Italian Accelerometric Archive Research Articles

CRISP: an archive for the site characterization of permanent Italian seismic stations

In this paper we describe an advanced database for the site characterization of seismic stations, named “CRISP—Caratterizzazione della RIsposta sismica dei Siti Permanenti della rete sismica” (http://crisp.ingv.it, quoted with https://doi.org/10.13127/crisp), designed for the Italian National Seismic Network (Rete Sismica Nazionale, RSN, operated by Istituto Nazionale di Geofisica e Vulcanologia). For each site, CRISP collects easily accessible station information, such as position, type(s) of instrumentation, instrument housing, thematic map(s) and descriptive attributes (e.g., geological characteristics, etc.), seismic analysis of recordings, and available geophysical investigations (shear-wave velocity [VS] profile, non-linear decay curve). The archive also provides key proxy indicators derived from the available data, such as the time-averaged shear-wave velocity of the upper 30 m from the surface (VS30) and site and topographic classes according to the different seismic codes. Standardized procedures have been applied as motivated by the need for a homogenous set of information for all the stations. According to European Plate Observing System infrastructural objectives for the standardization of seismological data, CRISP is integrated into pre-existing INGV instrument infrastructures, shares content with the Italian Accelerometric Archive, and complies map information about the stations, as well as local geology, through web services managed by Istituto Superiore per la Protezione e la Ricerca Ambientale. The design of the CRISP archive allows the database to be continually updated and expanded whenever new data are available from the scientific community, such as the ones related to new seismic stations, map information, geophysical surveys, and seismological analyses.

Applying the damage assessment for rapid response approach to the august 24 M6 event of the seismic sequence in central Italy (2016)

Seismic monitoring networks are increasingly being used in urban areas to record and locate earthquakes. Recordings in the proximity of buildings also allow assessing, as a first approximation, the expected building damage. The DARR (Damage Assessment for Rapid Response) method provides local-scale information on expected damage patterns. The potential of this approach is discussed here for the August 24 M6 event of the Central Italy seismic sequence (2016–2017). We focus only on the first event of the sequence because cumulative damage is outside the scope of this study. The earthquake recordings are available from two Italian monitoring networks: the Italian Accelerometric Archive (ITACA) and the OSS (Osservatorio Sismico delle Strutture), which collects data from monitored buildings and bridges in Italy. We selected four target areas (Amatrice, Norcia, Visso and Sulmona) characterized by different epicentral distances and building typologies, that suffered different levels of damage during the M6 event on 24 August 2016. Using recordings either in the free field or in the basement of buildings, the expected relative displacement of building typologies common in the studied areas is calculated with the DARR method. Using predefined damage thresholds from literature, the obtained results allow quantifying the expected damage for dominant building typologies in the surroundings of the recording sites. We investigate and discuss the potential use and applicability of the DARR method in different areas depending on the epicentral distance and building characteristics. The results indicate that the DARR approach is useful for supporting and improving rapid response activities after a seismic event.

Consistency Check of ITACAext, the Flatfile of the Italian Accelerometric Archive

We present the results of a consistency check performed over a flatfile of accelerometric data extracted from the ITalian ACcelerometric Archive (ITACA), enriched with velocimetric records of events with magnitude M < 4.0. The flatfile, called ITACAext, includes 31,967 waveforms from 1709 shallow crustal earthquakes, in the magnitude range from 3.0 to 6.9, and occurred in the period of 1972–2019 in Italy. The consistency check is carried out by decomposing the residuals obtained from a reference ground motion model, for the ordinates of the 5% damped acceleration response spectra. The residual components are subsequently analyzed to identify a list of events, stations, and records that significantly deviate from the median trends predicted by the model. The results indicate that about 10% of events and stations are outliers, while only 1% of the waveforms present anomalous amplitudes. The asymmetrical azimuthal coverage of seismic stations around the epicenter is the most common issue that can affect the estimates of the repeatable event residual term. On the other hand, peculiarities in the site-response or wrong estimates of the soil parameters (i.e., the average shear-wave velocity in the first 30 m of the subsoil) are the main issues related to the repeatable station residuals. Finally, single records can show large residuals because of issues related to signal acquisition (e.g., multiple events, noisy records) or possible near-source effects (e.g., rupture directivity).

