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Current seismic structural design makes use of a ground motion intensity that has a certain probability of being exceeded at a site of interest in a time interval or, equivalently, exceedance return period. The design intensities with the same return period are often collected in the form of maps deriving from probabilistic seismic hazard analysis (PSHA) for each of the sites of interest. Probability theory underlying PSHA dictates that, in any time interval, design intensities are expected to be exceeded in a fraction of sites that depends on the return period the map refers to. In the case of Italy, three different nationwide PSHA studies can be currently considered of relevance. In the study, the estimated areal fraction of the Italian territory exposed to exceedance of the design intensity from 2008 to 2019 was quantified for the three hazard models, based on ShakeMap data for instrumental earthquakes. In addition, the same fraction was calculated considering a sparse catalog of inferred ShakeMap for historical earthquakes that occurred over almost 1000 years. It was found that, despite the apparent differences in the hazard models, the estimated fraction of territory exposed to exceedance is comparable for all the considered hazard maps. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System (GNSS) is a well-known and fundamental tool for crustal monitoring projects and tectonic studies, thanks to its high coverage and the high quality of the data they provide. In particular, at slowly convergent margins, where deformation rates are of the order of a few millimetres per year, GNSS monitoring proves to be beneficial in detecting the diffuse deformation responsible for tectonic stress accrual. Its strength lies in the high precision achieved by GNSS permanent stations, especially when long-term data and stable structures are available at the stations. North-eastern Italy is a tectonically active region located in the northernmost sector of the Adria microplate, slowly converging with the Eurasia plate, characterized by low deformation rates and moderate seismicity. It greatly benefits from continuous and high-precision geodetic monitoring, since it has been equipped with a permanent GNSS network providing real-time data and daily observations over 2 decades. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to the regional seismic hazard assessment. This paper describes GNSS time series spanning 2 decades of stations located in north-eastern Italy and surroundings as well as the outgoing velocity field. The documented dataset has been retrieved by processing the GNSS observations with the GAMIT/GLOBK software ver10.71, which allows calculation of high-precision coordinate time series, position and velocity for each GNSS station by taking advantage of the high-performance computing resources of the Italian High-Performance Computing Centre (CINECA) clusters. The GNSS observations (raw and standard RINEX – Receiver INdependent EXchange – formats) and the time series estimated with the same procedure are currently daily continued, collected and stored in the framework of a long-term monitoring project. Instead, velocity solutions are intended for annual updates. The time series and velocity field dataset documented here are available on Zenodo (10.5281/zenodo.8055800, Tunini et al., 2024). [ABSTRACT FROM AUTHOR]

A seismic hazard can be quantified by using probabilities. Modern seismic forecasting models (e.g., Operational Earthquake Forecasting systems) allow us to quantify the short-term variations in such probabilities. Indeed these probabilities change with time and space, in particular after strong seismic events. However, the short-term seismic hazard could also change during seismic swarms, i.e., a sequence with several small-/medium-sized events. The goal of this work is to quantify these changes, using the Italian Operational Earthquake Forecasting system, and also estimate the variations in the Gutenberg–Richter b-value. We focus our attention on three seismic swarms that occurred in Central Italy in October–November 2023. Our results indicate that short-term variations in seismic hazard are limited, less than an order of magnitude, and also that b-value variations are not significant. Placing our findings in a more general context, we can state that according to currently available models and catalogs, the occurrence of seismic swarms does not significantly affect the short-term seismic hazard. [ABSTRACT FROM AUTHOR]

A key challenge in paleoseismology is constraining the timing and occurrence of past earthquakes to create an earthquake history along faults that can be used for testing or building fault-based seismic hazard assessments. We present a new methodological approach and accompanying code (Paleoseismic EArthquake CHronologies, PEACH) to meet this challenge. By using the integration of multi-site paleoseismic records through probabilistic modeling of the event times and an unconditioned correlation, PEACH improves the objectivity of constraining paleoearthquake chronologies along faults, including highly populated records and poorly dated events. Our approach reduces uncertainties in event times and allows increased resolution of the trench records. By extension, the approach can potentially reduce the uncertainties in the estimation of parameters for seismic hazard assessment such as earthquake recurrence times and coefficient of variation. We test and discuss this methodology in two well-studied cases: the Paganica Fault in Italy and the Wasatch Fault in the United States. [ABSTRACT FROM AUTHOR]

Effective site characterization in highly urbanized coastal lowlands requires accurate stratigraphic and geophysical investigations. In these regions, which typically host shallowly buried paleovalley systems formed in response to Quaternary glacio‐eustatic fluctuations, the marked lithologic contrast between soft sediment paleovalley fills and the adjacent, stiff substrate has the potential to modify earthquake motions, and assessment of critical parameters, such as shear wave velocities (VS) and resonance frequencies (f), should be coupled with detailed stratigraphic architecture. To evaluate the potential of the microtremor horizontal‐to‐vertical spectral ratio (mHVSR) for paleovalley recognition and mapping, we performed mHVSR measurements along the Adriatic coastal plain of Italy, where two paleovalley systems (Pescara and Manfredonia) have been recently identified. In both areas, we detected rapid lateral variations in resonance frequencies and highlighted laterally continuous impedance contrasts. Relying on a robust stratigraphic framework, we carefully evaluated the relation between geological and geophysical data and identified the stratigraphic surfaces responsible for the observed resonances. We derived VS models for the sediment fill, reconstructing the geometry of the two buried paleovalleys. We address the importance of evaluating the geological context when designing microzonation studies, for a reliable interpretation of changes in resonance frequencies. Plain Language Summary: When earthquakes occur, buildings shake differently based on several factors, including seismic wave velocity, natural resonance frequencies, and local geological characteristics. Beneath modern coastal lowlands, the presence of paleovalley systems can significantly modify the ground motion. Identification of these buried bodies is therefore essential to assess and reduce seismic hazard. Paleovalleys are shallow incisions formed under periods of fluvial erosion in response to Quaternary climate fluctuations, and subsequently filled with very soft clay. These bodies are found worldwide, and do not have any geomorphological evidence, making their recognition challenging. Geologists typically use expensive sediment core analysis to identify paleovalleys, but this method can only provide spotty information. Geophysical exploration techniques that rely on microtremors (small vibrations on the Earth) can complement mapping of these buried bodies. In this work, we tested this technique in Pescara and Mafredonia (Adriatic coastal plain, Italy), providing dense information about paleovalley geometries and geophysical parameters crucial for predicting how the ground will shake during an earthquake. This study also highlights the importance of integrating disciplines to improve our understanding of subsoil and to design future studies to mitigate seismic hazards. Key Points: Paleovalley fills are key sediment bodies made up of soft clay, tens of m thick and few km wide, buried beneath coastal lowlands worldwideMicrotremor‐based paleovalley profiles and stratigraphic cross‐sections exhibit strong similarityMicrotremor can provide shear wave velocities and resonance frequencies of paleovalleys, key parameters for seismic hazard mitigation [ABSTRACT FROM AUTHOR]

The probability distribution of the interevent time between two successive earthquakes has been the subject of numerous studies for its key role in seismic hazard assessment. In recent decades, many distributions have been considered, and there has been a long debate about the possible universality of the shape of this distribution when the interevent times are properly rescaled. In this work, we aim to discover if there is a link between the different phases of a seismic cycle and the variations in the distribution that best fits the interevent times. To do this, we consider the seismic activity related to the M w 6.1 L'Aquila earthquake that occurred on 6 April 2009 in central Italy by analyzing the sequence of events recorded from April 2005 to July 2009, and then the seismic activity linked to the sequence of the Amatrice-Norcia earthquakes of M w 6 and 6.5, respectively, and recorded in the period from January 2009 to June 2018. We take into account some of the most studied distributions in the literature: q-exponential, q-generalized gamma, gamma and exponential distributions and, according to the Bayesian paradigm, we compare the value of their posterior marginal likelihood in shifting time windows with a fixed number of data. The results suggest that the distribution providing the best performance changes over time and its variations may be associated with different phases of the seismic crisis. [ABSTRACT FROM AUTHOR]

