EGU2020-5374, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-5374
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Crust and upper mantle structure of the Ligurian Sea revealed by ambient noise tomography using ocean bottom seismometer data

Felix Noah Wolf1, Dietrich Lange1, Heidrun Kopp1,2, Anke Dannowski1, Ingo Grevemeyer1, Wayne Crawford3, Nikolaus Froitzheim4, Martin Thorwart2, Anne Paul5, and the AlpArray Working Group*
Felix Noah Wolf et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Kiel University, Kiel, Germany
  • 3Institut de physique du globe de Paris, Paris, France
  • 4ISTerre - Institut des Sciences de la Terre, Grenoble, France
  • 5University of Bonn, Bonn, Germany
  • *A full list of authors appears at the end of the abstract

The Liguro-Provencal-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 at roughly 32–24 Ma is associated with rifting, shaping the Ligurian Sea. It is highly debated though, whether oceanic or atypical oceanic crust was formed or if the crust is continental and experienced extreme thinning during the opening of the basin.

To investigate the velocity structure of the Ligurian Sea a network (LOBSTER) of 29 broadband Ocean Bottom Seismometer (OBS) was installed jointly by GEOMAR (Germany) and ISTerre (France). The LOBSTER array measured continuously for eight months between June 2017 and February 2018 and is part of the AlpArray seismic network. AlpArray is a European initiative to further reveal the geophysical and geological properties of the greater Alpine area.

We contribute to the debate by surveying the type of crust and lithosphere flooring the Ligurian Sea.
Because of additional noise sources in the ocean, causing instrument tilt or seafloor compliance, OBS data are rarely used for ambient noise studies. However, we extensively pre-process the data to improve the signal-to-noise ratio. Then, we calculate daily cross-correlation functions for the LOBSTER array and surrounding land stations. Additionally, we correlate short time windows that include strong events. The cross-correlations of these are dominated by earthquake signals and allow us to derive surface wave group velocities for longer periods than using ambient noise only. Finally, phase velocity maps are obtained by inverting Green’s functions derived from cross-correlation of ambient noise and teleseismic events, respectively. The phase velocity maps show strong heterogeneities for short periods (5-15 s, corresponding to shallow depths). Causes for these include varying sediment thickness, fault zones and magmatism. For longer periods (20-80 s) the velocity structure smoothens and reveals mantle velocities north-northwest of the basin centre. This might hint on an asymmetric opening of the basin. We do not see strong indications for an oceanic spreading centre in the Ligurian basin.

AlpArray Working Group:

http://www.alparray.ethz.ch/

How to cite: Wolf, F. N., Lange, D., Kopp, H., Dannowski, A., Grevemeyer, I., Crawford, W., Froitzheim, N., Thorwart, M., and Paul, A. and the AlpArray Working Group: Crust and upper mantle structure of the Ligurian Sea revealed by ambient noise tomography using ocean bottom seismometer data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5374, https://doi.org/10.5194/egusphere-egu2020-5374, 2020

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