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During recent seismic events, such as 2010 Darfield and 2016 Ecuador earthquakes, widespread liquefaction has been observed in sand deposits with silt content. Nevertheless, the presence of non-plastic fines implies variable liquefaction resistance of sands. The goal of this research is the assessment of the influence of non-plastic fines and mixture-packing conditions on liquefaction triggering. A series of monotonic and cyclic consolidated undrained triaxial as well as resonant column tests is carried out on reconstituted soil specimens. The behavior of loose, medium and dense silty sands is analyzed, using different fine contents and confining pressures. The results show that the behavior of mixtures strongly depends on the packing configuration of coarse and fine particles. The experimental results are analyzed in terms of equivalent intergranular void ratio, which is identified in the literature as an adequate state parameter to characterize the global effect of fine particles. The estimation of the equivalent intergranular void ratio requires the determination of the active fine fraction b participating in the force transfer. An original formula is proposed for the parameter b based on packing configuration. The validation of the proposed formula is undertaken through comparisons with the present experimental results but also with results reported in the literature. The proposed expression to estimate the active fine fraction b allows a satisfactory prediction of liquefaction triggering in sand-fines mixtures independently from the fine content.

Landslides are among the most frequent secondary effects related to seismic events. The prediction of the expected displacements of landslides activated by seismic shaking (1st-time failures and reactivated landslides) is therefore a substantial feature for the hazard assessment in high seismicity regions. Several databases collecting geological and geometrical information on worldwide landslides events are available in literature. This study presents the result of statistical analyses on morphometric, topographic and geotechnical parameters extracted from existing landslide databases (Domej et al., 2020; Martino et al., 2019; Tanyas et al., 2019). The aim is to define a procedure to generate 2D step-like-slope landslide models representative of the most common landslides in terms of failure mechanism (divided into two main categories: purely rotational and translational landslides), volume, and geotechnical properties. Rock falls and toppling, flow-like landslides and deep-seated landslides were excluded from the initial dataset, because they are associated with peculiar physical processes during the failure and the propagation. The performed statistical analysis allowed to identify the most frequent values of depth/length ratios, volume and slope angle, from which other geometrical measurements were analytically derived. In addition, various landslide locations along the slope were considered to cover most of the real cases. This resulted in 36 different landslides/slopes shapes. Landslides dynamic/geotechnical parameters (shear wave velocity, density, strength) were selected to be consistent with those inferred for rocks, cohesive soils and granular soils by statistical analysis. The representativeness of the inferred models is assessed by comparing the theoretical geometries with the real ones detected in the Campotosto Basin (Central Apennines, Italy), a high seismicity area very close to the Amatrice village, which was strongly hit by the recent 2016-2017 (M 6.5) Central Italy seismic sequence as well as by the 2009 (M 5.9) L’Aquila earthquake. The simplified landslide models represent the first part of a major study on the prediction of seismically induced landslide displacements. The aim is to improve the existing Newmark’s approach–based PARSIFAL (Probabilistic Approach to pRovide Scenarios of earthquake-Induced slope FAiLures) method (Martino et al., 2019) to assess the earthquake-induced displacements at a regional scale, by introducing corrective factors derived from parametric dynamic numerical simulations on the simplified geometries; such factors should incorporate some aspects of the complex seismic waves/landslides slopes interaction. Such a procedure will allow to overcome the Newmark’s method limitations and to extend the advantages of the numerical analyses, the use of which is generally limited to studies at slope scale, over larger areas.

The mechanical behavior of binary granular mixtures strongly depends on their initial packing density, stress level, fine content, particle size distribution, mineralogy, and shape. This r...

The Seismic Microzonation of level 3 (SM3) is nowadays a world-wide accepted tool for the mitigation of seismic risk. The SM3 is a complex process involving different disciplines ranging from Geology and Applied Seismology to Structural and Geotechnical Engineering. The outcome of a SM3 is presented on a zoning map in terms of a selected ground shaking intensity parameter and susceptibility to main ground instability (soil liquefaction, settlements, landslides, fault ruptures). In an advanced SM3 study for a given area, four main interdisciplinary steps can be recognized: (1) definition of the reference input motions, (2) construction of the subsoil model, (3) performing of numerical analyses and computing of amplification factors, (4) identification of zones with different geotechnical hazard potential and drawing up of the SM3 map. After the 2016–2017 Central Italy seismic sequence, intensive studies have been performed to obtain SM3 maps in 137 municipalities most damaged by the earthquakes. The aim of these studies has been to obtain a clear background on site effects to perform a correct reconstruction of the municipalities. In the paper, main results and critical issues of the above-mentioned steps of SM3 procedure are discussed together with some remarks on the use of SM3 output in supporting seismic design for reconstruction.

The Vallerano district in Rome is built on an alluvial valley with a very complex geological setting (highly heterogeneous soil deposits) due to the depositional activity of Tiber River tributaries ongoing since the Pleistocene age. A high-resolution engineering-geological model of the valley was reconstructed through field investigations, boreholes log-stratigraphies and geophysical investigations. 2D FEM numerical modelling of the alluvial valley allowed to assess the local response in terms of seismic wave propagation on surface, amplification function and cumulative kinetic energy. Soil layering and basin effects combine to induce a complex local seismic response. Different typologies of seismic waves are present in the seismograms and surface waves have been also detected. Retrograde Rayleigh surface waves have been identified and extracted through a procedure based on the time-frequency Normalized Inner Product. The spatial analysis of the extracted Rayleigh waves highlights that the local seismic response of the valley is strongly influenced by edge-generated surface waves. The results suggest that amplification is strongly related to the thickness of the soil deposits, whereas the elongated duration is more related to a layered basin structure. The soil layering and the basin effects on the generation of surface waves have been assessed and quantified.

