GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 1.3 130 HOW HISTORIC SEISMICITY AND GNSS DATA CAN BE MERGED TO GENERATE A TIME DEPENDENT 3D MODEL OF THE ELASTIC STRESS IN THE CENTRAL APENNINES A. Caporali, M. Bertocco, J. Zurutuza University of Padova, Dept. of Geosciences Seismicity in the Central Apennines is characterized by normal faulting with dip NE‐SW near 45°. If the stress at the hypocenter of the 2016 Norcia (Mw = 6.5) and 2009 L’Aquila (Mw = 6.3 on the Paganica fault) earthquakes originated only from stress transfer from previous historical events, the orientation of the principal stress axes would have been inconsistent with the observed tensional re- gime. The additional contribution of a regional stress is thus required, but Global Navigation Satellite System geodesy provides only stress rates. We empirically estimate a time multiplier for the regional stress rate, computed with a dense Global Navigation Satellite System network, such that the princi- pal stress axes resulting from the sum of the stress transferred by previous events and the regional stress rate multiplied by the empirical temporal scale are consistent with normal faulting, both at the L’Aquila and Norcia hypocenters. Based on a Catalogue of 36 events of magnitude larger than 5.6, we estimate the total Coulomb stress at depths and along planes parallel to those of L’Aquila and Norcia. Based on this time calibrated model of the elastic stress, we map in space and time the Coulomb stress. We provide evidence of an asymmetry of the Coulomb stress leading to a stress concentra- tion near the hypocenter of the two events just prior of the 2009 and 2016 earthquakes. This stress anomaly disappeared after the two events, with a Coulomb stress change of about 2 MPa, which is not dissimilar from the expected stress drop. Similar stress patterns are observed for earlier events, which took place in 1461 at L’Aquila, 1703 on the Montereale plain, and in 1703 at Norcia/Valnerina. The 1997 sequence of Colfiorito exhibits a similar, anisotropic Coulomb stress pattern. Other areas with a similar stress anisotropy could be seismic gaps. Currently the Coulomb stress resulting from the regional stress and the transferred stress concentrates in the Gran Sasso area and on the faults to the South East. Fig. 1 contains a one -slide summary of the work. Corresponding author: Alessandro.caporali@unipd.it