Abstract
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.
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Acknowledgments
This thesis work was prepared jointly at the host laboratory ISTERRE in Grenoble (France) with USTO MB-Oran (Algeria) University funding from the Algerian-French cooperation program (PROFAS). We are very thankful to the authors or main contributors of the different vulnerability approaches (S. Lagomarsino (DICAT, Genoa, Italy) and C. Negulescu (BRGM Orléans, France) for RISK-UE, and P. Guéguen (ISTerre, Grenoble, France) for VULNERALP), for their help and provision of the basic documentation of these methods. We are also very grateful to CTC of Oran (technical organism in charge of the Technical Control of Construction) and DUC Of Oran (Office of urban planning and construction) for their help and provision of data.
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Senouci, A., Bard, P.Y., Farsi, M.N. et al. Robustness and uncertainties of seismic damage estimates at urban scale: a methodological comparison on the example of the city of Oran (Algeria). Bull Earthquake Eng 11, 1191–1215 (2013). https://doi.org/10.1007/s10518-012-9406-3
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DOI: https://doi.org/10.1007/s10518-012-9406-3