Insights into the fragmentation of the Adria Plate

Abstract

This study gives an interpretation of the current tectonics and kinematics of the Adria Plate, a region mostly coinciding with Italy and its surroundings. We have examined the spatial distribution and kinematics of seismicity by using an updated dataset obtained integrating the available catalogues of earthquakes and focal mechanisms. Moreover, to highlight the distribution of seismicity and of the asso- ciated strain patterns, we have elaborated a seismic flux map of the Italian region, which is a map of the energy released per unit time and per unit area. Seismic flux represents the energy released and provides a synthetic and continuous view of areas with greater seismicity and associated strain patterns with respect to the plot of earthquakes only. The seismic data, and the results of some elaborations car- ried out using these datasets have been compared with the present-day state of stress and slip rates of the major active faults of some sectors of Italy, as well as with the horizontal kinematics highlighted by GPS observations. The distribution and kinematics of earthquakes and active faults, the seismic flux, and GPS velocities, suggest that the Adria Plate is currently behaving as an ensemble of independent blocks rather than as a unique rigid plate. The Adria Plate can be thus subdivided into three major blocks and a number of smaller blocks moving independently under the action of a first-order mechanism related to the ongoing, roughly N-S, Europe-Africa convergence vector. This complicated setting may promote the occurrence of mutual relationships between blocks, and generate peculiar local kinematics causing seis- mic activity. We infer that the great majority of the seismic events occur at the boundaries of the main or minor blocks, and therefore the alignments of seismicity allows the individuation of the different blocks and the main seismogenic belts. A major crustal structure subdivides the Adria Plate into a western and two eastern blocks, and approximately coincides with the axial zone of the Apennines along which most of the seismicity is concentrated.