Rock mass damaging has become a topic of great interest in the engineering-geology research community during the last decades as it can significantly influence slopes stability. In this sense, the study of mechanics and dynamics of jointed rock masses represents a challenge because it will allow to better understand how external continuous and transient stressors can influence the short- to long-term stability controlling their pre-failure behavior. Consequently, the detection of permanent changes in physical and mechanical parameters, due to periodic or transient stressors, is an important target to mitigate the related geological risk as it can potentially lead rock masses to failure, especially when infrastructures and natural or cultural heritages are exposed elements. In this framework, the Acuto field laboratory (Central Italy) has been designed and implemented in 2016 within an abandoned quarry by employing an integrated geotechnical and geophysical monitoring system, with the aim of investigating how natural and anthropic conditioning factors could lead fractured rock masses to failure. The integrated monitoring system, which is installed on a potentially unstable 20-m3 jointed rock block, is composed of several strain devices (i.e., strain gauges -SG- and jointmeters -JM-), one fully equipped weather station, one rock thermometer, eight high-sensitivity microseismic uniaxial accelerometers and optical and InfraRed Thermal cameras. The acquisition of long-term monitoring time-series, coupling multimethodological approaches, allowed to establish cause-to-effect relationships among different environmental stressors and induced strain effects, highlighting the continuous action of thermal stresses on rock mass deformations both at the daily and seasonal timescales. In fact, while the analysis of thermal and strain monitoring data allowed to characterize the cyclic contraction and relaxation response of major rock fractures and microcracks to temperature fluctuations, the microseismic monitoring array was able to detect during thermal transient (i.e., freezing conditions) the occurrence of microseismic emissions potentially related to the genesis or progressive growth of pre-existing cracks.Starting from 2018, experimental activities at the Acuto field lab are supported by the “Dipartimento di Eccellenza” project of the Italian Ministry of Education Universities and Research funds attributed to the Department of Earth Sciences of the University of Rome “Sapienza”. In this framework, the Acuto filed laboratory will undergo a structural upgrade that will be aimed at the investigation of two new sectors of the abandoned quarry. These new sectors will be instrumented with innovative thermal profiles probe, fiber Brag grating sensors and traditional SG and JM for detailed stress-strain monitoring, acoustic emission sensors and high-frequency and low-frequency geophones for ambient seismic noise monitoring and microseismic events detection as well as accelerometers for evaluating the rock mass response in the case of seismic shaking. The main goal of such an improvement will be both technical and methodological, and will shed light on the application of integrated geophysical and geotechnical monitoring approaches in investigating the multiscale rock mass damaging process as well as the detection of rock mass failure precursors by using non-conventional combinations and configurations of geotechnical and broad-band geophysical devices.

The morphological evolution of landslide slopes is generally controlled by the combination of weathering, tectonics, gravity and river erosion. Among them, seismic shaking plays a fundamental role in landslide activity and mobility in high seismicity regions. It can result in important modifications of landslide geometry and consequently, of its response to external loadings. In particular, morphological changes in landslide slope can imply changes in the interactions between seismic waves and landslide mass, which could theoretically modify the hazard related to the earthquake-induced effects. This study aims at pointing out the effects of slope morpho-evolution on the long-term modification of earthquake-induced landslide dynamics, which is here quantified in terms of expected seismically induced displacements, considering unaltered seismic hazard conditions. The Albuñuelas landslide was selected, located in Andalusia (South Spain) which is one of the most seismic regions of Spain. This landslide is a large roto-translational process whose last earthquake-induced reactivation occurred during the 1884 Andalusia Earthquake (Mw 6.5), causing relevant damages to the Albuñuelas village. Data available from field surveys and geophysical investigations, allowed to derive the current engineering-geological model of the landslide slope. According to the available geological and geomorphological data, the slope shape was back-deformed to reproduce the landslide geomorphological evolution sequence over time, until its first-time failure. The reconstructed sequence is consistent with a geomorphological evolution mainly driven by the combination of earthquake-induced re-activations and low rates of deformation caused by the intense incision of the Albuñuelas River, responsible for the valley deepening. 2D-dynamic stress-strain numerical simulations were performed on several stages of such sequence applying 17 equivalent signals derived following the LEMA_DES (Levelled-Energy Mutifrequential Analysis for Deriving Equivalent Signals) approach with an Arias Intensity of 0.1 m/s, according to the Andalusia regional seismic hazard. The outputs were expressed in terms of seismically induced displacements vs. characteristic periods diagrams, in order to highlight the role of signal frequency content as well as the effect of the landslide 2D-geometry (Tl) and thickness (Ts) on the resulting displacements. Since the morpho-evolution resulted in a progressive increasing of the landslide mass length and its dislodgment into several blocks since the first-time failure, the landslide mobility was analysed over time at each single-block scale. The comparison revealed a not neglectable modification of the Albuñuelas landslide susceptibility to the local seismic hazard over time, highlighting the necessity to understand the mechanisms driving the natural system evolution to provide more reliable earthquake-induced hazard scenarios.

Earthquake-induced landslide mass mobility is a topic of particular relevance for the analysis of earthquake-induced ground effects scenarios. The landslide masses already existing on the slopes interact with the seismic waves that propagate from the bedrock, giving rise to effects of amplification of the seismic motion at specific frequencies connected to their geometry and their dynamic properties. The quantification of the earthquake-induced displacements expected in landslide masses through numerical models under dynamic conditions highlights how, especially for medium-low energy levels of the seismic input, the displacements thus obtained are generally higher than those computed by conventional approaches (e.g. Newmark method applied to the hypothesis of rigid or deformable block and related semiempirical relations). A series of case studies has also proved that the geometry of significantly dislodged landslide masses (i.e. segmented into kinematically distinct portions, namely “blocks”) due to their geomorphological evolution over time, significantly controls the seismic-induced displacements obtained by numerical models. In particular, the results highlight that the maximum displacements computed through the numerical models do not correspond to seismic inputs whose characteristic periods coincide to those of the resonance or of the length of the landslide mass but are more directly connected to the smaller dimensions of the individual blocks in which the landslide mass is segmented.

