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: We used strong-motion records from the 2012 May 20 and 29 Emilia-Romagna earthquakes ( M w 6.1 and 5.9, respectively) and four aftershocks with magnitudes ranging between 4.9 and 5.5 to analyse the S -wave spectral amplitude decay with distance and estimate acceleration source functions and site effects. The data set consists of six earthquakes, 44 stations and 248 records with hypocentral distances in the range 10 〈 r  〈 100 km. We rotated the accelerograms to calculate transverse and radial components of the acceleration spectrum. We found non-parametric attenuation functions that describe the spectral amplitude decay of SH and SV waves with distance at 60 different frequencies between 0.1 and 40 Hz. These attenuation functions provide an estimate of the quality factor Q at each frequency analysed. Assuming that geometrical spreading is 1/ r for r  ≤ r x and 1/( r x r ) 0.5 for r  〉 r x with r x  = 60 km and normalizing at 15 km (the recording distance where the attenuation functions start to decay), we find that the average Q for SH waves can be approximated by Q SH  = 82 ± 1 f  1.2±0.02 and by Q SV  = 79 ± 1 f  1.24±0.03 for SV waves in the frequency range 0.10 ≤ f  ≤ 10.7 Hz. At higher frequencies, 11.8 ≤ f  ≤ 40 Hz, the frequency dependence of Q weakens and is approximated by Q SH  = 301 ± 1 f   0.36±0.04 and Q SV  = 384 ± 1 f  0.28±0.04 . These results indicate that the S -wave attenuation is radially isotropic at local distances in the epicentral area. Nevertheless, we used these attenuation parameters separately to correct the radial (with Q SV ) and transverse (with Q SH ) components of the acceleration spectra and to separate source and site effects using a non-parametric spectral inversion scheme. We found that the source function of the main event and the bigger aftershocks show enhanced low frequency radiation between 0.4 and 3.0 Hz. We converted the source functions into far-field source acceleration spectra and interpreted the resulting source spectra in terms of Brune's model. The stress drops obtained range between approximately 0.9 and 2.9 MPa. Although all the recording stations used are located in the Po Plain, the site functions obtained from the spectral inversion show important amplification variability between the sites. We compared these site functions with the average horizontal to vertical spectral ratios calculated for each station, and we found consistent results for most stations.

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: In this study we derive a spectral model describing the source, propagation and site characteristics of S waves recorded in central Italy. To this end, we compile and analyse a high-quality data set composed of more than 9000 acceleration and velocity waveforms in the local magnitude ( M l ) range 3.0–5.8 recorded at epicentral distances smaller than 120 km. The data set spans the time period from 2008 January 1 to 2013 May 31, and includes also the 2009 L'Aquila (moment magnitude M w 6.1, M l = 5.8) sequence. This data set is suitable for the application of data-driven approaches to derive the empirical functions for source, attenuation and site terms. Therefore, we apply a non-parametric inversion scheme to the acceleration Fourier spectra of the S waves of 261 earthquakes recorded at 129 stations. In a second step, with the aim of defining spectral models suitable for the implementation in numerical simulation codes, we represent the obtained non-parametric source and propagation terms by fitting standard parametric models. The frequency-dependent attenuation with distance r shows a complex trend that we parametrize in terms of geometrical spreading, anelastic attenuation and high-frequency decay parameter k. The geometrical spreading term is described by a piecewise linear model with crossover distances at 10 and 70 km: in the first segment, the spectral ordinates decay as 〈 tex – mathid = " IM 0001" 〉 r – 1.01 while in the second as 〈 tex – mathid = " IM 0002" 〉 r – 1.68 . Beyond 70 km, the attenuation decreases and the spectral amplitude attenuate as 〈 tex – mathid = " IM 0003" 〉 r – 0.64 . The quality factor Q ( f ) and the high-frequency attenuation parameter k , are 〈 tex – mathid = " IM 0004" 〉 Q ( f ) = 290 f 0.16 and k = 0.012 s, respectively, the latter being applied only for frequencies higher than 10 Hz. The source spectra are well described by 2 models, from which seismic moment and stress drops of 231 earthquakes are estimated. We calibrate a new regional relationship between seismic moment and local magnitude that improves the existing ones and extends the validity range to 3.0–5.8. We find a significant stress drop increase with seismic moment for events with M w larger than 3.75, with so-called scaling parameter  close to 1.5. We also observe that the overall offset of the stress-drop scaling is controlled by earthquake depth. We evaluate the performance of the proposed parametric models through the residual analysis of the Fourier spectra in the frequency range 0.5–25 Hz. The results show that the considered stress-drop scaling with magnitude and depth reduces, on average, the standard deviation by 18 per cent with respect to a constant stress-drop model. The overall quality of fit (standard deviation between 0.20 and 0.27, in the frequency range 1–20 Hz) indicates that the spectral model calibrated in this study can be used to predict ground motion in the L'Aquila region.

Description: In this study we derive a spectral model describing the source, propagation and site characteristics of S waves recorded in central Italy. To this end, we compile and analyse a high-quality data set composed of more than 9000 acceleration and velocity waveforms in the local magnitude ( M l ) range 3.0–5.8 recorded at epicentral distances smaller than 120 km. The data set spans the time period from 2008 January 1 to 2013 May 31, and includes also the 2009 L'Aquila (moment magnitude M w 6.1, M l = 5.8) sequence. This data set is suitable for the application of data-driven approaches to derive the empirical functions for source, attenuation and site terms. Therefore, we apply a non-parametric inversion scheme to the acceleration Fourier spectra of the S waves of 261 earthquakes recorded at 129 stations. In a second step, with the aim of defining spectral models suitable for the implementation in numerical simulation codes, we represent the obtained non-parametric source and propagation terms by fitting standard parametric models. The frequency-dependent attenuation with distance r shows a complex trend that we parametrize in terms of geometrical spreading, anelastic attenuation and high-frequency decay parameter k. The geometrical spreading term is described by a piecewise linear model with crossover distances at 10 and 70 km: in the first segment, the spectral ordinates decay as 〈 tex – mathid = " IM 0001" 〉 r – 1.01 while in the second as 〈 tex – mathid = " IM 0002" 〉 r – 1.68 . Beyond 70 km, the attenuation decreases and the spectral amplitude attenuate as 〈 tex – mathid = " IM 0003" 〉 r – 0.64 . The quality factor Q ( f ) and the high-frequency attenuation parameter k , are 〈 tex – mathid = " IM 0004" 〉 Q ( f ) = 290 f 0.16 and k = 0.012 s, respectively, the latter being applied only for frequencies higher than 10 Hz. The source spectra are well described by 2 models, from which seismic moment and stress drops of 231 earthquakes are estimated. We calibrate a new regional relationship between seismic moment and local magnitude that improves the existing ones and extends the validity range to 3.0–5.8. We find a significant stress drop increase with seismic moment for events with M w larger than 3.75, with so-called scaling parameter  close to 1.5. We also observe that the overall offset of the stress-drop scaling is controlled by earthquake depth. We evaluate the performance of the proposed parametric models through the residual analysis of the Fourier spectra in the frequency range 0.5–25 Hz. The results show that the considered stress-drop scaling with magnitude and depth reduces, on average, the standard deviation by 18 per cent with respect to a constant stress-drop model. The overall quality of fit (standard deviation between 0.20 and 0.27, in the frequency range 1–20 Hz) indicates that the spectral model calibrated in this study can be used to predict ground motion in the L'Aquila region.

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〉