Seismic vulnerability analysis of historical masonry buildings, addressed to earthquake emergency management and protection strategy planning, requires large-scale vulnerability and damage assessment. In this sense, two seismic vulnerability index methods and damage estimation have been adapted and applied to a pilot-scale urban area located in Annaba city (Algeria). The first method is based on the EMS-98 building typologies, and the second is based on the Italian GNDT approach. To accomplish this task, the authors employed an existing data survey, which, however, was not originally developed for seismic purposes. It was used herein to provide input to the vulnerability methods. The main goal of this research is not only to assess the seismic vulnerability and expected damage within Annaba, but also to adapt the two mentioned approaches to the existing data survey, aiming to use such nonspecific building database and to study the possibility of its application for seismic risk estimation in similar regions. The results obtained from the application of these two methods were integrated and compared using a geographic information system, proving that the vulnerability of the buildings surveyed in Annaba is significant, and therefore risk mitigation efforts and public awareness are required.

Seismic vulnerability assessment of historical masonry buildings located in Annaba city (Algeria) using non ad-hoc data survey

The main purpose of risk reduction methodological and operational approaches is to protect lives and properties against the impact of natural or industrial disaster. Although it is unrealistic to expect to live in a risk free environment, it is possible to reduce this risk through appropriate prediction and management strategies. This work presents an integrated framework for seismic damage assessment at urban scale in Algeria. Its main objective is the proposal of simplified methodological and operational approaches to assess urban vulnerability and socio-economic losses. It relies on the performance of probable seismic scenarios in urban areas exposed to earthquakes. This will enable decision makers to take adequate preventive measures and develop appropriate mitigation strategies, i.e. crisis prevention and management plans to reduce the losses. It deals with the assessment of building seismic risk of urban areas in Algeria by using the RADIUS Model (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) after a prior adaptation to the Algerian context. It estimates also the expected number of victims and their spatial distributions. This concept is adopted to estimate the urban seismic risk of the Great-Blida region (consisting of 4 cities, namely Blida, Ouled-Yaich, Bouarfa and Beni-Mered), west of Algiers region, by performing an earthquake scenario. The region of Blida has experienced strong earthquakes during the last centuries generating seismic intensities ranging between X and XI, of which that most significant, occurred on Mars 2, 1825. It represents an important administrative, military, economic and scientific pole, and features a high concentration of population (1390 inhabitants/km2). In order to draw reliable results, an extensive survey was carried out concerning the buildings (approximately 46,000 units). The data were mapped and stored in databases using GIS tools. The results of this earthquake scenario show that serious damages would be observed in the studied area. The results reported in this study will drive the decision-making, by the local authorities, adapted to the specific socio-environmental vulnerability context at the Great-Blida urban scale. For this purpose, the paper proposes a list of operational measures contributing to the seismic risk reduction, relying on the resilience-building demand. A complementary study, i.e. a separate paper (second part), deals about assessment of seismic risk related to road infrastructures and lifelines devoted to the Algerian urban context.

Seismic vulnerability assessment at urban scale: Case of Algerian buildings

. We propose the use of variable resolution boundaries
based on central Voronoi tessellations (CVTs) to spatially aggregate building
exposure models for risk assessment to various natural hazards. Such a
framework is especially beneficial when the spatial distribution of the
considered hazards presents intensity measures with contrasting footprints
and spatial correlations, such as in coastal environments. This work avoids
the incorrect assumption that a single intensity value from hazards with low
spatial correlation (e.g. tsunami) can be considered to be representative
within large-sized geo-cells for physical vulnerability assessment, without,
at the same time, increasing the complexity of the overall model. We present
decoupled earthquake and tsunami scenario-based risk estimates for the
residential building stock of Lima (Peru). We observe that earthquake loss
models for far-field subduction sources are practically insensitive to the
exposure resolution. Conversely, tsunami loss models and associated
uncertainties depend on the spatial correlations of the hazard intensities
as well as on the resolution of the exposure models. We note that for the
portfolio located in the coastal area exposed to both perils in Lima, the
ground shaking dominates the losses for lower-magnitude earthquakes, whilst
tsunamis cause the most damage for larger-magnitude events. For the latter,
two sets of existing empirical flow depth fragility models are used,
resulting in large differences in the calculated losses. This study,
therefore, raises awareness about the uncertainties associated with the
selection of fragility models and spatial aggregation entities for exposure
modelling and loss mapping.

/pdf/variable-resolution-building-exposure-modelling-for-4eqo4n6qb2.pdf

Variable-resolution building exposure modelling for earthquake and tsunami scenario-based risk assessment: an application case in Lima, Peru

Seismic scenarios are tools used to assess seismic risk at the city level. This allows the assessment of the vulnerability of exposed elements to risk (buildings, bridges, etc.). In the case of Chlef city (formerly El Asnam), this evaluation type proves to be useful given the seismic hazard to which it is exposed and the building park size. This city has been shaken in the past by several earthquakes including that of the El Asnam 1980 (Ms = 7.3), which caused hundreds of casualties and destroyed 70% of the city. In this paper, a seismic vulnerability assessment at urban scale and three seismic damage scenarios are simulated using the “RISK-UE” methodology. First, a recreation of the El Asnam 1980 earthquake, considering the urban conditions of the 1980s, is done. A difference of about 12% between observed and simulated damage is observed. Secondly, two senarios considering the current urban conditions are simulated then, vulnerabilty curves are developed. The simulations purpose is to detect the most vulnerable typologies and districts in the event of a similar earthquake and to provide decision support elements to the local seismic risk manager. The results show a structural damage decrease compared to the 1980 urban conditions.