Generic-To-Reference Rock Scaling Factors for Seismic Ground Motion in Italy

ABSTRACT In this article, we apply the reference-rock identification method (RRIM; Lanzano et al., 2020) to the ITalian ACcelerometric Archive, which includes more than 1600 recording stations in Italy and in the neighboring countries, with different levels of site characterization. The RRIM is based on the identification and the evaluation of site parameters representing the reference site conditions (Steidl et al., 1996) and the construction of the scoring scheme to classify the candidate stations. Given the large number of sites, the preselection of candidates is performed via residual analysis, selecting those characterized by flat site response and amplitude similar or lower than the one for the generic rock (average shear-wave velocity in the uppermost 30 m, VS30=800 m/s). The main results of this study are: (1) a list of reference rock sites in Italy, with an associated score; (2) a scenario-independent generic-to-reference rock corrective factor for the ground-motion model for shallow active crustal events in Italy (ITA18; Lanzano, Luzi, et al., 2019); (3) a model for the generic-to-reference rock corrective factor, parametrized in terms of VS30 and κ0, that is, the high-frequency decay parameter (Anderson and Hough, 1984). A collateral product is a set of coefficients for the prediction of 81 ordinates of the Fourier amplitude spectra (FAS) in the frequency interval 0.1–30 Hz, calibrated with the same dataset and functional form of ITA18 for acceleration response spectra (SA). The application of RRIM allowed us to identify 116 stations with average measured VS30∼900 m/s. The corrective factor allows to scale both SA and FAS spectra, and has a significant effect at high frequencies, reducing the ground motion by up to a factor 1.7 at f = 10 Hz. The introduction of κ0 in the corrective term modeling is effective from 2 Hz onward and results in a reduction of variability at high frequencies (f > 10 Hz).

Accessing European Strong-Motion Data: An Update on ORFEUS Coordinated Services

AbstractStrong ground motion records and free open access to strong-motion data repositories are fundamental inputs to seismology, engineering seismology, soil dynamics, and earthquake engineering science and practice. This article presents the current status and outlook of the Observatories and Research Facilities for European Seismology (ORFEUS) coordinated strong-motion seismology services, namely the rapid raw strong-motion (RRSM) and the engineering strong-motion (ESM) databases and associated web interfaces and webservices. We compare and discuss the role and use of these two systems using the Mw 6.5 Norcia (Central Italy) earthquake that occurred on 30 October 2016 as an example of a well-recorded earthquake that triggered major interest in the seismological and earthquake engineering communities. The RRSM is a fully automated system for rapid dissemination of earthquake shaking information, whereas the ESM provides quality-checked, manually processed waveforms and reviewed earthquake information. The RRSM uses only data from the European Integrated Waveform Data Archive, whereas the ESM also includes offline data from other sources, such as the ITalian ACcelerometric Archive (ITACA). Advanced software tools are also included in the ESM to allow users to process strong-motion data and to select ground-motion waveform sets for seismic structural analyses. The RRSM and ESM are complementary services designed for a variety of possible stakeholders, ranging from scientists to the educated general public. The RRSM and ESM are developed, organized, and reviewed by selected members of the seismological community in Europe, including strong-motion data providers and expert users. Global access and usage of the data is encouraged. The ESM is presently the reference database for harmonized seismic hazard and risk studies in Europe. ORFEUS strong-motion data are open, “Findable, Accessible, Interoperable, and Reusable,” and accompanied by licensing information. The users are encouraged to properly cite the data providers, using the digital object identifiers of the seismic networks.

Relationships between ground motion parameters and macroseismic intensity for Italy

