ALBERT

Description: This article describes the Engineering Strong-Motion Database (ESM), developed in the framework of the European project Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation (NERA, see Data and Resources ). ESM is specifically designed to provide end users only with quality-checked, uniformly processed strong-motion data and relevant parameters and has done so since 1969 in the Euro-Mediterranean region. The database was designed for a large variety of stakeholders (expert seismologists, earthquake engineers, students, and professionals) with a user-friendly and straightforward web interface. Users can access earthquake and station information and download waveforms of events with magnitude≥4.0 (unprocessed and processed acceleration, velocity, and displacement, and acceleration and displacement response spectra at 5% damping). Specific tools are also available to users to process strong-motion data and select ground-motion suites for code-based seismic structural analyses.

Description: The first stage of the trial in L'Aquila (Italy) ended with a conviction of seven experts, convened by the head of Civil Protection on 31 March 2009, for multiple manslaughter and serious injuries. They were sentenced to six years in jail, perpetual interdiction from public office and a fine of several million euros to be paid to the victims of the earthquake of 6 April 2009 (moment magnitude 6.3) for having caused, by their negligent conduct, the death of 29 persons and the injury of several others. The verdict had a tremendous impact on the scientific community and on the way scientists deliver their expert opinions to decision makers and society. This paper analyses the scientific argumentations reported in the Verdict Motivations, where scientific data and results were largely debated and misused to demonstrate that they should have been considered as a tool to predict an impending large earthquake. Moreover, we show that the supposed message of reassurance was not generated at the experts’ meeting or by the official Istituto Nazionale di Geofisica e Vulcanologia reports. The media had a key role in conveying information during the seismic swarm, contributing to the risk perception. We stress that prevention actions based on seismic hazard knowledge are the best defence against earthquakes.

Description: The goal of this article is to investigate the possibility of reducing the uncertainty of the ground motion predicted for a specific target area (Po Plain and northeastern Italy), by calibrating a set of ad hoc ground-motion prediction equations (GMPEs). The derived GMPEs account for peculiarities that are not generally considered by standard predictive models, such as (1) an attenuation rate dependent on distance ranges and geological domains; (2) enhancement of short-period spectral ordinates, due to the reflection of S waves at the Moho discontinuity; and (3) generation of surface waves inside an alluvial basin. The analyzed strong-motion dataset was compiled by selecting events in the 4.0–6.4 magnitude range, records with distances shorter than 200 km, and focal depths shallower than 30 km; the major contribution comes from the recent 2012 Emilia sequence (first mainshock, 20 May 2012 M w  6.1; second mainshock, 29 May 2015 M w  6.0). The GMPEs are derived for the geometrical mean of horizontal components of peak ground acceleration, peak ground velocity, and 5% damped spectral acceleration in the 0.04–4 s period range. The derived region-specific models led to a reduction of the hazard levels for several intensity measures, with respect to the values obtained by considering the reference Italian attenuation model ( Bindi et al. , 2011 ), as exemplified by the comparison of the hazard curves computed for two specific sites. Online Material: Database of Northern Italy (DBNI) flat-file and tables of northern Italy ground-motion prediction equations (GMPEs) (NI15) regression coefficients and variability components for use with Joyner–Boore and hypocentral distances.

