The complexity of the geological setting of the Italian peninsula implies variable site conditions affecting seismic hazard. Their extensive mapping is needed for a reliable assessment of the induced risk on residential areas, industrial agglomerations, infrastructures, strategic sites, cultural heritage spread on the entire national territory. The research meets the need for a national reference map providing co-seismic ground deformation at the scale of interest of land use planning and bridging the information gap now existing among the urbanized areas covered by seismic microzonation studies. The project aims at defining a multidisciplinary procedure for a multiscale mapping of the local seismic hazard of Italy, exploiting the potentialities of having spatially extensive information for combining site-specific to regional estimates of site effects. The key elements are: i) full exploitation of geological/geomorphological data, ii) extensive numerical modelling, and iii) empirical testing of local hazard estimates. The study deals with the regional scale analysis and classification of the landscape and the geological-technical properties of the near-surface stratigraphic configurations (GeoMorpho-Stratigraphic Units, GMSUs), which affect seismic hazard.  The GMSUs are obtained by combining geomorphological analysis and automated landscape classification procedures, field-based lithostratigraphic constraints, instrumental signatures from geophysical investigations, and geotechnical parameters. Distinct parameterizations will be assessed for each GMSUs to feed simplified numerical models to quantify synthetic hazard indicators suitable for risk evaluations and land use planning. Outcomes will be managed through a coherent probabilistic approach to bound relevant uncertainty as a function of locally available data. Outcomes will be tested by considering site-specific analyses.

How to cite: Albarello, D.: Assessing seismic site effects at regional scale: the SERENA research project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3611, https://doi.org/10.5194/egusphere-egu24-3611, 2024.

It is widely recognized that the amplification of ground motion during earthquakes is attributed to the interference of seismic waves trapped between the free surface and impedance contrasts in the shallow subsoil. Seismic Microzonation (SM) studies are devoted to evaluating these site effects, but their application in wider contexts is a hard and expensive task. To estimate seismic site effects at regional scale, the most viable approach is to utilize detailed geological and geomorphological data (1:10.000-1:50.000), which are available for large part of Italy.

In the frame of the national research project “SERENA”, in this study a procedure is proposed and tested to constrain entity of 1D seismostratigraphical ground motion amplification based on geological information at the most detailed scale available. In particular, amplification factors are estimated for Seismically Homogeneous Microzones (SHM) defined on the basis geological information. Each SHM is represented as a stack flat homogeneous layers each characterized in terms of engineering-geological units by following the seismic microzonation standards. Seismic properties of each layer (shear waves velocity, density, damping and G/G0 curves) and respective range of variability are determined on the basis of the most recent literature.

This information feeds a linear equivalent numerical approach and the Inverse Random Vibration Theory to compute the expected seismic response at each SHM. To account for the relevant uncertainty, 100 random profiles were generated for each SHM, which were compatible with available data. Outcomes of the relevant numerical simulations were considered to assess uncertainty affecting amplification estimates at each SHM.

Through this procedure, approximately 4000 SHM were identified, distributed across over 80,000 formation outcrops mapped on Geological map of Tuscany Region, selected by dedicated ArcgisPro ^TM/Arcpy ^TM scripts elaborated for this aim. The 50th percentile of the amplification factor distribution for each SHM was taken into consideration. This process aimed to create a new map of amplification factors for the entire territory of Tuscany, achieving an optimal spatial resolution of 1:10,000.

To assess the reliability of the results obtained from numerical simulations, and evaluate the possible presence of biases, outcomes of the numerical procedure here considered  were compared with those from second and third levels of Seismic Microzonation studies available in Tuscany. Approximately 1500 benchmark samples were identified, revealing distinct trends among various SHM, particularly between those with outcropping sedimentary covers and those with exposed geological bedrock.

In general, amplification estimates provided by the approach here proposed provide a slight overestimate of the ones provided by the detailed seismic microzonation studies (less than 10% on average). However, this overestimate is largely within the range of uncertainty affecting regional estimates and mostly concern SHMs where bedrock outcrops.

It is worth to note that by no way the proposed approach should be considered as substitute of detailed local studies. Anyway it could be considered to provide ex-ante evaluations to be used as a preliminary reference for large scale risk analysis and for a preliminary assessment of expected ground motion effects where more detailed studies are not available so far.