The prompt identification of faults responsible for moderate‐to‐large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post‐processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30‐km‐long, NW‐SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source. Plain Language Summary: The Northern Apennines chain is characterized by thrust faults running from the Po Plain to the Adriatic Sea on the northeastern side of peninsular Italy. These thrusts are buried below ≈2,000 m cover of Plio‐Pleistocene deposits. Controversies arose about these thrust faults' activity and earthquake potential based on their hidden geological signature and the scanty seismicity that could be associated with them. The earthquake (magnitude 5.5) that occurred on 9 November 2022, offshore Pesaro revived this argument. In this work, we analyze the geological structure of the crustal volume affected by the seismic sequence, exploiting seismic reflection profiles and well‐log data to identify the earthquake causative fault. Our results demonstrate that the earthquake ruptured a well‐known fault of the Northern Apennines' buried thrust front, supporting that it is indeed active and seismogenic. The size and architecture of this thrust front suggest that it could generate even larger earthquakes (Mw > 6.5). This type of geological study is instrumental to understanding the geometry of earthquake faults, particularly in offshore areas, because they constitute reliable inputs for earthquake hazard models and, when done promptly after an earthquake, provide key elements for other studies on the seismic source and the unfolding of the ongoing seismic sequence. Key Points: 9 November 2022, earthquake consistent with activity of the Cornelia thrust, a fault system running off the central Adriatic coastThe seismic reflection profiles in the area allowed for delineating the thrust and its earthquake potential with a much finer resolutionThe properties of the causative fault suggest that the activation of adjacent segments is a plausible scenario that deserves consideration [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems are well-known fundamental tools for crustal monitoring projects and tectonic studies, thanks to the high coverage and the high-quality data. In slow convergent margins, in particular, where the deformation rates are of the order of few mm/yr, the GNSS monitoring is beneficial to detect the diffused deformation which is responsible for the tectonic stress accrual. Its strength is the high precision reached by GNSS permanent stations, particularly if long span-data and stable monuments are available at all the stations. North-East Italy is a region which can take the most from continuous and high-precision geodetic monitoring, since it is a tectonically active region located in the northernmost sector of the Adria microplate, slowly converging with the Eurasia plate, but characterised by low deformation rates and moderate seismicity. Furthermore, this region is equipped with a permanent GNSS network providing real-time data and daily observations over two decades. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to the regional seismic hazard assessment. This paper describes GNSS time series spanning two decades of stations located in the NE-Italy and surroundings, as well as the outcoming velocity field. The documented dataset has been retrieved by processing the GNSS observations with the GAMIT/GLOBK software ver10.71, which allows calculating high-precision coordinate time series, position and velocity for each GNSS station, and by taking advantage of the high-performance computing resources of the Italian High-Performance Computing Centre (CINECA) clusters. The GNSS observations (raw and standard RINEX formats) and the time series estimated with the same procedure are currently daily continued, collected and stored in the framework of a long-term monitoring project. Instead, velocity solutions are planned to be updated annually. The time series and velocity field dataset documented here is available at https://doi.org/10.13120/b6aj-2s32 (Tunini et al., 2023). [ABSTRACT FROM AUTHOR]

A key challenge in paleoseismology is constraining the timing and occurrence of past earthquakes to create an earthquake history along faults that can be used for testing or building fault-based seismic hazard assessments. We present a new methodological approach and accompanying code (Paleoseismic EArthquake CHronologies, PEACH) to meet this challenge. By using integration of multi-site paleoseismic records through probabilistic modelling of the event times and an unconditioned correlation, PEACH improves the objectivity of constraining paleoearthquake chronologies along faults, including highly populated records and poorly dated events. Our approach reduces uncertainties in event times and allows increased resolution of the trench records. By extension, the approach can potentially reduce the uncertainties in the estimation of parameters for seismic hazard assessment such as the earthquake recurrence times and coefficient of variation. We test and discuss this methodology in two well-studied cases: the Paganica Fault in Italy and the Wasatch Fault System in the United States. [ABSTRACT FROM AUTHOR]

Deep fluid circulation likely triggered the large extensional events of the 2016–2017 Central Italy seismic sequence. Nevertheless, the connection between fault mechanisms, main crustal‐scale thrusts, and the circulation and interaction of fluids with tectonic structures controlling the sequence is still debated. Here, we show that the 3D temporal and spatial mapping of peak delays, proxy of scattering attenuation, detects thrusts and sedimentary structures and their control on fluid overpressure and release. After the mainshocks, scattering attenuation drastically increases across the hanging wall of the Monti Sibillini and Acquasanta thrusts, revealing fracturing and fluid migration. Before the sequence, low‐scattering volumes within Triassic formations highlight regions of fluid overpressure, which enhances rock compaction. Our results highlight the control of thrusts and paleogeography on the sequence and hint at the monitoring potential of the technique for the seismic hazard assessment of the Central Apennines and other tectonic regions. Plain Language Summary: There is widespread evidence that the Amatrice‐Visso‐Norcia seismic sequence (2016–2017, Central Italy) was triggered by fluid circulation across the Apennine Chain. However, how, and why fluids migrated across the fault network is still under debate. Seismic attenuation describes how seismic waves lose energy during their propagation. When used as an imaging attribute, it has demonstrated the potential to recover the spatial extension and mechanisms of fracturing and fluid movement across volcanoes and faults. Here, we map scattering attenuation through the peak delay measurements in 3D before (2013–2016) and during the 2016–2017 sequence. Scattering attenuation separated fractured zones from regions of compaction, controlled, before and during the sequence by thrusts and lithological differences. High scattering (strong fracturing) increases through time due to intense fracturing, while low scattering (higher compaction of the rocks) marks areas where earthquakes will occur. Our results highlight the importance of the main thrusts, as they separate compartments of the shallow crust characterized by different scattering attenuation anomalies, the Triassic deposits in fluid accumulation, and subsequent triggering of normal faults. Key Points: Scattering attenuation detects the control of thrusts and lithology on post‐seismic fracturing and fluid migration during the AVN sequenceOverpressurized fluids compact low‐scattering rocks at thrusts' roots before earthquakesDetecting fluid overpressure and fracturing suggests an unexploited monitoring potential of scattering attenuation [ABSTRACT FROM AUTHOR]

Probabilistic seismic hazard analysis (PSHA) is widely employed worldwide as the rational way to quantify the uncertainty associated to earthquake occurrence and effects. When PSHA is carried out for a whole country, its results are typically expressed in the form of maps of ground motion intensities that all have the same exceedance return period. Classical PSHA relies on data that continuously increase due to instrumental seismic monitoring, and on models that continuously evolve with the knowledge on each of its many aspects. Therefore, it can happen that different, equally legitimate, hazard maps for the same region can show apparently irreconcilable differences, sparking public debate. This situation is currently ongoing in Italy, where the process of governmental enforcement of a new hazard map is delayed. The discussion is complicated by the fact that the events of interest to hazard assessment are intentionally rare at any of the sites the maps refer to, thus impeding empirical validation at any specific site. The presented study, pursuing a regional approach instead, overcoming the issues of site specific PSHA validation, evaluated three different authoritative PSHA studies for Italy. Formal tests were performed directly testing the output of PSHA, that is probabilistic predictions, against the observed ground shaking exceedance frequencies, obtained from about fifty years of continuous monitoring of seismic activities across the country. The bulk of analyses reveals that, apparently alternative hazard maps are, in fact, hardly distinguishable in the light of observations. [ABSTRACT FROM AUTHOR]

The paper illustrates the construction of abacuses for the semi-quantitative assessment of stratigraphic seismic amplification phenomena, applicable in the eastern Abruzzo region (central Italy). The abacuses provide three expected Amplification Factors (Fas): Fa0.1-0.5, Fa0.4-0.8, Fa0.7-1.1, performed as the ratio between the integral of output and input, in the mentioned time intervals, considering the acceleration response spectra. The choice derives from the fact that these parameters are better correlated to the response of the buildings, characterised by their own different periods. To prepare the abacuses, a procedure was adopted that took into consideration the geological analysis of the area, the collection of all the available geophysical and geotechnical data, the choice of the seismic inputs representative of the seismic hazard, the identification of the main seismic stratigraphic sequences and the numerical analysis aimed at evaluating the Fa. The abacus consists of a series of tables prepared in order to take account of the stratigraphic variability in the area, as a function of the basic seismic hazard level and the vibration period interval to calculate the Fa. By knowing the stratigraphic and mechanical characteristics of the site and using the abacuses, the values of the Fa are obtained. [ABSTRACT FROM AUTHOR]

Advances in physics‐based earthquake simulations, utilizing high‐performance computing, have been exploited to better understand the generation and characteristics of the high‐frequency seismic wavefield. However, direct comparison to ground motion observations of a specific earthquake is challenging. We here propose a new approach to simulate data‐fused broadband ground motion synthetics using 3D dynamic rupture modeling of the 2016 Mw 6.2 Amatrice, Italy earthquake. We augment a smooth, best‐fitting model from Bayesian dynamic rupture source inversion of strong‐motion data (<1 Hz) with fractal fault roughness, frictional heterogeneities, viscoelastic attenuation, and topography. The required consistency to match long periods allows us to quantify the role of small‐scale dynamic source heterogeneities, such as the 3D roughness drag, from observational broadband seismic waveforms. We demonstrate that 3D data‐constrained fully dynamic rupture synthetics show good agreement with various observed ground‐motion metrics up to ∼5 Hz and are an important avenue toward non‐ergodic, physics‐based seismic hazard assessment. Plain Language Summary: Models of earthquakes are used to better understand the origin and features of strong seismic shaking using supercomputers. But the connection of such computer simulations with actual measurements is complex. This study suggests a new way to use observations, computer models, and physics to model details of the damaging ground shaking recorded during the 2016 Amatrice, Italy, earthquake. We start from an earlier, relatively low‐resolution earthquake model that matches seismograms at low frequencies (<0.5–1 Hz), derived using many Monte Carlo simulations. We carefully enhance this earthquake model by adding roughness to the slipping fault, smaller‐scale variations of the frictional resistance of this fault to earthquake slip, mountains and basins scattering the seismic waves, and the effects of anelastic damping of wave amplitudes while they propagate. We show that we now also match the seismic waves at frequencies up to 5 Hz, while not losing the good match at long periods. This result is important to better understand how hazardous earthquakes in specific regions may be. Our modeling indicates which ingredients are required in computer simulations to generate realistic ground motions for physics‐based seismic hazard assessment. Key Points: We propose a novel approach to design data‐driven, 3D physics‐based broadband dynamic rupture scenarios from low‐resolution modelsOur synthetics fit observations in terms of velocity and accelerations waveforms, as well as Fourier‐amplitude‐spectra up to ∼5 HzAnalyzing the role of earthquake modeling ingredients highlights the importance of dynamic source heterogeneity for broadband ground‐motion [ABSTRACT FROM AUTHOR]

