Seismotectonic Study of the Ain Temouchent Region in North Western...

Journal of Applied Sciences Research, 5(9): 1254-1258, 2009
© 2009, INSInet Publication
Seismotectonic Study of the Ain Temouchent Region in North Western Algeria
1,2
1
A. Bourezg Belkhir, 3H. Djellit, 1Jin Zhen Min
Faculty of Earth Sciences,. China University of Geosciences, Lu Mo Road 388, Wuhan
430074, PR China.
2
Faculty of Earth Sciences, Abou Bakr Belkaid University, Tlemcen 13000, Algeria.
3
Centre de recherche en astronomie astrophysique et géophysique, CRAAG, route de
l’Observatoire, BP 63 Bouzaréah, Alger.
Abstract: The plate dynamics in the central western Mediterranean region is characterized by a collision
between the Eurasian and African plates. In response to this dynamics, many systems of faults and folds
having a NE-SW and E-W trending have been generated along the Tell Atlas of Algeria. The Ain
Temouchent region (North western Algeria), is characterized by a low to moderate seismic activity.
Indeed, through history, no important earthquakes have been mentioned by the seismic catalog
(BENOUAR, 1994). Only a few seismic events have been reported in the region during the twentieth
century. During the last twenty years, we can outline as more important three events that occurred in the
vicinity of the epicenter of the Ain Temouchent event. These are the events of 16.01.1980 (Io = V, M
= 3.8), 15.07.1985 (Io = V, M = 4.1), 17.12.1992 (Io = V, M = 4.8), all with magnitudes lower than 5.0.
Key words: Plate dynamics, collision, faults, folds, earthquake, epicenter, magnitude.
The study of seismotectonics of the Ain
Temouchent region required the uses of two methods
of: analyzing the historical seismicity and tectonics
characters. The materials used were: Topographic,
geologic and tectonic map.
moderate events (M $5.5). The strongest earthquake (Io
= IX-X) documented in the area is that of October 9th
1790 which jolted the town of Oran. According to
Chesneau 1892 this event is the most disastrous one
known in Algeria. It caused the complete destruction of
the town, many casualties, life lost and material
damage. Among the local population nearly 3000
people have died, and their habitations were destroyed
subsequently, another earthquake occurred on March
1819 in the Mascara region. This earthquake of
intensity IX destroyed a huge number of farms, wine
cellars, etc. T hen, on November 29th, 1887 the region
was impacted by an earthquake of maximum intensity
X, which caused the loss of some 20 people,
destroying 331 housing units [2 ]. In order to get an idea
about the seismic activity of the region Tables 1 give
a brief summary.
The Ain Temouchent region, in comparison to the
Oran and Mascara regions, is characterized by a low to
moderate seismic activity (Fig. 2). Indeed, through
history, no important earthquakes have been mentioned
by the seismic catalog [1 2 ,1 ,2 ]. Only a few seismic events
have been reported in the region during the twentieth
century (Table 1).
Historical Seismicity: The studied region has a special
seismic character. A kind of a seismic gap (seismic
quietness) is observed since 1790 for relatively
During the last twenty years, we can outline as
more important three events that occurred in the
vicinity of the epicenter of the Ain Temouchent event.
INTRODUCTION
The Ain Temouchent region is located in the
western extremity of the lower Cheliff basin [7 ,1 4 ]. This
was later developed after the major structuring of the
Tell domain, one of the segments of the Alpine chain
of Northern Africa [8 ]. The Ain Temouchent region is
bordered on the east by the Oran Sebkha (a salt lake)
and on the west by the coastal massif of Beni Saf. In
the north, the region is limited by the volcanic
sedimentary units of Bouzedjar and in the south by the
periclinal ending of the Sebah Chioukh Mountains and
western Tessala massifs (Fig. 1).
The geology, seismicity and seismotectonics of the
western part of North Algeria have been the subject of
numerous studies: for example Rothé [1 1 ,1 0 ,1 4 ,8 ].
M ATERIALS AND M ETHODS
Corresponding Author: A. Bourezg Belkhir, Faculty of Earth Sciences,. China University of Geosciences, Lu Mo Road 388,
Wuhan 430074, PR China.
Email: [email protected] .
Tel: 00862767885851
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J. Appl. Sci. Res., 5(9): 1254-1258, 2009
These are the events of 16.01.1980 (Io = V, M =3.8),
15.07.1985 (Io = V, M = 4.1), 17.12.1992 (Io = V, M
=4.8), all with magnitudes lower than 5.0. W e believe
that it is difficult to envisage this region with a weak
seismicity in the past because it is located in the
Eurasiatic-African plate boundary.
A possible explanation for the low seismic activity
of the Ain Temouchent region may be the lack of
historical documents, human witnesses, and absence of
seismological stations. W e recall, also, that a
consequence of the earthquake of 1790, which
destroyed the city of Oran, was the departure of the
Spanish and, probably, a decrease in the population. In
the Oranie region, before installation of the Algerian
seismological network in 1990, the seismic monitoring
was carried out by only one station [5 ]. It was the
Tlemcen station (TEC), which operated between 1978
and 1992. Subsequently, there is a major gap in the
knowledge of the seismic activity before 1978 and
consequently it is not possible to precisely perceive of
the real seismic activity of the region.
