GNGTS 2017 - 36° Convegno Nazionale

24 GNGTS 2017 S essione 1.1 domains. However, observations and inferred rupture histories raise concern on the concept of maximum expected magnitude. Two sequences experienced foreshocks activity located along structural discontinuities between the main faults (1997 Colfiorito) and along the main fault plane (2009 L’Aquila). These sequences lasting for months, marked the onset of large variations in elastic properties of the crustal volumes modelled in terms of dilatancy and diffusion processes, corroborating the hypothesis that fluids play a key role in the nucleation process of extensional faults and seismicity pattern evolution as testified by main fault planes sometimes activated before the occurrence of the largest event on the fault plnae itself. Differently the still on-going 2016-2017 seismic sequence did not show any standard foreshocks activity, while it seems to be loaded by strain partitioning affected by a mid-crustal layer characterized by seismic activity showing changes in the rate of earthquake production during the months before the sequence onset and during the aftershock sequence. Main shocks nucleate close to the base of the seismogenic layer and nearby intersections between the normal faults and the preexisting compressional-transpressional structures. These lateral geometrical and lithological heterogeneities also control the coseismic slip distribution as imaged by seismological and geodetic data. We will approach the comparison between these three seismic sequences believing on the relevance to reconsider a posteriori our understanding of the role played by the three- dimensional geological structures and the mechanical properties of fault zones to accommodate the deformation and cause fault activation with the aim of contributing to the understanding of the beginning and evolution of the seismic sequences. Acknowledgements The Authors are indebted with Raffaele Di Stefano, Maddalena Michele, Alessandro Vuan and Monica Sugan, for providing original data of the 2016-17 seismic sequence. LARGE FRAME RING LASER GYROSCOPES AS GEOPHYSICAL TOOLS A. Di Virgilio 1 , J. Belfi 1 , N. Beverini 1 , G. Carelli 1,2 , U. Giacomelli 1,2 , E. Maccioni 1,2 1 INFN - Sezione di Pisa, Italy 2 Dipartimento di Fisica, Università di Pisa, Italy The observation with high accuracy of the rotational motion of Earth crust motion is of large interest in different fields of scientific research. Rotation and angle measurements are of great importance for different fields of scientific research: the General Relativity provides terms of rotation originated from the kinetic term, Earth science studies the earth’s angular velocity and all its variations, tides and all its perturbations, the normal modes of Earth, the angular perturbations associated with the movement of the plates, the deformations of a hydrological, volcanic nature or connected to anthropic activities, without neglecting the rotational signals produced by the earthquakes that bring relevant information complementary to the classical linear seismology. In particular, the measure of low frequency rotation components has a very large potential in applied geophysics and risk evaluation for monitoring the movements of the fluids in the underground and the soil subsidence, due to industrial activity, like natural gas extraction and stocking in geological reservoirs, geothermic fields cultivation or the proposed methods of geological trapping of CO 2 . Only recently this kind of measurements are becoming available. In the past, direct mea- surement of seismic rotations has been ignored for a long time because rotational effects were