Description: 〈span〉〈div〉Abstract〈/div〉In this study, we propose an approach to generate spatially correlated seismic ground‐motion fields for loss assessment and risk analysis. Differently from the majority of spatial correlation models, usually calibrated on within‐earthquake residuals, we use the sum of the source‐, site‐, and path‐systematic effects (namely corrective terms) of the ground‐motion model (GMM), obtained relaxing the ergodic assumption. In this way, we build a scenario‐related spatial correlation model of the corrective terms by which adjusting the median predictions of ground motion and the associated variability. We show a case study focused on the Po Plain area in northern Italy, presenting a series of peculiar features (i.e., availability of a dense dataset of seismic records with uniform soil classification and very large plain with variable thickness of the sedimentary cover) that make its study particularly suitable for the purpose of developing and validating the proposed approach.The study exploits the repeatable corrective terms, estimated by 〈a href="https://pubs.geoscienceworld.org/bssa#rf24"〉Lanzano 〈span〉et al.〈/span〉 (2017)〈/a〉 in northern Italy, using a local GMM (〈a href="https://pubs.geoscienceworld.org/bssa#rf23"〉Lanzano 〈span〉et al.〈/span〉, 2016〈/a〉), which predicts the geometric mean of horizontal response spectral accelerations in the 0.01–4 s period range. Our results show that the implementation of a spatially correlated model of the systematic terms provides reliable shaking fields at various periods and spatial patterns compliant with the deepest geomorphology of the area, which is an aspect not accounted by the GMM model. The possibility to define 〈span〉a priori〈/span〉 fields of systematic effects depending on local characteristics could be usefully adopted either to simulate future ground‐motion scenarios or to reconstruct past events.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This work aims to revise the 〈a href="https://pubs.geoscienceworld.org/bssa#rf10"〉Bindi 〈span〉et al.〈/span〉 (2011)〈/a〉 ground‐motion model for shallow crustal earthquakes in Italy (hereinafter, ITA10), calibrated in the magnitude range 4.0–6.9 using strong‐motion data recorded up to the 2009 L’Aquila sequence. The improvement of ITA10 is needed because of the large number of strong‐motion records made available in Italy after the occurrence of the most recent seismic sequences (2012 Emilia, Northern Italy; 2016–2017 Central Italy). The new data collection allows us to extend the magnitude range beyond 6.9 and to include vibration periods up to 10 s. Instead of the geometric mean of the horizontal components of ground motion, the median of orientation independent amplitudes (RotD50) is selected as a measure of the ground‐motion parameters, and the rupture distance is introduced as an alternative source‐to‐site metric to the Joyner–Boore distance (RJB). The site effects are accounted for by a linear dependence on the time‐averaged shear‐wave velocity in the upper 30 m, VS30. A breakdown of the ground‐motion variability is performed into between‐event and site‐to‐site components to make the model suitable for the evaluation of nonergodic probabilistic seismic hazard. We also build a heteroscedastic model for aleatory variability as a function of moment magnitude and VS30. The evaluation of the epistemic uncertainty in the median prediction is also provided to be introduced in the logic trees for the probabilistic seismic hazard assessment. We obtain changes in median predictions with respect to ITA10 at distances lower than 10 km and for strong events (Mw〉6.5); moreover, the total standard deviations are significantly lower at intermediate and long periods, with an average reduction of about 20%.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This work aims to revise the 〈a href="https://pubs.geoscienceworld.org/bssa#rf10"〉Bindi 〈span〉et al.〈/span〉 (2011)〈/a〉 ground‐motion model for shallow crustal earthquakes in Italy (hereinafter, ITA10), calibrated in the magnitude range 4.0–6.9 using strong‐motion data recorded up to the 2009 L’Aquila sequence. The improvement of ITA10 is needed because of the large number of strong‐motion records made available in Italy after the occurrence of the most recent seismic sequences (2012 Emilia, Northern Italy; 2016–2017 Central Italy). The new data collection allows us to extend the magnitude range beyond 6.9 and to include vibration periods up to 10 s. Instead of the geometric mean of the horizontal components of ground motion, the median of orientation independent amplitudes (RotD50) is selected as a measure of the ground‐motion parameters, and the rupture distance is introduced as an alternative source‐to‐site metric to the Joyner–Boore distance (RJB). The site effects are accounted for by a linear dependence on the time‐averaged shear‐wave velocity in the upper 30 m, VS30. A breakdown of the ground‐motion variability is performed into between‐event and site‐to‐site components to make the model suitable for the evaluation of nonergodic probabilistic seismic hazard. We also build a heteroscedastic model for aleatory variability as a function of moment magnitude and VS30. The evaluation of the epistemic uncertainty in the median prediction is also provided to be introduced in the logic trees for the probabilistic seismic hazard assessment. We obtain changes in median predictions with respect to ITA10 at distances lower than 10 km and for strong events (Mw〉6.5); moreover, the total standard deviations are significantly lower at intermediate and long periods, with an average reduction of about 20%.〈/span〉