This study reports a comparative analysis of the environmental conditions and micro-seismicity recorded on a rock wall resulting from an intense meteorological event. The findings are focused on a quarry wall located in the Acuto Field Laboratory (Central Italy), where multi-parametric environmental monitoring is operating and an Artificial intelligence Camera Prototype has been placed to detect rock falls reaching a railway target. Six accelerometers were installed to detect micro-seismic events caused by the expected strong thermal transient caused by the Buran storm on February 2018. Within a few hours, a steep decrease in the average air and rock mass temperature down to 8 °C was recorded, and −4 °C and −8 °C were reached for the rock and air temperatures, respectively. A total of 103 micro-seismic events were analysed with respect to both rainfall and thermal forcing: while no correlation with rainfall was reported, the steep thermal transient was responsible for the strain effect that occurred during the heating phase of the rock mass following the Buran storm. An elastic deformation event with a maximum daily amplitude of 165 μ strain was recorded by the strain gages installed on the mm-joints due to the rock heating and cooling caused by the variation in temperature. The collected evidences show the relevance of short thermal transients in modifying stress conditions within rock masses and their relationship to a peculiar micro-seismic response. The main outcomes established the key role played by integrated monitoring systems to better understand the relationship between vibrational behaviour and environmental forcings in terms of understanding the precursors to rock failure.

Rock mass damaging investigation is a main research topic in the ambit of rock fall hazard assessment. Roads and railways interruptions, as well as damages of buildings, are among the main inconveniences due to the detachment of unstable sectors of highly jointed rock masses. The contribution of rock mass creep together with natural and anthropic forcings leads to the accumulation of inelastic strain within the rock mass and to the formation of new joints or to the extension and movement of the pre-existing ones. The associated stress release produces tiny vibratory signals (known as microseismic emissions) that can be detected by on-site installed microseismic monitoring networks. Monthly and annual microseismic monitoring data can provide information on seismicity increase over certain periods and on the deterioration of rock properties as the elastic moduli. However, other seismic attributes may support the comprehension of rock mass damaging processes. In particular, the analysis over time of the damping ratio associated with the microseismic emissions could indicate transient and permanent changes within the micro-joint network. This analysis approach has been already conducted on a three-month long microseismic dataset collected at the Acuto field-lab, which is hosted in an abandoned quarry and is mainly exposed to environmental forcings (rainfalls and thermal cycles); moreover, to account also for anthropic vibrations, preliminary studies were carried out on a rock mass located in proximity of a railway. As a further perspective, the investigation of multi-year seismic dataset acquired on unstable rock masses will allow to better inspect the reliability of this analysis approach for rock mass damaging assessment.

Modeling seismic waves and vibrations propagating into geological structures has always been a challenge since large scale models as well as detailed basin geometry and soil layering are both needed. The optimal accuracy to model the propagation process depends on the frequency range but also on the excitation level.

Earthquake-induced displacements of landslides are significantly conditioned by their 1D and 2D interactions with seismic waves, as currently proven by several studies. Nevertheless, the role of a more complex geological setting, responsible for a heterogeneous composition of the landslide mass, can significantly influence these phenomena. The heterogeneity can also depend on multiple phases of the landslide activity, responsible for dislodging the whole landslide mass into submasses, each one delimited by secondary scarps and characterized by individual mobility. Hence, in the framework of the European project “MARSite – Marmara Supersite: new directions in seismic hazard assessment through focused Earth observation in the Marmara Supersite”, the Buyukcekmece landslide, located approximately 30 km W of Istanbul (Turkey), was considered as a case study. This landslide involves a large mass of approximately 140 million cubic metres, composed of silty clays, tuffs and sands ascribable to Cenozoic geological formations. The landslide is characterized by multiple phases of activity with a composite rototranslational mechanism, which created seven submasses delimited by secondary scarps. The scheme of water circulation in the landslide slope, based on piezometer data as well as on a geological survey, accounts for two flow nets: the first, shallower flow net is located in superficial sandy deposits, outcropping in the dislodged landslide submasses; the second, deeper flow net is located in the main sliding surface. A slope stability analysis following a global limit equilibrium approach provided a distribution of the pseudostatic coefficient vs. pore water pressure. The results show that the stability of the landslide submasses increases moving downslope, and reactivations are expected in the case of earthquakes with a return period between 475 and 2475 yr, according to the local seismic hazard. Dynamic numerical modelling was also performed using the stress-strain finite difference code FLAC 7.0 to derive the distributions of horizontal displacements vs. characteristic period ratios, defined as the period due to depth (Ts) and total length (Tl) of the landslide mass over the earthquake characteristic period (Tm). The obtained results indicate that an effective characteristic period of the landslide (Tl⁎), related to the length of a single counter-slope tilted submass, can provide a more correct explanation for the effect of seismic wave interactions on earthquake-induced displacements. This result indicates that the earthquake-induced mobility of the Buyukcekmece landslide is strongly conditioned by its composite rototranslational mechanisms. In general, these results indicate that landslide evolution can induce a change over time for the characteristic periods related to the dimensions of the dislodged landslide portions and then modify its interactions with seismic waves.

Monitoring rock mass damaging through the analysis of seismic records is an affirmed tool to manage rock fall risk in view of mitigation strategies . This study proposes a novel approach, named DAmping RaTio Anomalies Monitoring (DaRtAM), to detect the rock mass damaging by measuring variation over time of the damping ratio related to in-situ recorded vibrational events. Although damping-based damage detection techniques are well known for structural monitoring, only few applications exist for rock mass damage investigation not including in-situ long term rock mass monitoring. Here, a three-month-long seismic dataset recorded on a rock wall (Acuto Field Laboratory) by means of six one-component accelerometers was analysed with a STA/LTA algorithm that allowed to extract 19013 vibrational events. The damping ratio of the signals was derived as a function of frequency, averaged in a daily time window and analysed over time to output short-term anomalies and long-term trend. Although the limited time period analysed did not allow to observe significant trend variation of the damping ratio, 131 short-term anomalies were found in the collected seismic records. As it results from this study, the proposed approach is suitable for detecting rock mass damaging and, as a future perspective, will be applied to yearly-lasting vibrational datasets. This approach may be more effective with data acquired in environments characterised by recurrent forcings, such as coastal cliffs forced by sea and wind storms, rock walls stressed by thermal cycles, quarry walls involved in human activities or rocky trenches close to roads and railways.

