GNGTS 2018 - 37° Convegno Nazionale

28 GNGTS 2018 S essione 1.1 Scisciani, V., Agostini, S., Calamita, F., Pace, P., Cilli, A., Giori, I., & Paltrinieri, W., 2014. Positive inversion tectonics in foreland fold-and-thrust belts: A reappraisal of the Umbria–Marche Northern Apennines (Central Italy) by integrating geological and geophysical data. Tectonophysics,  637 , 218-237. Scisciani, V., Agostini, S., Calamita, F., Pace, P., Cilli, A., Giori, I., & Paltrinieri, W., 2014. Positive inversion tectonics in foreland fold-and-thrust belts: A reappraisal of the Umbria–Marche Northern Apennines (Central Italy) by integrating geological and geophysical data. Tectonophysics, 637, 218-237. Scognamiglio, L., Tinti, E., Casarotti, E., Pucci, S., Villani, F., Cocco, M., Magnoni F., Michelini A. & Dreger, D., 2018. Complex Fault Geometry and Rupture Dynamics of the MW 6.5, 30 October 2016, Central Italy Earthquake. Journal of Geophysical Research: Solid Earth, 123(4), 2943-2964. Tinti, E., Scognamiglio, L., Michelini, A., & Cocco, M., 2016. Slip heterogeneity and directivity of the ML 6.0, 2016, Amatrice earthquake estimated with rapid finite-fault inversion. Geophysical Research Letters, 43 (20). Valoroso, L., Chiaraluce, L., Piccinini, D., Di Stefano, R., Schaff, D., & Waldhauser, F., 2013. Radiography of a normal fault system by 64,000 high-precision earthquake locations: The 2009 L’Aquila (central Italy) case study.  Journal of Geophysical Research: Solid Earth, 118(3), 1156-1176. Ziegler, P. A., Cloetingh, S., & van Wees, J. D. (1995). Dynamics of intra-plate compressional deformation: the Alpine foreland and other examples. Tectonophysics, 252(1-4), 7-59. A DYNAMIC STRESS MAP FOR THE CENTRAL APENNINES A. Caporali, J. Zurutuza, M. Bertocco Dept. of Geosciences, University of Padova, Italy Introduction. Stress at or near faults at a given epoch is controlled mostly by the stress transfer from previous earthquakes in the area and by a regional stress. The first can be estimated (Wedmore et al. , 2017) by integrating the stress associated to individual earthquakes using Catalogue data and the DISS of INGV (Basili et al. , 2008; DISS Working Group, 2015) using the classical formulation of Okada or Kostrov, in the approximation of an elastic halfspace (Caporali et al. , 2011; D’Agostino, 2014). The second can be estimated by timewise integration of the 2D plane stress rate inferred from a GNSS velocity field (Fig.1), from an initial state of stress. Other contributions exist (e.g. viscous dissipation of stress in the mantle; stress diffusion by fluids through pores, for example) but will not be considered here. Elastic rheology is here assumed to apply to the entire seismogenic layer. Stress is variable with time and space. Although stress maps give us a general idea of stress orientations (Montone and Mariucci, 2016; Heidbach et al. , 2010), the angles of the stress tensor eigenvectors change a) with time (Hardebeck and Okada, 2018) because (at least) of stress transfer from parent events and the regional stress, and b) with depth, as it can be verified by computing at different depths the stress transferred at a point by parent earthquakes. It follows that a stress map should ideally be in 4 dimensions: space and time. To attempt a first draft of a simplified 4D stress map, a simple approach approximates the stress tensor at any point (x,y,z,t) in a seismic province by the sum with sign of the regional stress rate inferred by GNSS data multiplied by a (tbd) scaling time T, intended as a stress reservoir, and the stress associated to the dislocation of all known events in the province, intended as a stress sink. The stress at a point may decrease or also increase as a consequence of an earthquake, depending on the position of the point in the stress pattern of the earthquake. The scaling time T is not known but we may expect it to be of the order of magnitude of the time taken to increase the stress by an amount roughly comparable to a stress drop of some MPa in the study area, hence somewhere between 500 and 5000 (?) years. Possible constraints on T could be: