GNGTS 2014 - Atti del 33° Convegno Nazionale

32 GNGTS 2014 S essione 1.1 Comparing Seismic, Geodetic and Geologic Scalar Moment-rates at Mt. Etna volcano (Italy):� ���� ����������� ������� ��� ����������� some preliminary results for seismogenic zones in the eastern flank G. Barberi, F. Cannavò, O. Cocina, M. Palano, L. Scarfì, R. Azzaro Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Sezione di Catania, Italy Introduction. ��� ���������� �� ��� ������� ��� �������� ������������ ��� ������� ������� The comparison of the seismic and geodetic moment-rates can provide crucial insights for understanding fault behaviour in tectonically active zone, with obvious implications on seismic hazard assessment. It is well acknowledged that when the seismic moment-rate is lower than geodetic one, the exceeding geodetic moment-rate can be released either through earthquakes or in aseismic mode. Geodetically observed moment-rates may include both elastic and inelastic deformations, and since only the elastic component is responsible for earthquakes, comparison of geodetic and seismic moment-rate should not balance in regions affected by creeping faults or where significant amounts of deformation take place plastically. It is the case of Etna, slow aseismic slip due to fault creep being a common mode of displacement along many of the fault segments in the eastern flank. Generally, the combined moment-rate estimations based on earthquake catalogues, coupled with fault scale geological observations allow overcoming these limitations. Taking advantage of the availability for the Mt. Etna region of extensive geophysical and geological datasets, here we propose a methodology aimed to estimate and compare in terms of seismic ����������� ���� ��� ���������� efficiency, i.e. the percentage of brittle deformation with respect to the overall strain observed, ��� ������ �������� the scalar seismic, geodetic and geologic moment-rates �� ���� of this important seismogenic zone of the volcano. Seismic data. In order to study the seismotectonic features of the eastern flank, we analyzed seismic data recorded in the period from January 2005 to December 2013. The choice of this time-span is justified by the development of a modern seismic network, equipped with ������� �������� ��� ������ digital stations and broad- band sensors. In particular, the upgrade of the seismic monitoring system operating in eastern Sicily (Fig. 1), has allowed to improve the small magnitude detection capabilities and hence the application of the latest analytical techniques for the study of seismic sources. Over the considered period about ����� 4,570 seismic events with a magnitude between 1.0 and 4.8 (magnitude of completeness ≥ 1.5), are located in the Etna area (Fig. 2). In general, most of seismicity is clustered in the eastern and south-eastern sectors of the volcano at � ����� �� �� �� �� ���� ���� a depth of 15 km or less ���� (red in Fig. 2), confirming the instability of this sector and the continuous fault activity, while shallower events (H < 5 km) are related to the Pernicana fault to the north (green in Fig. 2) and crustal earthquakes Fig. 1 – Sketch map of Mt. Etna. Continuous GPS stations are reported as red points, while seismic stations are reported as blue diamonds. The highlighted boxes represents the surface projection of the prismatic bodies used for the moment-rates estimations. Abbreviations: PF, Pernicana fault; RF, Ragalna fault; TMF, Tremestieri fault; TCF, Trecastagni fault; NER: NE rift; SR: South rift. The inset reports a simplified structural map of eastern Sicily; AMC: Apenninic-Maghrebian Chain; HF: Hyblean Foreland.