Characterizing the potential effect of local site conditions on the amplification of ground motions is a critical aspect of seismic hazard and risk assessment. The aim of this study is to investigate the reliability and the limit of using the average shear wave velocity in the upper 30 m of the soil profile v s , 30 , as single proxy, to characterize seismic site effects for weak and strong events. To this regard, a dataset of 300 one-dimensional soil profiles with a given v s , 30 are generated through a Monte Carlo approach. Their seismic responses are computed for a set of 40 real accelerograms, with different seismic features. The vertical propagation from the bottom of the generated columns is modeled using a finite element spatial discretization, accounting for both linear and nonlinear soil behavior. The site dominant frequency f 0 and the shear wave velocity gradient in the profile B 30 are proposed as proxies to characterize seismic site effects and the variability of the response spectra for the numerical signals, at the free surface of the set of columns, is discussed. Correlations between site-specific amplification factors deduced using the numerical response spectra and the proposed site proxies are analyzed for different sub-ranges of periods. The obtained amplification factors are then compared to those proposed by different international and national design codes. The results, obtained under assumption of linear and nonlinear behavior of soil, emphasize the need to introduce complementary site parameters proxies, in addition to v s , 30 , to characterize the expected site effects in design response spectra.

The assessment of landslide hazards and design of strategies for managing the related risk have been widely studied topics in the scientific community due to the settlements, infrastructures and tourist and cultural heritage sites that may be threatened by deformations involving unstable slopes. Engineering geological and geophysical techniques have been recently integrated in multidisciplinary approaches to study gravity-induced slope instabilities and monitor their evolution. The slope that hosts the Peschiera Springs drainage plant (Central Italy) is involved in a mass rock creep process associated with deep karst dissolution. Due to the importance of this infrastructure, which provides water to the Rome aqueduct, an accelerometric network was installed in 2008, and a nanoseismic array was added in 2014. In this paper, data recorded by the nanoseismic array were used to locate 397 microseismic events related to the slope instability process, distinguished into two types with different waveforms: 16 failures and 381 collapses. The failures were distributed throughout the slope, while the collapses exhibited two spatially separate clusters below the groundwater level, at a depth where karst processes produce cavities. The clusters were analysed as two distinct microseismic sources characterised by specific frequency-magnitude curves of events that describe their attitude to produce events of different magnitudes. Regarding the accelerometric network, an automated procedure was developed for quickly analysing the seismic records, which include signals from teleseisms and near- to far-field earthquakes that can induce deformation in the landslide-involved slope. The results obtained by the two seismic monitoring systems were integrated with the aim of implementing a landslide hazard matrix based on the statistical frequency of the occurrence of such events and their probability of exceedance during a reference period, providing a useful tool for managing the related landslide risk.

For many geotechnical purposes, the proper estimation of shapes and dimensions of landslide rupture zones is of significant importance. Very often this exact delineation is difficult due to the lack of information on rupture zone extents in 3D. Based on a global landslide inventory, this study presents a refined statistical analysis correlating dimension-related and shape-related parameters characterizing a rupture zone in 3D to its volume. Dimension-parameters are approximated by linear regressions increasing with greater volumes, whereas shape-related parameters appear stable throughout the entire range of volumes. Revealing themselves as very stable, these correlations can be used, hence, to extrapolate from a distinct parameter to the volume of a landslide rupture zone. In a second stage, ratios of dimension-related parameters are correlated with rupture zone volumes. Also, this type of correlation delivers very stable results showing that ratios are constant throughout the entire range of volumes. Making use of this ratio consistency, it is possible to deduce one of the two parameters when the other one is given. This latter aspect seems to be promising for remote sensing surveys when initial rupture areas or rupture volumes should be delineated.

Dynamic site amplification and soil classification are important issues related to earthquake engineering. While most of the studies are dedicated to engineering seismology and earthquake engineering, similar approaches for soil classification and site amplification have not been yet fully established in the field of urban vibrations. In this study, several parameters of a given site have been investigated to synthetically describe the geometrical and mechanical properties that control the amplification phenomena (i.e. average velocity and velocity gradient-based proxy). The results of FEM analyses of wave propagation have been processed in the frequency domain and analysed with respect to the proposed parameters and the distance from the source. Finally, the velocity-gradient-based parameters coupled to the spectral analysis can be considered as a coherent methodology for reliable vibration predictions and site classification in order to assess vibration sensitivity.

A ~1000 m3 rockslide occurred close to Lorca (SE Spain) during the main shock (Mw = 5.1) of the May 2011 seismic sequence. The location of the rockslide, within 10 km of the earthquake epicenter and along the southern slope of a valley in which similar geological conditions occur on both slopes of the valley, suggests a significant near-field effect due to local seismic response. This could be related to the specific interaction between the topography and the obliquely propagating seismic waves. A dynamic stress strain numerical model was constructed using the FLAC 7.0 finite difference code to back analyze the Lorca rockslide event and relate its occurrence to both the local seismic amplification and the interaction between seismic waves and local topography. The results indicate that only for seismic waves with incidence angles in the range 0°–50° are the occurred slope instabilities expected. These results do not significantly change when varying the values for either stiffness or strength parameters within the range of the experimental data., This work was partially funded by research groups VIGROB-53 and VIGROB-184 (Universidad de Alicante) and by the projects tec2008–06764–c02–02 and CGL2011–30153–c02–02.

The influence of pore water pressure has to be taken into account when the propagation of seismic waves in saturated soils is simulated, because it controls the strength decrease during the dynamic process and can induce phenomena such as cyclic mobility and liquefaction. The decrease of effective stresses leads to permanent deformation in the soil and damages to the surface structures. This research aims at validating a 1-directional propagation model of 3-component seismic waves (1D-3C) in a horizontally layered soil, in the case of saturated soil. A 3-D non-linear elasto-plastic model for soils is used and the variation of the shear modulus reduction curve with the pore water pressure is taken into account during the seismic event. In the case of multiaxial stress states induced by a 3C seismic motion, if no additional information is available, the modulus reduction curves in shear and compression, normalized with respect to the elastic moduli, are assumed identical, since the Poisson's ratio is supposed to be constant during the process. The multiaxial stress state in saturated soils induced by a 3C seismic motion is analysed for various stress paths. The 1D-3C wave propagation model is used to compute the seismic response of the Kushiro soil profile (Japan). The stratigraphy and geotechnical properties are deduced from in situ and laboratory tests provided by the PRENOLIN benchmark. Numerical results are in correct agreement with the records at the surface in terms of acceleration envelope