The relation between macroseismic intensity and ground shaking makes it possible to transform instrumental Ground Motion Parameters (GMPs) in macroseismic intensity and vice versa, and is therefore useful for making comparisons between estimates of seismic hazard determined in terms of GMPs and macroseismic intensity, and for other engineering and seismological applications. Empirical relationships between macroseismic intensity and different recorded GMPs for the Italian territory are presented in this paper. The coefficients are calibrated using a dataset of horizontal geometrical mean GMPs, i.e. peak ground acceleration, peak ground velocity, spectral acceleration at 0.2, 0.3, 1.0 and 2.0 s from the ITalian ACcelerometric Archive (ITACA; Luzi et al. in Italian Accelerometric Archive v3.0, Istituto Nazionale di Geofisica e Vulcanologia, Dipartimento della Protezione Civile Nazionale, 2019. https://doi.org/10.13127/itaca.3.0), and macroseismic intensity at Mercalli–Cancani–Sieberg (MCS) scale from the database DBMI15 (Locati et al. in Database Macrosismico Italiano (DBMI15), versione 2.0, Istituto Nazionale di Geofisica e Vulcanologia (INGV), 2019. https://doi.org/10.13127/DBMI/DBMI15.2). A dataset is obtained that corresponds to 240 pairs of macroseismic intensity-GMPs from 67 Italian earthquakes in the time window 1972–2016 with moment magnitude ranging from 4.2 to 6.8 and macroseismic intensity in the range [2, 10–11]. The final dataset correlates strong motion stations and macroseismic intensity observations generally within 2 km from each other, and each association is manually validated through an expert judgement. The adopted functional form is non-linear, predicting macroseismic intensity as a function of LogGMPs and vice versa by performing separate regressions. The set of empirical conversion relationships GMP–IMCS–GMP and the associated standard deviations are compared with previous models. In order to verify the proposed model, a map in terms of PGA is obtained, starting from the PSHA in terms of intensities (Gomez Capera et al. in Bull Seismol Soc Am 100(4):614–1631, 2010. https://doi.org/10.1785/0120090212) and then using the empirical relationship here proposed in PGA, and compared with the National Italian seismic hazard map (Stucchi et al. in Bull Seismol Soc Am 101(4):1885–1911, 2011. https://doi.org/10.1785/0120100130).

Site classification of Italian accelerometric stations from cluster analysis of residuals of peak ground motion data regressions

One basic element for seismic hazard assessment is the empirical definition of ground motion prediction equations (GMPE) to estimate shaking expected for earthquakes of given magnitude and distance. GMPEs are calibrated from data of accelerometric stations, distinguishing among site categories of different lithological type (e.g. hard rocks, more or less stiff soils) expected to cause different levels of ground motion amplification. Such a site classification is commonly based on geological observations and/or geophysical parameters like the mean propagation velocity of seismic waves through subsoil surficial layers. However, doubts have been raised about the effectiveness of results obtained from these conventional methods. Here we propose a methodology of accelerometric site classification relying on peak ground motion observations, exploiting the large amount of such observations available in the Italian National accelerometric database. The method is based on a cluster analysis of differences between observations and predictions provided by GMPEs whose functional form does not comprise site class among the explanatory variables. The new method was applied to the ITalian ACcelerometric Archive (ITACA), extracting a “training” dataset (used to calibrate some GMPEs through regressions) and a “validation” dataset (to select the optimal GMPE form). A cluster analysis was then applied to regression residuals, grouping stations into three categories with increasing value of residual average. Checking the reclassification effectiveness through the examination of differences between independent “validation” observations and predictions of GMPEs adopting the new classification, these proved to be more consistent with site response properties than predictions provided by GMPEs using current classification.

Reversible ground motion-to-intensity conversion equations based on the EMS-98 scale

The relation between observed macroseismic intensities and recorded ground motion parameters is a matter of interest in earthquake engineering, and it has been widely discussed in literature in the past. Several relationships already exist, correlating macroseismic intensity and peak ground motion parameters (i.e. PGA, PGV or PGD, respectively peak ground acceleration, velocity and displacement). However, most of these formulations are based on Mercalli-Cancani-Sieberg (MCS) scale, developed using regional databases and difficult to be applied at large scale. In this research, new formulations are proposed that correlate European Macroseismic Scale (EMS-98) with ground shaking parameters (PGMs), Arias intensity and Housner intensity. An initial PGM/EMS-98 intensity dataset was assembled for this scope, collecting 610 data pairs of observations, from 35 different Italian seismic events derived from the Parametric Catalogue of Italian Earthquakes (CPTI15) and the Italian Accelerometric Archive (ITACA), subsequently filtered considering only tectonic events and data pairs with site – station distances lower than 3 km. The resulting final dataset of 220 data pairs from 22 earthquakes was thus used to obtain regression relationships, finally compared with existing models based on the Modified Mercalli (MM) scale and MCS scale.

