Seismic velocity structure of the Calabrian subduction system: new insights from the CHIANTI wide-angle seismic survey

Subduction Interface Processes Meeting (SIP), An International Conference Zooming On Subduction Zones, 19-21 April 2017, BarcelonaIn the Western Mediterranean, the Calabrian subduction system formed as a result of the Neogene E and SE subduction of the Ionian Lithosphere underneath Calabria. The back-arc region is represented by the Tyrrhenian basin, where recent geophysical results revealed abrupt variations in back-arc extension and magmatic crustal accretion. However, little is known regarding the lithospheric transition between the back-arc and the frontal domain of the subduction system. Here we present preliminary results from the CHIANTI amphibious 2D wide-angle seismic (WAS) survey carried out in 2014. The goal of this experiment was to image the entire Calabrian subduction system from the Tyrrhenian back-arc domain to the fore-arc in the Ionian Sea, across Calabria along a 550 km long transect. The data were acquired by 43 ocean bottom seismometers (OBS) and 3 land stations, and inverted for both Vp and critical reflections using a joint refraction and reflection travel time tomography method. From NW to SE, in the Tyrrhenian Basin, the 2D Vp tomographic model shows abrupt variations of the velocity structure. Between the Vavilov and Marsili basins, in the back-arc domain, a relatively thick and low velocity block is interpreted as a remnant continental crust. To the southeast, OBS sections in the Marsili Basin lack any apparent PmP-like arrival. The velocity structure of this basin reveals a continuous vertical velocity gradient of ~1 s-1. This structure resembles to that of the Vavilov Basin, where the basement is made of exhumed mantle rocks. The transition between the Marsili Basin and Calabria is marked by a steep Moho geometry that deepens from 10 to 20 km of depth in less than 150 km of profile from NW to SE. Southeast Calabria, the model shows a strong horizontal velocity gradient that is interpreted as the backstop of the subduction. In the Ionian, a 3-5 km thick sedimentary wedge thickens towards the northwest. No interplate geometry is retrieved below this sedimentary wedge as the data suffers from strong attenuationPeer Reviewe