Preprints
https://doi.org/10.5194/se-2021-55
https://doi.org/10.5194/se-2021-55

  07 May 2021

07 May 2021

Review status: this preprint is currently under review for the journal SE.

3D crustal structure of the Ligurian Sea revealed by ambient noise tomography using ocean bottom seismometer data

Felix Noah Wolf1, Dietrich Lange1, Anke Dannowski1, Martin Thorwart2, Wayne Crawford3, Lars Wiesenberg2, Ingo Grevemeyer1, Heidrun Kopp1,2, and the AlpArray Working Group Felix Noah Wolf et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24148, Germany
  • 2Institute of Geosciences, Kiel University, Kiel, 24118, Germany
  • 3Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, Paris, 75238 Cedex 5, France
  • A full list of team members appears at the end of the paper.

Abstract. The Liguro-Provençal basin was formed as a back-arc basin of the retreating Calabrian-Apennines subduction zone during the Oligocene and Miocene. The resulting rotation of the Corsica-Sardinia block is associated with rifting, shaping the Ligurian Sea. It is still debated whether oceanic or atypical oceanic crust was formed or if the crust is continental and experienced extreme thinning during the opening of the basin. We invert velocity models using an amphibious network of seismic stations, including 22 broadband Ocean Bottom Seismometers (OBS) to investigate the lithospheric structure of the Ligurian sea. The instruments were installed in the Ligurian Sea for eight months between June 2017 and February 2018 as part of the AlpArray seismic network. Because of additional noise sources in the ocean, OBS data are rarely used for ambient noise studies. However, we attentively pre-process the data, including corrections for instrument tilt and seafloor compliance. We took extra care to exclude higher modes of the ambient-noise Rayleigh waves. We calculate daily cross-correlation functions for the LOBSTER array and surrounding land stations. Additionally, we correlate short time windows that include teleseismic earthquakes that allow us to derive surface wave group velocities for longer periods than using ambient noise only. Group velocity maps are obtained by inverting Green’s functions derived from the cross-correlation of ambient noise and teleseismic events, respectively. We then used the resulting 3D group velocity information to calculate 1D depth inversions for S-wave velocities. The shear-wave velocity results show a deepening of the Moho from 12 km at the southwestern basin centre to 20–25 km at the Ligurian coast in the northeast and over 30 km at the Provençal coast. We find no hint on mantle serpentinisation and no evidence for an Alpine slab, at least down to depths of 25 km. However, we see a separation of the southwestern and northeastern Ligurian Basin that coincides with the promoted prolongation of the Alpine front.

Felix Noah Wolf et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-55', Anonymous Referee #1, 02 Jun 2021
  • RC2: 'Comment on se-2021-55', Anonymous Referee #2, 09 Aug 2021
  • EC1: 'Editor's Comments on se-2021-55', M. R. Handy, 13 Aug 2021

Felix Noah Wolf et al.

Felix Noah Wolf et al.

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Short summary
The Ligurian Sea opened ~30–15 Ma during the SE migration of the Calabrian subduction zone. Using ambient seismic noise from stations on land and at the ocean bottom, we calculated a 3D shear-velocity model of the Ligurian Basin. We find a shallow crust-mantle transition at the southwestern basin centre that deepens towards the Liguro-Provencal coast. We see no evidence for an Alpine slab beneath the basin. However, a separation of SW and NE basin appears to prolong the onshore Alpine front.