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Attenuation of Intensity for the Zemmouri
Earthquake of 21 May 2003 (Mw 6.8): Insights
for the Seismic Hazard and Historical
Earthquake Sources in Northern Algeria
S. Maouche, A. Harbi and M. Meghraoui
Foreword
On the basis of the detailed macroseismic study of the 21 May, 2003
Zemmouri earthquake (Mw
8), we measured the epicentral distance to about
600 intensity-observation localities and analysed the resulting dataset by regression
procedures. The earthquake that is the most destructive event in Algeria since 1980
caused 2,280 casualties and the collapse and serious damage of more than 30,000
buildings. The coastal epicentre location makes the earthquake an important case
study useful for a better understanding of the seismic hazard of the Algiers region.
Different regression curves are calculated using various directions and the resulting
attenuation distribution shows diverse behaviours related to the specific geological
structures. Significant variations of intensity are related to the sedimentary versus
basement and rocky areas. These results extend our knowledge on the interaction
between the damage distribution and the local soil conditions. Moreover, the com-
parison of the Zemmouri earthquake with historical offshore and coastal seismic
events, the 1856 Djidjelli earthquake to the east and the 1891 Villebourg earthquake
to the west, allows us to infer new conclusions on the seismogenic sources along the
Algerian coastal area.
=
6
.
1 Introduction
The Tell Atlas of Northern Algeria has been the site of several destructive earth-
quakes during the last seven centuries that cover the historical catalogue (Rothe 1950,
Mokrane et al. 1994, Benouar 1994; Table 1, Fig. 1). This high rate of earthquake
activity is due to the Tell Atlas location along the convergent domain at the plate
boundary between Africa and Eurasia. The most recent Zemmouri earthquake of
21 May 2003 (Mw 6.8) allowed us to characterize a newly identified active zone
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