GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 81 as a re-orientation of the micro-cracks caused by a migration of fluid or an over-pressured fluid zone. In the first period, August 24 th -October 25 th , are oriented from N-S between south Amatrice and east Arquata area and rotated to E-W at northeast of Norcia village. Fast axes related to the second period, October 26 th - January 17 th , are more variable: from N-S between Accumoli and east Arquata, to NW-SE between Cascia, Norcia and Preci villages, to E-W in the southeastern part of Cascia and NE-SW in the northeastern of Norcia. Anoteworthy variation of fast direction in time is observed at northeast of Norcia. Finally, in the last period, January 18 th -February 28 th , are mainly oriented NW-SE. The average value of delay time is roughly 0.064 s, while at single stations we evaluated values ranging from 0.024 s to 0.090 s. Interpolated dt reveal higher values in the hanging-wall of the activated fault system, mainly located in the southeastern part of Norcia. The values of delay time resulting from this study are comparable with those found in previous studies in Central Italy: 2009 L’Aquila sequence (Baccheschi et al. , 2016, Pastori et al. , 2012), 2010 Pietralunga sequence (Guerri et al. , 2012), 2005-2006 Val d’Agri experiment (Pastori et al. , 2009) and 2000-2001 Citta di Castello experiment (Piccinini et al. , 2006). References Chiaraluce L., Di Stefano R., Tinti E., Scognamiglio L., Michele M., Casarotti E., Cattaneo M., De Gori P., Chiarabba C., Monachesi G., Lombardi A., Valoroso L., Latorre D, Marzorati S.; 2017: The 2016 Central Italy Seismic Sequence: AFirst Look at the Mainshocks, Aftershocks, and Source Models. SRL, 88 (3), doi 10.1785/0220160221. Crampin S.; 1993: Arguments for EDA. Canadian Journal of Exploration Geophysics, 29(1), 18-30. Baccheschi P., Pastori M., Piccinini D., Margheriti L.; 2016: Shear wave splitting of the 2009 l’Aquila seismic sequence: fluid saturated microcracks and crustal fractures in the Abruzzi region (central Apennines, Italy). Geophys. J. Int. 204, 1531–1549, doi: 10.1093/gji/ggv536. Guerri M., Pastori M., Margheriti L., D’Alema E., Piccinini D., Barchi M.R.; 2012: Seismic anisotropy and micro- seismicity in the upper crust at north of Gubbio basin (central Italy): relation with the subsurface geological structures and the active stress field. 31° Convegno GNGTS - Gruppo Nazionale di Geofisica della Terra Solida, TEMA 1: Geodinamica, Sessione 1.1:Terremoti e Faglie, pag. 134-143. Michele M., Di Stefano R., Chiaraluce L., Cattaneo M., De Gori P., Monachesi G., Latorre D., Marzorati S., Valoroso L., Ladina C., Chiarabba C., Lauciani V. ,Fares M.; 2016: The Amatrice 2016 seismic sequence: a preliminary look at the mainshock and aftershocks distribution. Annals Of Geophysics, 59, Fast Track 5, doi 10.4401/ag-7227. Pastori M., Piccinini D, Valoroso L., Wuestefeld A., Zaccarelli L., Bianco F., Kendall M., Di Bucci D., Margheriti L., Barchi M.R.; 2012: Crustal fracturing field and presence of fluid as revealed by seismic anisotropy: case histories from seismogenic areas in the Apennines (Italy). Bollettino di Geofisica Teorica e Applicata, 53(4), 417-433. DOI 10.4430/bgta0047. Pastori M., Piccinini D., Margheriti L., Improta L., Valoroso L., Chiaraluce L. and Chiarabba C.; 2009: Stress aligned cracks in the upper crust of the Val d’Agri region as revealed by shear wave splitting. Geophys. J. Int., 179, 601–614. Piccinini D., Margheriti M., Chiaraluce L., Cocco M.; 2006: Space and time variation of crustal anisotropy during the 1997 Umbria-Marche, central Italy, seismic sequence. GJI, 167(3), 1482-1490. Zatsepin S.V., Crampin S.; 1995: Rock deformation a non-linear anisotropic poro-elastic theory (APE) for pre- stressed fluid-saturated rock. International Union of Geodesy and Geophysics, General Assembly, vol.21, Week B, pp. 340.