GNGTS 2015 - Atti del 34° Convegno Nazionale

32 GNGTS 2015 S essione 1.1 Monaco C., Bianca M., Catalano S., De Guidi G., Tortorici L.; 2002. Sudden change in the Late Quaternary tectonic regime in eastern Sicily: evidences from geological and geomorphological features . ����� ���� ����� ���� ������ Boll. Soc. Geol. It., Volume speciale n.1, 901-913. Monaco C., Tapponnier P., Tortorici L., Gillot P.Y.; 1997. Late Quaternary slip rates on the Acireale-Piedimonte normal faults and tectonic origin of Mt. Etna (Sicily ). Earth Planet. Sci. Lett. 147, 125-139. Monaco C. and Tortorici L.; 2000. Active faulting in the Calabrian arc and eastern Sicily . J. Geodyn., 29, 407-424. Musumeci C., Patanè D., Scarfì L. and Gresta, S.; 2005. Stress Directions and Shear-Wave Anisotropy: Observations from Local Earthquakes in Southeastern Sicily , Italy. Bull. Seism. Soc. Amer., 95 (4), 1359-1374. Nicolich R., Laigle M., Hirn A., Cernobori L. and Gallart, J.; 2000. Crustal structure of the ionian margin of Sicily; Etna volcano in the frame of regional evolution , Tectonophysics, 329, 121-139. Pavano F. Romagnoli G., Tortorici G., Catalano S.; 2015. Active tectonics along the Nebrodi–Peloritani boundary in northeastern Sicily (Southern Italy) . ��������������� ���� ����� ������������������������������� Tectonophysics, 659, 1-11. doi:10.1016/j.tecto.2015.07.024 Pedley H.M., Grasso M., Maniscalco R., Bencke B., Di Stefano A., Giuffrida S., Sturiale G.; 2001. The sedimentology and Palaeoenvironment of Quaternary temperate carbonates and their distribution around the northern Hyblean Mountains (SE Sicily) . Boll. Soc. Geol. It., 121, 233-255. Scarfì L., MessinaA., Cassisi C.; 2013. Sicily and southern Calabria focal mechanism database: a valuable tool for local and regional stress-field determination . ������ �� ����������� ��� ����� Annals of Geophysics, 56, 1-16. Graviquakes and elastoquakes C. Doglioni 1,2 , E. Carminati 1,2 , P. Petricca 3 and F. Riguzzi 4 1 Dipartimento di Scienze della Terra, Università Sapienza, Roma, Italy 2 Istituto di Geologia Ambientale e Geoingegneria, CNR, Roma, Italy 3 GFZ-German Research Centre for Geosciences, Potsdam, Germany 4 Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy Fault activation is crucial for the understanding of earthquakes and their prediction. Earthquakes are usually interpreted as the rupture of an asperity along a fault, when the shear stress overcomes the fault strength. But why do faults move episodically? Why is seismicity not more randomly distributed if an earthquake is simply associated with an asperity, which should be smeared out after fault motion? The origin of the earthquake recurrence or seismic cycle, consisting of a long interseismic period followed by a coseismic (and postseismic) period, remains quite obscure. The length of the interseismic period between two earthquakes along the same fault has been proposed to be controlled by a number of physical parameters, e.g., the relative velocity between the two walls of the fault, the composition of the crust, the mineralogy and foliation of the fault rocks, the morphology and length of the fault plane, the thermal state, the friction on the fault, the fluid pore-pressure, etc.. All these parameters entail first a long, static accumulation of energy during the interseismic period, which is eventually radiated coseismically when the friction on the fault has overcome. In this article we contribute to this topic with a geological model to explain the activation of a crustal fault, where the aforementioned physical parameters could determine the timescale of the recurrence or the magnitude. In particular, we investigate the role of the brittle-ductile transition (BDT) in the evolution of crustal seismicity. The BDT depth generally represents the lower limit of most crustal seismicity. We propose a model that links the continuous ductile deformation at depth with the brittle episodic behavior of shallow crustal layers, and show how the BDT may play a triggering role in fault movement. The model is tested numerically and applied to two areas where normal fault and thrust related earthquakes occurred, i.e., in the central Apennines (2009) and Taiwan (1999). GPS interseismic and coseismic data, dissipated energy from the two cases are shown to be consistent with model predictions, where normal faults and thrusts have opposite behavior. Similar to the effects of the lithostatic load, which enhances the rupture of normal