SYNTHESIS: a web repository of synthetic waveforms

We present a web-repository (SYNTHESIS 0.2, SYNTHEtic SeISmograms database) designed to archive and distribute synthetic waveforms computed by physic-based models. The structure of the database derives from the ITalian ACcelerometric Archive (ITACA Working Group in ITalian ACcelerometric Archive, version 2.1, 2016. doi: 10.13127/ITACA/2.1), devoted to archive and distribute recorded strong motion data. To date, SYNTHESIS includes more than 4500 simulated accelerograms associated to earthquake scenarios of either occurred events or possible future events. The database also includes information about kinematic rupture models and propagation medium related to the synthetic waveforms. The main features of the SYNTHESIS web-portal for dissemination of synthetics are here illustrated. A wide range of key fields enables the user to interactively retrieve simulated waveforms, modeling parameters and information on simulation sites. A range of display options allows users to view data in different frameworks, to extract and download synthetic waveforms and to display maps of selected peak ground motion parameters. SYNTHESIS is a prototype designed to fulfill specific needs of two Italian projects, and developed with the aim of promoting the use of simulated waveforms for hazard analysis. Ground motion simulations can be employed in a variety of applications, such as: (1) to evaluate shaking scenarios for seismic risk mitigation; (2) to define seismic inputs for site response or structural response analyses; (3) to integrate observed data for the calibration of ground motion prediction equations and (4) to evaluate the different components of the ground motion variability.

Predicting the macroseismic intensity from early radiated P wave energy for on‐site earthquake early warning in Italy

AbstractEarthquake Early Warning Systems (EEWS) are potentially effective tools for risk mitigation in active seismic regions. The present study explores the possibility of predicting the macroseismic intensity within EEW timeframes using the squared velocity integral (IV2) measured on the early P wave signals, a proxy for the P wave radiated energy of earthquakes. This study shows that IV2 correlates better than the peak displacement measured on P waves with both the peak ground velocity and the Housner Intensity, with the latter being recognized by engineers as a reliable proxy for damage assessment. Therefore, using the strong motion recordings of the Italian Accelerometric Archive, a novel relationship between the parameter IV2 and the macroseismic intensity (IM) has been derived. The validity of this relationship has been assessed using the strong motion recordings of the Istituto Nazionale di Geofisica e Vulcanologia Strong Motion Data and Osservatorio Sismico delle Strutture databases, as well as, in the case of the MW 6, 29 May 2012 Emilia earthquake (Italy), comparing the predicted intensities with the ones observed after a macroseismic survey. Our results indicate that P wave IV2 can become a key parameter for the design of on‐site EEWS, capable of proving real‐time predictions of the IM at target sites.

Spatial Correlation of Spectral Acceleration in European Data

Abstract Quantification of regional seismic risk is based on spatially correlated random fields and requires modeling of the joint distribution of ground‐motion intensity measures at all sites of interest. In particular, when a portfolio of buildings or a transportation/distribution network (lifeline) is of concern, correlation models for elastic spectral acceleration (SA) may also be required in order to estimate the expected loss in case of seismic events. The presented study focuses on semi‐empirical estimation of spatial correlation as a function of intersite separation distance. In fact, this paper complements, and is based on, preceding work of the authors referring to spatial correlation of peak ground acceleration and velocity (Esposito and Iervolino, 2011). The evaluation of correlation for ground‐motion residuals was performed on data from multiple earthquakes, considering different ground‐motion prediction equations fitted to the same records. Correlation analyses, carried out through geostatistical tools, considered two datasets: the Italian Accelerometric Archive and the European Strong‐Motion Database. Results appear generally consistent with previous research on the same topic. Finally, simple relationships providing the correlation range of intraevent residuals of SA, as a function of structural period, were derived for each dataset. The developed models are useful for earthquake engineering applications where spatial correlation of peak ground motion is required.

Using Pad-Stripped Acausally Filtered Strong-Motion Data

Most strong-motion data processing involves acausal low-cut filtering, which requires the addition of sometimes lengthy zero pads to the data. These padded sections are commonly removed by organizations supplying data, but this can lead to incompatibilities in measures of ground motion derived in the usual way from the padded and the pad-stripped data. One way around this is to use the correct initial conditions in the pad-stripped time series when computing displacements, velocities, and linear oscillator response. Another way of ensuring compatibility is to use post- processing of the pad-stripped acceleration time series. Using 4071 horizontal and vertical acceleration time series from the Turkish strong-motion database, we show that the procedures used by two organizations—ITACA (ITalian ACcelerometric Archive) and PEER NGA (Pacific Earthquake Engineering Research Center-Next Generation Attenuation)—lead to little bias and distortion of derived seismic-intensity measures.

