GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 59 Alparone et al. (2012), results denote formal location uncertainties in the order of 200 m both in horizontal and vertical directions. Locations and event time-occurrence point out that the activity of that fault during the considered period is substantially related to the strongest earthquake (MW 4.9), on December 26th. The hypocenter of this event is very close to the cosismic fractures identified at the surface and his focal mechanism (Fig. 1) (http://sismoweb.ct.ingv.it/focal/ ; see Scarfì et al. , 2013) indicates a dextral strike slip movement on a sub-vertical NW-SE oriented plane. After that shock, most of the seismicity in the sector moves at about 1 km east of the northern tip of the Fiandaca Pennisi fault with hypocentres 1-3 km deep. The focal solution of a ML 2.5 event, indicating normal movement on a NE-SW plane, would suggest the activation of neighboring structures (Monaco et al. , 2019). Coseismic fractures. The fracture zone extends for about 8 km through the village centres and rural countryside with average direction changing fromN150° E to N130° E from southeaster to the north western sector of the shear zone (Fig. 1). The damage mainly consists of shallow and deep cracks affecting the soil surface, walls of buildings (both infilling and bearing walls), fractures and rotations of retaining walls, sidewalks, curbs and pavings. Fractures and cracks are usually aligned along bands with variable width ranging from 2 to more than 40 m. The width is highly variable ranged between 10 and 110 mt. Fractures are systematically arranged and their orientation provides important information to infer the kinematics of the main fault zone. Fractures measured have been interpreted as Riedel’s R or T type fractures in a right lateral shear zone (Riedel, 1929; Mercier and Vergely, 1996). The average direction of T-type cracks Fig. 1 - DEM of the area affected by the fault. Coloured areas show the coseismic ground fractures of historical earthquakes of Fiandaca Pennisi fault. Yellow triangles indicate the benchmarks of GNSS positioning UNICT_NET framework; the star indicate the epicentre of 26 th December 2019 earthquake with relative focal mechanism.