Stavroula Fotopoulou

Recommendations for the quantitative analysis of landslide risk

This paper presents recommended methodologies for the quantitative analysis of landslide hazard, vulnerability and risk at different spatial scales (site-specific, local, regional and national), as well as for the verification and validation of the results. The methodologies described focus on the evaluation of the probabilities of occurrence of different landslide types with certain characteristics. Methods used to determine the spatial distribution of landslide intensity, the characterisation of the elements at risk, the assessment of the potential degree of damage and the quantification of the vulnerability of the elements at risk, and those used to perform the quantitative risk analysis are also described. The paper is intended for use by scientists and practising engineers, geologists and other landslide experts.

Vulnerability assessment for reinforced concrete buildings exposed to landslides

The methodologies available for the analytical quantification of the vulnerability of buildings which are subject to actions resulting from slope instabilities and landslides are relatively limited in comparison with other components of quantitative landslide risk assessment. This paper provides a general methodology for calculating the vulnerabilities of reinforced concrete frame structures that are subject to three types of slope instability: slow-moving landslides, rapid flow-type slides and rockfalls. The vulnerability is expressed using sets of fragility curves. A description of the general framework and of the specialised procedures employed is presented here, separately for each landslide mechanism, through the example of a single-bay one-storey reinforced concrete frame. The properties of the frame are taken into account as variables with associated uncertainties. The derived vulnerability curves presented here can be used directly by risk assessment practitioners without having to repeat the procedure, given the expected range of landslide intensities and for similar building typologies and ranges of structural characteristics. This permits the applicability of the calculated vulnerability to a wide variety of similar frames for a range of landslide intensity parameters.

Vulnerability assessment of reinforced concrete buildings subjected to seismically triggered slow-moving earth slides

The objective of this paper is to develop an efficient analytical method for assessing the vulnerability of low-rise reinforced concrete buildings subjected to seismically induced slow-moving earth slides. Vulnerability is defined in terms of probabilistic fragility curves, which describe the probability of exceeding a certain limit state of the building, on a given slope, versus the Peak Horizontal Ground Acceleration (PHGA) at the assumed “seismic bedrock”, allowing for the quantification of various sources of uncertainty. The proposed method is based on a two-step, uncoupled approach. In the first step, the differential permanent landslide displacements at the building’s foundation level are estimated using a dynamic non-linear finite difference slope model. In the second step, the calculated differential permanent displacements are statically imposed at the foundation level to assess the building’s response to differing permanent seismic ground displacements using a finite element code. Structural limit states are defined in terms of threshold values of strains for the reinforced concrete structural components. The method is applied to typical low-rise reinforced concrete frame buildings on shallow foundations with varying strength and stiffness characteristics (isolated footings and continuous slab foundation), standing near the crest of a relatively slow-moving earth slide. Two different slope models are selected representing a cohesive and a purely frictional soil material. The paper describes the method and the derived fragility curves for the selected building and slope typologies that could be used in quantitative risk assessment studies at site-specific and local scales.

Assessment of socioeconomic vulnerability to landslides using an indicator-based approach: methodology and case studies

The severity of the impact of a natural hazard on a society depends on, among other factors, the intensity of the hazard and the exposure and resistance ability of the elements at risk (e.g., persons, buildings and infrastructures). Social conditions strongly influence the vulnerability factors for both direct and indirect impact and therefore control the possibility to transform the occurrence of a natural hazard into a natural disaster. This article presents a model to assess the relative socioeconomic vulnerability to landslides at the local to regional scale. The model applies an indicator-based approach. The indicators represent the underlying factors that influence a community’s ability to prepare for, deal with, and recover from the damage and loss associated with landslides. The proposed model includes indicators that characterize the demographic, social and economic setting as well as indicators representing the degree of preparedness, effectiveness of the response and capacity to recover. Although this model focuses primarily on the indirect losses, it could easily be extended to include physical indicators accounting for the direct losses. Each indicator is individually ranked from 1 (lowest vulnerability) to 5 (highest vulnerability) and weighted, based on its overall degree of influence. The final vulnerability estimate is formulated as a weighted average of the individual indicator scores. The proposed model is applied for six case studies in Europe. The case studies demonstrate that the method gives a reasonable ranking of the vulnerability. The practical experience achieved through the case studies shows that the model is straightforward for users with knowledge on landslide locations and with access to local census data.

Predictive relationships for seismically induced slope displacements using numerical analysis results

The aim of the paper is threefold: first, to evaluate earthquake-induced slope displacements using numerical dynamic analysis considering different real acceleration time histories as input motion and varying the resistance and the compliance of the sliding mass; then, to assess the reliability of the numerical approach by comparing the numerically calculated seismically induced slope displacements with predictions using available empirical models and finally, based on the numerical analysis results, to propose new displacement predictive models applicable in earthquake engineering practice, which relate the co-seismic slope displacement with the best correlated intensity parameters. Linear regression analyses are performed to correlate the computed displacements with various intensity measures (IMs). Optimal scalar and vector IMs are identified in a rigorous way based on proficiency (i.e. a composite measure of efficiency and practicality) and sufficiency criteria. The correlation coefficient between the IMs is also considered for the selection of appropriate vector IMs. Both scalar and vector regression analytical predictive expressions are proposed appropriate for probabilistic or deterministic evaluation of the co-seismic permanent slope displacements in regional and local scale. A generic example proves the reliability of the proposed analytical expressions.