We investigate crustal deformation within the upper plate of the Ionian Subduction Zone (ISZ) at different time scales by (i) refining geodetic rates of crustal extension from continuous Global Navigation Satellite System (GNSS) measurements and (ii) mapping sequence of Late Quaternary raised marine terraces tectonically deformed by the West Crati normal fault, in northern Calabria. This region experienced damaging earthquakes in 1184 (M 6.75) and 1854 (M 6.3), possibly on the E-dipping West Crati fault (WCF) which, however, is not unanimously considered to be a seismogenic source. We report geodetic measurements of extension and strain rates across the strike of the E-dipping WCF and throughout the northern Calabria obtained by using velocities from 18 permanent GNSS stations with a series length longer than 4.5 years. These results suggest that crustal extension may be seismically accommodated in this region by a few normal faults. Furthermore, by applying a synchronous correlation approach, we refine the chronology of understudied tectonically deformed palaeoshorelines mapped on the footwall and along the strike of the WCF, facilitating calculation of the associated fault-controlled uplift rates. Raised Late Quaternary palaeoshorelines are preserved on the footwall of the WCF indicating that "regional" uplift, likely related to the deformation associated either with the subduction or mantle upwelling processes, is affected by local footwall uplift. We show that GIS-based elevations of Late Quaternary palaeoshorelines, as well as temporally constant uplift rates, vary along the strike of the WCF, implying normal faulting activity through time. This suggests that (i) the fault slip rate governing seismic hazard has also been constant over the Late Quaternary, over multiple earthquake cycles, and (ii) our geodetically derived fault throw rate for the WCF is likely a more than reasonable value to be used over longer time scales for an improved seismic hazard assessment. Overall, we emphasize the importance of mapping crustal deformation within the upper plate above subduction zones to avoid unreliable interpretations relating to the mechanism controlling regional uplift. [ABSTRACT FROM AUTHOR]

Conventional probabilistic seismic hazard analysis (PSHA) only considers mainshock events and uses a time‐independent earthquake rupture forecast to describe the occurrence of mainshocks. This approach neglects the long‐term time‐dependency of mainshocks on specific fault segments, the interaction of adjacent faults, and the spatial and temporal clustering of aftershocks. This study integrates a recently proposed advanced fault‐based PSHA framework with an aftershock simulator based on the Epidemic‐Type Aftershock Sequence (ETAS) model, to overcome the aforementioned limitations. Central Italy is used as a case study to illustrate the proposed framework. The case‐study hazard curves show that including state‐of‐the‐art advances in fault‐based PSHA may increase the ground‐motion amplitudes for low return periods, and decrease the ground‐motion amplitudes for high return periods, relative to a conventional PSHA approach. The magnitude of ground‐motion estimate increases due to aftershock inclusion is dependent on the selected site and return period. Sensitivity analyses of the results demonstrate that: (a) close to modeled faults, high‐return‐period hazard estimates are more affected by fault‐related inputs than the aftershock inclusion; (b) close to modeled faults, the influence of aftershock inclusion is higher for low return periods than high ones; (c) away from modeled faults, aftershocks inclusion greatly affects the variance of the hazard results; and (d) fault interaction has a limited effect on the variance of the hazard estimates compared to other analysis inputs. This study could help with the future implementation of complex fault modeling approaches and aftershock hazard in seismic risk models. Plain Language Summary: State‐of‐practice seismic hazard assessments do not usually consider the actual geometry of the faults, the time at which earthquakes occurred in the past, and the elevated hazard due to aftershocks. This study proposes a framework to address these shortcomings, which is demonstrated through a case study involving several sites in Central Italy. The case‐study results demonstrate how conventional estimates of earthquake hazard can be affected by using state‐of‐the‐art methodologies to model faults and aftershocks. In particular, complex fault modeling can increase the seismic hazard for low return periods, and decrease the seismic hazard for high return periods, relative to a conventional hazard estimation approach. The inclusion of aftershocks increases seismic hazard as expected, but the size of the increase is highly dependent on the selected site and the return period of ground shaking. This study could help the future implementation of more complex hazard modeling approaches in earthquake risk assessments. Key Points: This study integrates recent advances in fault‐based seismic hazard assessment with the Epidemic‐Type Aftershock Sequence modelFault‐based seismic hazard assessment produces different ground‐motion estimates compared to conventional hazard assessment approachesClose to modeled faults, the influence of aftershock inclusion on seismic hazard estimates is generally highest for low return periods [ABSTRACT FROM AUTHOR]

With seismic catalogues becoming progressively larger, extracting information becomes challenging and calls upon using sophisticated statistical analysis. Data are typically clustered by machine learning algorithms to find patterns or identify regions of interest that require further exploration. Here, we investigate two density-based clustering algorithms, DBSCAN and OPTICS, for their capability to analyse the spatial distribution of seismicity and their effectiveness in discovering highly active seismic volumes of arbitrary shapes in large data sets. In particular, we study the influence of varying input parameters on the cluster solutions. By exploring the parameter space, we identify a crossover region with optimal solutions in between two phases with opposite behaviours (i.e. only clustered and only unclustered data points). Using a synthetic case with various geometric structures, we find that solutions in the crossover region consistently have the largest clusters and best represent the individual structures. For identifying strong anisotropic structures, we illustrate the usefulness of data rescaling. Applying the clustering algorithms to seismic catalogues of recent earthquake sequences (2016 Central Italy and 2016 Kumamoto) confirms that cluster solutions in the crossover region are the best candidates to identify 3-D features of tectonic structures that were activated in a seismic sequence. Finally, we propose a list of recipes that generalizes our analyses to obtain such solutions for other seismic sequences. [ABSTRACT FROM AUTHOR]

The performance of a large number of critical infrastructure systems needs to be periodically re-evaluated. This is especially so when such systems are located in seismic areas and are subjected to ageing effects. Seismic re-evaluations are typically performed using numerical response history analyses based on a geotechnical model of the infrastructure and using hazard-consistent ground motions. We depart from the Viadotto Italia (the tallest multi-span bridge in Italy, located in a high-seismicity region) to draw best practices on how to construct a robust geotechnical model and derive appropriate target response spectra to be used in forward applications. Our proposed framework starts with the analysis of historical and new information and data. We then describe how to perform a multi-epoch consistency analysis that deals with the reliability and level of uncertainty of the data, culminating with the definition of a pragmatic geotechnical model that builds upon all available data, including investigation information produced at different spatial resolutions and quality levels. We also propose a consistent approach to perform site-specific probabilistic seismic hazard analysis to develop appropriate ground motions. This last step builds upon experiences with a data-rich high-seismicity zone in southern Italy, where both shallow crustal faults and deep subduction sources are present. [ABSTRACT FROM AUTHOR]

Regional-scale analyses of susceptibility to liquefaction are seldom performed in data-scarce areas. However, in spite of data limitations, such efforts can still provide useful information in case of populated, seismically active regions. The present work focuses on susceptibility zonation for soil liquefaction that might occur due to ground shaking in the Foggia Province, a data-scarce, seismically active area of about 7000 km2 located in southern Italy. The Analytical Hierarchy Process (AHP) approach is used to obtain the susceptibility to liquefaction map of the whole area, while a geological and geotechnical database including 531 boreholes from 84 localities is used for cross-validation. The data are processed by means of a simplified quantitative method to determine liquefaction potential and assess whether a specific area is prone to liquefaction or not. Our results, along with an AUC − ROC = 0.89 test value, indicate that there are widespread areas of medium to high and very high susceptibility, and that the most susceptible zones are localized along the Adriatic Sea coastline and watercourses. The final susceptibility to liquefaction map represents a step forward towards the assessment of secondary seismic hazard in the study area, thus supporting the regional and local administrations responsible for land-use planning and risk mitigation. [ABSTRACT FROM AUTHOR]

Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network, used to monitor natural and/or induced micro-seismicity, estimates focal mechanisms as a function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P / S long-period spectral-level ratios and the P polarities to infer the fault plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operating in the Campania–Lucania Apennines (southern Italy) aimed to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose is effective and can be adapted for other case studies with a double purpose. It can be a valid tool to design or to test the performance of local seismic networks, and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies. [ABSTRACT FROM AUTHOR]

Design ground motion intensities determine the actions for which structures are checked, in the conventional approach of seismic codes, not to fail the target performances. On the other hand, due to inherent characteristics of probabilistic seismic hazard analysis (PSHA), it is expected that site-specific design intensity based on PSHA is exceeded in the epicentral area of moderate-to-high magnitude earthquakes. In the context of regional seismic loss assessment and of the evolution of seismic codes from the regulator perspective, it is useful to gather insights about the extent of the zone around the earthquake source where code-conforming structures are expected to be systematically exposed to seismic actions larger than those accounted for in design. To assess such areal extent based on empirical evidence is the scope of the study presented in the paper. To this aim, peak ground acceleration ShakeMap data for Italian earthquakes from 2008 to 2020 were compared to the current design intensities in the same areas for which the maps are available. This allowed, first, to develop simple semi-empirical models of the exceedance area versus the magnitude of the earthquakes. Second, it allowed to model the probability that an earthquake of given magnitude causes exceedance of the design intensity via logistic regressions. Coupling the first and second class of models provides an approximation of the expected exceedance (logarithmic) area upon occurrence of an earthquake of given magnitude. Such an area can be of several thousand square kilometers for earthquakes occurring relatively frequently in countries such as Italy. [ABSTRACT FROM AUTHOR]

The preparation, initiation and occurrence dynamics of earthquakes in Italy are governed by several frequently unknown physical mechanisms and parameters. Understanding these mechanisms is crucial for developing new techniques and approaches for earthquake monitoring and hazard assessments. Here, we develop a first-order numerical model simulating quasi-static crustal interseismic loading, coseismic brittle episodic dislocation and post-seismic relaxation for extensional and compressional earthquakes in Italy based on a common framework of lithostatic and tectonic forces. Our model includes an upper crust, where the fault is locked, and a deep crust, where the fault experiences steady shear. The results indicate that during the interseismic phase, the contrasting behaviour between the upper locked fault segment and lower creeping fault segment generates a stretched volume at depth in the hangingwall via extensional tectonics while a contracted volume forms via compressional tectonics. The interseismic stress and strain gradients invert at the coseismic stage, with the interseismic dilated volume contracting during the coseismic stage, and vice versa. Moreover, interseismic stress gradients promote coseismic gravitational subsidence of the hangingwall for normal fault earthquakes and elastic uplift for reverse fault earthquakes. Finally, the post-seismic relaxation is characterized by further ground subsidence and uplift for normal and reverse faulting earthquakes, respectively, which is consistent with the faulting style. The fault is the passive feature, with slipping generating the seismic waves, whereas the energy activating the movement is stored mostly in the hangingwall volume. The main source of energy for normal faulting and thrust is provided by the lithostatic load and elastic load, respectively. [ABSTRACT FROM AUTHOR]

The 2016–2017 central Italy earthquake sequence began with the first main shock near the town of Amatrice on August 24 (M w 6.0), and was followed by two subsequent large events near Visso on October 26 (M w 5.9) and Norcia on October 30 (M w 6.5), plus a cluster of four events with M w > 5.0 within few hours on 18 January 2017. The affected area had been monitored before the sequence started by the permanent Italian National Seismic Network (RSNC), and was enhanced during the sequence by temporary stations deployed by the National Institute of Geophysics and Volcanology and the British Geological Survey. By the middle of September, there was a dense network of 155 stations, with a mean separation in the epicentral area of 6–10 km, comparable to the most likely earthquake depth range in the region. This network configuration was kept stable for an entire year, producing 2.5 TB of continuous waveform recordings. Here we describe how this data was used to develop a large and comprehensive earthquake catalogue using the Complete Automatic Seismic Processor (CASP) procedure. This procedure detected more than 450 000 events in the year following the first main shock, and determined their phase arrival times through an advanced picker engine (RSNI-Picker2), producing a set of about 7 million P - and 10 million S -wave arrival times. These were then used to locate the events using a non-linear location (NLL) algorithm, a 1-D velocity model calibrated for the area, and station corrections and then to compute their local magnitudes (M L). The procedure was validated by comparison of the derived data for phase picks and earthquake parameters with a handpicked reference catalogue (hereinafter referred to as 'RefCat'). The automated procedure takes less than 12 hr on an Intel Core-i7 workstation to analyse the primary waveform data and to detect and locate 3000 events on the most seismically active day of the sequence. This proves the concept that the CASP algorithm can provide effectively real-time data for input into daily operational earthquake forecasts, The results show that there have been significant improvements compared to RefCat obtained in the same period using manual phase picks. The number of detected and located events is higher (from 84 401 to 450 000), the magnitude of completeness is lower (from M L 1.4 to 0.6), and also the number of phase picks is greater with an average number of 72 picked arrival for a M L = 1.4 compared with 30 phases for RefCat using manual phase picking. These propagate into formal uncertainties of ±0.9 km in epicentral location and ±1.5 km in depth for the enhanced catalogue for the vast majority of the events. Together, these provide a significant improvement in the resolution of fine structures such as local planar structures and clusters, in particular the identification of shallow events occurring in parts of the crust previously thought to be inactive. The lower completeness magnitude provides a rich data set for development and testing of analysis techniques of seismic sequences evolution, including real-time, operational monitoring of b -value, time-dependent hazard evaluation and aftershock forecasting. [ABSTRACT FROM AUTHOR]

The classical procedure of the probabilistic seismic hazard analysis (PSHA) requires a Poissonian distribution of earthquakes. Seismic catalogues follow a Poisson distribution just after the application of a declustering algorithm that leaves only one earthquake for each seismic sequence (usually the stronger, i.e. the main shock). Removing earthquakes from the seismic catalogues leads to underestimation of the annual rates of the events and consequently associate with low seismic hazard as indicated by several studies. In this study, we aim investigating the performance of two declustering methods on the Italian instrumental catalogue and the impact of declustering on estimation of the b- value and on the seismic hazard analysis. To this end, first the spatial variation in the seismicity rate was estimated from the declustered catalogues using the adaptive smoothed seismicity approach, considering small earthquakes (M w ≥ 3.0). We then corrected the seismicity rates using new approach that allows for counting all events in the complete seismic catalogue by simply changing the magnitude frequency distribution. The impact of declustering on seismic hazard analysis is illustrated using PSHA maps in terms of peak ground acceleration and spectral acceleration in 2 s, with 10 per cent and 2 per cent probability of exceedance in 50 yr, for Italy. We observed that the hazard calculated from the declustered catalogues was always lower than the hazard computed using the complete catalogue. These results are in agreement with previous results obtained in different parts of the world. [ABSTRACT FROM AUTHOR]

In this paper we present an updated and homogeneous earthquake data set for Italy compiled by joining the Italian Macroseismic Database DBMI15 and the Engineering Strong-Motion (ESM) accelerometric data bank. The database has been compiled through an extensive procedure of selection and revision based on two main steps: 1) the removal of several earthquakes in DBMI15 because the data source has been considered to be largely unreliable and 2) the extraction of all the localities reporting intensity data which are located within 3 km from the accelerograph stations that recorded the data. The final data set includes 323 recordings from 65 earthquakes and 227 stations in the time span 1972-2016. The events are characterized by magnitudes in the range 4.0-6.9 and depths in the range 0.3-45.0 km. Here, we illustrate the data collection and the properties of the database in terms of recording, event and station distributions as well as Mercalli-Cancani-Sieberg (MCS) macroseismic intensity points. Furthermore, we discuss the most relevant features of engineering interest showing several statistics with reference to the most significant metadata (such as moment magnitude, several distance metrics, style of faulting etc). The data set can be downloaded from data repository Zenodo at https://doi.org/10.13127/inge.1; (Oliveti et., 2020). [ABSTRACT FROM AUTHOR]

