Strong ground motion characteristics of 2016 Central Italy earthquakes and implications for ground motion modeling

The 2016 Central Italy earthquake sequence produced three mainshocks: (1) M6.1 24 August, (2) M5.9 26 October, and (3) M6.5 30 October. Each mainshock was followed by many aftershocks, some of which with M > 5.0. All earthquake events occurred on southeast-northwest trending normal faults. As part of reconnaissance activities of these events performed by the Geotechnical Extreme Events Reconnaissance Association (GEER), ground motion data was processed and analyzed. After processing all data using procedures developed during the latest Next Generation Attenuation (NGA-West2) project, we analyze strong motion characteristics of all three mainshocks, two selected large aftershocks (M5.3 24 August and M4.8 26 August) and a foreshock (M5.4 26 October). Our analysis shows that stations near the hanging wall, exhibit fling-step in some cases but no obvious rupture directivity effects. We compare ground motion intensity measures (including peak ground acceleration and velocity, PGA and PGV, respectively) to Italy-specific and global ground motion models. Overall, the data exhibit fast attenuation at large distance (>100 km), which is captured by Italy-adjusted global models, but not by Italy-specific models. We also found that global models tend to over-predict ground motions at short periods. Both features were also observed from the 2009 L’Aquila earthquake data and may represent regional features. We estimate the spatial distribution of PGA for the three mainshocks by means of a Kriging analysis performed on within-event residuals using a global semi-variogram model. We found that the ground motion is most intense south-west of the Mt.Vettore - Mt.Bove normal fault. Given the importance of Italian normal fault earthquakes in worldwide ground motion databases, this data set is of global significance for studies of normal fault ground motions

The new ITACA monograph: main features and data compiling

The activities carried out within Task 2 aim to collect, organize and synthesize geological, geomorphological, geotechnical and geophysical data for the location site of the Accelerometric National Network (RAN) stations in Italy, managed by the Department of Civil Protection. Knowledge of geological and geomorphological context, and the mechanical and dynamic characteristics of the stations subsoil is an important factor for studies on the attenuation laws and the choice of accelerograms related to the subsoil category provided by seismic code. Having to produce on a large number of sites (over 600), this knowledge have to be rationalized and homogenized so as to arrive at a common and comparable level of information. With this goal has been organized and implemented the activities within Task 2

Definition of the standard format to prepare descriptive monographs of ITACA stations

In the previous S6 Project (2004-2007 DPC-INGV Framework Program) a monograph was carried out, that was drawn up for many stations, that were part of the former ENEL accelerometric network. In these monographs all the ENEL documentation about geological information as well as geognostic and geophysical data was included. Knowledge of geological and geomorphological context, and the mechanical and dynamic characteristics of the stations subsoil is fundamental for studies on the attenuation laws and the selection of accelerograms to be used as a seismic input for dynamic analyses for which a classification of the stations subsoil according to the EC8 and national code provisions is necessary. Considering the huge number of sites (over 600), this knowledge have to be rationalized and homogenized so as to arrive at a common and comparable level of information. The station monograph carried out within the past S6 INGV Project had tried to fill the gap in the knowledge of the recording station characteristics, with the advantage of providing a first screening on the quantity and quality of available data; however the collected data included in the monograph turned out to be uneven and incomplete since a robust standard for the collection, homogenization, representation and synthesis of data was not provided. Moreover, expert judgment for assessing quality of data, especially those derived from geotechnical and geophysical tests, was not taken into consideration. This problem has been addressed by Task 2, which has produced a new standard monograph for the ITACA stations. The new release of the station monograph is the first product of the 5 S4 Project (deliverable D3) and can be downloaded from the project website (http://esse4.mi.ingv.it). The new ITACA monograph provides a minimum level of information, homogeneous for all station sites, including multi-disciplinary data to satisfy the needs of different users and duly considers information previously not included. In detail, the new ITACA monograph consists in the following 12 cognitive modules, and various sub-modules

Caratteristiche geologiche e classificazione di sito delle stazioni accelerometriche della RAN ubicate a L'Aquila

L’evento sismico del 6 aprile 2009 è stato registrato da 57 stazioni accelerometriche delle RAN (Rete Accelerometrica Nazionale, gestita dal Dipartimento della Protezione Civile), alcune delle quali ubicate nella città di L’Aquila (stazione AQK) o nella porzione della Valle dell’Aterno a NW della città (AQA, AQF, AQG, AQM, AQP, AQV). Uno degli obiettivi del Progetto S4, finanziato nell’ambito della Convenzione 2007‐ 2009 tra l’Istituto Nazionale di Geofisica e il Dipartimento della Protezione Civile, consiste nella classificazione dei siti di ubicazione delle postazioni accelerometriche utilizzando le categorie di sottosuolo previste nell’EC8‐NTC2008. Nell’ambito del Task 2 è stata rilasciata una versione preliminare di tale classificazione (vers. 1.0), ottenuta soltanto su base litologica, utilizzando una mappa prodotta dall’INGV in un precedente progetto sismologico (Progetto S6 della Convenzione DPC‐INGV 2005‐ 2007). Questa mappa litologica deriva dalla Carta Geologica d’Italia in scala 1:100.000, mediante l’accorpamento in classi delle Formazioni Geologiche secondo un criterio litologico e di età del deposito. Alle varie classi litologiche ottenute è stata quindi attribuita una delle cinque categorie di sottosuolo (A, B, C, D, E) dell’EC8‐ NTC2008. Per le stazioni per le quali sono disponibili i profili di velocità delle onde di taglio VS, la categoria di sottosuolo è stata eventualmente corretta, scegliendo la classificazione ottenuta dal profilo di velocità delle onde di taglio nei primi 30 metri. Nei giorni successivi all’evento del 6 aprile 2009, i ricercatori dell’UR2 e dell’UR6 del Progetto S4, impegnati nel Task 2, hanno effettuato sopralluoghi finalizzati alla verifica della localizzazione geografica, delle condizioni morfologiche e geologiche locali di alcune stazioni di registrazione ubicate nell’area aquilana. Sulla base delle informazioni raccolte e dei dati acquisiti, è stata prodotta una versione aggiornata (vers. 1.1) della classificazione di sito per le suddette stazioni, attualmente disponibile sul sito web del Progetto S4 (http://esse4.mi.ingv.it)

