Description of the seismogenic zones of NAF region
Thirty six seismogenic zones have been defined for North Africa (Figure 2), following the
criteria generally adopted for the deterministic approach. Some of these zones were described in
previous works dealing with the deterministic seismic hazard assessment in Algeria, Morocco and
Egypt (Aoudia et al. 2000; Vaccari et al. 2001; El-Sayed et al. 2001). The seismogenic zones of Tunisia
and Libya are for the first time defined in this study, while for Egypt the earlier seismotectonic model
has been revised as follows. The seismic source zones of Egypt were considered in many studies (e.g.
El-Sayed and Wahlstrom 1996; Abou Elenean 1997; Badawy 1998). El-Sayed and Wahlstrom (1996)
divided the activity that affects Egypt into four seismic zones. These zones are known as the northern
Red Sea-Gulf of Suez-Cairo-Alexandria, Gulf of Aqaba-Levant Fault, Eastern Mediterranean-Cairo, and
Egypt-Mediterranean Coast. Abou Elenean (1997) divided Egypt into five active seismic zones; the
Gulf of Suez-northern part of Eastern Desert zone, the southwest Cairo zone, the northern part of
Red Sea, the Gulf of Aqaba zone and the Aswan zone. Based upon geologic evidences, geotectonic
provinces, seismicity and other relevant data. Badawy (1998) defined three seismic sources in
northern Egypt. The first one includes the Aqaba-Dead Sea fault system, the second at the mouth of
the Gulf of Suez, and the third extends from the southern part of the Gulf of Suez to Ismailia City.
Depending on the distribution of earthquakes of M  4, Deif (1998) divided the northern Red SeaGulf of Suez trend into three seismogenic provinces. On the other hand, Deif (1998) defined four
seismic sources in the southern part of Egypt, Abu-Dabbab region, El-Gilf El-Kebir Plateau, Wadi
Halfa, and the northern part of Lake Naser. Mahmoud (2003) divided Egypt into eight seismic zones.
The first is located southwest of the Cairo city and is considered as important because it is close to
Cairo City. The second zone extends from the Gulf of Suez towards the northern part of the Eastern
Desert. The third, fourth and fifth zones are located along the Levant Fault System. The sixth zone is
located in Aswan area and is related to known active faults in this area. The seventh zone extends
parallel to the East Mediterranean Coast. The eighth zone extends westward parallel to the Egyptian
Mediterranean coastal line from the northern Nile Delta to the border with Libya, but its activity is
scattered and does not clarify any trend. Abd-El Fattah et al. (1997) identified eleven earthquake
seismic zones based on many geological studies, the recent seismicity, focal mechanisms and
regional stress pattern, four of which are located along the Levant trend and the Gulf of Aqaba zone.
The other parts of the country are divided into the additional 7 zones; four of them cover the area of
the Gulf of Suez source zone and its extension towards the Cairo Suez district source zone while the
other remaining three are the southwest Cairo zone, Aswan source zone and the northern coastal
zone. In this study, we divided Egypt into 10 zones (see ESM). The previously selected seismic zones
were modified and updated based on the recent seismic activity recorded by the Egyptian National
Seismological Network.
In Algeria (Figure 2) with respect to earlier study, changes have been introduced in the Mitidja
basin (zone 9), Babor-Jijel zone (zone 12), Hodna zone (zone 14) which includes now the region of
Biskra, known to have experienced a damaging earthquake in 1869 (I0 VIII EMS, Harbi et al. 2003a;b),
and Guelma zone (Zone 15) which has been extended towards the south. The new information on
historical and recent seismicity is carefully merged; it mainly concerns the revision of strong events,
e.g. Djidjelli, 1856 (I0 IX EMS, Ms 6.6); M'sila, 1885 (I0 IX EMS, Ms 5.9); Gouraya (I0 IX EMS, Ms≥6.0),
and the study of the recent earthquakes (Zemmouri 2003, Béni Ourtilane 2000, Laalam 2006,
Tadjenna 2006, etc.). In Morocco, the definition of the seismogenic zones was completely modified
with respect to previous studies (Vaccari et al. 2001).
Here below, readers may find details about the active tectonics and main seismicity of the
seismotectonic source zones presented in Figure 2. Map of the active and Quaternary faults is shown
in Figure 1.