/pdf/buildings-vulnerability-assessment-and-damage-seismic-va2ecesqbn.pdf

Buildings Vulnerability Assessment and Damage Seismic Scenarios at Urban Scale: Application to Chlef City (Algeria)

/pdf/recording-disaster-losses-for-improving-risk-modelling-3qnzaf2vpn.pdf

Recording disaster losses for improving risk modelling capacities

The city of Oran is exposed to a significant seismic hazard, as almost all the northern Algeria territory, where numerous casualties and severe damage occurred in the last decades due to several moderate to large earthquakes. A mitigation policy should include the establishment of priorities to reduce the vulnerability of existing buildings based on the knowledge of the actual urban fabrics. The complexity of vulnerability assessment requires a gradual approach from the urban scale to the building scale. The study reported in this paper corresponds to the first step of such an approach, i.e., a preliminary study of the seismic vulnerability and expected damage within an urban district of the city of Oran, based on a non-dedicated data base from a building survey previously performed for other purposes. The main goals of this study are twofold: (1) an assessment of the degree of uncertainty and robustness of such results through a comparison of the results derived from different urban vulnerability methods (GNDT 2; RISK-UE LM1; and VULNERALP 2.0) and (2) an assessment of the actual level of seismic risk in the city of Oran. Cross-method comparisons and correlations highlight a satisfactory agreement between mean damage estimates at the urban scale, despite significant scattering at the single building scale, and uncertainty levels which vary significantly from one method to the other. For a given scenario, the three methods provide damage estimates lying within half an EMS damage degree of one another, with some systematic positive bias for VULNERALP and negative bias for RISK-UE LM1, especially for masonry buildings. The expected mean damage is very important for intensities 9 and 10, with an average damage grade around 3-4 for intensity 9 and 4-5 for intensity 10. The spatial distribution of damage systematically exhibits larger values in the northern, older, commercial area, than in the southern, more recent and more residential area, in relation to the building typology and the existence of several aggravating factors. Some areas of higher vulnerability / damage can be distinguished, which should receive particular attention for retrofitting priorities or urban planning decisions, also taking into account their cultural heritage value.

Robustness and uncertainties of seismic damage estimates at urban scale: a methodological comparison on the example of the city of Oran (Algeria)

https://hal.archives-ouvertes.fr/hal-01989168/document

Mapping seismic vulnerability at urban scale: Discussion on relevant cartography representations and smoothing for urban planning purposes on the Oran case study

The assessment of urban seismic vulnerability should always account for the robustness and uncertainty of the used methods. This paper presents a comparison on preliminary evaluations of expected damage within an urban district of the city of Oran (Algeria) in order to exploit a non-dedicated set of data issued from a technical survey of the buildings. Three different methods are used (GNDT 2; RISK-UE LM1; and VULNERALP 2.0). Cross-method comparisons highlight a satisfactory agreement between mean damage estimates at the urban scale, despite significant scattering at the single building scale, and uncertainty levels which vary significantly from one method to the other. For a given scenario, the three methods provide damage estimates lying within half an EMS damage degree of one another, with some systematic positive bias for VULNERALP and negative bias for RISK-UE LM1, especially for masonry buildings.

Qualitative methods to estimate seismic damage at urban scale: A case study in Oran (Algeria)

The exposition of Algerian towns to earthquakes raises a number of issues related to the urbanization of territories in earthquake-prone areas and also to the maintenance of the existent urban fabric. In particular, the assessment of the actual seismic risk and of the vulnerability of the existing building stock is a key information in view of setting up priorities in a long term prevention policy. The current standard method in the EuroMediterranean area is the RISK-EU approach, and more specifically its first "macroseismic" level, which is essentially based on the building typology. The aim of the present study is to provide the first elements in view of assessing the seismic risk in the city of Oran. This has been achieved through an investigation of the building typology inside a sample "intramural city" perimeter by exterior visual screening along itineraries. In addition to the identification of the main building types, it also allowed to gather information of the additional vulnerability parameters as listed in the RISK-EU method. The results indicate rather high vulnerability indexes for both masonry and RC buildings, due to a number of aggravating factors which could be identified for each building typology. This preliminary study lays the ground for further investigations both in the whole greater Oran area, and for damage estimates in the case of various scenario earthquakes.

Abbas Senouci

Papers

Robustness and uncertainties of seismic damage estimates at urban scale: a methodological comparison on the example of the city of Oran (Algeria)

Mapping seismic vulnerability at urban scale: Discussion on relevant cartography representations and smoothing for urban planning purposes on the Oran case study

Qualitative methods to estimate seismic damage at urban scale: A case study in Oran (Algeria)

Classification of buildings of Oran city (Algeria) based on their seismic vulnerability

A methodological comparison of three methods of vulnerability evaluation on the example of Oran city (Algeria)