Stochastic approach to study the site response in presence of shear wave velocity inversion: Application to seismic microzonation studies in Italy

Fabozzi, Stefania; Catalano, Stefano; Falcone, Gaetano; Naso, Giuseppe; Pagliaroli, Alessandro; Peronace, Edoardo; Porchia, Attilio; Romagnoli, Gino; Moscatelli, Massimiliano

doi:10.1016/j.enggeo.2020.105914

Cited by 18 publications

(10 citation statements)

References 30 publications

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“…Finally, as already mentioned in §1, the applicability of the proposed methodology is limited to lithostratigraphic alternations exhibiting internal contrast of impedance comparable with ones considered in the present work (≤150 m/s). Thus it is not applicable in presence of higher contrast of impedance as, for example, in the case of marine and fluvial terraces, alluvial and coastal plains, intermountain basins, cliffs and lava rock layers where the contrast of impedance plays a not negligible rule as observed in Fabozzi et al, 2021.…”

Section: Discussionmentioning

confidence: 99%

The possible use of equivalent homogeneous subsoil models for 1D seismic response analyses in seismic microzonation studies

Fabozzi

Albarello

Pagliaroli

et al. 2022

Bull Earthquake Eng

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The possibility is here explored to use an 'equivalent' homogeneous configuration to simulate 1D seismic response of heterogeneous engineering-geological bodies when relatively weak seismic impedance contrasts (≤150 m/s) only exist above the seismic bedrock. This equivalent configuration is obtained by considering an equivalent Vs value the harmonic average of the actual Vs values and a linear combination of G/G0 and D curves relative to the lithotechnical components present in the actual configuration. To evaluate feasibility of this approach, a wide set of numerical simulations was carried out by randomly generating subsoil layering including sequences of alternating thin layers of geotechnical units (e.g., sands and clays) each characterized by a characteristic nonlinear curve. Outcomes of these simulations are compared with those provided by considering a single homogeneous layer characterized by equivalent nonlinear curves obtained as a weighted average of the original curves. By comparing the heterogeneous and the homogeneous columns seismic response in terms of amplification factors and fundamental period, the results confirm the possibility to model a 1D column characterized by a generic lithostratigraphic succession with an equivalent one without introducing significative errors that, at least for the studied cases, do not exceed the 6%. This conclusion is substantially confirmed by extending the comparison to a real case, i.e. the 113 m-thick heterogeneous soil profile at Mirandola site (Norther Italy), presented in the last part. INTRODUCTIONAccounting for nonlinear behavior of soil under dynamic loads is necessary to provide a consistent modelling of local seismic response during strong earthquakes (Kramer, 1996). Two methods of analysis can essentially be chosen to this purpose: equivalent linear, based on a series of iterative analyses assuming a visco-elastic soil behavior, or a true nonlinear approach, this latter involving a broad range of simplified (i.e., hyperbolic family models) and advanced soil constitutive models (Hashash et al., 2010). The nonlinear curves, i.e. the normalized shear modulus (G/G0-g) and the damping ratio (D-g) curves, are directly employed in the equivalent linear strategy or used to calibrate the constitutive parameters in the true nonlinear approach. In the Seismic Microzonation (SM) studies the equivalent linear analysis is still the preferred approach because the limited data generally available on cyclic behavior as well as the large number of numerical simulations to be carried out (Pagliaroli, 2018). A crucial step in these analyses is defining variation of shear modulus and damping ratio when excitation strength increases (G/G0-g and D-g curves). These can be obtained ad hoc from laboratory

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Section: Discussionmentioning

confidence: 99%

The possible use of equivalent homogeneous subsoil models for 1D seismic response analyses in seismic microzonation studies

Fabozzi

Albarello

Pagliaroli

et al. 2022

Bull Earthquake Eng

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“…Motion characteristics close to the natural frequency of the soil, also depending on the velocity of stratified soil deposits, are considered another explanation for soil amplification (Kramer, 1996). Fabozzi et al (2021) stated that the shear wave velocity of the soil profiles generally increases with depth due to cementation, age of soil deposit and overburden stress. However, the seismic response distribution is associated with the uncertainties of soil properties, including the soil profile, which in some studies is defined as epistemic uncertainty in soil parameters (Boushehri et al, 2022).…”

