Abstract
<p>The Emilia earthquakes of May 20, 2012 (Ml 5.9, INGV; Mw 6.11, http://www.bo.ingv.it/RCMT/) and May 29, 2012 (Ml 5.8, INGV; Mw 5.96, http://www.bo.ingv.it/RCMT/) struck an area that in the national reference seismic hazard model [MPS04; http://zonesismiche.mi.ingv.it, and Stucchi et al. 2011] is characterized by expected horizontal peak ground acceleration (PGA) with a 10% probability of exceedance in 50 years that ranges between 0.10 g and 0.15 g (Figure 1), which is a medium level of seismic hazard in Italy. The strong impact of the earthquakes on a region that is not included among the most hazardous areas of Italy, and the ground motion data recorded by accelerometric networks, have given the impression to the population and the media that the current seismic hazard map is not correct, and thus needs to be updated. Since the MPS04 seismic hazard model was adopted by the current Italian building code [Norme Tecniche per le Costruzioni 2008, hereafter termed NTC08; http://www.cslp.it/cslp/] as the basis to define seismic action (the design spectra), any modification to the seismic hazard model would also affect the building code. The aim of this paper is to briefly present the data that support the seismic hazard model in the area, and to perform some comparisons between recorded ground motion with seismic hazard estimates and design spectra. All of the comparisons presented in this study are for the horizontal components only, as the Italian hazard model did not perform any estimates for the vertical component. […]</p><br />
Highlights
The Emilia earthquakes of May 20, 2012 (ML 5.9, INGV; MW 6.11, http://www.bo.ingv.it/RCMT/) and May 29, 2012 (ML 5.8, INGV; MW 5.96, http://www.bo.ingv.it/RCMT/) struck an area that in the national reference seismic hazard model [MPS04; http://zonesismiche.mi.ingv.it, and Stucchi et al 2011] is characterized by expected horizontal peak ground acceleration (PGA) with a 10% probability of exceedance in 50 years that ranges between 0.10 g and 0.15 g (Figure 1), which is a medium level of seismic hazard in Italy
This model provides the basic data to be considered to update the seismic zoning of municipalities, and it was used in the determination of the design spectra in the Italian building code (NTC08)
The two main shocks of the Emilia seismic sequence of May 20 and 29, 2012, together with the April 6, 2009, L'Aquila event (MW 6.3), are the strongest earthquakes to have occurred in Italy since the release of the reference MPS04 seismic hazard model and of the current Italian building code (NTC08), which has been in force since July 1, 2009
Summary
The Emilia earthquakes of May 20, 2012 (ML 5.9, INGV; MW 6.11, http://www.bo.ingv.it/RCMT/) and May 29, 2012 (ML 5.8, INGV; MW 5.96, http://www.bo.ingv.it/RCMT/) struck an area that in the national reference seismic hazard model [MPS04; http://zonesismiche.mi.ingv.it, and Stucchi et al 2011] is characterized by expected horizontal peak ground acceleration (PGA) with a 10% probability of exceedance in 50 years that ranges between 0.10 g and 0.15 g (Figure 1), which is a medium level of seismic hazard in Italy. The output of the reference MPS04 seismic hazard model is given in terms of horizontal ground accelerations on rock for several return periods and several spectral periods, computed on a regular grid (5-km spacing) that covers the whole Italian territory.
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