GNGTS 2017 - 36° Convegno Nazionale

64 GNGTS 2017 S essione 1.1 the middle between them. We confirm the general relation of previously reported (Schorlemmer et al. , 2005) dependence of b -value on rake angle λ of focal mechanisms (FMs): maximum and minimum b are found for normal (λ ∼ -90°) and thrust (λ ∼ 90°) mechanisms respectively, even with smaller subsets of selection. However, as would be expected from Anderson (1905) theory of faulting, different fault orientations within thrust and normal regimes might influence b -value behavior, since thrust faults dip less with respect to normal faults. We firstly detect such variations into a plunge-based ternary representation (Fröhlich, 1992) of FMs, mostly in the normal-thrust parts of the diagram. Then, we combine the ternary analyses of b with analytical fault modeling and provide a new relation of b -value with differential stress to be applied for dip-slip fault modeling. Our findings provide a supplementary set of strong evidences for b -value dependence on state of stresses combing fault modeling and new data analyses technique: the remarkable consistency between the systematic b -value patterns and the well-known global tectonic features reflects theoretically expected stress differences in all considered details. We think that our results significantly improve the credibility that well assessed b -value variation is meaningful for physical interpretations and for seismic risk assessments. References Amitrano, D. (2003). Brittle-ductile transition and associated seismicity: Experimental and numerical studies and relationship with the b value, J. Geophys. Res., 108(B1), 2044, doi:10.1029/2001JB000680. Anderson, E. M., (1905), The dynamics of faulting, Trans. Edinburgh Geol. Soc., 8 (1905), pp. 387–402. Fröhlich, C. (1992), Triangle diagrams: Ternary graphs to display similarity and diversity of earthquake focal mechanisms, Physics of The Earth and Planetary Interiors, 75(1), 193–198, doi: 10.1016/0031-9201(92)90130-N. Gutenberg, R. and C. Richter (1944), Frequency of earthquakes in California, Bull. Seismol. Soc. Am., 34, 185–188. Scholz, C. H. (1968), The frequency-magnitude relation of microfracturing in rock and its relation to earthquakes, Bull. Seismol. Soc. Am., 58, 399–415. Scholz, C. H. (2015), On the stress dependence of the earthquake b value. Geophys. Res. Lett., 42: 1399–1402. doi: 10.1002/2014GL062863 Schorlemmer, D., S. Wiemer, and M. Wyss (2005), Variations in earthquake-size distribution across different stress regimes, Nature, 437, 539–542, doi:10.1038/nature04094. Uyeda, S., (1982), Subduction zones: An introduction to comparative subductology, Tectonophysics, 81 (3–4), pp. 133–159, doi.org/10.1016/0040-1951( 82)90126-3. The role of structural barrier on fault segmentation, rupture initiation and propagation during the 2016 Central Italy seismic sequence, a multidisciplinary seismological and geological approach A. Pizzi 1 , A. Di Domenica 1 , F. Gallovicˇ  2 , L. Luzi 3 , R. Puglia 3 1 University “G. d’Annunzio”, Chieti-Pescara, Italy 2 Faculty of Math. and Physics, Dept. of Geophysics, Charles University, Prague, Czech Republic 3 Istituto Nazionale di Geofisica e Vulcanologia, Milano, Italy Introduction. Faults segmentation study of active faults can be of great importance for seismic hazard assessments and microzonation analysis because it might permit to constrain the location, length and maximum expected magnitude of a seismogenic fault that will likely break during a single earthquake (e.g., Wells and Coppersmith, 1994). In the last few decades several studies pointed out that fault segment boundaries may correspond to peculiar geologic features such as major relay zones at faults step-over, pronounced bends or branch faults and large cross-faults (e.g., DePolo et al. , 1991). Many of these geologic features have therefore been