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This work aims to analyse the response to ground shaking of the Norcia intermountain basin (central Italy), where a temporary seismic network (Pilz and Parolai in Norcia basin (Italy) temporary seismic network. GFZ Data Services. 10.14470/8u7554472182, 2009) was installed from January to May 2009, during the L'Aquila (Mw 6.1) seismic sequence. Here we present the results of the application of various empirical approaches for the evaluation of local site effects, considering hundreds of records relevant to earthquakes in the local magnitude range 3.0-5.4. The site amplification was estimated considering either the standard spectral-ratio (SSRs, Borcherdt in Bull Seismol Soc Am 60:29-61, 1970) or the horizontal to vertical spectral-ratio technique (HVSRs, Lermo and Chavez-Garcia in Bull Seismol Soc Am 83:1501-1506, 1993) techniques, applied to the S-phase and the S-wave coda of selected earthquakes. The results evidence the amplification of both horizontal and vertical components of ground motion at frequencies spanning from about 0.5 Hz, in the deepest part of the basin, to 4 Hz at basin edges. HVSRs show lower amplitudes than SSRs, due to the amplification of the vertical component, highlighting as the single station spectral technique, suitable to estimate the fundamental resonance frequency of the sites, is not able to reliably describe the actual seismic response. Considering the shape of the basin, possible predominant amplification with particular direction are investigated by rotated SSRs that allow to evidence in the central part of the studied area a prevailing amplification of the S-train waves along the 140°N direction. Finally, the generation of surface waves within the basin was investigated by the Multiple Filter Technique analysis (MFT, Dziewonski et al. in Bull Seismol Soc Am 59:427-444, 1969), estimating the backazimuth of the identified surface waves using the method proposed by Baker and Stevens (Geophys Res Lett 31:L09611, 2004. 10.1029/2004GL019510). In particular, the favourable conditions for the generation of surface waves inside the basin, have been evaluated by comparing records relevant to earthquakes with different sources and magnitudes recorded in the last twenty-year by the permanent NRC accelerometric station. [ABSTRACT FROM AUTHOR]

In the framework of the S2 DPC-INGV 2014-2015 project (), several field surveys were designed with the aim to investigate the local seismic site response of selected Italian Accelerometric Network strong motion stations. In this study the results obtained at Sorbolo, Lesignano de' Bagni, and Castelfranco Veneto, three sites located in the Po alluvial basin (northern Italy), were presented. In particular, at each site, ambient vibration surveys were performed both in single stations and two dimensional arrays configurations. The ambient vibration arrays were analyzed to obtain at each site the shear-wave velocity (Vs) profile, until depths in correspondence of which the Vs show values higher than 800 m/s (i.e. lower bound for the soil category A, as now defined in the Italian seismic code for building). In this way, data were processed through a joint inversion computed using both the Rayleigh waves dispersion curve and the ellipticity curve deduced from the horizontal-to-vertical spectral ratios calculated from the microtremor single station measurements. In general, the obtained profiles show an increasing depth of the main Vs discontinuity (i.e. the seismic bedrock) from 60 to 320 m, moving from the edge to the central part of the Po alluvial basin. To support the outcomes of the field experiments, the available earthquakes recorded at each station in the last decades were processed in terms of the horizontal-to-vertical spectral ratios. Although in many cases the resonance frequencies are comparable with those obtained from microtremor, a high variability is observable depending on the selected portions of each single earthquake. Finally, residual analysis were carried out comparing the recorded ground motion to predicted data as provided by the actual Italian ground motion prediction equations, calibrated both at national and at regional scale. [ABSTRACT FROM AUTHOR]

In this study, we apply an empirical scoring method to evaluate the feasibility of probabilistic seismic hazard analyses at regional scale in Italy accounting for site amplification, which is taken into account through the application of a set of ground motion prediction equations (GMPEs) defined for specific ground types. Precisely, this method calculates the agreement (in terms of likelihood) between the hazard results computed using a specific hazard model and the number of ground-motion exceedances at a set of reference sites. Such a procedure is applied to quantify the likelihood of the outcomes of different hazard models, each based on a specific GMPE, with respect to the observations at 56 accelerometric sites operating in Italy for at least 25 years. Indirectly, this allows evaluating the influence of the selected GMPE in providing reliable hazard estimates. Seven possible GMPEs, applicable in active shallow crustal regions like Italy, have been examined taking into account the correlation among the hazard estimates provided by each computational model at the reference sites. Our results indicate that, although using GMPEs for pre-defined soil categories provides only a broad assessment of the hazard (since it ignores specific site response), large-scale hazard maps of Italy that are compatible with observations can be provided when suitable GMPEs are considered. A restricted number of GMPEs was found appropriate to this scope. [ABSTRACT FROM AUTHOR]