Engineering reconnaissance following the August 24, 2016 M6.0 Central Italy earthquake

An earthquake with a moment magnitude reported as 6.0 from INGV (Istituto Nazionale di Geofisica e Vulcanologia); occurred at 03:36 AM (local time) on 24 August 2016 in the central part of Italy. The epicenter was located at the borders of the Lazio, Abruzzi, Marche and Umbria regions, about 2.5 km north-east of the village of Accumoli and about 100 km from Rome. The hypocentral depth was about 8 km (INGV). We summarize preliminary findings of the Italy-US GEER (Geotechnical Extreme Events Reconnaissance) team, on damage distribution, causative faults, earthquake-induced landslides and rockfalls, building and bridge performance, and ground motion characterization. Our reconnaissance team used multidisciplinary approaches, combining expertise in geology, seismology, geomatics, geotechnical engineering, and structural engineering. Our approach was to combine traditional reconnaissance activities of on-ground recording and mapping of field conditions, with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. We anticipate that results from this study, will be useful for future post-earthquake reconnaissance efforts, and improved emergency respons

Semi-empirical relationships to assess the seismic performance of slopes from an updated version of the Italian seismic database

Funder: Dipartimento della Protezione Civile, Presidenza del Consiglio dei Ministri; doi: http://dx.doi.org/10.13039/100012783; Grant(s): ReLUIS research project - Working Pachage 16: Geotechnical Engineering - Task Group 2: Slope stabilityAbstractSeismic performance of slopes can be assessed through displacement-based procedures where earthquake-induced displacements are usually computed following Newmark-type calculations. These can be adopted to perform a parametric integration of earthquake records to evaluate permanent displacements for different slope characteristics and seismic input properties. Several semi-empirical relationships can be obtained for different purposes: obtaining site-specific displacement hazard curves following a fully-probabilistic approach, to assess the seismic risk associated with the slope; providing semi-empirical models within a deterministic framework, where the seismic-induced permanent displacement is compared with threshold values related to different levels of seismic performance; calibrating the seismic coefficient to be used in pseudo-static calculations, where a safety factor against limit conditions is computed. In this paper, semi-empirical relationships are obtained as a result of a parametric integration of an updated version of the Italian strong-motion database, that, in turn, is described and compared to older versions of the database and to well-known ground motion prediction equations. Permanent displacement is expressed as a function of either ground motion parameters, for a given yield seismic coefficient of the slope, or of both ground motion parameters and the seismic coefficient. The first are meant to be used as a tool to develop site-specific displacement hazard curves, while the last can be used to evaluate earthquake-induced slope displacements, as well as to calibrate the seismic coefficient to be used in a pseudo-static analysis. Influence of the vertical component of seismic motion on these semi-empirical relationships is also assessed.</jats:p

Developments in Ground Motion Predictive Models and Accelerometric Data Archiving in the Broader European Region

This paper summarizes the evolution of major strong-motion databases and ground-motion prediction equations (GMPEs) for shallow active crustal regions (SACRs) in Europe and surrounding regions. It concludes with some case studies to show the sensitivity of hazard results at different seismicity levels and exceedance rates for local (developed from country-specific databases) and global (based on databases of multiple countries) GMPEs of the same region. The case studies are enriched by considering other global GMPEs of SACRs that are recently developed in the USA. The hazard estimates computed from local and global GMPEs from the broader Europe as well as those obtained from global GMPEs developed in the US differ. These differences are generally significant and their variation depends on the annual exceedance rate and seismicity. Current efforts to improve the accelerometric data archives in the broader Europe as well as more refined GMPEs that will be developed from these databases would help the researchers to understand the above mentioned differences in seismic hazard

Dynamic properties of earth-core Italian dams from field and laboratory tests

The seismic design of new earth-core dams as well as the seismic re-assessment of existing ones with advanced numerical simulations require the knowledge of dynamic properties of core materials in a wide range of shear strains. The key parameters to be determined are the shear wave velocity Vs (or the maximum shear modulus G0) and the normalized modulus reduction and damping ratio curves (G/G0-c and D-c). Indeed, limited data do exist in the scientific literature on the in-field measured Vs profiles and on the laboratory cyclic/dynamic tests on undisturbed core samples. In this paper the dynamic properties of core materials of six zoned Italian dams are described and the main peculiarities are discussed, also in the light of the dynamic behaviour of natural soils