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Ambient noise-based eikonal tomography in a deeply incised, sediment-filled canyon (Rhône valley, France) using a dense array of seismic nodes

Authors

Olivar-Castaño,  Andrés
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Ohrnberger,  Matthias
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Pilz,  Marco
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Haendel,  Annabel
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Lavoué,  François
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Boué,  Pierre
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Olivar-Castaño, A., Ohrnberger, M., Pilz, M., Haendel, A., Lavoué, F., Boué, P. (2023): Ambient noise-based eikonal tomography in a deeply incised, sediment-filled canyon (Rhône valley, France) using a dense array of seismic nodes, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-4446


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5021875
Abstract
Common ambient noise tomography studies use straight ray tomography for deriving group or phase velocity maps from long-term cross correlation of station pairs. Being suitable for low frequencies and large inter-station distances, this simplification can be problematic in near-surface studies where higher frequencies are considered and stronger lateral velocity variations are encountered. The eikonal tomographic approach avoids the assumption of straight rays by computing local group or phase velocities from the gradient of the traveltimes measured between the virtual sources and receivers, therefore approximating the true propagation trajectories of surface waves. In this work, we applied the eikonal approach to data from a dense, one-month long seismic deployment consisting in 400 3-component nodes installed over a 10x10 km zone in the heavily industrialized area of the Tricastin Nuclear Site (Rhône valley). This area is located above a sediment-filled, deeply incised canyon dug during the Messinian Salinity Crisis. The extreme subsurface topography of this canyon makes this area an interesting target for an eikonal tomographic study. We implemented an automated method that measures the phase traveltimes of the fundamental mode of Rayleigh and Love waves from the ambient noise cross correlations’ phase spectra. We then applied the eikonal approach to the measured traveltimes, resulting in a set of phase velocity maps for Rayleigh waves that are in good agreement with the existing geological knowledge and cover a frequency range from 0.4 to more than 5 Hz.