GNGTS 2018 - 37° Convegno Nazionale

30 GNGTS 2018 S essione 1.1 In Central Italy the strike of the known faults and structures is quite well aligned to the horizontal eigenvectors (minimum/maximum) of the stress rate 2D tensor (Mastrolembo and Caporali, 2017) and to the Sh from stress maps (Montone and Mariucci, 2016). We will focus on two examples, Aquila 2009 and Amatrice/Norcia 2016 and will attempt to generate a simplified temporal map of the elastic stress in an area including these two examples and spanning a time history comparable with that of the seismic catalogues such as the CFTI15 of recent publication (Rovida et al. , 2016; Guidoboni et al. , 2018). Method. To this purpose we: • compile a list of events based on current knowledge (DISS and CFTI) and use Coulomb 3.4 (Toda et al. , 1998, King et al. , 1994; King and Cocco, 2000) to compute the transferred stress field at any point and depth due to i) All the events preceeding a selected event (epoch t - ); ii) The selected event itself (epoch t); Both (epoch t + ). • use GNSS velocity data to generate the 2D regional plane stress rate (wavelength ca. 50- 100 km, depth independent across the seismogenic layer ca. 15-20 km). • convert the 2D stress rate to 3D: this requires an assumption! For example the horizontal stress is either maximum or minimum and the vertical stress is either minimum or Fig. 2 - Stress rotations at the hypocenter of the L’Aquila 2009 event in the occasion of the (from left to right) 1315, 1461, 1703 (Montereale) and 2009 events, assuming that the regional stress at epoch 2009 is approximated by the GPS stress rate times an empirical time constant of 2250 years. View from Top. The thick axes are the eigenversors of the 2009 Moment Tensor, as reference. Intermediate thick is the eigenversor of the stress axis before the event and thin is the eigenversor of the total stress immediately after. P axis (in red) is vertical at all epochs. Blue and black are respectively the tensional and null axes.