Multirisk assessment in Guadeloupe. Risk comparison between earthquake and storm surges based on potential direct economic losses
Résumé
The objective of this work is to compare the potential direct economic losses between two different hazards in Guadeloupe, earthquakes and storm surges, for different return periods. Probabilistic seismic hazard has been calculated fort return periods of 100, 1000 and 5000 years and 475 years map exists previously. The lithological and topographic amplifications are taken into account. In Guadeloupe, building stock was characterized in terms of main structural type during the SDRS Guadeloupe project (Bertil et al. 2008). This work has been complemented incorporating the total cost for each type of building, considering the construction cost. Vulnerability of current building, scholar and commercial buildings has been assessed using the vulnerability index method (RISK-UE method). The estimation of economic losses is done linking the physical damage state for each construction and damage ratios (repair cost/total repair cost). This result has been compared with the loss estimation coming from CCR data (Reinsurance Organism in France) after the Saintes earthquake (2004) (Figure 1). The storm surge hazard assessment process includes (1) the determination of 100-year cyclonic wave height and surge level and (2) the calculation of coastal inundation hazard maps for a 100-year return period scenario. The modeling of waves and surge induced by 300 cyclones over the 20th century in the area of Guadeloupe Island has been performed (Figure 2). The statistical analysis of wave heights is done and the statistical analysis of surge levels is still in progress. Due to the limited number of events available in the historical databases, the uncertainties of the results remain quite high. The assessment of inundation hazard maps will be performed with a simple method by crossing the water level with the topographic data to determine the areas lying below this level. For storm surge risk assessment the building typology is the same one considered for seismic risk, just adapting vulnerability functions. State of art of available vulnerability functions in storm surge and floods in tropical context has been done (CAPRA software, HAZUS software) even if these functions do not consider explicitly the local context in Guadeloupe. Damages caused by wind are not considered. Looking at past events damages in Martinique and Guadeloupe (Hugo 1989, Luis 1995, Lenny 1999, Dean 2007, Omar 2008) it has been seen the damage distribution pattern (very destructive zone, damaging zone and inundation zone). In general strong structural damages are caused by beach erosion and cannot be associated directly to water height. The past events data are not enough to build vulnerability functions. Potential direct economic losses will be estimated, crossing inundation maps with built areas and vulnerability function for each kind of construction.