How to cite: Carfagna, N., Pieruccini, P., Fantozzi, P. L., and Albarello, D.: Mapping seismostratigraphical amplification effects at regional scale from geological data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3608, https://doi.org/10.5194/egusphere-egu24-3608, 2024.

The Italian seismic code (NTC18) provides indications about the expected effects of some morphological configurations on the expected ground motion during earthquakes. In particular, two main 2D morphologies are identified as reference: cliffs and crests. Based on numerical simulations, the value of St is assumed to depend on the steepness of the cliffs and aspect ratio of the crest. A critical aspect of these estimates is that the considered configurations are defined in terms of steepness angles and aspect ratios, without any scale indication. Moreover, the considered morphologies are very schematic, and this prevents their simple application in the natural context: in most case an expert judgement is necessary, and this makes the final estimates potentially controversial and difficult to validate on the basis of empirical observations. To face this problem, in the frame of the PRIN project “SERENA”, a procedure has been developed for the automatic identification of areas prone to morphological amplification effects by following NTC18 prescriptions,  based on the Digital Terrain Model. The proposed approach allows the full exploitation of topographical data at the maximum resolution available. After a first application to restricted areas, the proposed procedure has been applied at National scale at the seismometric and accelerometric sites managed by INGV. The aim is twofold: first comparing outcomes of the new approach with the ones proposed by other Authors at the same sites, second to provide a sound basis of a coherent and reproducible estimate of St values to be compared with possible empirical evidence. In the presentation, the results obtained about the first aim will be presented and discussed.

How to cite: Ariano, M., Fantozzi, P. L., and Albarello, D.: A systematic analysis at stations of the Italian seismic network to test the role of local topographic effect., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3606, https://doi.org/10.5194/egusphere-egu24-3606, 2024.

During earthquakes, a high degree of spatial variation in damage distribution, encompassing both structural damage to buildings and co-seismic landslides, is commonly observed in mountainous regions near the seismic source. Among other factors, this spatial variability can be partly attributed to the amplification of seismic waves caused by surface topography. Our study focuses on predicting ground-motion amplification due to topography in close proximity to earthquakes and examining its potential influence on co-seismic landslide distribution patterns.

To achieve this goal, we employ neural network analysis on previously available synthetic data from 3D finite-differences simulations of seismic wave propagation. The analysis aims at developing a physics-based estimator of topographic site effects in close distances to the source, referred to as the i-FSC proxy (Illuminated Frequency Scaled Curvature). This proxy depends on the S-wavelength, the curvature of the topographic surface, and a new parameter called the "normalized seismic illumination angle", which quantifies the slope's exposure to the incoming wavefield. The inclusion of the illumination parameter substantially decreases the uncertainties of the proxy by a factor of 2 compared to estimators that rely solely on curvature as a key parameter. The i-FSC proxy is a user-friendly tool that does not require high computational resources; it utilizes only a digital elevation map and the position of the seismic source to predict amplification factors at any point on the surface topography. This estimator allows exploring the spatial variations in topographic amplification caused by nearby seismic sources, representing a significant breakthrough as areas closest to the fault typically sustain the most damage during earthquakes.

Subsequently, the i-FSC proxy is used to investigate the correlation between ground-motion amplification and the spatial distribution of earthquake-induced landslides triggered by large events such as the 2015 Gorkha earthquake (M_W 7.8). The results indicate that more than 71% of co-seismic landslides tend to be localized in amplified areas. Different physical controls on the landslide triggering at different frequencies have been identified. The results also highlight the crucial importance of considering the effect of topographic amplification, together with other classical factors such as slope steepness, for a better understanding of the complex mechanisms governing the spatial distribution of earthquake-induced landslides at local and regional scales. The obtained results could provide valuable insights for future researches, guiding efforts towards more effective risk assessment and mitigation strategies in mountainous regions.

How to cite: Bou Nassif, A., Maufroy, E., Lacroix, P., Chaljub, E., Causse, M., Marc, O., and Bard, P.-Y.: The i-FSC proxy for predicting near-source topographic site effects and studying earthquake-induced landslide distributions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12861, https://doi.org/10.5194/egusphere-egu24-12861, 2024.

