Abstract
This work is a study of the earthquake (Mw 6.8) that occurred on May 21, 2003 in Zemmouri–Boumerdes (Algeria) using methodology based on teleseismic data, uplift measurements, and synthetic aperture radar data. As a starting point, we fix the two source fault models obtained in this work (Solution 1: strike = 64°, dip = 50°, and rake = 97°; Solution 2: strike 256°, dip 40°, and rake = 91°) with a length of 60 km and width of 20 km to calculate the slip distribution that best explains the seismic and geodetic observations. The interferometric fringes revealed a strong displacement in the satellite direction (~53 cm) along the coast of Algeria between the cities of Boumerdes and Zemmouri. The inversion of teleseismic body waves for the two focal solution types (one plane dipping to the SE and the second plane dipping to the NW) showed distinct ruptures. However, both bilateral ruptures included two asperities, one near the hypocentre and the other at a shallower location. The maximum slip (Solution 1 = 3.8 m and Solution 2 = 4.0 m) occurred near the hypocentre in both seismic source models. The surface displacement model was obtained with Okada’s equations using the EDCMP algorithm. The three components of the displacements calculated were projected regarding the satellite direction (LOS—line-of-sight) for comparison with the interferogram. The geographic location of the fault plane was determined by comparing the uplift measurements with the vertical displacement models calculated with the source at several locations. The surface displacements calculated from these source models indicate that the model based on the SE plane and the epicentre location at 36.846°N and 3.660°E produces results closer to the interferogram and the uplift measurements.
Highlights
Since the beginning of the 21st century, changes in Algeria’s seismicity have been monitored by a telemetered seismic network
In 1990, a set of 32 stations were installed along the Tellian Atlas region, which is the most active seismic zone in northern Algeria
Upon reading the Algerian earthquake catalogue and looking at a map of the maximum observed intensities, we can see that all of northern Algeria is characterized by zones of high seismic risk
Summary
Since the beginning of the 21st century, changes in Algeria’s seismicity have been monitored by a telemetered seismic network. The entire pattern of seismicity shows that there is a concentration of seismic activity along the northern Algeria border, especially in the zone near the coast, that is defined along the plate boundary zone between Africa and Eurasia and ranges from the Azores to the Aegean Sea. The epicentres are clearly located along the Tellian Atlas where numerous earthquakes have occurred over the last few decades, and the largest shocks include the following: El-Asnam (October 10, 1980; Mw=7.3), Constantine (October 27, 1985; Mw=5.9), Tipasa-Chenoua (October 29, 1998; Mw=6.0), Mascara (August 18, 1994; Mw=5.7) and Algiers (September 4, 1996; Mw=5.5). A map of the maximum observed seismic intensities (see figure 7 of Ayadi and Bezzeghoud, 2015) of Algeria clearly shows that the seismogenic zones are concentrated along the Tellian Atlas of Algeria These zones (i.e., Oran, Mascara, El Asnam, Tipasa-Blida, Jijel, and Constantine) are concentrated linearly from the west to the east and define a boundary between the African and Eurasian plates.
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