Interdisciplinary approach for Tsunami Hazard Mitigation in Algeria (West Mediterranean)

Numerous tsunamis occurred in the West Mediterranean with magnitudes ranging from m=-1 to m=2 (Imamura-Iida scale). In Algeria, tsunamis are reported from the 14th century to 2003. Northern Algeria is located at the border between the African and the Eurasian plate. Destructive earthquakes with magnitude greater than 6.7 occurred 3 times in the last century. The North Algeria western region is characterized by the Murdjadjo anticline. A destructive earthquake hit Oran city on October 1790 (Intensity: X, West of Algeria). A tsunami was triggered in the Alboran sea. The Spanish and North Africa coasts were flooded. Run-up’s of 2 meters in height are reported in historical documents (Lopez Marinas and Salord, 1990). Here, the 1790 Alboran tsunami is studied from a modelling approach. The tsunami source is determined from the Okada equations and the tsunami propagation is estimated from the SWAN code (Mader, 2004). Results show that active thrust faulting related to the Murdjadjo structure is responsible for the tsunami. In the central part of Algeria, the Algiers city (capital of Algeria) was the location of destructive earthquakes (Intensity: X) that were followed by tsunamis in 1365 and in 1773. Flooding and run-up’s of 2 meters in height are reported in historical documents for the 1365 event. The central part of Algeria is the site of the Sahel anticline. A tsunami modelling is also performed considering the Sahel fault system as a potential tsunami source. Results show that it takes less than 15 minutes for the tsunami waves to reach the Spanish coast. Run-up’s are estimated lower than 2 meters in height. Discrepancies are attributed to the resolution of the bathymetry and the limits of the modelling. In the eastern region, historical reports also reveal run-up’s up to 5 meters in height after a tsunami triggered by a destructive earthquake in 1856 in Jijel city (intensity: VIII). From tsunami catalogs, seismic and tsunami data are plotted using a tsunami vulnerability parameter. The vulnerability index is estimated from the tsunami intensity and the seismic intensity using the Papadopoulos and the EMS scale. Results show that in Algeria, tsunami damages are minor relative to seismic damages. Since the 2004 Sumatra-Andaman tsunami, intergovernmental coordinated groups are working on an Indian and a Mediterranean tsunami alert system. To reduce vulnerability and increase resilience, it is very important to implement an efficiency warning system and a communication policy for fast urbanized coastal cities. In that context, lessons from the pacific case study are of major interest. Chile is marked by a very high seismic and tsunami hazard. The Iquique area is a threaten zone for a potential earthquake of magnitude greater than 8 and a local tsunami that could generate run-up’s up to 20 meters in height. In addition to the Pacific Tsunami Warning centre based in Hawaii, the Chile has elaborated a local tsunami warning centre. The Chilean case study is presented in discussion to highlight some lessons that may serve as an example for fast urbanized coastal cities that have to face local tsunamis.