The Outer Western Carpathians, situated in the central European segment of the Alpine-Himalayan orogenic zone, present an intriguing case of an accretionary wedge. This region is characterized by Mesozoic and Cenozoic flysch sedimentary rocks, comprising massive sandstone benches and intercalated clay layers. These formations have undergone significant deformation, including being thrust over the European foreland during the Paleogene and Neogene periods. The resulting hilly to mountainous terrain exhibits notable slope failures. Here we focused on the phenomenon of under-dip toppling –sandstone beds steeply dipping in the direction of the slope, which were locally overturned along systems of brittle fractures. Utilizing high-resolution LiDAR data, our study investigates the locations, geometrical characteristics, and tectonic settings of these toppling. In the Javorníky Mountains, these topples predominantly occur in SSE-dipping fold limbs, an orientation conducive to under-dip toppling. The mechanism of under-dip toppling, involving the lifting of the center of gravity of the toppled layers, presents a complex geomechanical challenge. Recent field investigations, including structural measurements on faults, electrical resistivity tomography (ERT) profiles, and ¹⁰Be dating, have identified active polyphase strike-slip surface ruptures in the region. These findings raise questions about the origins of toppling and their implications for understanding paleo-earthquakes in the area. Our preliminary analysis suggests a two-tiered approach to understanding toppling processes: firstly, exploring the deeper structural implications – could active tectonic faulting be the cause of the under-dip toppling? Secondly, we analyzed the mechanism of toppling near to the surface. By analyzing the geometry of near-surface persistent sandstone slabs and employing Pseudo-static analysis to assess seismic slope response, our results indicate that the layer while overturned may be attributed to strong paleo-seismic events. This study employs comprehensive site investigations and back analyses to understand a range of possible trigger and controlling mechanisms. It elucidates the geological conditions of slopes and performs a geomechanical analysis of under-dip toppling.

The research is part of the international bi-lateral project “Earthquake triggered landslides in recently active and stabilized accretionary wedges”, supported by the Czech Science Foundation (GAČR 22-24206J) and the Taiwanese Ministry of Science and Technology (NTSC 111-2923-M-008-006-MY3).

How to cite: Nguyễn, T.-T., Baroň, I., Dong, J.-J., Melichar, R., Hartvich, F., Klimeš, J., Černý, J., Šutjak, M., Kociánová, L., Dušek, V., Rowberry, M., Braucher, R., Tomasz, G., Hu, J.-C., Tseng, C.-H., Chen, Y.-C., and Lin, C.-H.: Under-Dip Toppling in the Outer Western Carpathians: Insight into Investigation of Slope Failures and Implication of Paleo-Seismic Activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2337, https://doi.org/10.5194/egusphere-egu24-2337, 2024.

Several studies have suggested that directions of earthquake-triggered landslides might be preferentially oriented according to the seismic waves’ characteristics.  Here we further address this issue by analyzing three landslide populations attributed to 1998 Ruei-Li Mw 6.5, 1999 Chi-Chi Mw 7.3 and 2022 Taitung Mw 6.9 earthquakes in Taiwan. In particular, we seek possible linkages between the patterns of co-seismic landsliding (predominant orientations) and the epicenter and fault rupture locations, by exploiting the assumption that surface waves with horizontal particle motions (Love waves) and horizontal shear waves, both characterized by transverse vibrations perpendicular to the direction of wave radiation from the source, are the major agents responsible for earthquake induced slope failures.

First, we take the aspect of each landslide source zone as representing the landslide directions. These directions are then statistically evaluated with respect to the epicentre and fault rupture positions for the characteristic segments of the landslide population. In the next step, we consider numerous possible pairs of the landslides to obtain intersections of the lines normal to their aspect directions using custom-designed Python code.

At each particular landslide population segment, the landslide displacement directions revealed slight preferential orientation with the maxima sub-perpendicular to the fault rupture. Symmetrically distributed and round landslide population of the Ruei-Li earthquake showed even better results than elongated landslide population of the Chi-Chi earthquake. In all three earthquake cases, the intersections maxima coincided with the maximum slip velocities and/or displacements along the fault ruptures, as revealed by GNSS. These promising results indicate that such an approach might be useful for identifying fault ruptures of old or even prehistoric earthquakes.   

The research was funded by the Grant Agency of the Czech Republic (GC22-24206J) and Taiwanese National Technological and Science Council (MOST/NTSC 111-2923-M-008-006-MY3).

