The Algiers, Algeria Earthquake (Mw 6. 8) of 21 May 2003: Preliminary Report

Abstract

On 21 May 2003, at 18:44 UTC (19:44 local time), a strong shallow earthquake of magnitude Mw 6.8 ( Ms 6.9) struck Algiers, the capital of Algeria, causing extensive damage in different wilayas (provinces) in the north-central part of Algeria. The epicenter was located offshore at 3.58°E 36.91°N 7 km to the north of Zemmouri in the province of Boumerdes, about 50 km northeast of Algiers (Yelles-Chauche et al., 2003). This earthquake took place where we have no evidence of previous significant earthquakes, either instrumental or historical. It is the largest and the most destructive to occur in northern Algeria since the 1980 El Asnam ( Mw 7.3) earthquake. The original location, obtained by the Centre de Recherche en Astronomie, Astrophysique et Geophysique (CRAAG), shown in Figure 1, is slightly different from those given by the European-Mediterranean Seismological Centre (EMSC) (3.76°E, 37.02°N and the U.S. Geological Survey (USGS) (3.78°E, 36.86°N The focal mechanism computed by the International Seismological Centre (ISC) corresponds to a northeast-southwest thrust fault (strike 54° dip 47° rake 86° According to Yagi (2003), the seismic moment was 2.4.1019 Nm. The mainshock was followed by a small tsunami, which affected the Spanish coast. Specifically, along the coast of the Balearic Islands, a sea wave of about 1.5 m height sunk a hundred small boats docked in the ports. During the mainshock, a temporary withdrawal of the sea of about 100 m was observed. This earthquake, with a macroseismic maximum intensity of IX-X in two small cities near the epicenter, Zemmouri and Boumerdes, and an intensity of VII-VIII in several districts of Algiers, caused significant economic and social losses, especially in the city of Boumerdes and the main villages in the region, such as Zemmouri, Dellys, and Thenia. In these cities, many modern buildings collapsed and …