GNGTS 2017 - 36° Convegno Nazionale

576 GNGTS 2017 S essione 3.1 We classify seven electrical resistivity units (labels A, B, B’, B’’, C, D’ and FZ in Fig. 3C) by applying a modified version of the steepest gradient-method (SGM - Villani and Sapia, 2017). This rigorous statistical analysis yields to a quantitative classification of the overall resistivity data distribution and depth to layers and allowed us to argue about fault zone displacement and rupture geometry including also the possible role of fluids flow in the damage zone. The latter, appears as a narrow and elongated relatively low-resistive (100-150 Ωm) region that we interpreted to be the result of the migration of water from the shallow aquifer squeezed by seismic waves through the fractures of the damage zone. Conclusion and future work. The use of such geophysical investigations has proved to be a powerful tool to characterize the structural setting of intramontane tectonic basins and to the imaging of active faults. We emphasize the benefit of combining two different easily deployable, relatively inexpensive geophysical methods in reconstructing the 3-D geometry of a tectonically controlled basin at depth providing the so far most complete 3-D model of the 2009 L’Aquila earthquake epicentral area. The outlined multidisciplinary approach is novel for active tectonic areas, and it represents an important reference to develop future studies in similar geological settings (i.e. Piano Grande di Castelluccio basin and others in the central Apennine). As for the Fig. 3 - A) Geological sketch of the Pian Grande di Castelluccio basin. The blue rectangle encloses the survey site area. Solid red line indicates the main fault strands that ruptured the surface during the 30 October 2016 Mw 6.5 earthquake. B) Close-up view of the coseismic rupture (red arrows) at the ERT survey site, looking towards the north. C) ERT resistivity sections for profiles P1 and P2 (2 m and 5 m spacing respectively) in DD configuration. The small black and white circles are interface points as inferred by the application of SGM along closely-spaced vertical and horizontal profiles. Labels represent interpreted electrical units. FZ identifies the main fault zone.