• Failure and damage analysis of masonry buildings after a seismic sequence. • Seismic signal analysis of two Italian seismic sequences. • Correlation of structural damage to seismic signal features. • New preventive strategies for the safeguard of built and cultural heritage. • Building damage management during the post-earthquake phase. The work analyses some observed structural criticalities in historical masonry structures emphasized by the seismic events of May 2012, in Emilia, and of August-October 2016, in Central Italy. The causes that brought to different damage scenarios in the historic centres and to the different degree of damage evolution of the buildings, have been investigated, comparing their construction and dynamic features, such as the natural vibration periods of the different construction typologies with the spectral accelerations and the amplification periods distinctive of the seismic events. In particular, starting from the evidence of the damage observed on the built heritage of some of the centres most affected by the two seismic sequences, and from the characteristics of the seismic signals recorded at the considered sites, it is proposed a study which analyses some criticalities, in relation to preventive purposes of the technical standards, specifically with reference to historical constructions. Among the main criticalities highlighted in the present work, it should be noted the remarkable difference between the design spectra and the spectra of the recorded seismic events (real earthquakes), and the circumstance that in reality the constructions generally are interested by more seismic shocks (multi-events) characterized by higher intensities with respect to the ones expected by the building code. Such feature gives rise to a criticality for the operators acting in the emergency phases of rescue and temporary securing, who find themselves operating in high hazardous conditions, due to the high vulnerability of already damaged built heritage induced by the main-shock, and by the high probability (near certainty) that, in the short period, events having intensities and characteristics similar to the main-shock may occur. Moreover, the evolution of the damages, with progressive crumbling associated to global or partial collapses, due to the sequence of shocks (multi-events), which had interested thousands of buildings in the historical centres (and not only) subjected to the seismic sequence, bare witness of criticalities in the preventive approach proposed at national level. The analysis of the criticalities highlighted in the present work allows to envisage an approach which considers for the structures, historical or not, adequate performance requirements with respect to the emergency, temporary and permanent securing phases, accounting for the multi-event seismic context typical of the Italian territory. [ABSTRACT FROM AUTHOR]

• The aggregates' connections significantly affect the structural response. • An old structure is analyzed with continuous and discontinuous numerical models. • Evaluation of the response under repeated accelerograms (seismic sequence) • Indications are given of the most appropriate approach for old structures' analysis. The structural assessment of ancient masonry structures is still a challenging task. The main reasons have been related to the shortage of information in the materials' characterization along with the complex geometry and different evolutions of its constituents' parts through the time. Scientific studies on the evaluation of the structural capacity and design of these masonry buildings have reported several modelling techniques. The goal of this work is to investigate the effectiveness of different numerical approaches in the simulation of the cyclic behaviour of historic masonry buildings under seismic loads. In addition, the damage level of the structural interconnections will be evaluated and what extent they affect the global instability. The specific case study seeks to examine an ancient palace with its civic tower hit by the 2016 Central Italy earthquake. A couple of masonry modelling are used: the first one is discontinuous (DM) and the second one is continuous (CM). Two models were set: one model replicated the structure as a whole, the other one considered only the tower. The DMs were studied with 3DEC© and LMGC90© software, where, in turn, different contact conditions were implemented. In parallel, the CMs were analysed with the Midas FEA NX©. The present research offers significant outcomes obtained from the non-linear dynamic analyses performed using the proper sequence recorded in that seismic event. Likewise, this document underlines the importance of the correct modelling techniques definition, based on the state of the case study, especially when an isolated tower is considered. [ABSTRACT FROM AUTHOR]

GPS measurements recorded at active sites in central Italy during the seismic events of greatest magnitude (24 August, 26 and 30 October 2016) were processed in kinematic mode according to the Precise Point Positioning (PPP) technique. The resulting data were the displacements and, by derivation with respect to time, the velocities and instantaneous horizontal accelerations. Elastic response spectra along the orthogonal walls of the site (if the GPS antenna was fixed to a building) or along the geographical directions (if the antenna was fixed to the ground) were obtained from the derived accelerations. The maximum amplitudes, i.e. "peak vibrations", were then extracted from the response spectra. These peaks, unlike the co-seismic movements, represent the maximum instantaneous vibrations recorded following the "shock" produced by the seismic waves and thus are representative of both the discomfort perceived by the populations and the structural damage. This study shows that GPS is becoming an increasingly important tool to measure and monitor the dynamic responses of a structure. The results also provide a complete picture of the displacements induced by the seismic sequences in the earthquake-affected areas, leaving unresolved some questions concerning the localization of the phenomena and the causes of the structural deformations. [ABSTRACT FROM AUTHOR]

The paper presents a predictive model for assessing the seismic vulnerability of small historic centres. The model, developed in the framing of other similar methods proposed in the past, needs a limited number of parameters and is based on information collected in the aftermath of the 2009 L’Aquila earthquake. First, a damage survey carried out on two historic centres hit by L’Aquila earthquake is presented and the most recurrent failure types are classified in terms of severity and extension, leading to damage probability matrices (DPMs). Second, the proposed predictive model is calibrated on the basis of simple observations on the buildings’ structural features. Finally, the model is validated through the application to a third historic centre characterized by the same features of the first two case studies. This application proves the generality of the proposed procedure by accurately reproducing the damage that was actually reported after the 2009 earthquake. The model provides useful information on the most effective anti-seismic strategies that could be implemented at the urban scale for seismic risk reduction. [ABSTRACT FROM AUTHOR]

We propose an objective and reproducible algorithmic path to forecast seismicity in Italy from long-term deformation models. These models are appropriate for Italy and its neighbouring countries and seas thanks to the availability of rich, reliable and regularly updated historical earthquake and seismogenic fault databases, and to the density of permanent GPS stations. However, so far little has been done to assess the seismic coupling of Italian active faults, that is to quantify their ability to release earthquakes. This must be determined in order to use geodetic and active faulting observations in alternative seismicity models, to overcome possible limitations of the earthquake record for the assessment of seismic hazard. We use a probabilistic method to assign upper crustal earthquakes from the historical catalogue to their presumed causative faults, then collect all the events into three subcatalogues corresponding to the compressional, extensional and strike-slip faulting classes. We then determine the parameters of their Gutenberg-Richter frequency/magnitude relations using maximum-likelihood methods and integrate these distributions to estimate the long-term seismic moment rate for each class. Finally, we compare these seismicity rates to the long-term tectonic deformation based on GPS data, thus determining the coupled thickness (and estimating seismic coupling) for each fault class. We find that in our study region the seismic coupling and the related coupled thickness is on average two times larger for extensional than for compressional faults. As for the spatial distribution of earthquake rates, a larger number of events is predicted for the extensional settings of the Apennines chain, in agreement with the inferred seismic coupling but also with the long-term strain rates. We also find that the frequency/magnitude distributions indicate that the largest earthquakes occur in extensional settings, whereas compressional faults are expected to host comparatively smaller events. [ABSTRACT FROM AUTHOR]

Seismic risk mitigation is a relevant issue in European regions, such as Italy, characterized by the presence of a large stock of vulnerable existing industrial buildings. Through a case study, the article proposes an integrated novel approach for the diagnosis of structures after a seismic event. The suggested monitoring system is based on recording the accelerations of a real structure during an earthquake and on their introduction as input into a Numerical Model (NM), suitably tuned, to outline a possible post-earthquake scenario. The leading idea of this approach is to provide an estimation of the health and remaining life of monitored structures and to detect and quantify the damage, some of the crucial issues of Structural Health Monitoring (SHM). The technique is applied to a real structure, an industrial building liable to some seismic vulnerabilities. The structure has never been subjected to an earthquake, so the actual accelerations could not be recorded. For this reason, they are acquired from a second NM subjected to real and simulated earthquakes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Extensive survey on bell towers in Naples was carried out. • Parametric structural modelling of masonry bell towers was created. • A vulnerability index is defined as a function of a collapse measure. • Global sensitivity analysis highlighted influential parameters on seismic vulnerability. • A simplified model with six parameters can achieve good accuracy. The safeguard of historical heritage cannot disregard a rational assessment of the seismic vulnerability of the assets, especially in areas as Italy where high exposure and hazard may lead to significant risk. In this context, while established empirical methods based on observed damage after earthquakes are available for some constructional typologies as churches and palaces, large-scale approaches for masonry bell towers aimed at defining a vulnerability ranking for prioritisation of intervention are still missing or not sufficiently validated. In this paper, a novel simplified vulnerability model is formulated through sensitivity-informed parameter reduction of a more detailed mechanics-based assessment methodology. The framework is based on (a) a parametric representation of the bell tower, (b) a mechanical model providing a measure of collapse, (c) a vulnerability definition based on the measure of collapse. The variation ranges of the input parameters are calibrated against the results of the surveys carried out in the historical centre of Naples. A global sensitivity analysis is then used to identify the most important parameters governing the vulnerability of the structure and remove the least influential parameters. Vulnerability models based on different amount of input data are finally proposed, and their accuracy is assessed comparatively with the original mechanical model. The results show that good accuracy can be obtained by using six geometrical and typological parameters, while further increase in the quality of the prediction may be achieved with the introduction of additional information regarding materials and constructional features, which can only be acquired by means of more detailed surveys on-site. [ABSTRACT FROM AUTHOR]

