GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 397 Gruppo di lavoro MS; 2008: Indirizzi e Criteri per la Microzonazione Sismica, Dipartimento della Protezione Civile e Conferenza delle Regioni e Province Autonome, 3 vol. e DVD. Jayaram N., Baker J.W.; 2009: Correlation model of spatially distributed ground motion intensities. Earthq Eng Struct Dyn 38:1687–1708 Jayaram N., Baker J.; 2010: Efficient sampling and data reduction techniques for probabilistic seismic lifeline risk assessment. Earthquake Engineering & Structural Dynamics 39(10): 1109-1131 NIBS; 2004: HAZUS-MH: technical manual. Technical report, Federal Emergency Management Agency (FEMA), Washington, DC Stergiou E., Kiremidjian A.S.; 2006: Treatment of uncertainties in seismic risk analysis of transportation systems. Engineer Thesis, Stanford University. Wald D. J., Allen T. I.; 2007: Topographic slope as a proxy for seismic site conditions and amplification, Bulletin of the Seismological Society of America, 97, no. 5, 1379-1395 Weatherill G., Burton P.W.; 2010: An alternative approach to probabilistic seismic hazard analysis in the Aegean region using Monte Carlo simulation. Tectonophysics 492:253–278 Weatherill G., Esposito S., Iervolino I., Franchin P., Cavalieri F.; 2014: Framework for seismic hazard analysis of spatially distributed systems, in: K. Pitilakis et al. (eds). SYNER-G: Systemic seismic vulnerability and risk assessment of complex urban, utility, lifeline systems and critical facilities. Methodology and applications. Springer, Netherlands. Site effects in the Pollino region from spectral and polarization analyses of seismic noise and earthquakes F. Napolitano 1 , A. Gervasi 2,3 , M. La Rocca 2 , I. Guerra 2 , R. Scarpa 1 1 Università degli Studi di Salerno, Italy 2 Università della Calabria, Italy 3 Istituto Nazionale di Geofisica e Vulcanologia, Italy Introduction. Site effects occur at any places where the propagation of seismic waves is affected by the local geological structure. This may produce changes in amplitude, duration, waveform and polarization of ground motion, as observed for a large number of earthquakes during the last decades (Bonilla et al. , 1997; Clemente-Chavez et al. , 2014). Site effects can increase significantly the damage produced by earthquakes (Cantore et al. , 2011; Cultrera et al. , 2016). The H/V spectral ratio (HVSR, Nakamura, 1989) of background seismic noise is probably the most used and efficient technique to estimate the site response in case of simple layered structures, overcoming the use of a reference site. Site effects can also modify the polarization of particle motion due to the proximity of fault damage zones (Pischiutta et al. , 2017; Panzera et al. , 2017) and topographic irregularities (Rigano et al. , 2008; Pischiutta et al. , 2010; Formisano et al. , 2012). Accross fault zones the horizontal polarization of seismic signals usually shows high angle respect to the fault strike direction. Instead, topographic effects usually manifest as a horizontal polarization nearly perpendicular to the ridge direction, or nearly parallel to the slope direction. In this paper we evaluated site effects in the Mt. Pollino area (Southern Italy) using HVSR method applied to both seismic noise and earthquakes. Furthermore we computed the polarization analysis of seismic noise to look for possible relationship with fault zones and topography. The Pollino area is located at the junction between the southern Apennines northeast-verging collision orogen and the Calabrian rollback subduction zone. Till a couple of decades ago it was generally considered as a gap in the crustal seismicity. More recent seismic catalogs and papers include maximum magnitudes in the 5.2 – 6.0 range (e.g., 1693 and 1708 earthquakes; Rovida et al. , 2011; Tertulliani and Cucci, 2014). Moreover, paleoseismological investigations of the southern slope of the Pollino area have identified faults capable of earthquakes of magnitude 6.5 – 7 (Cinti et al. , 2002). It seemed appropriate to perform a detailed study of site response to improve seismic hazard assessment. Data and methods. We applied the HVSR method to at least 20 hours of seismic noise for each site (Fig. 1), chosen at different time during night and day, for different week days