Semi-Empirical Assessment of Road Vulnerability to Seismically Induced Slides

The present paper aims at the proposition and quantification of a semi-empirical methodology to estimate physical vulnerability of roads subjected to earthquake induced landslide hazards. It is based on a modification of the existing engineering judgmental HAZUS fragility curves using an empirical model that relates the seismic permanent ground displacement (PGD) with the peak ground acceleration (PGA) for the Newmark rigid sliding block case. In this regard, it is possible to account for the specific characteristics of soil and local topography within the estimation of road vulnerability. Various sets of fragility curves can be constructed as a function of peak ground acceleration (PGA), considering the characteristics of the slope (i.e. yield coefficient, ky) and the earthquake magnitude. A preliminary application of the proposed methodology is performed with the aid of GIS tool to the roadway system of city of Grevena in NW Greece for three different earthquake scenarios. It is observed that the level of damage predicted using the aforementioned methodology is less severe compared to the corresponding level of damage anticipated using the HAZUS methodology.

VULNERABILITY ASSESSMENT OF RC BUILDINGS TO LANDSLIDE DISPLACEMENTS. APPLICATION TO CORNIGLIO CASE HISTORY, ITALY.

The present study shows an application to a specific case history (the Corniglio village major landslide) of a recently proposed analytical method for the vulnerability assessment of RC buildings subjected to earthquake induced slow-moving slides [5]. In particular, the method is applied to a representative building which suffered considerable damage by the landslide movement [7]. The main goal is to verify the reliability and applicability of the proposed procedure and of the respective fragility curves through the comparison of the numerical prediction with the observed building damage. Two different approaches of increased complexity were followed for the fragility analysis of the building. At first, two sets of the already developed fragility curves derived from an extensive parametric analysis [6] are selected as the more representative of the Corniglio case history. Thus, the results obtained from their application are compared with the observed building damage, for the measured level of building displacement. The direct comparison carried out proved that the proposed fragility curves could in general capture the performance of the studied RC building when affected by a landslide induced displacement. Then, to enhance the effective implementation of the proposed methodological framework within a more general probabilistic risk assessment study, appropriate fragility curves were defined for a specific building in Corniglio village by means of a straightforward numerical computation. In particular, a two-step numerical approach which includes soil structure dynamic analysis and a structural pseudo-static calculation was followed to assess the expected building induced stress and damage [5]. As in the previous step, the obtained fragility curves were tested through their comparison with the observed building damage data, for a given level of landslide displacement.

Building vulnerability to the 2008 Ilia- Achaia earthquake induced slides

The present paper, after providing a brief description of the recently developed analytical tool for assessing vulnerability of RC (reinforced concrete) structures to earthquake triggered earth slides, focuses on the exploration of the reliability and applicability of proposed procedure through its application to a real case study. In particular, the approach is implemented to a representative RC building located near the crest of the Kato Achaia slope where most of the structural damage was concentrated in consequence of the Ilia-Achaia, Greece 2008 (Mw = 6.4) earthquake. Both the structure and slope configuration are realistically reproduced using non-linear constitutive models to estimate the vulnerability of the reference building and to assess the validity of the developed methodological framework and the corresponding fragility relationships. In terms of numerical simulations, the analysis involves two consecutive steps: (a) estimation of the differential permanent deformation at the foundation level derived through a finite difference, non-linear, slope dynamic model and (b) static application of the computed differential displacement at the building ‘s supports via a fibre-based finite element (static time history) analysis. The proposed probabilistic fragility curves were found to adequately capture the simulated and recorded performance of the representative RC building affected by the slope co-seismic differential displacement.

Probabilistic assessment of the vulnerability of reinforced concrete buildings subjected to earthquake induced landslides

This study aims at the proposition of a probabilistic framework for the vulnerability assessment of reinforced concrete (RC) buildings subjected to seismically induced slope displacements due to landslide hazard. The proposed approach combines the seismic hazard analysis with the displacement hazard analysis and the fragility analysis of the structure. First, a probabilistic seismic hazard curve for the selected intensity measure(s) is derived together with the associated information for magnitude and magnitude/distance disaggregation based on a traditional probabilistic seismic hazard analysis (PSHA). Then, a displacement hazard curve is obtained based on the associated seismic hazard analysis results and appropriate scalar or vector models to predict the seismically induced slope displacements. Finally, a damage hazard curve of a typical RC frame structure subjected to the seismically induced landslide hazard is computed describing the annual rate of exceeding different damage limit states. Various sources of uncertainty are taken into account including the aleatory variability on the seismic and displacement hazard, the structural demand and the definition of damage limit states as well as the structure’s capacity. To incorporate epistemic uncertainties in the proposed framework, a logic tree analysis is proposed to derive a weighted mean and different fractiles damage hazard curves. The proposed approach is illustrated on a hypothetical low-rise RC frame structure impacted by the earthquake induced landslide hazard. The importance of the yield coefficients and displacement predictive models to the slope’s performance, structural response and vulnerability is highlighted.