Seismic source study of the 1989, October 29, Chenoua (Algeria) earthquake from aftershocks, broad-band and strong ground motion records

A. Bounif, M. Bezzeghoud, L. Dorbath, D. Legrand, A. Deschamps, L. Rivera, H. Benhallou


The broad-band teleseismics records of the earthquake of October 29,1989 in Algeria (MW = 6.0) allow a detailed
study of the rupture process of this earthquake. The focal mechanism obtained by P and SH modeling corresponds
to reverse faulting with a small amount of left-lateral movement along a fault striking 246° and dipping 56°. The
rupture is found to be complex with two sub-events separated in time but occurring on the same plane. The lowfrequency
records of an accelerometer located some 25 km to the west of the main shock are also better fi tted when
the rupture is composed of a double pulse. In the two cases, there is strong evidence for the rupture to propagate
from south-west towards north-east.The relocalisation of the main shock by using a master-event technique and
the data from Italian and Spanish stations led to the same conclusions. Soon after the main event, a temporary
seimic network was installed in the epicentral area. The aftershock clouds defi ne a SW-NE fault dipping to the NW
compatible with the results of the modelisations of the teleseismic body-waves and the accelerogram. The focal
mechanisms correspond mainly to reverse faulting. The maximum principal direction of the stress tensor obtained
from the inversion is about N-S and the minimum is vertical, typical of a compressive regime. The Chenoua
earthquake took place on a fault which was not recognized as active. Repeated comparable seismic events on this
fault and on the fault that borders the massif to the south explain this intriguing topographic feature.


North Africa;seismicity;earthquake

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X