GNGTS 2018 - 37° Convegno Nazionale

80 GNGTS 2018 S essione 1.1 Di Domenica A., Turtù A., Satolli S., Calamita F. (2012). Relationships between thrusts and normal faults in curved belts: New insight in the inversion tectonics of the Central-Northern Apennines (Italy). Journal of Structural Geology, 42, 104-117, http://dx.doi.org/10.1016/j.jsg.2012.06.008. Latorre D. (articolo in preparazione). A new catalogue of the Italian Seismicity from 1981 to 2015. Lomax A., Michelini A., Curtis A. (2008). Earthquake Location, Direct, Global-SearchMethods. Encyclopedia of Complexity and Systems Science, 316, 1-25. Marchetti A. et al. (2016). The Italian Seismic Bulletin: strategies, revised pickings and locations of the central Italy seismic sequence. Annals of Geophysics, 59, Fast Track 5. Doi: 10.4401/ag-7169. Margheriti L., Ciaccio M. G., Castello B., Nardi A., Marchetti A., Mariano Mele F., Latorre D., Lombardi A. M., Moretti M., Improta L., e il Bollettino Sismico Italiano Working Group (2018). Early aftershocks of the 2016 Mw 6.0 Amatrice, Mw 5.9 Visso and Mw 6.5 Norcia earthquakes in central Italy: analysis of the Seismic Bulletin. Geophysical Research Abstracts, Vol. 20, EGU2018-7383. Moro R., Basili A., Bono A., Marcocci C., Mazza S., Mele F. M. (2008). ISIDe, an Italian Seismic Data Base with minimum magnitude of completeness ML 1.8 . ESC, http://iside.rm.ingv.it/iside/. SEISMIC ANISOTROPY AS A TOOL TO IMAGE THE FRACTURE AND THE STRESS FIELDS IN THE CRUSTAL VOLUME INTERESTED BY THE “2016 -2018 CENTRAL ITALY SEISMIC SEQUENCE” M. Pastori, P. Baccheschi, L. Margheriti Istituto Nazionale di Geofisica e Vulcanologia, ONT, Roma, Italy Shear wave splitting is a clear manifestation of seismic anisotropy. Several studies worldwide demonstrate that seismic anisotropy is related to stress-aligned, filled-fluid micro-cracks and/or to macroscopic aligned fracture field (Extensive Dilatancy Anisotropy -EDA- model; Crampin, 1993). In this hypothesis, fast shear waves are polarized parallel to the strike of micro-cracks, cracks and faults inside the crust, which, in turns, are aligned to the SHmax of the active stress field. Delay time, between fast and slow splitted S-waves, is directly proportional to the density and to the aspect ratio of the cracks and to the thickness of the anisotropic layer. In the current work we present a huge collection of high-quality anisotropic parameters: fast polarization direction (F) and delay time (dt), of several earthquakes recorded during 6 months starting from the Mw 6.0 mainshock (August 24 th 2016, 01:36:32 UTC). The period also includes the following larger aftershocks: Mw 5.9 (October 26 th 2016), Mw 6.5 (October 30 th 2016) and Mw 5.5 (January 18 th 2017). Manual-revised P- and S- picking and high-precision locations of 39357 aftershocks (Michele et al. , 2016; Chiaraluce et al. , 2017) recorded at 31 three- component seismic stations are used to better understand the anisotropic pattern and to delineate the active crustal deformation resulting from the spatio-temporal evolution of the long 2016 -2018 Central Italy Seismic Sequence. The mean fast direction, resulting from 11865 no-null measurements, is ~ N146̊, which is in agreement with the NW-SE strike of the main Quaternary faults, with the NW-SE striking plane of the focal mechanisms and with the NE-SW local extension observed from the horizontal coseismic displacements. This global anisotropic trend is not enduring in time and space; looking at the interpolated values of F and dt for the study area we note an interesting behavior, that could suggest the presence of complex and strong seismic anisotropy anomalies in the crustal volume. Three different time periods, based on the occurrence of the largest earthquakes, have been identified to show the anisotropic pattern variations, as suggested by the Anisotropic-Poro- Elasticity model (APE; Zatsepin and Crampin, 1995) that describes these temporal variations