GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 53 As for the Bayesian inversion modelling, the fault length is assumed 26 km while the width is 13 km. We found that the optimal number of control points is 7x6 (see Fig. 3) and that stable results are obtained if the rise-time is set to the value expected by using the relationship proposed by Somerville et al. (1999) and equal to 0.4 s. The spacing of the finer grid is 0.06 km along both the strike and the dip of the fault. Fig. 3 - Final slip map for the May 20, 2012, Mw 5.8, Po Plain (Northern Italy) earthquake corresponding to the synthetic STFs shown in Fig. 2. The obtained best model corresponds to a rupture velocity of 1.7 km/s and to the slip map depicted in Fig. 3, which suggests a bilateral rupture with a peak slip value is 0.6 m. The fit between the observed and synthetic source time functions is shown in Fig. 2 and indicates that all but two the stations have a correlation coefficient larger than 0.7, with only one station lower than 0.6. Based on the crustal model proposed by Govoni et al. (2014), the obtained rupture velocity provides a relatively low Mach number of 0.4. A similar slow rupture velocity was observed also for the close 29 May, Mw 5.6, event (Causse et al. , 2017). References Archuleta, R. J., and S. H. Hartzell (1981). Effects of fault finiteness on near-source ground motion, Bull. Seism. Soc. Am., 71,939–957. Ben-Menahem, A. (1961). Radiation of seismic surface waves from finite moving sources, Bull. seism. Soc. Am., 51(3), 401–435. Causse, M., G. Cultrera, L. Moreau, A. Herrero, E. Schiappapietra, and F. Courboulex (2017). Bayesian rupture imaging in a complex medium: The 29 May 2012 Emilia, Northern Italy, earthquake, Geophys. Res. Lett., 44, 7783–7792, doi:10.1002/2017GL074698. Convertito V., N.A. Pino, and F. Di Luccio (2016). Investigating source directivity of moderate earthquakes by multiple approach: the 2013 Matese (southern Italy) Mw = 5.0 event, Geophys. J. Int., 207, 1513–1528, doi: 10.1093/gji/ggw360. Govoni, A., A. Marchetti, P. De Gori, M. Di Bona, F.P. Lucente, L. Improta, C. Chiarabba, A. Nardi, L. Margheriti, N.P. Agostinetti, R. Di Giovambattista, D. Latorre, M. Anselmi, M.G. Ciaccio, M. Moretti, C. Castellano, and D. Piccinini (2014). The 2012 Emilia seismic sequence (Northern Italy): imaging the thrust fault system by accurate aftershock location, Tectonophysics, 622, 44-55, 10.1016/j.tecto.2014.02.013. Király-Proag, E., C. Satriano, P. Bernard, and S. Wiemer (2019). Rupture process of the Mw 3.3 earthquake in the St. Gallen 2013 geothermal reservoir, Switzerland, Geophysical Research Letters, 46. https://doi. org/10.1029/2019GL082911. Mori, J.J., R.E. Abercrombie, and H. Kanamori (2003). Stress drops and radiated energies of the Northridge aftershocks, J. Geophys. Res., 108 (B11), 2545; doi:10.1029/200JB000474. Somerville, P. G., K. Irikura, R. Graves, S. Sawada, D. Wald, N. Abrahamson, Y. Iwasaki, T. Kagawa, N. Smith, and A. Kowada (1999). Characterizing crustal earthquake slip models for the predictionof strong ground motion, Seismol. Res. Lett., 70, 59–80.