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(Fig. 5a). A first study of the Djidjelli earthquake has been accomplished by
Ambraseys (1982) who published the corresponding isoseismals map (VI
+
and
VII
+
) and assigned intensity VIII MSK to the city of Djidjelli (now Jijel). Recently,
Harbi et al. (2003a) re-assessed the extent of the damage and the people reaction
by making a comprehensive research using contemporary accounts relative to this
event and confronting all the available reports, press accounts and published papers
(Aucapitaine 1856, Gaultier de Claubry 1856, De Senarmont 1857, Rothe 1950,
Ambraseys 1982; contemporary press:
Akhbar, Le Moniteur Algerien, L'illustration,
La Seybousse, Le Courrier mercantile, La Gazette de Lyon, 1856
). The analysis
shows macroseismic data with a relatively good description of the impact of the
earthquake on humans, man-made buildings and ground movements. Although the
maximum damage is reported in a rather small area (Fig. 5b), the mainshock caused
the loss of at least five lives and triggered a sea wave of 2-3 m high that flooded the
Djidjelli coast a number of times.
6.2 The Villebourg Earthquake
The earthquake of 15 January 1891 of Villebourg (now Larhat) is considered among
the largest event after the 2003 Zemmouri earthquake that occurred in the coastal
area of north-central Algeria. Due to the location of maximum damage, one may
question the inland epicentre location as previously suggested by Rothe (1950)
at 36.5
◦
N, 1.80
◦
E and Ambraseys and Vogt (1988) at 36.50
◦
N, 1.90
◦
E. There-
fore, it became important to reassess the macroseismic data in light of the new
information retrieved mainly from the local press reports. The most extensive ac-
counts are given in “La Depeche Algerienne” and the contemporary document
of Pomel (1891). All the macroseismic information (Appendix 2) retrieved from
the available sources at 20 sites, were carefully analysed and used in the re-
assessment of the ground shaking with reference to EMS intensity scale. As a
result of the analysis of the reconstructed macroseismic field, an isoseismal map
has been drawn (Fig. 6) and accordingly a macroseismic epicentre was located
on the coast, between Villebourg (Larhat nowadays) and Gouraya, at 36
◦
56N,
1
◦
85E.
All sources describe surface effects such as rock falls and landslides triggered by
the Villebourg earthquake. The retrospective study and related construction of the
macroseismic field of this earthquake coupled with a morphological analysis has
allowed a better understanding of the seismotectonic framework of the study area.
We present an aerial photo which shows the landslide (Fig. 7) on which the city of
Larhat (ex Villebourg) is constructed today. This landslide was certainly reactivated
during the earthquake (see Appendix 2) and is characterized by the presence of ma-
rine terraces showing multiple scarps displaying gliding planes inclined northwards.
The recent tectonics of the epicentral area is highlighted by a set of uplifted terraces
incised by the Damous River running parallel to the NE-SW trending active geolog-
ical structure.
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