STRUCTURAL GEOLOGY FOR SEISMOTECTONICS: AN INTERDISCIPLINARY 3D APPROACH (Invited Presentation)

The structural approach to seismotectonics is a powerful instrument not only for identifying and understanding earthquake-fault associations, but also for constraining the geometry of crustal structures at depth, and for a better understanding of regional geology and tectonic processes over time. The availability of sophisticated software that allows us to process many data and to build in 3D the geometry and kinematics of deformed bodies represents one of the instruments to constrain complex fault patterns and seismogenic patches. As in the case of the balanced section revolution in the Eighties, it is a must to recall that the 3D modelling only does allow to reconstruct plausible geometric configurations that well interconnect neighbouring structures, but the reliability of the interpretation relays on the quality of the input data, as well as on the level of knowledge of the regional tectonic context.

Here, I illustrate two case studies from Italy of 3D geological-seismological data integration, performed at the light of high-resolution seismic and structural data.

I focus on :

• the central Italy 2016 extensional seismic sequence (Mw 6.5), which activated in three months an intricate, interconnected pattern of west-dipping faults detaching at depths of 10-12 km on a regional east-deepening low-angle basal detachment, activating, in turn, a variety of minor antithetic and synthetic structures which played a relevant role in strain partitioning;
• the background seismicity of eastern Central Italy that illuminates two well distinct lithospheric-scale reverse shear zones, one corresponding to the Adriatic Basal Thrust and the other to a hidden and up to now unrevealed independent SW-dipping structures, referred to as Incipient Thrust.

The analysis of fault/slip data from exposed structures and focal mechanisms do allow us to reconstruct for each of the above significant faults along-strike and along-dip local and regional variations in shear strain trajectories, controlled or not by pre-existing structural and or rheological discontinuities, and to build a realistic 3D geometric-kinematic picture, especially useful for constraining seismotectonic scenarios and seismic hazard evaluations.