GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 69 De Luca G., Di Carlo G. and Tallini M. A record of changes in the Gran Sasso groundwater before, during and after the 2016 Amatrice earthquake, central Italy. Scientific Reports , doi: 10.1038/s41598-018-34444-1 (2018). Di Toro G. et al. Fault lubrication during earthquakes. Nature 471, 494–499; doi: 10.1038/nature09838 (2011). Hirth, G. and Beeler, N. M. The role of fluid pressure on frictional behaviour at the base of the seismogenic zone. Geology 43, 223–226; doi: 10.1130/G36361.1 (2015). Manga M. and Wang C. -Y. Earthquake Hydrology. In: Gerald Schubert (editor-in-chief), Treatise on Geophysics , 2 nd edition, Vol 4. Oxford: Elsevier, 305-328; doi: 10.1016/B978-0-444-53802-4.00082-8 (2015). Scuderia, M. M., Collettinia, C. and Marone, C. Frictional stability and earthquake triggering during fluid pressure stimulation of an experimental fault. Earth Planetary Science Letters 477, 84–96; doi: 10.1016/j.epsl.2017.08.009 (2017). Sibson, R. H. Fluid involvement in normal faulting. J. Geodynamics 29, 469–499 (2000). Violay, M. et al. Effect of water on the frictional behaviour of cohesive rocks during earthquakes. Geology 42, 27-30; doi: 10.1130/G34916.1 (2013). TECTONIC EARTHQUAKE SWARMS (TES) IN DIFFERENT SEISMOGENIC DOMAINS: COMPRESSIONAL AND EXTENSIONAL CASES FROM CENTRAL ITALY R. de Nardis 1 , L. Carbone 1 , C. Pandolfi 1 , F. Pietrolungo 1 , D. Talone 1 , G. Monachesi 2 , M. Cattaneo 2 , S. Marzorati 2 , G. Lavecchia 1 1 CRUST, DiSPUTer, Università “G. d’Annunzio”, Chieti Scalo 66013, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Ancona, Italy Earthquakes sequences without a clear triggering mainshock, referred to as earthquake swarms, have been observed in volcanic and hydrothermal areas for decades. Tectonic Earthquake Swarms (TES) is another category of swarms linked to active tectonic regions. In a seismic sequence, aftershocks are associated with a mainshock and their rate of occurrence can be generally described by the modified Omori law; their spatial distribution is observed to correlate with the static stress field changes of the main shock, suggesting that stress triggering plays an important role (Stein 1999). On the contrary, earthquake swarms are not characterized by a dominant earthquake and their temporal evolution cannot be described by any simple law comparable to the Omori law (Hainzl, 2004). The physical mechanisms proposed for the TES origin and evolution include: (1) rupture patches migrating or expanding due to the diffusion of pore-pressure lowering the effective normal stress on the rupture plane (Hainzl 2004); (2) slow-slip events or aseismic creep (themselves possibly driven by pressurised fluids) redistributing elastic stress along a large fault area (Passarelli et al. , 2015). TES show different style of energy release with respect to classic main shock-aftershock sequence, being characterised by the presence of numerous events with more or less the same size for the entire period of activity. Their seismic rate may increase and decrease in time with a variable velocity not following any theoretical model (Passarelli et al. , 2015). Studying TES offers the possibility to understand the nature and main features of the seismic activity linked to local stress condition with implications for the hazard and deformation of an area. TES were observed in several active tectonic locations in Italy, some of the most interesting cases are those released in the Pollino range (Brozzetti et al. , 2017) from 2010 to 2014, and in the proximity of the Alto Tiberina Fault, northern Italian Apennines, (Marzorati et al. , 2014) in two episodes in 2010 and 2013-14. In this second case the mechanism driving the seismicity was poorly understood and the hypothesis of aseismic transient and the role of fluids was discussed. The present work is aimed to compare the characteristics and features of clustered seismicity