International audience; Local wave amplification due to strong seismic motions in surficial multilayered soil is influenced by several parameters such as the wavefield polarization and the dynamic properties and impedance contrast between soil layers. The present research aims at investigating seismic motion amplification in the 2011 Tohoku earthquake through a one-directional three-component (1D-3C) wave propagation model. A 3D nonlinear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model. The soil rheology is modeled by mean of a multi-surface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan (MPII) type. Its major advantage is that the rheology is characterized by few commonly measured parameters. Ground motions are computed at the surface of soil profiles in the Tohoku area (Japan) by propagating 3C signals recorded at rock outcrops, during the 2011 Tohoku earthquake. Computed surface ground motions are compared to the Tohoku earthquake records at alluvial sites and the reliability of the 1D-3C model is corroborated. The 1D-3C approach is compared with the combination of three separate one-directional analyses of one motion component propagated independently (1D-1C approach). The 3D loading path due to the 3C-polarization leads to multiaxial stress interaction that reduces soil strength and increases nonlinear effects. Time histories and spectral amplitudes, for the Tohoku earthquake, are numerically reproduced. The 1D-3C approach allows the evaluation of various parameters of the 3C motion and 3D stress and strain evolution all over the soil profile.

The Buyukcekmece landslide is located in Turkey, W of Istanbul, about 15 km northward from the North Anatolian Fault Zone (NAFZ) and involves upper Oligocene to lower Miocene deposits, consisting of silty clays, tuffs and sands. No earthquake-induced re-activations are testified so far but due to the high seismicity of the area (struck by the 17th August 1999 Mw 7.4 Kocaeli and by the 12th November Mw 7.2 Duzce earthquakes) it was selected as the case-study in the framework of the European project “MARSite—Marmara Supersite: new directions in seismic hazard assessment through focused Earth observation in the Marmara Supersite”. Due to the existence of several secondary scarps, the original geological setting of the sedimentary deposits is significantly modified as many counter-slope-tilted landslide sub-masses can be identified in the landslide mass. Earthquake-induced displacements of the landslide were evaluated through a characteristic-period based (CPB) approach. To this aim, a stress-strain dynamic numerical modelling was carried out using several seismic inputs with Arias intensity (AI) values ranging from 1 and 0.01 m/s and characteristic periods, Tm, ranging from 0.3 to 16.5 s. Depending on the landslide dimensions (thickness and length), characteristic periods for thicknesses (Ts) and lengths (Tl), were computed to define the corresponding ratios over Tm. The obtained results indicate that the effective characteristic period of the landslide (Tl *) corresponds to the length of a single sub-mass, and not to the total length of the landslide. Moreover, for the lowest AI values the maximum earthquake-induced displacements correspond to Tm values close to resonance period of the landslide while for higher AI values, such a 2D interaction between landslide mass and seismic waves is much more evident.

A monitoring system is operative in the Peschiera Springs slope (Central Apennines, Italy) to mitigate the landslide risk related to the hosted main drainage plant of Rome aqueducts by providing alert warning. Such a strategy allows to avoid out-of-service episodes so reducing extra-costs of water distribution management. The Peschiera Springs slope is involved in a rock mass creep characterized by an average steady strain rate of 1 mm year−1 and responsible for several landforms including sinkholes, subvertical scarps and trenches. Moreover, an average aquifer discharge of 19 m3 s−1 causes an intense limestone dissolution concentrated in correspondence with release bands and discontinuities that dislodge the jointed rock mass. Since 2008, an accelerometric network has been operating within the slope; about 1300 microseismic local events were recorded up to now, distinguished in failures and collapses. A control index, based on frequency of occurrence and cumulative energy of the recorded microseismic events was defined to provide three levels of alert. In 2013, a temporary nanoseismic Seismic Navigation System (SNS) array was installed inside a tunnel of the drainage plant to integrate the pre-existent seismic monitoring system. This array allowed to record 37 microseismic events, which locations are in good agreement with the evolutionary geological model of the ongoing gravitational slope deformation. In 2014, a permanent nanoseismic SNS array was installed in the plant and allowed to record several sequences of underground collapses including more than 500 events. The nanoseismic monitoring system is allowing to: (1) increase the detection level of the monitoring system; (2) locate hypocentres of the events; and (3) detect precursors of the strongest events.

Multi-risk management requires a strong comprehension of possible effects induced by natural hazardous events. In this regard, landslides triggering due to earthquakes results from complex interactions between seismic waves and slopes. Multidisciplinary approaches can significantly contribute to better understand such interactions. The large Büyükçekmece landslide (about 1500 m wide and 1830 m long) located in Turkey (Avcilar peninsula), about 15 km northward from the North Anatolian Fault Zone (NAFZ), was selected as case-study in the framework of the European project “MARSite – Marmara Supersite: new directions in seismic hazard assessment through focused Earth observation in the Marmara Supersite”. The Avcilar area was recently affected by the 17th August 1999 Mw 7.4 Kocaeli and by the 12th November Mw 7.2 Düzce earthquakes. The Büyükçekmece landslide involves upper Oligocene to lower Miocene deposits, consisting of silty clays, tuffs and sands. No earthquake-induced re-activations are testified so far but the landslide area was interested by a very intense urbanization during the last decade. A detailed engineering-geological model for the local seismic response of the Büyükçekmece landslide slope was constructed based on geophysical measurements, data from a multisensor in-hole monitoring system and stress-strain numerical modelling. Several tens of earthquakes were recorded from October 2014 to May 2015 in the landslide site by considering in-hole and surface data. The reliability of the local seismic response obtained by numerical modelling respect to the empirically derived one was checked in terms of both site-to-reference spectral ratios and transfer function between surface and downhole sites inside the landslide mass. The 2D numerical amplification functions confirm that the local seismic response is a consequence of the complex geological setting of the landslide slope while no relevant amplification effects can be referred to topographic features. Based on these results, the interaction between seismic waves and the Büyükçekmece landslide slope cannot be neglected to evaluate the possibility of future landslide re-activations.

