Search

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 ocean bottom seismometer (OBS) network, consisting of 24 broadband OBSs deployed for 8 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 the 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–Miocene 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-related structures. Slightly different striking directions of presumed rift-related faults in the basin centre compared to faults further east and hence away from the rift basin may reflect the counter-clockwise rotation of the Corsica–Sardinia block. High mantle S-wave velocities and a low Vp/Vs ratio support the hypothesis of strengthening of crust and uppermost mantle during the Oligocene–Miocene rifting-related extension and thinning of continental crust. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Ligurian Basin is situated at the transition from the western Alpine orogeny to the Apennine system, an area where a change in subduction polarity ('Ligurian Knot') is observed. The Back-arc basin was generated by the southeast trench retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to continental thinning and subsidence, oceanic spreading with unroofing of mantle material was proposed for the late period of opening 21-16 Ma.To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active and passive seismic data have been recorded on ocean bottom seismometers. A seismic long-term network comprising of 29 broad band stations was installed from June 2017 to February 2018 in the framework of SPP2017 4D-MB, the German component of AlpArray. Refraction seismic profiles were shot to serve two aspects: (1) Determine the orientation of the horizontal components of the long-term ocean bottom seismometers and (2) estimate the velocity distribution of the upper lithosphere, to provide a better earth velocity model for the analysis of the passive seismic data. The ambient noise technique is applied to compute surface wave phase velocity maps of Rayleigh waves for the Ligurian Basin.Good quality data have been recorded, regional and teleseismic events could be detected by stations of the network. Active shots have been recorded by all stations on the seafloor during shooting. The majority of the refraction seismic data show mantle phases at offsets up to 70 km. The crust mantle boundary in the central basin is observed at ~9 km depth below seafloor. The mantle shows rather high velocities > 7.8 km/s. [ABSTRACT FROM AUTHOR]