The Central Apennines are among the most seismically active regions in Italy. This region is affected by an extension accommodated by active normal faults. Those faults with high seismogenic potential hosted Mw > 6 shallow damaging earthquakes, such as the Mw 6.5 event of Oct. 30, 2016. Although fault slip rates are crucial to seismic hazard assessments, in the Central Apennines, slip rate assessments encompassing several seismic cycles (> 10 ka) are sparse. This is particularly true for the Mt. Vettore-Mt. Bove Fault system that ruptured during the mainshocks of the 2016–2017 seismic sequence. In this study, we present new geochronological constraints of offset geomorphological markers along the northern portion of the fault system on the Mt. Porche Fault segment using in-situ produced 36Cl cosmogenic nuclides. Offset measurements were made using a 5-cm resolution DEM obtained through a drone survey and constrained a fault scarp height of 15.5 ± 1.4 m and a maximal cumulative offset estimated between 32 and 40.5 m. Samples were collected from the Valle Lunga terminal moraine at 1710 m asl and yielded 36Cl exposure ages of 12.7 + 2.2/−1.9 ka, while the abraded surface, located on top of the tectonic scarp yielded 36Cl exposure ages of 23.4 + 5.3/−4.3 ka. Using the fault scarp height and the exposure age of this abraded surface, we constrained a minimum vertical fault slip rate of 0.7 + 0.2/−0.1 mm/yr. Assuming the offset started to accumulate when climate conditions allowed the scarp preservation, we constrained a maximal vertical slip rate of 1.2 ± 0.2 mm/yr along the main fault of the Mt. Vettore-Mt. Bove Fault system. This rate is higher than those previously obtained from trenches along secondary branches of the Mt. Vettore-Mt. Bove Fault system. Besides, the yielded chronology for the last glacial maximum in that area at ~23 ka is in good agreement with the timing previously proposed for the LGM in the Apennines. • The last advance of the Valle Lunga glacial (Dryas), is dated at ~12.7 + 2.2/−1.9 ka. • Local LGM glacier retreat occurred ~23.4 + 5.3/−4.3 ka ago in the Valle Lunga. • The Mt. Vettore main fault has a minimum vertical slip rate of 0.7 + 0.2/−0.1 mm/yr. [ABSTRACT FROM AUTHOR]

• Manufacturing of full-scale large-size FREIs with polyester fibre and soft rubber compound. • Full-scale testing of two FREI large-size prototypes in unbounded configuration under static and dynamic loading. • Initial type tests as per standard provisions for conventional laminated rubber bearings [EN15129]. • Stable hysteretic behaviour up to 100% shear strain with damping ratio up to 20% of critical. • Satisfactory performance via numerical analysis of a case-study frame building isolated at the base with FREIs in comparison to laminated rubber bearings. Fiber reinforced elastomeric isolators (FREIs) have shown to be a promising option as an alternative to classical steel reinforced elastomeric isolators (SREIs). Previous investigations were limited to scaled-geometries without any attempt to test such devices under code-compliant protocols as per international standards. In the present study the authors investigated two circular full-scale (diameter 620 mm) FREIs manufactured with a non-standard process adopting a soft rubber compound and polyester fibers. Experimental tests were performed in unbounded configuration through the large anti-seismic device test facility at the EUROLAB of the University of Messina, Italy. A significant number of protocols were imposed to the prototypes in order to demonstrate the effect of different loading conditions, i.e., strain level, frequency of the excitation, axial load and repeated loading. The tests confirmed the significant dependency of mechanical behavior on axial load which tends to increase damping (i.e., higher friction mechanisms) while reducing stiffness (i.e., lower stability limits). Due to internal slippage at the fiber-rubber layers interface, damping capacity of FREIs achieved 20% of critical, i.e., significantly higher than that commonly achieved in SREIs with the same rubber compound. Even if adequate capacity was reached in compression, the run-in effect would limit the axial stiffness of FREIs. A significant roll-over phenomenon was detected under lateral loading up to a maximum shear strain of 100% without damage and permanent deformation after unloading. A numerical study finally demonstrated the effectiveness of FREIs when compared to SREIs in a base isolation system designed for a 3-storey reinforced concrete frame located in a high seismicity region in Italy. Lower axial stiffness of FREIs did not affect the seismic performance of the building due to limited rocking motion component and beneficial higher damping mechanism. This paper provides a significant contribution to the standardization of FREIs to be adopted in base isolation of conventional buildings. [ABSTRACT FROM AUTHOR]

The paper presents an automated procedure, named META-FORMA (MEchanical-Typological Approach FOR Masonry Aggregates), to investigate the global seismic performance of masonry aggregates according to a simplified approach. The proposed procedure faces the challenge of using few mechanical and geometrical parameters of individual buildings belonging to an existing masonry aggregate as the input of a proper vulnerability algorithm based on the direct interaction between the programming software MATLAB and the structural analysis and design software POR2000. In this way, all possible combinations of the input parameters can be taken into account and a large set of numerical models is generated and analysed by nonlinear static analyses. The output of the procedure is represented by the bilinear capacity curves of the equivalent single degree of freedom models and by the values of the capacity/demand ratios. The entire approach has been firstly accurately defined and after applied on the pilot case study of the historical centre of the municipality of Foggia, Puglia, Southern Italy. The main advantage that META-FORMA offers is the possibility to generate a wide mechanical/typological-based database, which provides a direct and simplified estimate of the seismic behaviour of masonry aggregates by knowing only few parameters, being at the same time simple and time-saving. Albeit the presented procedure has only developed for building aggregates with linear configurations and composed by the same repeated structural units, META-FORMA is open to further development and modification for accounting any kind of aggregation form. • Automated mechanical-typological procedure to investigate the seismic vulnerability of masonry aggregates: META-FORMA ; • META-FORMA : definition of input parameters, modelling and analysis of masonry aggregates and interpretation of outputs; • Application of the proposed procedure on the pilot case of the municipality of Foggia, Southern Italy; • Pros and cons of META-FORMA , as a powerful tool for the definition of the vulnerability response for masonry aggregates. [ABSTRACT FROM AUTHOR]

The paper presents a machine-learning based framework, named VULMA (VULnerability analysis using MAchine-learning), for vulnerability analysis of existing buildings. The underlying idea is to provide an indication of the seismic vulnerability by exploiting available photographs, which can be properly processed to provide some input data for empirical vulnerability algorithms. To this scope, a complete processing pipeline has been defined, which consists in four consecutive modules offering different and specific services. The first module, Street VULMA , performs the image gathering starting from the raw data; the second module, Data VULMA , provides a mean for the data labelling and storage; the third module, Bi VULMA , uses the collected data to train several machine-learning models for image classification; the fourth module, In VULMA , performs a ranking of the images, their analysis and consequently assigns the vulnerability index. The proposed procedure has been employed on the existing building portfolio in an extended area of the municipality of Bisceglie, Puglia, Southern Italy, for which all the modules have been tested and, above all, the machine-learning models of Bi VULMA have been trained. After, in order to test the efficiency and the reliability of the proposed tools, the entire procedure has been applied on five case study buildings. The results in terms of vulnerability index have been compared with the manual computations performed by the authors applying the same algorithm. Despite the proposed tool could be improved or modified in some of its modules, the obtained results show a good effectiveness of VULMA , which opens new scenarios in the field of vulnerability assessment procedures and risk mitigation strategies. • Proposal of a framework for the vulnerability analysis of existing building starting from a photo: VULMA ; • Definition of the four modules characterizing VULMA: Street VULMA , Data VULMA , Bi VULMA and In VULMA ; • Application and training of the proposed procedure to a dataset extracted from a municipality of Southern Italy and testing and validation of the tool; • Assessment and proposal of VULMA as new instrument for the definition of the vulnerability response of individual buildings and for the seismic risk estimate at large-scale. [ABSTRACT FROM AUTHOR]

• Seismic fragility analysis of existing concrete dams. • gPCE-based predictive models for the dynamic behaviour of concrete dams. • Hierarchical Bayesian framework for uncertainty reduction in the fragility analysis. • Operational modal analysis as source of information in the Bayesian inference. • MCMC-based algorithm for inverse problem resolution in OMA. Concrete gravity dams are critical infrastructures for communities to meet the basic human needs as well as rising standards of living. Most of the existing concrete gravity dams in Italy were built before the introduction of seismic regulations. Although no concrete gravity dams have as yet suffered a catastrophic collapse during or after a seismic event, their preservation remains a key aspect for communities, also in view of that older dams may have deteriorated to a critical level. For these reasons, researchers and practitioners in dam engineering are working to improve seismic fragility, and ultimately seismic risk, assessment procedures. Since no case histories are available, numerical modelling plays an important role, even though many uncertainties can affect the models and then the estimation of the seismic fragility. This paper presents a robust hierarchical Bayesian framework for the calibration of dynamic parameters of dam numerical models based on ambient vibrations, which allows an analyst to reduce uncertainties in the seismic fragility derivation. A probabilistic predictive model of the dam modal behaviour based on the general Polynomial Chaos Expansion is adopted in order to reduce the computational burden and a numerical algorithm for the solution of the inverse problem based on Markov Chain Monte Carlo is also presented. The proposed approach is applied to an existing large concrete gravity dam in Italy, and the effect of epistemic uncertainty reduction is finally evaluated in terms of fragility curves. [ABSTRACT FROM AUTHOR]

