GNGTS 2013 - Atti del 32° Convegno Nazionale

Variation of vibration period of a RC building during the Pollino seismic swarm M. Mucciarelli 1 , T.A. Stabile 2 , M.R. Gallipoli 2 , P. Comelli 1 , M. Bertoni 1 1 Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Dip. Centro di Ricerche Sismologiche, Udine, Italy 2 Consiglio Nazionale delle Ricerche, Istituto di Metodologie per l’Analisi Ambientale, CNR-IMAA, Tito (PZ), Italy Introduction. During the seismic sequence still on-going in the Pollino area, Southern Italy, we monitored the Reinforced Concrete (RC) building of the school in Rotonda, a regular, three-stories reinforced concrete frame, floors in bearing precast slabs, internal walls in concrete bocks and external infills in precast slabs (Fig. 1). Since October 2010 a seismic swarm is affecting the Pollino mountain range. As of September 2013 the sequence is still ongoing, with more than 1,800 events with M>1.5, and at least 700 perceived by the population (M>2.0). The spatial distribution is in three clusters, with the westernmost always active during the three years, the middle one activated in May 2012, and the easternmost activated by a 3.4 shock on December 19, 2012. Rotonda is at the Northern edge of the westernmost cluster, which is also the more active. Also the occurrence of the earthquakes in time is by clusters, whose inter-distance in time decreased by half every time for two years, until a Ml=5.0 event took place on October 26, 2012. The sequence has not stopped since then, but instead is still producing events greater than Ml=1.5 at a rate 10 time larger than the period prior to autumn 2010. The monitoring started in September 2011 with a single station atop the building, while after the Ml=5 event occurred in October 2012 a more complete system was installed with a GeoSIG Fig. 1 – The building hosting the school in Rotonda with indication of the vertical along which the accelerometers were installed. 441 GNGTS 2013 S essione 2.3