GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione A matrice 91 faults mapped at the surface do not connect with the seismogenic sources, and (b) that their evolution may be controlled by passive readjustments to coseismic strains or even by purely gravitational motions. Any seismic hazard analysis and estimate based on such faults should hence be regarded with great caution as it may not be representative of the true seismogenic potential. Our findings have at least four main categories of implications that need to be carefully considered to avoid gross misrepresentations of the local earthquake potential: a) the complex structure of the central Apennines fold-and-thrust belt causes the effective decoupling between the normal faults that affect the uppermost 2-3 km of the crust and current extension accommodated by larger faults lying beneath them. As a consequence, any surface fault carries little information on seismogenic processes at depth; b) for the same reasons, the evolution of large-scale, long-term landscape features – such as the history of basin architectures and the distribution of fluvial or marine terraces – should be regarded as the main and most sincere indication of ongoing long-term strain at depth; c) as the current geodynamic and geomorphic evolution of the Apennines is controlled more by regional uplift than by localized faulting, and in consideration of the above a), we should be extra careful not to interpret the largely climate- and gravity-controlled evolution of steep Apennines mountain slopes as evidence for continuing activity of surface faults [see the ample discussion on this topic supplied in Kastelic et al. (2016)]; d) for the same reasons, and based on the recent evidence from the Vettore Fault, from the Serrone Fault in the Fucino basin and from a number of large landslides controlled by older surface faults [see Moro et al. (2007) and Moro et al. (2011), respectively for the 1997 and 2009 earthquakes], extreme care should be taken when trenching scarps of unproven origin; since they may represent only the accumulation of deposits mobilized by shaking, they may carry information suitable for dating the shaking itself but not for deriving meaningful slip rates or M w estimates. References Basili, R., and M. M. Tiberti; 2016: New statistics of earthquake-fault dip angles . Paper ESC2016-447, presented at the 35th General Assembly of the European Seismological Commission, Trieste, 4-10 September 2016. Bigi, S., P. Casero, C. Chiarabba and D. Di Bucci; 2012: Contrasting surface active faults and deep seismogenic sources unveiled by the 2009 L’Aquila earthquake sequence (Italy) . Terra Nova, 25, 1, 21-29, doi:10.1111/ ter.12000. Bonini, L., Di Bucci D., Toscani G., Seno S., Valensise G.; 2014: On the complexity of surface ruptures during normal faulting earthquakes: excerpts from the 6 April 2009 L’Aquila (central Italy) earthquake (M w 6.3) . Solid Earth, 5, 389-408, DOI 10.5194/se-5-389-2014. Bonini, L., Basili R., Toscani G., Burrato P., Seno S., Valensise G.; 2015: The role of pre- existing discontinuities in the development of extensional faults: an analog modeling perspective . J. Struct. Geol. 74, 145–158. DOI 10.1016/j.jsg.2015.03.004. Chiaraluce, L., Barchi M.R., Collettini C., Mirabella F., Pucci S.; 2005: Connecting seismically active normal faults with Quaternary geological structures in a complex extensional environment: the Colfiorito 1997 case history (Northern Apennines, Italy) . Tectonics 24, TC1002, DOI 10.1029/2004TC001627. DISS Working Group; 2015: Database of Individual Seismogenic Sources (DISS), Version 3.2.0: A compilation of potential sources for earthquakes larger thanM5.5 in Italy and surrounding areas. http://diss.rm.ingv.it/diss/ © INGV 2015 - Istituto Nazionale di Geofisica e Vulcanologia - All rights reserved, doi: 10.6092 /INGV.IT -DISS3.2.0. Douglas, B., Funning, G.; 2016: Imaging active tectonics with InSAR and LiDAR . GETSI’s Earth-focused Modules and Courses for the Undergraduate Classroom, http://serc.carleton.edu/124395. Gruppo di lavoro IREA& INGV; 2016: Sequenza sismica di Amatrice: aggiornamento delle analisi interferometriche satellitari e modelli di sorgente. doi: 10.5281/zenodo.61682. Kastelic, V., Burrato P., Carafa M.M.C., Basili R.; 2016: Repeated surveys reveal non-tectonic exposure of supposedly active normal faults in the central Apennines, Italy . Submitted to J.Geophys. Res. Moro, M., Saroli M., Salvi S., Stramondo S., Doumaz F.; 2007: The relationship between seismic deformation and deep- seated gravitational movements during the 1997 Umbria–Marche (Central Italy) earthquakes . Geomorphology, 89, 297–307, DOI10.1016/j.geomorph.2006.12.013.