Section: Resultsmentioning

confidence: 99%

“…Fabozzi et al. (2021) stated that the shear wave velocity of the soil profiles generally increases with depth due to cementation, age of soil deposit and overburden stress. However, the seismic response distribution is associated with the uncertainties of soil properties, including the soil profile, which in some studies is defined as epistemic uncertainty in soil parameters (Boushehri et al., 2022).…”

Section: Resultsmentioning

confidence: 99%

Influence of input motion and surface layer properties on seismic site response: A stochastic simulation method–based MLR model

Yıldız

2023

Near Surface Geophysics

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Seismic site response analyses are simulations in which the effects of geological conditions on seismic waves are examined. The uncertainties that make these analyses crucial are defined as the source of motion, the travel path of seismic waves, and geological conditions. In this study, a series of non-linear seismic response analyses were performed using data from site investigation studies. The results of non-linear analyses performed under earthquakes with different characteristics based on real soil data were investigated in terms of acceleration time histories and response spectra. The relationship between site response with the surface layer properties and input motion properties used in the simulations was examined in a parametrical manner. Based on the results obtained, Monte Carlo simulation, which is a stochastic data simulation method, was performed. Additionally, multiple regression and variance analysis (ANOVA) was performed on the dataset created by both site response analysis and stochastic simulations. The MLR model displayed highly accurate results with a coefficient of determination, R 2 of 0.9763, and a standard error of 0.109. The efficiency level of the independent variables used as input parameters in the simulations on the dependent variable, AF was examined. It was revealed that the coefficient of lateral earth pressure at rest (K o ), earthquake motion (i.e., PGA of input motion) and surface layer thickness (d surface ) from the soil properties had the highest effect on the amplification factor.

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“…In this way, a reconnaissance of possible critical zones that need a more detailed and site-specific analysis can be accomplished. However, the basic hypotheses of the present study -that constrain the use of the proposed charts to a specific field of applicability -should be here underlined: i) the charts are valid for cavities with approximate flat roof, which are the most widespread in urban areas, hence their applications to arch roof could lead to an underestimation of FoS; ii) the charts are valid in presence of cavity excavated into a homogeneous lithotype rock, therefore they are not strictly applicable in presence of multiple lithotypes that may imply different site effects [15]. Any simplification in the use of the proposed charts outside the hypotheses under which they were obtained, can reduces their reliability.…”

Section: Methodsmentioning

confidence: 99%

Seismic Vulnerability of Shallow Underground Cavities in Soft Rock

Fabozzi¹,

Silva²,

Nocentini³

et al. 2021

Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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The instability risk of underground cavities is issue of concern particularly for areas densely urbanized as the case of many historical centers in Italy. Among the possible causes of the cavity damages up to collapse, the proposed work considers a particular triggering factor that is the dynamic loading induced by an earthquake. Thus, the seismic vulnerability of shallow cavities in soft rock is addressed by proposing a methodology based on an extensive parametric two-dimensional finite element analysis. The proposed methodology is extended to a significant number of realistic cases, considering the effect of the variability of some predisposing and triggering factors on the cavity stability like roof thickness and cavity width, presence of overburden on the top of the rock layer, seismic signal intensity. The seismic vulnerability of the studied cases is assessed through the minimum Factor of Safety calculated during the whole length of the dynamic analysis. Finally, the results of the parametric study are rearranged into 'seismic stability charts for cavities in soft rock' proposed to be adopted as preliminary level of screening, to assess the seismic vulnerability of shallow underground cavities in soft rock. The results of screening enable to identify the critical zones that need a detailed analysis, in consideration of their possible interaction with above-ground structures, infrastructures and human activities.

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Stochastic approach to study the site response in presence of shear wave velocity inversion: Application to seismic microzonation studies in Italy

Cited by 18 publications

References 30 publications

The possible use of equivalent homogeneous subsoil models for 1D seismic response analyses in seismic microzonation studies

The possible use of equivalent homogeneous subsoil models for 1D seismic response analyses in seismic microzonation studies

Influence of input motion and surface layer properties on seismic site response: A stochastic simulation method–based MLR model

Seismic Vulnerability of Shallow Underground Cavities in Soft Rock

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