Abstract
• In this work, we study the crust and the uppermost mantle structure beneath the Sicily Channel, by applying the ambient noise and earthquake tomography method. After computing cross-correlation of the continuous ambient noise signals and processing the earthquake data, we extracted 104 group velocity and 68 phase velocity dispersion curves corresponding to the fundamental mode of the Rayleigh waves. We computed the average velocity of those dispersion curves to obtain tomographic maps at periods ranging from 5 s to 40 s for the group velocities and from 10 s to 70 for the phase velocities. We inverted group and phase speeds to get the shear-wave velocity structure from the surface down to 100 km depth with a lateral resolution of about 200 km. The resulted velocity models reveal a thin crust with thickness value of 15 km beneath the southern part of the Tyrrhenian basin and a thickness value of 20 km beneath Mount Etna. The obtained thickness values are well correlated with the reported extension of the Tyrrhenian lithosphere due to the past earthquake tomography subduction and rollback of the Ionian slab beneath the Calabrian Arc. The crustal thickness increases and reaches values between 28 and 30 km beneath the Tunisian coasts and Sicily Channel. The S-wave models reveal also the presence of high velocity body beneath the island of Sicily. This finding can be interpreted as the presence of the Ionian slab subducting beneath the Calabrian Arc. Another high velocity body is observed beneath the southern part of the Tyrrhenian basin, it might be interpreted as the presence of fragments of the African continental lithosphere beneath the Tyrrhenian basin.
Highlights
The Sicily Channel, located between northern Africa and Sicily, represents the eastern part of the foreland Maghrebides-Apennines thrust belt that connects the African and the Eurasian plates.Velocity structure of the Sicily ChannelThis area is characterised by two principal tectonic regimes: A northeast-southwest extension due to the Sicily Channel rift, overlapping the northwest-southeast compression due to the Maghrebides-Sicily-Apennines accretionary prism [e.g. Corti et al, 2006]
Analysing and plotting group and phase velocity derivatives with respect to elastic parameters versus depth, we found that group velocity periods are sensitive to S-wave velocity structure in the depth range approximately between 1 and 60 km, while the phase velocity periods are sensitive to S-wave velocity structure depth down to 100 km
The Moho depth values are in agreement with the results from the recent 3d shear wave velocity study of the crust and uppermost mantle beneath the Tyrrhenian basin and margins done by Manu-Marfo et al [2019]
Summary
The Sicily Channel is showing bathymetric depths less than 400 m in the most of the area, while it reaches depth ranging from 1300 m to 1700 m beneath the Pantelleria, Malta and Linosa islands Those depressions are likely related to the NW-trending rift system crosscutting the Apennines-Maghrebides belt [Calò and Parisi, 2014; Civile et al, 2015; Bonaccorso and Mattia, 2000]. For deeper structures Spakman and Wortel [2004] and Piromallo and Morelli [2003] presented tomographic maps that reveal a low P wave velocities at depths of 150 to 200 km beneath the Sicily Channel These low velocities mark the rifting process occurring in the region. High resolution tomographic maps imaging the crust and upper mantle structures of the Mediterranean basin and Sicily Channel are lacking due to the limited number of available seismic stations.
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