General Tectonic Setting: The Ain Temouchent area
is located in the Tell Atlas, immediately NE of the
Tafna Quaternary basin and SE of the Mleta
Quaternary basin, (Fig. 3). T he 1999 Ain Temouchent
earthquake intensity map related to damage delimits a
zone around Ain Temouchent city, but no surface
faulting were visible [4 ]. The Mleta basin is limited to
the north by the N50° trending and 32–km-long
Murdjadjo active fold-related fault that may be
responsible of the 1790 Oran earthquake [1 1 ,3 ]. East of
the study area, the Tessala and Beni Choughrane
mountains and NE-SW fold-related faults experienced
the 1994 Mascara thrust arthquake (Benouar et al,
1994; Mw= 5.7, Fig. 2) which is comparable to the
Ain Temouchent 1999 event since it did not produce
surface faulting. The recent major earthquakes of El
Asnam 1980, M w 7=.3; Tipaza 1989, Mw =5.9;
Mascara 1994, M w= 5.7 and Zemmouri 2003, M w
=6.8 in northwest Algeria illustrate the pattern of active
deformation in the T ell Atlas. T he tectonic
characteristics correspond to thrust ruptures associated
with NE-SW trending fold-related faults showing enechelon right-stepping distribution [8 ,9 ,2 ]. The late
Quaternary active deformation of the Tell Atlas
mountain ranges of northwest Algeria consists of NESW trending thrust and fold system that result from 3
to 6 mm/yr convergent movements between Africa and
Eurasia [1 3 ] . The transpressive active deformation is
essentially due to the NNW SSE to NW -SE shortening
as inferred from P axes of thrust focal mechanisms.
Furthermore, minor reverse faults and liquefaction
features that affect Quaternary units are visible along
scarp morphology [4 ]. Other evidence of recent tectonic
activity is attested by (1) strongly folded late
Quaternary units and alluvial terraces visible in the
south-eastern flank of the anticline and (2) the
relationships between the morphology and the drainage
network. Analysis of topography suggests that the 40km-long Tafna fault crosses the Tafna River and
extends towards the SW . The Tafna fault is associated
with cumulative uplift of alluvial units and triangular
facets with progressive angular inconformity of late
Quaternary units. Active tectonics of the Ain
Temouchent region indicate the existence of a
previously unknown Tafna fault and related Berdani
fold with seismic characteristics comparable to other
active zones in the Tell Atlas.
CONCLUSION AND DISCUSSION
This study is focussing on the seismotectonics
aspect of the Ain Temouchent region. W e have tried to
summarise the major features present in the area in
order to enable the reader to obtain as detailed view as
possible of the area’s tectonic structure and also to
engage other seismological and geological studies in
the regions of Ain Temouchent
to define more
precisely their tectonic activity.
From the geological point of view, two main
geological units characterize the region of Ain
Temouchent: 1) the metamorphic basement represented
by quarzitic units and 2) the volcanic sedimentary
cover formed by Plioquaternary rocks. W e must notice
that in the Oran region, two volcanic episodes
synchronous to the Neogene tectonic phases have been
distinguished. The first one dated in the Messinian
period corresponding to a calco-alkalin volcanism, and
the second one, more recent of basaltic alkaline type
and dated in the Quaternary period. In general these
volcanic deposits follow the main accidents trending
N50°. [7 ,1 4 ] indicate that the Neogene and Quaternary
deposits were slightly affected by the NS to NW -SE
Quaternary compressionnal phases that affect the Tell
Atlas Mountains. The quasi-tabular aspect of the
geological formations confirms this fact. This lack of
deformation could explain the rather slow seismic
activity level of the region of Ain Temouchent.
Historical seismicity for the Ain Temouchent
region indicates a low level of seismic activity, with
the occurrence of earthquakes with magnitudes less
than 5.5. In the Algerian Maximum Observed Intensity
map, this region shows a maximum intensity of VI
(MM scale). The recent Ain Temouchent earthquake
(M w = 5.7) is the largest seismic event which occurred
in the Ain Temouchent region with a maximum
observed intensity of VII (MSK scale).
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J. Appl. Sci. Res., 5(9): 1254-1258, 2009
Fig. 1: Tectonic map of the north-western Algeria.
Fig. 2: Historical seismicity Map from 1359 to 1895 with the instrumental seismicity of northern Algeria from
1900 to 2005 (Sources, Benouar, 1994 and ISC).
Table 1: Seism ic evetns reported during the X entury fot the studied area.
D ate
Tim e
Lat.N
Lon.W
M
Io
O bservations
Ref.
13.05.1964
13 46 21
35.50E
01.50E
5.2
VII
Beni Saf region
M orrane et al., (1994)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------16.08.1967
13 46 09
35.50E
01.30E
M orrane et al., (1994)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------16.01.1980
21 40 00
35.35E
01.03E
3.8
V
Ain Tem ouchent
M orrane et al., (1994)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------15.07.1985
11 20 39
35.48E
01.22E
3.9
V
Bouzodjar
Benouar, 1994
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------18.07.1685
11 44 00
35.38E
01.20E
3.5
IV
Terga
M orrane et al., (1994)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------17.10.1992
20 43 21
35.18E
01.20E
4.8
V
Ain Tem ouchent
CRAAG
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------22.12.1999
17 36 53
35.25E
01.30E
5.7
VII
Ain Tem ouchent
This study
Io = isoseism al m axim um m tensity, M = m agnitude
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J. Appl. Sci. Res., 5(9): 1254-1258, 2009
Fig. 3: Tectonic map of the central Oranie region. The legend gives information on the age of the formations and
the structures.
ACKNOW LEDGM ENTS
AB foremost wishes to thank God Almighty
ALLAH, for his blessings, steady love and continuous
guide throughout stay in China. AB also would like to
express thanks to China Scholarship Council (CSC_
Beijing) and the M inistry of Higher Education and
Scientific Research (Algeria) for their financial support
and an anonymous referee, whose comments greatly
improved the research.
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