GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 61 Major findings. Our inversions suggest that rake angles larger than 80° on the Ferrara fault are not supported by both GPS and InSAR data, so that we infer that the slip of the May 20 th mainshock had a non-negligible eastward, transpressive component. Despite we considered a simple fault geometry, we obtained a solution misfit comparable with the one obtained in previous works considering more complex fault geometries. Moreover, the corrected Akaike’s Information Criterion (AICc) test (Amoruso and Crescentini, 2008) states that a more complex fault geometry does not make significant improvements, considering our dataset, in order to model the geodetic data. Comparing the HOM and LAY cases, we found that in the LAY case the slip distribution has a different magnitude, is shifted along both the strike and dip directions and it is better compatible with the hypocentral localization of the May 29 th mainshock with respect to the one obtained in the HOM case. We also found that the HOM case overestimates the Coulomb failure function (CFF) changes of several MPa, especially above 3.5 km of depth (Fig. 1). So that, in the LAY case CFF changes better justify the lack of seismicity in the shallow layers, according to the Coulomb failure theory and it enhances the mechanical interaction of the overall seismic sequence. References Amoruso, A.; Crescentini, L.; 2008: Inversion of synthetic geodetic data for the 1997 Colfiorito events: clues on the effects of layering, assessment of model parameter PDFs, and model selection criteria. Annals of Geophysics, [S.l.], v. 51, n. 2-3, dec. 2008. ISSN 2037-416X. doi :http://dx.doi.org/10.4401/ag-3027. Cheloni, D., R. Giuliani, N. D’Agostino, M. Mattone, M. Bonano, G. Fornaro, R. Lanari, D. Reale, and S. Atzori; 2016: New insights into fault activation and stress transfer between en echelon thrusts: The 2012 Emilia, Northern Italy, earthquake sequence , J. Geophys. Res. Solid Earth, 121, 4742–4766, doi:10.1002/2016JB012823. Govoni, A., Marchetti, A., De Gori, P., Di Bona, M., Lucente, F. P., Improta, L., … Piccinini, D.; 2014: The 2012 Emilia seismic sequence (Northern Italy): Imaging the thrust fault system by accurate aftershock location. Tectonophysics, 622, 44–55. https://doi.org/10.1016/j.tecto.2014.02.013 Hearn E. H. and Bürgmann R.; 2005: T he Effect of Elastic Layering on Inversions of GPS Data for Coseismic Slip and Resulting Stress Changes: Strike-Slip Earthquakes Bulletin of the Seismological Society of America October 2005 95:1637-1653; doi:10.1785/0120040158 Laske, G., Masters., G., Ma, Z. and Pasyanos, M.; 2013: Update on CRUST1.0 - A 1-degree Global Model of Earth’s Crust , Geophys. Res. Abstracts, 15, Abstract EGU2013-2658. Molinari, I., A. Argnani, A. Morelli, P. Basini; 2015: Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy . Bull. Seism. Soc. Am., 105, 753-764 Pezzo G, Boncori JPM, Tolomei C, Salvi S, Atzori S, Antonioli A, Trasatti E, Novali F, Serpelloni E, Candela L, Giuliani R; 2013: Coseismic deformation and source modeling of the May 2012 Emilia (Northern Italy) . Seismological Research Letters, 84, 645–55. Serpelloni E, Anderlini L, Avallone A, Cannelli V, Cavaliere A, Cheloni D, D’Ambrosio C, D’Anastasio E, Esposito A, Pietrantonio G, Pisani AR, Anzidei M, Cecere G, D’Agostino N, Del Mese S, Devoti R, Galvani A, Massucci A, Melini D, Riguzzi F, Selvaggi G, Sepe V; 2012: GPS observations of coseismic deformation following the May 20 and 29, 2012, Emilia seismic events (northern Italy): data, analysis and preliminary models. Annals of Geophysics, 55, 4. Wang R., Martı́n F.L., Roth F.; 2003: Computation of deformation induced by earthquakes in a multi-layered elastic crust—FORTRAN programs EDGRN/EDCMP , Computers & Geosciences, Volume 29, Issue 2, March 2003, Pages 195-207, ISSN 0098-3004. Fig. 1 - View from the south of the seismicity (yellow circles) distribution near the Ferrara and Mirandola faults before the May 29 mainshock. Hypocenters are taken from Govoni et al. (2014), stars represent the M≥5 events occurred during all the seismic sequence. The colors represent the difference between the absolute values of ΔCFF in the LAY case with respect to the HOM case. The black dashed lines represent the CRUST1.0 discontinuities. Receiver fault mechanism is assumed to be the same as the one characterizing the fault plane where ΔCFF is evaluated.