This article presents a set of Ground-Motion Prediction Equations (GMPEs) for Europe and the Middle East, derived from the RESORCE strong motion data bank, following a standard regression approach. The parametric GMPEs are derived for the peak ground acceleration, peak ground velocity, and 5 %-damped pseudo-absolute acceleration response spectra computed over 23 periods between 0.02 and 3 s, considering the average horizontal-component ground-motions. The GMPEs are valid for distances less than 300 km, hypocentral depth up to 35 km and over the magnitude range 4-7.6. Two metrics for the source-to-station distance (i.e. Joyner-Boore and hypocentral) are considered. The selected dataset is composed by 2,126 recordings (at a period of 0.1 s) related to 365 earthquakes, that includes strong-motion data from 697 stations.The EC8 soil classification (four classes from A to D) discriminates recording sites and four classes (normal, reverse, strike-slip, and unspecified) describe the style of faulting. A subset which contains only stations with measured Vs30 and earthquakes with specified focal mechanism (1,224 records from 345 stations and 255 earthquakes) is used to test of the accuracy of the median prediction and the variability associated to the broader data set. A random effect regression scheme is applied and bootstrap analyses are performed to estimate the 95 % confidence levels for the parameters. The total standard deviation sigma is decomposed into between-events and within-event components, and the site-to-site component is evaluated as well. The results show that the largest contribution to the total sigma is coming from the within-event component. When analyzing the residual distributions, no significant trends are observed that can be ascribed to the earthquake type (mainshock-aftershock classification) or to the non-linear site effects. The proposed GMPEs have lower median values than global models at short periods and large distances, while are consistent with global models at long periods $$(\hbox {T} > 1)$$ s. Consistency is found with two regional models developed for Turkey and Italy, as the considered dataset is dominated by waveforms recorded in these regions. [ABSTRACT FROM AUTHOR]

The 2009 Mw 6.3 L'Aquila event caused extensive damage in the city of L'Aquila and in some small towns in its vicinity. The most severe damage was recognized SE of L'Aquila town along the Aterno river valley. Although building vulnerability and near-source effects are strongly responsible for the high level of destruction, site effects have been invoked to explain the damage heterogeneities and the similarities between the 2009 macroseismic field with the intensities of historical earthquakes. The small village of Onna is settled on quaternary alluvium and suffered during the L'Aquila event an extremely heavy damage in the masonry structures with intensity IX-X on the Mercalli-Cancani-Sieberg (MCS) scale. The village of Monticchio, far less than 1.3 km from Onna, is mostly situated on Mesozoic limestone and suffered a smaller level of damaging (VI MCS). In the present paper, we analyze the aftershock recordings at seismic stations deployed in a small area of the middle-Aterno valley including Onna and Monticchio. The aim is to investigate local amplification effects caused by the near-surface geology. Because the seismological stations are close together, vulnerability and near-source effects are assumed to be constant. The waveform analysis shows that the ground motion at Onna is systematically characterized by large high-frequency content. The frequency resonance is varying from 2 to 3 Hz and it is related to alluvial sediments with a thickness of about 40 m that overlay a stiffer Pleistocene substrate. The ground motion recordings of Onna are well reproduced by the predictive equation for the Italian territory. [ABSTRACT FROM AUTHOR]

set of Ground Motion Prediction Equations (GMPEs) for the Italian territory is proposed, exploiting a new strong-motion data set become available since July 2007 through the Italian Accelerometric Archive (ITACA). The data set is composed by 561 three-component waveforms from 107 earthquakes with moment magnitude in the range 4.0–6.9, occurred in Italy from 1972 to 2007 and recorded by 206 stations at distances up to 100 km. The functional form used to derive GMPEs in Italy (Sabetta and Pugliese in Bull Seismol Soc Am 86(2):337–352, 1996) has been modified introducing a quadratic term for magnitude and a magnitude-dependent geometrical spreading. The coefficients for the prediction of horizontal and vertical peak ground acceleration, peak ground velocity and 5% damped acceleration response spectra are evaluated. This paper illustrates the new data set, the regression analysis and the comparisons with recently derived GMPEs in Europe and in the Next Generation Attenuation of Ground Motions (NGA) Project. [ABSTRACT FROM AUTHOR]

In this work we present and discuss the results of ambient seismic noise analyses computed at four sites where seismic stations, managed by the INGV ( Italian Institute for Geophysics and Vulcanology) and the DPC ( Italian Department of Civil Protection), are installed inside buildings. The experiments were performed considering different types of installation: sensor located at the bottom of a school, directly installed on rock (case 1); sensor located at the bottom of a medieval fortress, built on an isolate hill, directly installed on rock (case 2); sensor installed on the foundations of a medieval fortress, built on an isolate hill (case 3); sensor installed on the foundations of a school, built on alluvial deposits (case 4). Since recent works proposed the use of spectral ratio techniques to study the dynamic characterization of buildings, ambient seismic-noise measurements were performed for each site close to the stations (at the base of the structures), at the top of the structures and outside the buildings. In order to check the source of vibrations both horizontal to vertical spectral ratio (HVNR) and standard spectral ratio (SSR) techniques were applied. For all stations the results from ambient seismic noise were compared to those obtained from earthquakes (HVSR). In order to detect preferential directions of amplification, for each site average HVNRs and HVSRs were computed considering one azimuth for each set of 5°. We obtain different results for different types of installation: in cases 1 and 2, where the sensors are directly installed on rock, the vibrations of the structure do not affect the noise measures performed close to the stations, which show flat HVNR in the whole frequency range: in both cases the eigenfrequency of the building is given by the HVNR calculated from the measures performed at the top of the structure. In cases 3 and 4, where the sensors are installed on the foundations of the considered structures, both the amplification peaks between 5 and 9 Hz (case 3) and between 5.5 and 7 Hz (case 4) include the contribution of the free oscillations of the buildings. In particular, in case 4, HVNRs performed outside building highlight possible soil–structure resonance effects in case of an earthquake. [ABSTRACT FROM AUTHOR]