The recording stations of the Italian strong motion network: geological information and site classification

One of the main objectives of the ITACA (ITalian ACcelerometric Archive) strong motion database, promoted by the Italian Department of Civil Protection, was to improve the characterization of the recording sites from a geological and geophysical point of view and to provide their seismic classification according to the seismic norms pertinent to Italy, namely the Eurocode 8 and the National Technical Norms for Constructions. A standard format to summarize the available information for the recording stations was first produced, in terms of a technical report dynamically linked to the database, i.e., some of the relevant information is automatically updated when the corresponding fields of the database are modified. Then, an important activity of collection, qualification and synthesis of available data was carried out, especially for stations that recorded the strongest earthquakes in Italy in the last 40 years, and for which a relevant number of studies have been published. In spite of this activity, among the more than 700 strong motion stations present in the ITACA database, only a limited number of them could be characterized by quantitative information on subsurface soil properties. For this reason, a dual seismic site classification criterion was implemented, either based on the standard Vs,30 scheme, or, in the absence of such information, based on an expert opinion supported by shallow geology maps, mostly at 1:100,000 scale, and when available on the H/V ratios calculated on recordings. Owing to the relevance in the Italian geographic and morphological context, a special care was also given to the topographic classification of stations, based on suitable criteria developed within a GIS environment.

PGA and PGV Spatial Correlation Models Based on European Multievent Datasets

Abstract Spatial modeling of ground motion intensity measures (IMs) is required for risk assessment of spatially distributed engineering systems. For example, when a lifeline system is of concern, classical site-specific hazard tools, which treat IMs at different locations independently, may not be adequate to accurately assess the seismic risk. In fact, in this case, modeling of ground motion as a random field is required; it basically consists of assigning a correlation structure to the IM of interest. This work focuses on semiempirical estimation of the correlation coefficient, as a function of intersite separation distance, between residuals with respect to ground motion prediction equations (GMPEs) of horizontal peak ground acceleration (PGA) and peak ground velocity (PGV). In particular, subsets of the European Strong-Motion Database (ESD) and the Italian Accelerometric Archive (ITACA) were employed to evaluate the intraevent residual correlation based on multiple earthquakes, considering different GMPEs fitted to the same records. The analyses were carried out through geostatistical tools, which enabled results to be found that are generally consistent between the two datasets. Correlation for PGV appears to attenuate more gradually with respect to PGA. In order to better understand the dependency of the results on the adopted estimation approach and dataset, some aspects related to the working hypotheses are critically discussed. Finally, estimated correlation models are used to develop illustrative applications of regional probabilistic seismic-hazard analysis.

Engineering ground motion record selection in the ITalian ACcelerometric Archive

This paper introduces REXELite, an internet version of REXEL, a software for automatic selection of ground motion suites for nonlinear dynamic analysis of structures. REXELite was developed with the aim of integrating an advanced earthquake records’ repository, such as the ITalian ACcelerometric Archive (ITACA), with a tool to define seismic input for engineering seismic analysis according to international standards (with priority to Europe). In fact, REXELite allows to define target design spectra according either to Eurocode 8 or to the Italian building code, and to search ITACA for suitable sets of seven records (comprised of one or two horizontal ground motion components) matching such target spectra: on average, in a user-specified period range, and with the desired tolerance. The records in the set also have, individually and according to some criteria, the most similar spectral shape with respect to that of the code. Selection options include magnitude, source-to-site distance, soil conditions and, if desired, linear scaling of records to reduce further record-to-record variability of the selected suite.

Italian strong motion records in ITACA: overview and record processing

The published version 1.0 of the new Italian strong-motion database ITACA (Italian ACcelerometric Archive, http://itaca.mi.ingv.it) includes to date (December 2010) about 4,000 three-component waveforms up to M 6.9, from more than 1,800 earthquakes up to 6.9, recorded by about 400 stations in the period 1972–2009. The uncorrected and corrected strong motion data are archived and can be retrieved with their metadata, concerning events, stations and waveforms. The aim of this paper is to present the procedures for processing the records included in ITACA, accounting for the heterogeneity of this data set, both in terms of quality and amplitude of records as well as illustrating the main features of the ITACA strong-motion dataset. Later, we focus on the “exceptional” ground-motion records, that we, conventionally, denote as those having peak acceleration and peak velocity larger than 300 cm/s2 and 15 cm/s, respectively. These records are less than 2% of the whole ITACA dataset but they are the most relevant for the seismic hazard and engineering implications. Such large peak values, recorded at distances up to 30 km, are related not only to the strongest Italian earthquakes, but also to events with magnitude down to 4. Furthermore, we investigate the dependence of the largest peak values on horizontal and vertical directions and on source-to-site distance.

