Geodynamics of the Central Mediterranean (GEOMED) inferred from ambient seismic noise

Ma#hew Agius1, Fabrizio Magrini1, Giovanni Diaferia1,2, Fabio Cammarano1, Claudio Faccenna1, Francesca Funiciello1, Emanuel Kästle3 and Mark van der Meijde4 Geodynamics of the Central Mediterranean A multidisciplinary investigation of the Sicily Channel region 1 Università Roma Tre, Dipar3mento di Scienze, Roma, Italy (ma<hew.agius@uniroma3.it). 2 Is3tuto Nazionale di Geofisica e Vulcanologia, Rome, Italy. 3 Ins3tute of Geological Sciences, Freie Universität Berlin, Berlin, Germany. 4 Faculty of Geo-Informa3on Science and Earth Observa3on, University of Twente, The Netherlands. h<ps://geomed-msca.eu

The Central Mediterranean, the area encompassing Italy, Sardinia, Tunisia, and Libya, is characterised by multiple tectonic processes (plate convergence, subduction, and backarc extension). The evolution and interaction of the plate margins within this relatively small area are still being unravelled, particularly at the adjacent region known as the Sicily Channel located between Sicily, Tunisia, Libya, and Malta. This Channel is characterised by a seismically and volcanically active rift zone. Much of the observations we have today for the southern parts of the Calabrian arc are either limited to the surface and the upper crust, or are broader and deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. The project GEOMED (https://geomedmsca.eu) addresses this issue by processing all the seismic data available in the region in order to understand better the geodynamics of the Central Mediterranean.
We use seismic surface waves to infer the structures and dynamics of the Central Mediterranean, from the Central Apennines to the African foreland, with a special focus on the Sicily Channel Rift Zone (SCRZ).

Radial anisotropy 3. Shear velocity model
We use ambient seismic noise data recorded on 83 sta3ons opera3ng in the Central Mediterranean between 1995-2018. A sta3on-pair dispersion curve is calculated for each year; smooth con3nuous parts of the curves are selected and outliers are removed. Average phase veloci3es are determined for the annual measurements. We compile >2,000 Rayleigh-and Love-wave dispersion curves spanning the period range 5-100 seconds (Bensen 2007; Boschi 2012; Kästle 2016).
We first invert Rayleigh and Love dispersion curves to phase velocity maps (Boschi 1999). From the phase velocity maps we then derive a 3D VS model by nonlinear joint inversion (Wathelet 2008; Kästle 2018).

Introduc:on ▲Smooth, broadband Rayleigh-and Love-wave dispersion curves.
Dashed grey curve: Regional average. • The crustal radial anisotropy across the SCRZ shows the extent of the extension across the Channel from SW-NE between Lampedusa and Sicily to SE-NW between Pantelleria and Sicily as inferred from GPS.
• The SCRZ has a thin lithosphere, underlain by a LVZ in the upper mantle assumed to be the asthenosphere.
• The LVZ suggests higher temperatures, which in turn facilitates flow likely to be verLcal as inferred from negaLve radial anisotropy.  (Agius 2013). Green: Radial anisotropy. Different tectonic structures are seen between 5-40 km depth. Tyrrhenian Sea has high velociLes at 10 km. At 40 km the SCRZ has relaLvely higher velociLes.

Crustal dynamics
Inferred crustal thickness coincides with high/low elevaLon eg, thin beneath the Tyrrhenian Sea and Sicily Channel, thick beneath mountains. Thickness also matches closely with Receiver FuncLon (<5 km for Sicily, Sardinia, Malta).
Shallow radial anisotropy correlates with areas characterised by subduction and intraplate volcanism, areas experiencing extension and compression, and areas rising and subsiding. The Sicily Channel is characterised by extension and subsidence. The anisotropy maps out deformation of the entire region.
The +ve/-ve radial anisotropy coincide with crustal deformaLon from earthquake focal mechanisms. The Tyrrhenian Sea and Sicily Channel have shallow +ve radial anisotropy underlain by -ve radial anisotropy.
1D profile validates the tomography model. The crust of the SCRZ is ~20 km, velocity is in the range of 2.5-3.3 km/s, and has strong +ve radial anisotropy. The uppermost mantle has a lowvelocity zone (LVZ) suggesting a thin lithosphere. The asthenosphere has -ve anisotropy.
• We present a new, robust, isotropic shear-velocity model of the Central Mediterranean, based on manually selected dispersion curves of surface waves generated from ambient seismic noise.
• The thinnest crust is found across the Tyrrhenian (<10 km) followed by the SCRZ (20 km), thicker beneath conLnental blocks and mountain ranges.
• Upper crustal radial anisotropy maps the dynamics of the region. Areas experiencing extension have +ve anisotropy, intraplate volcanism and subsidence. Areas experiencing compression have -ve anisotropy, subducLon volcanism and rising elevaLon.