Basin inversion: reactivated rift structures in the central Ligurian Sea revealed using ocean bottom seismometers
|Author(s)||Thorwart Martin1, Dannowski Anke2, Grevemeyer Ingo2, Lange Dietrich2, Kopp Heidrun1, 2, Petersen Florian2, Crawford Wayne3, Paul Anne4, The Alparray Working Group|
|Affiliation(s)||1 : CAU, Institute of Geosciences, Christian-Albrechts-Universität zu Kiel, 24105 Kiel, Germany
2 : GEOMAR, Marine Geodynamics, Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany
3 : IPGP, Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, Paris, 75238 Cedex 5, France
4 : Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, UGE, ISTerre, 38000 Grenoble, France
|Source||Solid Earth (1869-9510) (Copernicus GmbH), 2021-11 , Vol. 12 , N. 11 , P. 2553-2571|
|Note||Special issue | New insights on the tectonic evolution of the Alps and the adjacent orogens Editor(s): Mark Handy, Emanuel Kästle, Giancarlo Molli, Anne Paul, Claudia Piromallo, Christian Sue, Mirijam Vrabec, and CharLotte Krawczyk|
The northern margin of the Ligurian Basin shows notable seismicity at the Alpine front, including frequent magnitude 4 events. Seismicity decreases offshore towards the Basin centre and Corsica, revealing a diffuse distribution of low magnitude earthquakes. We analyse data of the amphibious AlpArray seismic network with focus on the offshore component, the AlpArray OBS network, consisting of 24 broadband ocean bottom seismometers deployed for eight months, to reveal the seismicity and depth distribution of micro-earthquakes beneath the Ligurian Sea.
Two clusters occurred between ~10 km to ~16 km depth below sea surface, within the lower crust and uppermost mantle. Thrust faulting focal mechanisms indicate compression and an inversion of the Ligurian Basin, which is an abandoned Oligocene rift basin. The Basin inversion is suggested to be related to the Africa-Europe plate convergence. The locations and focal mechanisms of seismicity suggest reactivation of pre-existing rift structures. Slightly different striking directions of faults in the basin centre compared to faults further east and hence away from the abandoned rift may mimic the counter-clockwise rotation of the Corsica-Sardinia block during ~20–16 Ma. The observed cluster events support the hypothesis of strengthening of crust and uppermost mantle during rifting related extension and thinning of continental crust.