Breaking Adria: adjoint tomography of a disappearing continental microplate

Abstract

The Adria plate plays a peculiar role in the geodynamics of the Central Mediterranean. It is the foreland of non-coeval mountain ranges and its margins are consumed in the process by subduction systems under the Alps to the north, the Apennines to the west and the Dinarides to the east. The complex behavior of this system and the large heterogeneity in data availability lead to a fragmented understanding of the Adria plate. In particular, its lithospheric structure, in terms of Vp and Vs profiles, is poorly known due to a lack of seismic stations, poor earthquake location quality (large observational gaps) and the consequent lack of coverage by classical seismic tomography methods. The uncertainties increase the difficulty of correctly assessing the seismic hazard along the Adriatic coasts (including tsunami hazard). Recently, we have proposed IMAGINE_IT, a reference 3D high-reso- lution seismic tomography of the Italian lithosphere. Enhanced accuracy is enabled by three-dimensional wavefield simulations based on SPECFEM3D in combination with an adjoint-state method. The Adria plate is located at the eastern border of the volume considered in the simulations, nevertheless, our tomography is able to image this plate with an unprecedented resolution and supports the idea that it is made of two distinct microplates having dif- ferent fabric and behavior and separated by the Gargano deformation zone. We have highlighted a northern portion with more complex wavespeed anomalies and a thinner crust, and a southern part with a more regularly layered wavespeed structure and a thicker crust. Here, we focus on additional details of those images, such as the mid-Adriatic ridge and a new set of iterations that exploit 7 years of additional data (IMAGINE_IT was limited to data until 2015) and the 2016-2019 AlpArray very dense regional arrays of broadband seismic stations which provide a new opportunity to improve our comprehension of the area.