DInSAR data provide a powerful tool to recognize the Earth's surface where permanent deformations are concentrated and undergo the strongest ground motion during an earthquake, i.e., defining the epicentral area. We analyzed three recent seismic events in the Apennines belt in Italy related to extensional and contractional earthquakes and documented that the largest macroseismic intensity is recorded where the ground underwent the largest vertical component of motion and the stronger vertical component of the peak ground acceleration. Besides site amplification effects that may occur everywhere even outside the epicentral area, we infer that the vertical oscillations in the so-called near-field allow the horizontal shaking to be more effective, hence producing larger damage above the active crustal volume. The active volume is the one moving vertically and is contemporaneously crossed by seismic waves nucleated by the shear on the fault. The surrounding passive volume in the far field is only crossed by seismic waves. The near field areas are elliptical and cover areas of 300–600 km2 for a range of M w 6–6.9, and they should be the areas where the highest seismic hazard must be expected. Therefore, their area is too large to be neglected for seismic hazard assessment. • Coseismic vertical deformation is recorded for three Apenninic seismic sequences. • Vertical deformation coincides with the largest shaking recorded (PGA). • Maximum vertical DInSar data delimit the highest macroseismic and intensity measures. • The largest damage is recorded in the so-called active crustal volume. • The active volume is where vertical displacement occurs while crossed by seismic waves. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes the in situ non-destructive dynamic tests performed on a lower colonnade of the Dome of the Siena Cathedral (Italy). Tests were aimed at both measuring the fundamental natural frequency of stone columns and identifying their boundary conditions (pinned or clamped). Eight columns were dynamically investigated four times under subsequent impulsive loads (hammer impact test) for a total number of 32 dynamic tests. These tests were a part of a larger experimental campaign aimed to assess the actual static behavior and the seismic vulnerability of the whole Cathedral. In the paper the tests on the stone columns are described at first; secondly the main results, together with the techniques adopted for the signal analysis, are reported in detail. The results of several parametric numerical analyses are also discussed and eventually the use and limitations of the obtained results are critically discussed. [Copyright &y& Elsevier]

SUMMARY On 2009 April 6 a Mw = 6.3 earthquake struck the Abruzzi region (Central Italy) and caused severe destruction in L'Aquila and the surrounding area. In this work we present a Finite Element analysis of the event based on a realistic complex 3-D model, accounting for topographic relief and rheological heterogeneities deduced from local tomography. Finite Element computed Green's functions were implemented in a linear inversion of GPS coseismic displacements, to retrieve the slip distribution on the rupture plane. The inverted slip models basically agree with previous studies carried out on homogeneous domains, but reveal the presence of a single high slip patch, whereas half-space or 1-D approaches obtain a more complex slip pattern. Our results point out that the introduction of 3-D features significantly influences the obtained source model, suggesting a trade-off between domain complexities and source details. [ABSTRACT FROM AUTHOR]

SUMMARY Urgent urban-planning problems related to the 2009 April, Mw 6.3, L'Aquila earthquake prompted immediate excavation of palaeoseismological trenches across the active faults bordering the Aterno river valley; namely, the Mt. Marine, Mt. Pettino and Paganica faults. Cross-cutting correlations amongst existing and new trenches that were strengthened by radiocarbon ages and archaeological constraints show unambiguously that these three investigated structures have been active since the Last Glacial Maximum period, as seen by the metric offset that affected the whole slope/alluvial sedimentary succession up to the historical deposits. Moreover, in agreement with both 18th century accounts and previous palaeoseismological data, we can affirm now that these faults were responsible for the catastrophic 1703 February 2, earthquake ( Mw 6.7). The data indicate that the Paganica-San Demetrio fault system has ruptured in the past both together with the conterminous Mt. Pettino-Mt. Marine fault system, along more than 30 km and causing an Mw 6.7 earthquake, and on its own, along ca. 19 km, as in the recent 2009 event and in the similar 1461 AD event. This behaviour of the L'Aquila faults has important implications in terms of seismic hazard assessment, while it also casts new light on the ongoing fault linkage processes amongst these L'Aquila faults. [ABSTRACT FROM AUTHOR]

Abstract: The influence of underground cavities in assessing local seismic response was studied in some test sites in the urban area of Catania. The investigations were performed both in a natural cavity and in artificial tunnels, taking into account the near-surface geological features. Earthquake and ambient noise records were processed through spectral ratio techniques, investigating also on the possible directional effects. A set of 70 local and regional earthquakes was recorded by seismic stations deployed nearby a grotto located in the northern part of the town as well as in a reference site on the bedrock. As regards ambient noise measurements, about 30 recording sites were selected, locating the mobile stations inside the cavities as well as along short profiles crossing them. Spectral ratios coming out from performed measurements show that spectral peaks in the frequency range 3.0–7.0 Hz appear stable nearby the cavity, and show a tendency to be less pronounced at increasing distance from it. Moreover, the natural period of buildings erected nearby and over the considered cavity was evaluated to investigate on possible soil-structure interactions. The results so far obtained point out that the height of the cavities plays an important role. It appears evident that only cavities having height greater than about 4m show significant H/V amplification peaks. Moreover, spectral ratios deriving from measurements performed inside the cavities show less pronounced spectral peaks than those obtained from measurements over and outside the cavities. Investigations about the interaction with nearby edifices show slight increments in the amplitude of spectral peaks representing the fundamental period of buildings located over the investigated grotto. Finally, our observations set into evidence a tendency toward a pronounced polarization of the ground motion that is parallel to the main axis of the grotto. [Copyright &y& Elsevier]

Abstract: The influence of site effects on landslide triggering during earthquakes has been inferred in several studies, but its evaluation is made difficult by the complexity of factors controlling the dynamic response of potentially unstable slopes and also by the lack of local ground motion instrumental observations. This work explores this problem and reports new findings based on an ongoing long term accelerometric monitoring conducted on a landslide-prone test area in the Apennine Mountains, Italy, where the presence of site effects enhancing seismic susceptibility of local slopes has been invoked on the basis of historic accounts of landsliding triggered at large epicentral distance. The recordings relative to low-to-moderate magnitude earthquakes showed significant amplifications affecting hillslope portions covered by thick (>5m) colluvia and pronounced amplification maxima oriented along the local maximum slope direction on a recent deep-seated landslide. While the amplifications seem most likely linked to high impedance contrast between surface materials and underlying substratum, the causes of directivity are less clear. The case of the monitored test site together with evidence of site response directivity identified on other hillslopes, suggest that the directivity phenomena can result from a combination of topographic, lithological and structural factors that act together to re-distribute shaking energy, focusing it on site-specific directions. Thus, it is difficult to single out the critical factors controlling such phenomena and no general criterion for the identification of sites affected by directivity is proposed here. Nevertheless, the presence and orientation of site response directivity can be revealed through reconnaissance techniques by using recordings of seismic weak motion and/or ambient microtremors, and calculating azimuthal variation of shaking energy and horizontal-to-vertical ground motion spectral ratios. A comparison with the recordings obtained during the recent MW =6.3 earthquake that hit the Abruzzo region in April 2009 demonstrated that analysis relying on data from low energy events can furnish valid indications for slope behaviour also under stronger shaking, provided the data are well differentiated in terms of distance, azimuth and source characteristics. Furthermore, the comparative analysis of the Abruzzo earthquake recordings at a landslide and reference sites showed that directivity properties of strong shaking had been correctly anticipated using earlier weak motion observations. However, under the complex slope conditions the identification of resonance frequencies from horizontal-to-vertical spectral ratios estimated from weak-motion accelerometric recordings does not seem reliable, and better results have been obtained by velocimetric microtremor recordings. [Copyright &y& Elsevier]

Abstract: This study concerns measurements of radon and thoron emissions from soil carried out in 2004 on the eastern flank of Mt. Etna, in a zone characterized by the presence of numerous seismogenic and aseismic faults. The statistical treatment of the geochemical data allowed recognizing anomaly thresholds for both parameters and producing distribution maps that highlighted a significant spatial correlation between soil gas anomalies and tectonic lineaments. The seismic activity occurring in and around the study area during 2004 was analyzed, producing maps of hypocentral depth and released seismic energy. Both radon and thoron anomalies were located in areas affected by relatively deep (5–10 km depth) seismic activity, while less evident correlation was found between soil gas anomalies and the released seismic energy. This study confirms that mapping the distribution of radon and thoron in soil gas can reveal hidden faults buried by recent soil cover or faults that are not clearly visible at the surface. The correlation between soil gas data and earthquakes depth and intensity can give some hints on the source of gas and/or on fault dynamics. [Copyright &y& Elsevier]

