A procedure to estimate the seismic hazard in an urban area: an application to Acireale (Eastern Sicily) |
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| Authors: | Sebastiano Imposa Francesco Barone Domenico Bella Massimo Cristaldi Stefano Gresta |
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| Institution: | 1.Dipartimento di Scienze Geologiche,Università di Catania,Catania,Italy;2.Centro di Ricerche sulle cause di degrado per il recupero dei Beni Culturali e Monumentali (C.Ri.Be.Cu.M.),Università di Catania,Catania,Italy;3.Centro Scientifico per l’Ambiente (C.S.A.)–Acireale,Acireale,Italy;4.IES Solutions srl,Catania,Italy |
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| Abstract: | A “standard procedure” to characterize the seismic hazard of a given area was proposed. It is based on a multidisciplinary
approach implying: (1) the knowledge of the seismic history of the area; (2) detailed geological surveys; (3)seismic noise
measurements; (4) simulations of earthquake scenarios. The downtown of Acireale, a typical baroque town located on Eastern
Sicily, was chosen as the “test area”. A catalog of the local seismogenic faults (able to generate earthquakes in historical
times) has been compiled, as well as a seismic catalog for the effects of both local and regional earthquakes. The analysis
of both catalogs allowed us to make the following conclusions: (1) the most important seismogenic faults affecting the Acireale
municipality do not affect the downtown, while the related local earthquakes attenuate their energy (and intensity) in short
(few km) distances; (2) the highest seismic intensity (degree X) experienced in Acireale downtown was caused by the 1693 regional earthquake; (3) over the last 140 years, the downtown has
experienced the highest intensity value of VII only once, while six times the intensity was VI. On the whole, this implies
a moderate seismic hazard. The estimation of the seismic hazard has been also approached by the experimental method of recording
seismic noise. Measurements have been performed at seven different sites, where drills gave detailed information on the shallow
subsurface geology to obtain HV (horizontal/vertical) spectral ratios. On the whole, the highest site amplification factor
was moderate (about 7). A further investigation based on synthetic seismograms (and spectra) produced by simulating two given
earthquake scenarios was also performed. The two scenarios are, respectively, representative of the largest expected earthquake
in the area (the 1693 shock) and of a moderate (magnitude ca. 5.5) local earthquake (as the 1818 one). Moderate to strong
locally expected accelerations were evidenced. |
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