Boccaletti, Mario

The city of Florence possesses a concentration of cultural and artistic treasures which is unique in the world. In this sense it has a particularly high seismic exposure and a potentially high vulnerability. In order to better evaluate its seismic hazard and risk, we analyzed the seismic response of the urban area of Florence by performing a multidisciplinary study on the effects of earthquakes on the city. By a computer aided methodology we re-evaluated the seismic intensity reports of the May 18 and June 6, 1895 earthquakes in different parts of the city and compared these data with recent studies on surface geology, active tectonics and actual fault movements in the Florence basin. We concluded that more detailed studies of soil response are needed to form a basis for public policy.

Recent satellite geodetic measurements help to clearly define the velocity field in the Aegean-Anatolian area. The velocity field can be broadly characterized by anticlockwise rotation of this region relative to Eurasia, around a pole located at Lat. 32.73, Long. 32.03, north of the Egyptian shoreline. Studies of the fault kinematics in the region also provide information on the time evolution of the stress field. In this work, we model deformation in the Aegean-Anatolian region to better understand the tectonic origin of the observed stress and velocity fields. We found that the observed deformation pattern can be well reproduced by imposing simple boundary conditions including: (1) northward displacement of the Arabian plate, (2) locking of eastward motion in northwestern Greece and (3) suction force at the Hellenic trench. The observed variation in the stress field occurred at 0.9 Ma can be partially explained by a change in the activity of the North Anatolian fault.

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.