International audience

International audience; In this work, we study seismic wave amplification in alluvial basins having 3D standard geometries through the Fast Multipole Boundary Element Method in the frequency domain. We investigate how much 3D amplification differs from the 1D (horizontal layering) case. Considering incident fields of plane harmonic waves, we examine the relationships between the amplification level and the most relevant physical parameters of the problem (impedance contrast, 3D aspect ratio, vertical and oblique incidence of plane waves). The FMBEM results show that the most important parameters for wave amplification are the impedance contrast and the so-called equivalent shape ratio. Using these two parameters, we derive simple rules to compute the fundamental frequency for various 3D basin shapes and the corresponding 3D/1D amplification factor for 5% damping. Effects on amplification due to 3D basin asymmetry are also studied and incorporated in the derived rules.

Seismic waves due to strong earthquakes propagating in surficial soil layers may both reduce soil stiffness and increase the energy dissipation into the soil. To investigate seismic wave amplification in such cases, past studies have been devoted to one-directional shear wave propagation in a soil column (1D-propagation) considering one motion component only (1C-polarization). Three independent purely 1C computations may be performed ('1D-1C' approach) and directly superimposed in the case of weak motions (linear behaviour). This research aims at studying local site effects by considering seismic wave propagation in a 1-D soil profile accounting for the influence of the 3-D loading path and non-linear hysteretic behaviour of the soil. In the proposed '1D-3C' approach, the three components (3C-polarization) of the incident wave are simultaneously propagated into a horizontal multilayered soil. A 3-D non-linear constitutive relation for the soil is implemented in the framework of the Finite Element Method in the time domain. The complex rheology of soils is modelled by mean of a multisurface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan type. The great advantage of this choice is that the only data needed to describe the model is the modulus reduction curve. A parametric study is carried out to characterize the changes in the seismic motion of the surficial layers due to both incident wavefield properties and soil non-linearities. The numerical simulations show a seismic response depending on several parameters such as polarization of seismic waves, material elastic and dynamic properties, as well as on the impedance contrast between layers and frequency content and oscillatory character of the input motion. The 3-D loading path due to the 3C-polarization leads to multi-axial stress interaction that reduces soil strength and increases non-linear effects. The non-linear behaviour of the soil may have beneficial or detrimental effects on the seismic response at the free surface, depending on the energy dissipation rate. Free surface time histories, stress-strain hysteresis loops and in-depth profiles of octahedral stress and strain are estimated for each soil column. The combination of three separate 1D-1C non-linear analyses is compared to the proposed 1D-3C approach, evidencing the influence of the 3C-polarization and the 3-D loading path on strong seismic motions.

On 11 May 2011, a moderate magnitude (Mw 5.1) earthquake struck the city of Lorca (SE Spain) and nearby areas, causing notable damage, injuries and fatalities. Field inspection of the area affected allowed the location and characterization of more than 250 induced landslides, mainly of disrupted type (rock/soil falls, disrupted soil slides and rock avalanches). This number was very high when compared with the inventories of previous events of similar magnitude (Mw 4.7 to 5.0) in the zone and with the results of previous models for predicting slope behavior during earthquakes. Several factors are proposed here to explain the observed differences: (i) the comparatively high magnitude (Mw 4.5) of a foreshock of the seismic series that may have weakened the slopes; (ii) the high peak ground motion values recorded for these events and (iii) the occurrence of topographic site effects. The results of this study point out the importance of including such effects as improvements in the models for studying the regional behavior of slopes.

International audience; The numerical analysis of elastic wave propagation in unbounded media may be difficult to handle due to spurious waves reflected at the model artificial boundaries. Several sophisticated techniques such as nonreflecting boundary conditions, infinite elements or absorbing layers (e.g. Perfectly Matched Layers) lead to an important reduction of such spurious reflections. In this Note, a simple and efficient absorbing layer method is proposed in the framework of the Finite Element Method. This method considers Rayleigh/Caughey damping in the absorbing layer and its principle is presented first. The efficiency of the method is then shown through 1D Finite Element simulations considering homogeneous and heterogeneous damping in the absorbing layer. 2D models are considered afterwards to assess the efficiency of the absorbing layer method for various wave types (surface waves, body waves) and incidences (normal to grazing). The method is shown to be efficient for different types of elastic waves and may thus be used for various elastodynamic problems in unbounded domains.

In this study, near-surface geophysical techniques are used to investigate the physical characteristics of the Buyukcekmece landslide (Istanbul, Turkey). The Buyukcekmece landslide has continuous activity at a low velocity and is classified as a complex mechanism. It includes rototranslational parts, several secondary scarps, several landslide terraces, and evidence of two earth flows. It mainly develops in the clayey layers of the Danismen Formation. According to our findings, P-wave velocities ranging from 300 m/s to 2400 m/s do not provide notable discrimination between sliding mass and stable soil. They show variations in blocks reflecting a complex structure. We obtained the S-wave velocity structure of the landslide up to 80 m by combining the analysis of MASW and ReMi. It is clear that S-wave velocities are lower in the landslide compared to those of the stable area. Identical S-wave velocities for the entire area at depths higher than 60 m may point out the maximum thickness of the landslide mass. Resonance frequencies obtained from the H/V analysis of the landslide area are generally higher than those of the stable area. The depths computed by using an empirical relationship between the resonance frequency and the soil thickness point out the failure surfaces from 10 to 50 m moving downslope from the landslide crown area. The resistivity values within the landslide are generally lower than 30 Ω m, i.e., a typical value for remolded clayey debris. The geophysical results reflect an overview of the geological model, but the complexity of the landslide makes it difficult to map the landslide structure in detail.

The interaction between seismic waves and slopes is an important topic to provide reliable scenarios for earthquake-(re)triggered landslides. The physical properties of seismic waves as well as slope topography and geology can significantly modify the local seismic response, influencing landslide triggering. A novel approach is here applied to two case studies in Andalusia (southern Spain) for computing the expected earthquake-induced displacements of existing landslide masses. Towards this aim, dynamic stress–strain numerical modelling was carried out using a selection of seismic signals characterized by different spectral content and energy. In situ geophysical measurements, consisting of noise records and temporary seismometric arrays, were carried out to control the numerical outputs in terms of local seismic response. The results consist of relationships between the characteristic period, Tm, of the seismic signals and the characteristic periods of the landslide masses, related to the thickness (Ts) and length (Tl), respectively. These relationships show that the larger the horizontal dimension (i.e. length of landslide) of a landslide is, the more effective the contribution (to the resulting coseismic displacement) of the long-period seismic waves is, as the maximum displacements are expected for a low Tm at each energy level of the input. On the other hand, when the local seismic response mainly depends on stratigraphy (i.e. landslide thickness), the maximum expected displacements occur close to the resonance period of the landslide, except for high-energy seismic inputs. The authors would like to thank the European Union ERDF for financial support via the “Monitorización sísmica de deslizamientos. Criterios de reactivación y alerta temprana” project of the “Programa Operativo FEDER de Andalucia 2007-2013”.

