Journal of Seismology

, Volume 16, Issue 1, pp 35–53 | Cite as

The 1992 Tafilalt seismic crisis (Anti-Atlas, Morocco)

  • Ihsane Bensaid
  • Taj-Eddine Cherkaoui
  • Fida Medina
  • Bento Caldeira
  • Elisa Buforn
  • Anas Emran
  • Youssef Hahou
Original article


The Tafilalt region, located at the eastern end of the Anti-Atlas chain in Morocco, was shaken on 23 and 30 October 1992 by two moderate earthquakes of magnitude mb ∼ 5 and intensity ∼ VI MSK64, which caused two deaths and great damage in the area between Erfoud and Rissani. The review of data available on the seismic crisis allowed us to improve the knowledge on the macroseismic, instrumental and source parameters of the earthquakes. The main results of the present study are: (1) location of the epicentres with the help of data from a close portable network allowed us to propose new epicentral coordinates at 31.361° N, 4.182° W (23 October) and 31.286° N, 4.347° W (30 October); both events have focal depths of 2 km; (2) the shock of 30 October was followed by a series of 305 aftershocks, most of which were located west of Rissani; the 61 best-constrained events had focal depths of 5 to 19 km and magnitudes 0.7 to 3; (3) the largest damage was located in an area between the two epicentres within the Tafilalt valley and was probably amplified by site effects due to the proximity of the water table within the Quaternary sediments; (4) focal mechanisms of the main events correspond to strike-slip faulting with fault planes oriented N–S (left lateral) and E–W (right lateral); the only mechanism available for the aftershocks also corresponds to strike-slip faulting; (5) spectral analysis shows that the scalar seismic moment (Mo) of the first event is slightly larger than the second; the corresponding values of Mw are 5.1 and 5.0, respectively; (6) the dimensions of the faults for a circular fault model are 7.7 ± 1.4 and 7.4 ± 1.2 km, respectively; the average displacement is 4 cm for the first event and 3.7 cm for the second; the stress drop is 0.4 and 0.3 MPa, respectively, in agreement with standard values; (7) the Coulomb Stress test performed for both earthquakes suggests a relationship between both events only when the used location is at the limit of the horizontal uncertainty; (8) finally, the occurrence of these shocks suggests that the Anti-Atlas is undergoing tectonic deformation in addition to thermal uplift as suggested by recent publications.


Maghreb Seismology Seismotectonics Focal mechanisms Rissani Fault dimension Coulomb stress 



This study has been partially supported by the Universidad Complutense de Madrid, project AE1/09-16586 to I. Bensaid and E. Buforn. We are particularly indebted to Pr. Denis Hatzfeld (IRIGM, Observatory of Grenoble) for providing the seismograms of the microseismic campaign carried out in the Khénifra province in collaboration with the Scientific Institute (T.-E. Cherkaoui), to two anonymous reviewers for their valuable comments which helped improving the manuscript, and to Prof. Lahsen Baidder (University Hassan II–Casablanca) for sending us useful documentation. We acknowledge the help of several colleagues in Tunisia, Ivory Coast and France, who gently provided copies of seismograms. We thank M’hamed Bikraoui, Mohamed Laami (technicians) and Abderrahim El Alaoui and Lakbir El Bekraoui for their help in the fieldwork during the survey of 1992. The local authorities and the Royal Gendarmery provided valuable help in the field. Finally, Hind El Hachimi and Nadia Mhammdi kindly helped us in preparing the first draft of the structural map of Tafilalt.


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Authors and Affiliations

  • Ihsane Bensaid
    • 1
    • 2
  • Taj-Eddine Cherkaoui
    • 3
  • Fida Medina
    • 4
  • Bento Caldeira
    • 5
  • Elisa Buforn
    • 6
  • Anas Emran
    • 4
  • Youssef Hahou
    • 7
  1. 1.Département des Sciences de la Terre, Institut Scientifique, Laboratoire de Physique du Globe, Equipe Sismologie et MagnétismeUniversité Mohammed V-AgdalRabatMorocco
  2. 2.Ecole Mohammedia d’IngénieursUniversité Mohammed V-AgdalRabatMorocco
  3. 3.Département des Sciences de la TerreInstitut ScientifiqueRabatMorocco
  4. 4.Département des Sciences de la Terre, Institut Scientifique, Laboratoire de Géologie et Télédetection (associé CNRST URAC 46), Equipe Télédétection, Ressources et Risques naturelsUniversité Mohammed V-AgdalRabatMorocco
  5. 5.Centro GeofísicoUniversidade de EvoraEvoraPortugal
  6. 6.Departamento de Geofisica y MeteorologiaUniversidad ComplutenseMadridSpain
  7. 7.Centre National pour la Recherche Scientifique et TechniqueInstitut National de GéophysiqueRabatMorocco

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