The ITalian ACcelerometric Archive (ITACA): processing of strong-motion data

The Italian strong-motion database was created during a joint project between Istituto Nazionale di Geofisica e Vulcanologia (INGV, Italian Institute for Geophysics and Vulcanology) and Dipartimento della Protezione Civile (DPC, Italian Civil Protection). The aim of the project was the collection, homogenization and distribution of strong motion data acquired in Italy in the period 1972–2004 by different institutions, namely Ente Nazionale per l’Energia Elettrica (ENEL, Italian electricity company), Ente per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA, Italian energy and environment organization) and DPC. Recently the strong-motion data relative to the 23th December 2009, Parma (Mw = 5.4 and Mw = 4.9) and to the April 2009 L’Aquila sequences (13 earthquakes with 4.1 ≤ Mw ≤ 6.3) were included in the Italian Accelerometric Archive (ITACA) database (beta release). The database contains 7,038 waveforms from analog and digital instruments, generated by 1.019 earthquakes with magnitude up to 6.9 and can be accessed on-line at the web site http://itaca.mi.ingv.it. The strong motion data are provided in the unprocessed and processed versions. This article describes the steps followed to process the acceleration time series recorded by analogue and digital instruments. The procedures implemented involve: baseline removal, instrumental correction, band pass filtering with acausal filters, integration of the corrected acceleration in order to obtain velocity and displacement waveforms, computation of acceleration response spectra and strong motion parameters. This procedure is applied to each accelerogram and it is realised to preserve the low frequency content of the records.

Italian accelerometric archive: geological, geophysical and geotechnical investigations at strong-motion stations

Geological, geophysical and geotechnical investigations, for the characterization of the strong-motion recording sites managed by the Italian Civil Protection, have been carried out in the framework of the project “Italian strong-motion database in the period 1972–2004”. The project aimed at creating an updated database of strong-motion data acquired in Italy by different institutions in the time span 1972–2004, and at improving the quality of disseminated data. This article illustrates the state of the recording site characterization before the beginning of the project, explains the criteria adopted to select the sites where geophysical/geotechnical investigation have been performed and describes the results of the promoted field surveys.

Interevent and Interstation Variability Computed for the Italian Accelerometric Archive (ITACA)

Abstract The interevent and interstation ground-motion variability of the updated Italian strong-motion database (Italian Accelerometric Archive [ITACA]) has been explored through the development of new empirical ground-motion prediction equations (GMPEs) for Italy. The regressions have been performed on 241 three-component waveforms from 27 earthquakes with moment magnitudes ranging from 4.8 to 6.9, recorded by 146 stations at distances up to 200 km. The site classification follows the schemes previously proposed for Italy, in which two soil classes are defined, considering both shear-wave velocity and deposit thickness. The regression analysis uses the values of the explanatory variables (magnitude, fault distance, site class, and style of faulting) recently revised in the framework of a project funded by the Italian Department of Civil Protection. The equations have been derived for peak ground acceleration, peak ground velocity, and 5% damped spectral accelerations at 18 periods from 0.03 to 2 sec. The residual variance has been decomposed into interevent, interstation, and record-to-record components by applying a random effect regression scheme. The interevent and interstation error distributions have been analyzed as function of periods to detect sites and events for which predicted values significantly deviate from observations. For periods up to 0.35 sec, the interstation is the dominant component of variance, indicating that an improvement in the site classification could lead to a refinement of the GMPEs. For longer periods, the three components of variance provide similar contributions, indicating that a reduction of the uncertainty can be achieved by reducing the epistemic uncertainty affecting the physical model. The interevent error highlights the peculiarity of few earthquakes, suggesting that the evaluation of regional GMPEs can be important when specific scenario studies should be carried out. The interstation variability allows us to detect stations with peculiar site response and to assess the goodness of the considered site classification scheme.

Horizontal and vertical ground motion prediction equations derived from the Italian Accelerometric Archive (ITACA)

A 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.