Following the Mw 6.3 L'Aquila Earthquake of 2009 April 6, the Colle di Roio village, central Italy, suffered severe building damages. The village is located on top of an elongated carbonate ridge characterized by a complex subsurface structure, a condition prone to seismic amplification due to topographic and stratigraphic effects. We address the role of the subsurface structure and topography in the ground-motion amplification observed at the ridge top. To characterize the subsurface structure of the ridge we performed geological investigations and ambient vibration measurements in single-station as well as 2-D-array configuration. Geological investigations pointed out that the ridge top is characterized by the presence of fractured rock material as a consequence of its anticlinal fold structure. Horizontal-to-vertical spectral ratio (HVSR) processing of ambient vibration records showed a broad peak in the HVSR functions in the frequency range 4-6 Hz and 2-D-array data demonstrated that locally the subsurface structure at the ridge top cannot be considered homogeneous. In summer 2009, we further installed one accelerometric station on the ridge top to experimentally evaluate the site amplification. By means of HVSR analysis of a sample of 18 weak-motion records (H/V), we found that ground-motion amplification occurs in a narrow frequency range centred around 4 Hz with mean ratio amplitude of 6. We also analysed the dependence of seismic amplification on the azimuth by calculating H/V ratios for horizontal components rotated into a range of azimuths. This analysis showed that the higher level of horizontal amplification occurs in the direction perpendicular to the ridge trending direction.With the aim of evaluating the contribution of the topography and the local subsurface structure on the observed seismic amplification, we performed 2-D finite-difference modelling of wave propagation through the ridge, adopting both homogeneous and heterogeneous models. We were able to reproduce the frequency-dependent amplification only by using an heterogeneous 2-D model with a lowvelocity layer (shear wave velocity of 400 m s-1 and maximum thickness of 20 m) at the ridge top. From the comparison between observations and numerical results, we suggest that the amplification at the Colle di Roio ridge top is due to the interplay between local shear wave velocity structure and topography, rather than to topography alone. © The Authors 2016.

T; This study is focused on evaluating local response and the earthquake-induced strains in a highly heterogeneous alluvial valley through numerical modelling approach. The case study is located S of Rome, in correspondence to the Fosso di Vallerano alluvial valley. A high-resolution engineering-geological model of the alluvial deposits that fill the valley was derived by field investigations. Several tens of borehole log-stratigraphies were also taken into account. Outputs of 1D and 2D numerical models were analysed in terms of maximum shear strain (MSS) and Shear Strain Concentration Index (SSCI) to highlight where shear strain concentrates in the engineering-geological model as well as role of lateral heterogeneities in the distribution of shear strain within the alluvial deposits. The here reported preliminary results show that earthquakeinduced strain effects: i) can be mainly referred to 2D conditions, ii) are mainly influenced by the heterogeneity of the alluvial deposits, iii) are poorly influenced by the shape of the bedrock.

La caractérisation de l’aléa sismique constitue un enjeu majeur dans le domaine du génie civil. En ingénierie des vibrations, il n’existe pas de domaine d’étude similaire bien que cette question soit décisive pour la prédiction de l’impact et de la gêne occasionnée (population, environnement, ouvrages, industrie de pointe). Cette caractérisation passe nécessairement par la connaissance des diverses sources de vibrations : exploitation des infrastructures (ferrées et routières), travaux de construction ou de rénovation (vibrofonçage, battages). Elle dépend fortement du mode de propagation des ondes mécaniques entre la source et le récepteur selon les sols (sites) et leur stratification. La nocivité des vibrations (i.e. capacité à occasionner des dégâts) dépendra donc du type de source, de la propagation, mais également de la réponse dynamique du récepteur exprimée en fonction de ses propriétés modales. Dans cet article, des simulations numériques sont combinées à des enregistrements de vibrations, liées à l’exploitation d’infrastructures ou engendrées par des chantiers. Dans l’hypothèse de sols à comportement viscoélastique et pour une configuration stratigraphique donnée, les niveaux de vibrations envisageables à la surface libre s’estiment en fonction de la distance à la source. Les enregistrements considérés permettent d’identifier des indicateurs pertinents et de proposer une classification simplifiée des sources et des sites. On combine ainsi les caractéristiques spectrales des sources (représentées par leur Transformée de Fourier) et la propagation entre la source et le récepteur au moyen d’une fonction de transfert (rapport spectral entre vibration à une distance donnée et celle au niveau de la source). La correspondance entre les propriétés spectrales des sources et celles d’un site donné est quantifiée par le facteur d’immunité (IMF) indépendamment du récepteur à considérer. Cette quantification représente l’ « aléa vibratoire » qui indique le niveau vibratoire attendu en entrée au niveau du récepteur. Ceci est similaire à la définition de l’aléa sismique utilisée dans l’Eurocode 8 pour les études de dimensionnement et renforcement sismique. En utilisant les paramètres comme le gradient de vitesse et le contenu spectral des enregistrements, les effets induits ont été analysés pour de multiples sources. Des indicateurs pertinents (vitesse moyenne à faible profondeur et gradient de vitesse) sont introduits afin de proposer une classification simplifiée de l’aléa vibratoire pour les différentes sources considérées. En cas d’absence de mesure pour une source et un site donnés, cette classification empirique pourra être utilisée afin d’estimer le niveau vibratoire attendu en entrée d’un récepteur.