How to cite: Baroň, I., Shen, K.-T., Dong, J.-J., Tseng, C.-H., Yang, C.-M., Wasowski, J., Jelének, J., Klimeš, J., Chen, Y.-C., Lee, C.-T., and Gao, J.-Q.: Co-seismic landslide directions may help identifying earthquake fault ruptures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7738, https://doi.org/10.5194/egusphere-egu24-7738, 2024.

Landslides often occur as a consequence of natural hazards among which earthquakes are one of the main triggering factors. The effects of earthquake-induced ground shaking are often sufficient to cause the failure of slopes that were marginally to moderately stable before the earthquake. In this study, we define screening maps for Italy that classify sites in terms of their potentiality of triggering earthquake-induced landslides based on seismic hazard. To this end, we analyze seismic hazard maps and hazard disaggregation results on a national scale. First, as instabilities occur for acceleration values exceeding critical acceleration, we compare surface peak ground acceleration values derived from national hazard maps with critical acceleration thresholds proposed in the scientific literature. Then, magnitude-distance (M-R) scenarios from hazard disaggregation are analyzed in relation to upper-bound M-R curves for seismic landslide triggering. Landslide triggering can not be discounted if the value of the source-to-site distance R associated with magnitude M is lower than the reference upper-bound value and surface peak ground acceleration exceeds a given critical acceleration value.

Most of the work concerns the analysis of hazard disaggregation results to define the controlling M-R scenarios. First, joint probability mass functions (PMFs) of magnitude and distance are analyzed to identify all modal scenarios (i.e., local maxima). To this end, we treat each PMF as an image and apply morphological image processing techniques to find local maxima. Specifically, the maximum (dilation) filter operation is applied. Local maxima are detected by checking for element-wise equality between the original and filtered matrices. Then, for each computation node, mean and modal M-R scenarios are compared to upper-bound M-R curves for earthquake-induced landslides selected from the scientific literature and the preferred M-R pair is selected as follows:

• if all M-R pairs stand above the reference upper-bound curve, then the triggering of earthquake-induced landslides can be neglected.
• if at least one M-R pair is below the reference upper-bound curve, then the triggering of earthquake-induced landslides can not be discounted.
• if more than one M-R pair lies below the reference upper-bound curve, then the triggering of earthquake-induced landslides can not be excluded and the M-R scenario that contributes the most to the hazard (i.e., the M-R pair with the largest PMF value) is selected as the preferred magnitude.

As sites respond at specific characteristic frequencies (depending on local geological characteristics) and disaggregation results may vary with response period (T), the previous procedure is repeated considering disaggregation results associated with different spectral periods (i.e., spectral acceleration for different response periods). This allows us to define the controlling M-R pair for each site in relation to geological conditions (through site classification).

The entire workflow is replicated for three types of landslides (disrupted slides and falls, coherent slides, and lateral spreads and flows), thus leading to three maps that show areas in Italy where the triggering of landslides due to seismic activity can not be excluded. The reliability of our results is finally checked by comparing them with observations of past seismic landslides in Italy.

How to cite: Barani, S., Azhideh, S., Ferretti, G., Pepe, G., and Scafidi, D.: Evaluation of the triggering potential of seismic landslides in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13036, https://doi.org/10.5194/egusphere-egu24-13036, 2024.

The North East Region (NER) of India is a Tectonically Active Zone with Noteworthy Intraplate Seismic Activity over the Past 200 Years. The tectonics and seismicity of large intraplate earthquakes in NER are poorly understood. As a result, the Kopili Fault (KF) has a complex tectonic setting with a history of past two large earthquakes of 1869 Cachar earthquake (M_w-7.4) and 1943 Hajoi earthquake (M_w-7.2) are being observed. Paleoseismological evidence reveals valuable insights into seismic hazard and the historical occurrence of earthquakes, as manifested in preserved liquefaction features. Field studies carried out by excavating trenches in five sites have uncovered secondary evidence of significant liquefaction-induced deformation features, known as seismites, occurring at a depth of approximately 2-3 meters below the surface. These features manifest as sand dykes and sills, exhibiting variations in colour, grain size, and sediment indurations across the sites. The findings from the excavated trenches have been summarized, incorporating multiple analyses to differentiate the seismites from depositional features. To aid in this distinction, the study utilized the Anisotropy of Magnetic Susceptibility (AMS) technique.

