The imaging of Brittle Ductile Transition beneath the Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity

The thermo-rheology properties of the rocks are a crucial point to understand the mechanical behaviour of the crust in young and tectonically active area. As a consequence, several studies have been performed since last decades in order to understand the role of thermic state in the evolution of volcanic areas. In this context, the knowledge of the Brittle-Ductile transition inside the crust may provide insights to verify the roles that some hypothesized mechanisms, such as slab pull, crustal delamination might have played in the evolution of a tectonically active region. The goal of our study was the 3D imaging of the crust rheology beneath the active Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity. Despite many works have been done on the internal structure of the active volcanoes, the determination of the 3D rheological stratification of the crust below the caldera has not yet been tackled. To fill this gap of knowledge, we proposed for the first time the 3D geometry of the Brittle-Ductile transition calculated numerically on the basis of geological, geochemical, and geophysical data. We first performed a 3D numerical modelling of thermal field by using the a priori geological and geophysical information by consideration of thermal proprieties and mechanical heterogeneities of the crust beneath the caldera. We developed a 3D conductive/adventive time-dependent thermal numerical model solving the Fourier equation and further we used the retrieved thermal model to image a 3D rheological stratification of the shallow crust below the volcanic district.