The Peschiera Springs slope (RI), which hosts the drainage plant of the Rome's aqueduct, is affected by a gravitational slope deformation process, that is responsible for a rock-mass lateral spreading, associated to several landforms including sinkholes, subvertical scarps and trenches. An experiment, based on an innovative method of monitoring, was carried out to record microseismic events generated by underground instabilities such as failures and collapses. At this aim a SNS (Seismic Navigation System) array was installed during the year 2013 inside a the tunnel of the drainage plant in order to carry out a continuous monitoring. The nanoseismic monitoring, allowed to record 37 microseismic events. The seismic records were managed by NanoseismicSuite software that allowed to identify and characterize two different typologies of events: 19 underground collapses and 18 underground failures. The locations of these events are in good agreement with the evolutionary geological model of the ongoing gravitational slope deformation, i.e. with the spatial distribution of the main trenches and scarps on the slope. © Società Geologica Italiana, Roma 2015.

Following the seismic microzonation studies of the L’Aquila area, Central Italy, hit by the Mw 6.3 L’Aquila earthquake of 6th April 2009, we observed ground motion amplification at the hilltop of the Colle di Roio limestone ridge. In particular, horizontal-to-vertical spectral ratio amplitude of weak motion waveforms showed average peak level above 5 in the frequency range 4-5 Hz. In order to evaluate the contribution of topography and subsoil heterogeneity on the observed response, we performed 2D numerical simulations of wave propagation through the ridge using a finite difference approach. Different hypothesis of model configuration, consistent with the available geological data, were tested. A homogeneous model was considered to evaluate the effect of surface topography on ground motion amplification, while several heterogeneous models were considered in order to examine the interaction between topography and heterogeneity on the seismic response. Results were analyzed in terms of synthetic horizontal-to-vertical (H/V) spectral ratios and the latter were compared to the observed ones. The results showed that the observed ground motion amplification level cannot be explained only by surface topography effect and that the assumption of an heterogeneous model with complex inner geometry may fairly reproduce the observations. © Springer International Publishing Switzerland 2015.

The SERIES project “Experimental and Numerical Investigations of Nonlinearity in soils using Advanced Laboratory-Scaled models” (ENINALS) was focused on the centrifuge modeling of seismically-induced strains vs. stratigraphic features and it was applied to the heterogeneous alluvia of the Tiber River in the Rome historical centre. Four soil samples, representing two homogeneous soil columns (only clay and only sand respectively) and two heterogeneous soil columns (including a clay level between two sand ones) were tested in the IFSTTAR centrifuge. The applied dynamic input represents the maximum expected seismic action in Rome and it was reproduced at the centrifuge shaking device following three approaches: (i) a natural time history, (ii) an equivalent sinusoidal signal, and (iii) a multifrequential equivalent signal derived by the recently proposed LEMA_DES approach. The here reported preliminary results: (i) demonstrate the reliability of a “cut and install” procedure for realizing the saturated multilayer samples; (ii) give new insights on the reliability of multifrequencial dynamic equivalent signals for scale-reduced analogical modeling.

Regional and teleseismic earthquakes can induce displacements along joints in a landslideinvolved rocky slope in Central Italy. The rarity of these effects is due to specific physical properties of the seismic signals associated with: (i) the energy content, (ii) the distribution of relative energy and peak of ground acceleration related to the ground motion components and (iii) the spectral amplitude distribution in the frequency domain; these properties allow the triggering earthquakes to be distinguished from the others. The observed effects are relevant when compared to the direction of the landslide movement and the dimensions of the involved rock mass volume. The landslide movement is less constrained in the direction parallel to the dip of the slope and the landslide dimensions are associated with characteristic periods that control the landslide deformational response in relation to the spectral content of the ground motion. The earthquake-induced displacements are significant because they have the same order of magnitude as the average annual cumulative displacement based on a decade of strain measurements within the slope. © The Author 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society.

A novel unconventional pseudostatic analysis is proposed here to infer on the sensitivity of a landslide to earthquakes characterized by different physical properties. Several sine waves with different amplitudes, frequencies and phases were applied to the landslide mass assuming limit equilibrium conditions. The unconventional approach was used for the Diezma landslide case study. The landslide is located 25 km from the city of Granada (Spain). Although the slope had repeatedly suffered small-scale stability problems since the construction of the A-92 highway, a larger failure occurred on 18 March 2001 and damaged the highway between kilometers 272.6 and 272.8. The landslide had an estimated volume of 1.2 Mm3 and involved a disordered deposit of silt and clay with heterometric blocks within the Numidoide Formation, which outcrops along the contact between the Malaguide and Dorsal domains of the Betic Cordillera mountain range. Despite the 18 million Euros spent since 1999 on geotechnical investigations and stabilization solutions, the numerous reactivations that occurred through 2010 and 2013 demonstrate the persistent activity of the landslide. The geometry of the large slope failure corresponding to the first activation of the Diezma landslide was used to back-analyze the stability of the slope based on a high-resolution engineering-geological model. The model was developed from the analysis of numerous borehole logs as well as from geophysical investigations consisting of seismic noise measurements. The results demonstrate that the safety factor (SF) of the Diezma landslide varies significantly for frequencies less than 1 Hz; moreover, unstable conditions are reached at frequency values between 0.5 and 1 Hz for water pressure distributions corresponding to Bishop factors (ru) between 0 and 0.36. To estimate the co-seismic displacements, the geometrical and mechanical properties of the landslide mass were used to derive its characteristic periods for thickness (Ts) and length (Tl), which were compared with the characteristic period of the earthquake (Tm). The results indicate that the maximum expected co-seismic displacements are up to 2 m for an earthquake with a Tm value close to 1 s and an Arias Intensity on the order of 1 m/s.

In the framework of a Project issued by the Italian National Institute of Geophysics and Volcanology (INGV) a Research Unit (RU) has been granted with the commitment to provide a link between the seismic shaking and the triggering of ground failures such as liquefaction. The main goals have regarded both the enlargement of the base of observables for a better constrain of the seismic hazard assessments and the analysis of the triggering and causative factors of permanent ground deformations. Nevertheless, when analyzing the non-linear soil response under which liquefaction occur, some insights into site-effects have been also provided, thus contributing to the general task of the site-specific hazard. The paper illustrates the analyses and investigations carried out within the aim of the project, some of them are still provisional due to the huge amount of data produced and the strong effort required to analyze all the matters related to the observed phenomena.