The tsunami induced by the 2003 Zemmouri earthquake (MW=6.9, Algeria):: modelling and results

A strong tsunami with sea disturbances observed along the Algerian coast, but with significant damage mainly in the Balearic Islands (Spain) harbours, affected the western Mediterranean following the 2003 Zemmouri earthquake (M-W 6.9, Algeria). An average regional uplift of 0.55 m was measured along the shoreline in the epicentral area. Field observations, main shock and aftershocks characteristics are consistent with thrust along a similar to 55-km-long rupture, trending NE-SW, dipping SE. The seismotectonic parameters indicate a hypocentre 7-8 km deep and a possible fault break between 5 and 15 km offshore. Several tide gauges located in the western Mediterranean Coast indicated an average of 0.4 m of sea-level change with a maximum of 2 m in the Balearic Islands. We generated high-resolution bathymetry grids from the Algerian coasts to the Balearic Islands coasts in order to test different seismic sources (with different fault rupture location, strike and dip) and model the tsunami initiation and propagation. For the modelling we employed the Crank-Nicolson numerical schema with a finite difference method and the Okada elastic dislocation theory for the fault rupture. We also highlight the different factors responsible for waves' amplification around the Balearic coast. The best fit between synthetic and real data (tide gauges, GPS levelling and coastal uplift as compared to run-up values) are obtained for a thrust rupture comparable with the earthquake fault inferred from seismotectonic studies and located within 15 km offshore. An analysis of T waves reinforces the earthquake rupture origin for the tsunami. This study presents the results and modelling of a major tsunami recorded in the western Mediterranean Sea.