GNGTS 2013 - Atti del 32° Convegno Nazionale

Etna, accommodated by aseismic folding at the front of the chain, south of the volcanic edifice, and seismogenic oblique thrusting at crustal depth under the northwestern sector of the volca- no. Moreover, the NNW-SSE direction of the axis of compression obtained by seismological data is consistent with that suggested by geological and geodetic data. In particular, a large WSW-ENE trending anticline is growing west of Catania (the Catania anticline). For its location, within a middle-late Pleistocene fold system, and growth rates, consistent with detachment fold models, we exclude that this structure have only developed in response to volcanic spreading, as proposed by previous authors. Moreover, the gentle slope of the southern flank of the volcano (5-6° on average) would not be a sufficient gradient to drive the process and, mainly, the steady deformation growth rate is in contrast with the episodic magmatic injections that are invoked as another promoting mechanism of the spreading. We therefore propose the occurrence of detachment folding at the chain front, as response of a shallow thrust migrating within the clayish foredeep deposits or at the top of the buried foreland sequence. In conclusion, our analysis confirms that, besides the activity related to the volcanic feeding system, the seismic pattern under Mt. Etna edifice can be certainly related to the regional dy- namics. The compressive stress is converted into elastic accumulation and then in earthquakes along the ramps to the rear of the chain, whereas along the frontal detachment it is accom- modated by aseismic ductile deformation. In fact, despite the high rates of convergence, the seismicity is moderate at the front of the chain and the “seismic efficiency” of the Sicilian Basal Thrust is greater in correspondence of ramps at the rear, where strong earthquakes can occur. Acknowledgement. This work was funded by a DPC-INGV 2012 grant, Project V3 “Multi-disciplinary analysis of the relationship between tectonic and volcanic activity” and by grant of University of Catania - PRA n. 20104001082 -. References Altamimi Z., Collilieux X., Legrand J., Garayt B., Boucher C. 2007. ITRF2005: A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters. Journal of Geophysical Research, 112, B09401. Azzaro R., Bonforte A., Branca S., Guglielmino F. 2013. Geometry and kinematics of the fault systems controlling the unstable flank of Etna volcano (Sicily). Journal of Volcanology and Geothermal Research, 251, 5-15. 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