide T-wave arrival times. In absence of a pressure sensor, azimetry based on the OBS horizontal components provides information about T-wave backazimuth with an 180° ambiguity. Beamforming is also possible on one close constellation of five OBS. All these observable quantities make it possible to study 3D effects affecting T-wave generation and propagation. Only the closest OBS constellation (100 km from Beirut) shows back azimuths consistent with great-circle propagation. Two OBS located near Eratosthenes seamount show two distinct T-wave arrivals with different azimuths. We model T-wave generation through vertical modes and horizontal rays. This procedure computes the phase speed of ultra-low-frequency (ULF) acoustic modes that varies with water depth over the computation domain. Phase speed is then used for 2D ray tracing. 3D effects are modeled through variations of phase speed and its spatial derivatives. Vertical modes and horizontal rays are usually based on modes of a Pekeris (fluid-fluid) waveguide. Our implementation instead uses the modes of a fluid-solid waveguide, which are expected to better model T-wave behavior at ULF. The eigenrays between the OBS and Beirut port are calculated for different mode orders, as well as associated backazimuths and travel times. The agreement between simulated and measured backazimuths and travel times is satisfying. Departure from great-circle propagation is mainly explained by T-wave generation of the Levant coast, 100 km south of Beirut, and horizontal refraction on Eratosthenes seamount.
• Corresponding author: Dr Jean Lecoulant
  Affiliation: Institut de recherche de l’École navale
  Country: France