Description: 〈span〉〈div〉ABSTRACT〈/div〉The availability of high‐quality waveforms recorded in epicentral areas of moderate‐to‐strong earthquakes is a key factor for investigating ground‐motion characteristics close to the seismic source. In this study, near‐source strong‐motion waveforms (named NESS1) were collected from worldwide public archives with the aim of building a flat file of high‐quality metadata and intensity measures (IMs) of engineering interest. Particular attention was paid to the retrieval of reliable information about event sources, such as geometries and rupture mechanisms that are necessary to model near‐source effects for engineering seismology and earthquake engineering applications. The accelerometric records are manually and uniformly processed, and the associated information is fully traceable. NESS1 consists of about 800 three‐component waveforms relative to 700 accelerometric stations, caused by 74 events with moment magnitude larger than 5.5 and hypocentral depth shallower than 40 km, with Joyner–Boore distance up to 140 km. Ground‐motion data were selected to have a maximum source‐to‐site distance within one fault length, defined through seismological scaling relations. About 40 records exhibit peak acceleration or peak velocity exceeding 1g or 120  cm/s, and they represent some of the largest ground motion ever recorded. Evidence of near‐source effects was recognized in the NESS1 dataset, such as velocity pulses, large vertical ground motions, directional and hanging‐wall amplifications and fling step. In particular, around 30% of the records was found to exhibit pulse‐like characteristics that are possibly due to forward rupture directivity.〈/span〉

Description: Since August 2016, central Italy has been struck by one of the most important seismic sequences ever recorded in the country. In this study, a strong-motion data set, consisting of nearly 10,000 waveforms, has been analyzed to gather insights about the main features of ground motion, in terms of regional variability, shaking intensity, and near-source effects. In particular, the shake maps from the three main events in the sequence have been calculated to evaluate the distribution of shaking at a regional scale, and a residual analysis has been performed, aimed at interpreting the strong-motion parameters as functions of source distance, azimuth, and local site conditions. Particular attention has been dedicated to near-source effects (i.e., hanging wall/footwall, forward-directivity, or fling-step effects). Finally, ground-motion intensities in the near-source area have been discussed with respect to the values used for structural design. In general, the areas of maximum shaking appear to reflect, primarily, rupture complexity on the finite faults. Large ground-motion variability is observed along the Apennine direction (northwest–southeast) that can be attributed to source-directivity effects, especially evident in the case of small-magnitude aftershocks. Amplifications are observed in correspondence to intramountain basins, fluvial valleys, and the loose deposits along the Adriatic coast. Near-source ground motions exhibit hanging-wall effects, forward-directivity pulses, and permanent displacement.

Description: A fundamental problem for site-specific ground-motion prediction, commonly required in seismic-hazard assessment, lies in the fact that ground-motion observations over long enough time periods are unavailable at the vast majority of sites. For this reason, most of the ground-motion prediction equations have been derived using observed data from multiple stations and seismic sources, and the standard deviation (sigma) is related to the statistics of the spatial variability of ground motion instead of temporal variability at a single site (ergodic assumption). In this paper, we explore the variability at single sites, decomposing sigma into different parts so that the various contributions to the variability can be identified and the standard deviation for empirical ground-motion prediction models quantified by removing the ergodic assumption. The analysis was conducted using three different data sets. Sigma obtained for Italy using the ergodic assumption is about 0.35log10 units ( Bindi, Pacor, et al. , 2011 ) and decreases to about 0.3 when single stations are considered (15% reduction). The values of single-station sigma obtained in this study for multiple-source data sets are rather stable, in the range 0.18–0.2log10 units, comparable to the findings of previous studies. The reduction of the epistemic uncertainty achieved through the restriction of the analysis to a particular seismic source leads to a sigma of about 0.25log10 units when the ergodic assumption is removed, suggesting that sigma at a particular site, due to a particular earthquake source, may reduce the sigma obtained for the Italian territory by Bindi, Pacor, et al. (2011) by about 30%. Online Material: Tables of ground-motion prediction equation coefficients, site terms, and event-corrected single-station standard deviations.