L. Luzi

Pan-European ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5 %-damped PSA at spectral periods up to 3.0 s using the RESORCE dataset

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.

Ground-Motion Predictions from Empirical Attenuation Relationships versus Recorded Data: The Case of the 1997–1998 Umbria-Marche, Central Italy, Strong-Motion Data Set

We evaluate the goodness of fit of attenuation relations commonly used for the Italian national territory (Sabetta and Pugliese, 1996) by using the maximum likelihood approaches of Spudich et al. (1999) and Scherbaum et al. (2004). According to the classification scheme proposed by Scherbaum et al. (2004), the Sabetta and Pugliese (1996) relationships show consistent discrepancies between the predicted and the observed peak ground acceleration (pga) at rock sites in the Umbria- Marche region, central Italy; however, at soft sites the agreement between observations and prediction is satisfactory. The bias of the residuals, computed with the Sabetta and Pugliese (1996) models for pga, peak ground velocity, (pgv) and pseudovelocity response spectrum (psv) (for M l = 4–6 and epicentral distances up to 100 km) is negative. This means that on the average, the predictions overestimate the observations, but the overestimation decreases with increasing magnitude. Then, we present regional predictive relations (UMA05) for maximum horizontal pga, pgv, and 5%-damped psv, derived from the strong-motion data recorded in the Umbria-Marche area and classified as to four site categories. The UMA05 attenuation relationships for rock sites are log 10 (PGA) = −2.487 + M 1 − 1.280 log 10 ( R 2 + 3.94 2 ) 0.5 ± 0.268 log 10 (PGV) = −1.803 + 0.687 M 1 − 1.150 log 10 ( R 2 + 2.74 2 ) 0.5 ± 0.300 and log 10 (PGA) = −2.500 + 0.544 M 1 − 1.284 log 10 R h ± 0.292 log 10 (PGV) = −1.752 + 0.685 M 1 − 1.167 log 10 R h ± 0.297, where pga is measured in fraction of g and pgv in centimeters per second, M l is the local magnitude in the range 4–6, R is the epicentral distance in the range 1–100 km, and R h is the hypocentral distance in kilometers. We used the random effect model (Brillinger and Priesler, 1985; Abrahamson and Youngs, 1992; Joyner and Boore, 1993; Joyner and Boore, 1994) to estimate the component of variance related to the earthquake-to-earthquake, station-to-station, and record-to-record variability, and to quantify the benefit of introducing a site classification in the attenuation model to reduce the variance. The introduction of the site classification in the attenuation model allows a reduction of the station-to-station component of variability (from 0.19 to 0.14 for pga, and from 0.21 to 0.18 for pgv). We also found that the record- to-record component represents the largest contribution to the model uncertainty.

Comparisons among the five ground-motion models developed using RESORCE for the prediction of response spectral accelerations due to earthquakes in Europe and the Middle East

This article presents comparisons among the five ground-motion models described in other articles within this special issue, in terms of data selection criteria, characteristics of the models and predicted peak ground and response spectral accelerations. Comparisons are also made with predictions from the Next Generation Attenuation (NGA) models to which the models presented here have similarities (e.g. a common master database has been used) but also differences (e.g. some models in this issue are nonparametric). As a result of the differing data selection criteria and derivation techniques the predicted median ground motions show considerable differences (up to a factor of two for certain scenarios), particularly for magnitudes and distances close to or beyond the range of the available observations. The predicted influence of style-of-faulting shows much variation among models whereas site amplification factors are more similar, with peak amplification at around 1s. These differences are greater than those among predictions from the NGA models. The models for aleatory variability (sigma), however, are similar and suggest that ground-motion variability from this region is slightly higher than that predicted by the NGA models, based primarily on data from California and Taiwan.

Site Response of Strong Motion Stations in the Umbria, Central Italy, Region

We used near-field and regional records from 16 earthquakes ( M L 4.6-5.9) located in the epicentral area of the 1997 Umbria-Marche sequence to estimate the site response of 40 strong motion stations. The distribution of hypocenters covers a distance range from 5 to 100 km. We estimated site amplification factors using two techniques, namely a generalized spectral inversion method and horizontal-to-vertical-component spectral ratios (HVSRs) of ground acceleration. For the first approach, we inverted observed spectral amplitudes for site, Q , and source using a reference site. Since the site response estimated using HVSRs assumes that the vertical component of motion is amplification free, we also separated source and site effects by inverting the vertical component of the acceleration spectra. We found that although most of the stations do not show important amplifications on the vertical component, a few of them have a significant vertical amplification at low frequencies ( f Q , representative of the S -wave train, shows a frequency dependence that can be approximated by the relation Q S = 31.2 f 1.2 , between 0.3 and 9.5 Hz. However, at high frequencies ( f > 10 Hz), this dependence weakens, and Q S takes an approximately constant value of 438.

Fault segmentation as constraint to the occurrence of the main shocks of the 2016 Central Italy seismic sequence

We perform the finite-extent fault inversion of the three main events of the 2016 Central Italy seismic sequence using near-source strong-motion records. We demonstrate that both earthquakes nucleation and rupture propagation were controlled by segmentation of the (N)NW–(S)SE-trending Quaternary normal faults. The first shock of the sequence (August 24th, Mw 6.0) ruptured at the relay zone between the Laga Mts (LF) and the Cordone del Vettore (CVF) normal faults. The second shock (October 26th, Mw 5.9) nucleated at a minor relay zone within the Mt. Vettore–Mt. Bove fault (VBF), while the third and largest one (October 30th, Mw 6.5) initiated at the relay zone between the VBF and CVF, triggering the multiple rupture of the VBF, CVF and probably LF. We show that this latter relay zone corresponds to the deeper, high-angle, fault-zone of the Sibillini Mts cross-structure, a thrust-ramp inherited from the Miocene-Pliocene contractional phase of the Apennines. This structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest Mw 6.5 event that crossed the barrier itself. We suggest that the “young” CVF have started to cut through the barrier acting as a soft-linkage between the two long-lived LF and VBF. The evidence that coseismic cumulative slip shows a maximum at the CVF, provided by both slip inversion and original surface rupture data, suggests that the CVF is growing faster than the adjacent faults.

The Engineering Strong‐Motion Database: A Platform to Access Pan‐European Accelerometric Data

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][1]). 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. [1]: #sec-13

The Central Italy Seismic Sequence between August and December 2016: Analysis of Strong‐Motion Observations

ABSTRACT 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.

Analysis of the Frequency Dependence of the S-Wave Radiation Pattern from Local Earthquakes in Central Italy

We used local earthquakes recorded in central Italy during the 1997– 1998 Umbria-Marche sequence to analyze the frequency dependence of the S -wave radiation pattern. We rotated the north–south and east–west ground-motion components into radial and transversal components to study the S -wave energy partition into sv and sh waves. We separated source and path effects using a generalized spectral inversion technique in the frequency band from 0.23 to 30.7 Hz. We found that the quality factor Q for both sv and sh waves have approximately the same value and show the same frequency dependence reported in previous studies in central Italy. We found that at 0.34 Hz the fraction of sh energy is similar to that expected from a double-couple source. Thus, we used this frequency as reference to investigate the variation of the radiation pattern at other frequencies (0.26–23.55 Hz). We observed that the sh -wave energy approaches to the expected sh radiation at low frequencies ( f f > 0.5 Hz). This observation suggests that the radiation pattern of sv and sh waves are stochastic in a wider frequency band than previously reported for other regions like Japan (Takenaka et al. , 2003).

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.