The stereographic projection and bootstrap plots for the host sediment at the NB site clearly depict a vertical orientation for Kmin, while Kint and Kmax are distributed around the horizontal plane, indicative of sediment formation through fluvial activity. In the doublet liquefaction dykes NBRD and NBLD, all three axes exhibit random scattering. Notably, Kmin is sub-vertical, and Kmax is sub-horizontal in the southeast direction. The Degree of Anisotropy (Pj), Lineation (L), and Shape parameter (T) plots for the host specimen fall within the oblate field, whereas liquefaction dykes exhibit a distribution ranging from prolate to triaxial. In our presentation, we delve into a detailed discussion on how Anisotropy of Magnetic Susceptibility (AMS) serves as a valuable tool for comprehending seismite behavior and their occurrences, particularly in relation to large to great earthquakes.

Understanding the tectonic and seismic characteristics of the Kopili Fault is crucial for assessing and managing earthquake risk in Northeastern India. Our studies will likely contribute to improved earthquake preparedness and resilience in the region for future prospecting.

How to cite: md., M. B., b.v., L., v.m., R., k., D., s.n., P., and s., P.: Examining Seismites using Anisotropy of magnetic susceptibility in and around the Kopili Fault Zone, Northeast India: A Characterization Study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15852, https://doi.org/10.5194/egusphere-egu24-15852, 2024.

NaTech events define the interaction between natural hazards and industrial accidents leading to major fires, explosions or toxic releases where hazardous substances are involved. Among NaTech events, earthquake is one of the most important, because it affects the entire plant and can cause simultaneous damage to different equipment. This study evaluates the local seismic response at the Bussi MHIP Chemical Company, located in Abruzzo region (Central Italy). It is a representative Major-Hazard Industrial Plant (MHIP) subject to Italian standard Decree (D.Lgs. 105/2015; Directive 2012/18/EC - Seveso III), which requires a multidisciplinary approach, given the high complexity of the problem and the numerous types of equipment. We focus on the EURECO plant, located inside the Bussi MHIP, which is featured by high seismicity with potential seismic amplification phenomena due to its complex geo-lithological setting. In the present framework, the influence of soil profile properties under the EURECO plant is investigated through a stochastic site response analysis. We aim to conduct a sensitivity analysis to assess the amplification factor (AF) variability with the randomness of soil properties and geological setting. The implementation of a geological reference model was supported by building a geo-database based on 125 collected boreholes stratigraphies, which identify the main lithological units and their spatial relationships. The limited availability of deep boreholes led to the adoption of other 110 virtual boreholes, where lithological column was extrapolated from stratigraphic sections, geological maps and information from the literature. This approach allowed us to integrate and combine actual with virtual subsurface data, through expert interpretation. Soil properties were collected from a review of relevant literature and previous Seismic Microzonation studies of geologically compatible areas. From this collection, we derived physical (e.g., g, Vs) and dynamic (e.g., shear modulus G/G0, damping D) properties for each soil type. In this study, the shear modulus and damping curves proposed by Darandeli (2001) and modified by Gaudiosi (2023) were applied to each soil type. The geotechnical properties and the variability associated with their distributions have a high impact on the seismic response of a site.  From the geological model, we defined the range of variability of the parameters associated with each seismic unit (e.g. Vs shear waves, bedrock depth, geomechanical properties). We assumed two scenarios in the ultimate conditions of the plant, the Safe Life State (SLV) and the Collapse Limit State (SLC) according to the National Building Code (NTC2018). The seismic inputs were selected using the Probabilistic Seismic Hazard Analysis (PSHA) approach. We performed numerical simulations of 1D – 1D stochastic -2D site response to take into account the influence of the variability of soil parameters and selected seismic input on amplification factor (AF). The development of a seismic response analysis for each simulation allowed us to calculate the AF for the EURECO plant within the estimated fundamental period of vibration of a specific H₂0₂ storage tank located inside it. The simulated seismic scenarios could involve the overturning of the storage tank, leading to fires or the release of toxic substances.

How to cite: Berardo, G., Giannini, L. M., Marino, A., and Scarascia Mugnozza, G.: Probabilistic modelling of soil properties variability for local seismic response analysis in NaTech events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18376, https://doi.org/10.5194/egusphere-egu24-18376, 2024.