In this study the attenuation mechanism of seismic wave energy in north central Italy is estimated using low-magnitude earthquake local data recorded at six stations managed by INGV. Most of the analysed events are located along the Alpine chain in the zone of Iseo and Garda lakes, while a minor part in the Po valley. The zone investigated is characterized by the occurrence of significantly intense earthquakes (magnitude up to 6.6) the most recent occurred in 2004 close to the city of Salò on the coast of the Garda lake ( M= 5.0). Due to the high population density and presence of industrial activity the investigated area is characterized by a high seismic risk. First, the ordinary Multiple Lapse Time Window Analysis (MLTWA) method is applied in the assumption of uniform velocity and scattering and the couple of B, the seismic albedo and , the extinction length inverse (corresponding to the total attenuation coefficient) is calculated in the frequency bands of 1.5, 3, 6 and 12 Hz. To retrieve more realistic estimates, the obtained values of and are corrected taking into account the effects of a depth-dependent earth model, consisting of an earth structure characterized by a transparent upper mantle and a heterogeneous crust. We find that the corrected intrinsic and scattering attenuation parameters (which are proportional to the inverse of the intrinsic/scattering quality factors, and ) are strongly frequency dependent, with a prevalence of scattering attenuation over the intrinsic dissipation. The corrected and uncorrected values of total Q are in agreement with the total Q values obtained with different approaches for the same area. [ABSTRACT FROM AUTHOR]

It has long been observed that damage due to earthquakes depends greatly on local geological conditions. Alpine valleys represent a typical populated environment where large amplifications can take place owing to the presence of surface soils with poor mechanical properties combined to complex topography of the rock basin. In the framework of the EU Interreg IIIB SISMOVALP Project ‘Seismic hazard and alpine valley response analysis’, a stretch of the Tagliamento River Valley (TRV), located in the north-western part of the Friuli Region (Italy) and close to the epicentre of the 1976 Mw= 6.4 earthquake, has been investigated with the aim to define the buried shape of the valley itself. Two non-invasive, low cost, independent geophysical methods were used: (i) detailed gravity survey and (ii) H/V spectral ratio (HVSR) of microtremors. Because of structural geological complexity and active tectonics of the Friuli region, an irregular valley shape was expected in this area. The independent analysis performed by gravity and passive noise, and complemented with refraction seismic velocity profiles, confirms this hypothesis and leads to two models that were consistent, but for some small scale details. The maximum depth estimated is about 400–450 m in the southern part of the valley, while a mean value of 150–180 m is estimated in the northern part. The sediment thickness obtained for this stretch of the TRV is quite large if compared to eastern Alps Plio-Quaternary rates; therefore the valley shape imaged by this study better corresponds to the top of carbonate rocks. Finally, on the basis of the obtained morphology and some direct measurements, we conclude that the TRV features an overall 1-D seismic response (i.e. the resonance is related only to the sediment thickness rather than to the cross-section shape), but in its deepest part some limited 2-D effects could take place. [ABSTRACT FROM AUTHOR]

A key issue in our understanding of the earthquake cycle and seismic hazard is the behaviour of an active fault during the interseismic phase. Locked and creeping faults represent two end-members of mechanical behaviours that are given two extreme rupturing hazard levels, that is, high and low, respectively. Geophysical and space geodetic analyses are carried out over the Pollino Range, an extensional environment within the Africa–Eurasia plate boundary, to disclose the behaviour of the long-lasting quiescent Castrovillari normal fault. Fault trenching evidenced at least four large earthquakes (6.5–7.0 Mw) in the past and an elapsed time of 1200 yr since the last event. Inversion of Differential Interferometric Synthetic Aperture Radar and Global Positioning System over a decade shows fast creeping at all depths of the fault plane. The velocity-strengthening creeping zone reaches maximum rates 20 mm yr−1 against an average rate of about 3–9 mm yr−1. It limits the southern-weakening locked part of the fault. An essential condition for the generation of a large earthquake on the Castrovillari fault, as has occurred in the past, is a rupture through the velocity-strengthening zone. The Castrovillari fault yields the best evidence for being both a strong and weak fault during its earthquake cycle. Creeping at rates faster than its tectonically driven ones, it must thus consist of a mix of unstable and conditionally stable patches ready to sustain a sizeable earthquake. Quantifying and mapping the slip rate over the fault plane is important because they influence fault moment budget estimate and helps to constrain constitutive laws of fault zones. Aseismic slip also redistributes stress in the crust, thereby affecting the locations of future earthquakes. [ABSTRACT FROM AUTHOR]

The existence of active low-angle normal faults has been questioned because the standard theory of fault mechanics precludes normal faults from slipping at low (<30°) dip angles, and there is an apparent deficiency of large normal fault earthquakes globally with a shallow dipping fault plane. The Alto Tiberina fault, Italy, is a low-angle normal fault (with dip 15°-20°) that has been clearly imaged with seismic reflection profiles and is highlighted by microseismicity. The fault is thought to be the main structure accommodating extension in the region. However, few large earthquakes have been documented on or near the fault for more than 2 ka. Analysis of data from a recently established network of continuous global positioning system (GPS) stations in the Umbria-March region, Italy, shows that the Alto Tiberina low-angle normal fault in the Northern Apennines is actively slipping at a shallow depth within the brittle crust. Crustal deformation models that best fit the GPS are consistent with both a shallow dip and active, mostly aseismic, creep of ∼2.4 ± 0.3 mm/a below 4 ± 2 km locking depth along the Alto Tiberina fault. [ABSTRACT FROM AUTHOR]

An evaluation of the actual reliability of probabilistic seismic hazard (PSH) assessments, provided by existing numerical techniques, is mandatory to orientate new researches and improvements. Two procedures devoted to this task are proposed, which are based on the comparison of the hazard estimates with empirical observations (e.g. strong-motion data). These procedures have been applied to the estimates provided by the methodology adopted for most recent seismic hazard evaluations in Italy. The analysis shows that a significant mismatch exists between peak ground acceleration values characterized by an exceedence probability of 10 per cent in 30 yr and what has actually been observed at 68 accelerometric stations located on stiff soil, where continuous seismicity monitoring has been performed in the last 30 yr. Although this finding should be considered with caution, it suggests that a future re-examination of the adopted PSH computational model could be useful to avoid possible underestimates of seismic hazard in Italy. [ABSTRACT FROM AUTHOR]

Prediction of surface ground motion based on advanced approaches is a non-trivial task at large area. In fact, advanced approaches require a detailed geological and geotechnical subsoil model based on geological, physical and mechanical properties retrieved from in situ investigations and laboratory data, and to perform time consuming numerical simulation of the seismic site response. Bearing in mind that there is a lack of available site investigations and laboratory data at large area, simplified methods based on "soft data" are often adopted. On this regard, a methodology to perform seismic site response analyses at national scale is proposed in this paper, based on the following assumptions: 1) homogeneous areas were identified at national scale based both on morpho-geological and lithological properties, in order to classify and analyse site-data archived in the Italian database of seismic microzonation studies; 2) geotechnical subsoil one-dimensional models of the Italian site conditions were defined according to site-data; 3) in accordance with the reference seismic hazard levels, pseudo-acceleration response spectra were selected as input motions for numerical simulations. About thirty million numerical simulations of seismic site response were performed, and national maps of seismic shaking amplification factors were produced in terms of ratio of response spectra referred to three intervals of period. This estimation of surface ground motion based on the proposed procedure is a supporting tool for large area territorial and emergency planning. • Numerical models of national site conditions were identified from Italian database. • Numerical models were extended down to the seismic bedrock. • Morpho-geological clusters were used to spatialize input and output data. • National maps of amplified seismic intensity were proposed. • The proposed procedure will support seismic risk mitigation at large area. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the seismic hazard of a region in southern Italy by analysing stress release models from the Bayesian viewpoint; the data are drawn from the most recent version of the parametric catalogue of Italian earthquakes. For estimation we just use the events up to 1992, then we forecast the date of the next event through a stochastic simulation method and we compare the result with the really occurred shocks in the span 1993–2002. The original version of the stress release model, proposed by Vere-Jones in 1978, transposes Reid's elastic rebound theory in the framework of stochastic point processes. Since the nineties enriched versions of this model have appeared in the literature, applied to historical catalogues from China, Iran, Japan; they envisage the identification of independent or interacting tectonic subunits constituting the region under exam. It follows that the stress release models, designed for regional analyses, are evolving towards studies on fault segments, realizing some degree of convergence to those models that start from an individual fault and, considering the interactions with nearby segments, are driven to studies on regional scale. The optimal performance of the models we consider depends on a set of choices among which: the seismogenic region and possible subzones, the threshold magnitude, the length of the time period. In this paper, we focus our attention on the influence of the subdivision of the region under exam into tectonic units; in the light of the recent studies on the fault segmentation model of Italy we propose a partition of Sannio-Matese-Ofanto-Irpinia, one of the most seismically active region in southern Italy. The results show that the performance of the stress release models improves in terms of both fitting and forecasting when the region is split up into parts including new information about potential seismogenic sources. [ABSTRACT FROM AUTHOR]