Zone 1: The Atlas zone
This zone includes the junction of the High Central Atlas, High Eastern Atlas and the Middle
Atlas. It is bordered in the north by the frontal E-W overlapping of the Rifan chain. It is characterized
by the presence of kilometric crustal faults with NE-SW (Middle Atlas), E-W (High Eastern Atlas) and
ENE-WSW (High central and western Atlas) directions, with crustal character which borders the
Atlasic belt. These accidents mio-pliocene and quaternary reverses faults with strike-slip component
are associated with folds (Ait Brahim 1991; Medina and Cherkaoui 1991; Ait Brahim et al. 2002).
These deformations are better observed on the northern edge (Moulouya basin) than in the
southern edge (Ouarzazate basin) (Fedan 1988; Aït Brahim 1991; Hinaj et al. 2001; Aït Brahim et al.
2002). This area is characterized by the presence of large earthquakes: the Agadir, 29th February
1960 (Mw 6.1, I0 IX-X) which destroyed the major part of the city; the Azilal earthquake on
14/10/1936 (Mw 5.2, I0 VII) and the Taroudant earthquake on 20/04/1955 (I0 VII, Mw 5.2) (El Mrabet
2005).
Zone 2: Nador-Oran- Béni Chougrane zone
This zone extends from Morocco to Algeria. In Morocco, it includes the Yusuf fault, which
corresponds to a great system of dextral strike-slip with an EW to ESE-WNW direction (AlvarezMarron 1999) to which are associated NE-SW fold systems. In the continent, this zone is
characterized by the presence of the quaternary volcanic faults of Gourougo (Nador) (Ait Brahim et
al. 2001; Ait Brahim 2002). To the western part of Algeria, the Oran-Beni Chougrane zone is
represented by the Beni Chougrane mountains to the south and Habra basin to the North. The Beni
Chougrane mountains are made of Cretaceous napes unconformably covered by folded Neogene and
Quaternary deposits. The south-eastern edge of these mountains is separated from the flat Ghriss
alluvial basin by a 30 km long NE-SW striking and NW dipping thrust fault showing highly deformed
young quaternary deposits and striations within vertical bedding planes (Meghraoui 1988). To the
northwest, the Beni Chougrane are also bounded by a Quaternary alluvial basin (Habra basin), which
is the western continuation of the Cheliff basin. South-east dipping thrust faulting limits the Habra
basin and Beni Chougrane fold and thrust belt, while in the middle of it, another southeast dipping
thrust affects the Neogene formations. A thrust sequence with folds having a transport direction to
the southeast, accompanied by antithetic thrusting, constitutes the structural framework of the BeniChougrane mountains. Several damaging historical earthquakes occurred in this zone (Vogt and
Ambraseys 1988) confirming its seismogenic character. For the recorded seismicity, the largest event
is the August 1994, Mw = 5.9 earthquake (Benouar et al. 1994; Ayadi et al. 2002; Bezzeghoud and
Buforn 1999). It occurred very close to the epicentre of the shock of July 13, 1967 (Ms = 5.1). The
faulting mechanism of the 18 August 1994 can be correlated to the NE-SW striking thrust and fold
system of the Beni Chougrane mountains. This faulting system accommodates one part of the
vertical and horizontal movements associated with NNW-SSE directed shortening of the crust in this
zone. Recently, another damaging earthquake occurred in this region at Ain Temouchent on 22
December 1999 (Mw 5.7). The study of this seismic event and the field investigations carried out by
Belabbès et al. (2008) allowed to highlight the tectonic activity of a previously unknown Tafna fault
and related Berdani fold with seismic characteristics comparable to other active zones in the Tell
Atlas. Other structures that are taking up one big part of the deformation are the Saline d’Arzew and
the Murdjadjo active folds. Thomas (1985) and Meghraoui (1988) provided a detailed description of
these two compressive structures. The Saline d’Arzew fault-related fold has a length of 40 km and a
topographic offset of 205±20 m. It is an asymmetric fold lying on the northern part of a young
Quaternary basin. The Murdjadjo active fold (Meghraoui 1988) is striking NE–SW, with a transport
direction to the SE and a topographic offset of 490-20 m. It has 60 km of length. This area was struck
by destructive and damaging historical earthquakes (Table 1).
Zone 3: Alhoceima zone
This zone contains the southern part of the Alboran Sea and the central Rif including the
Nekor (NE-SW) and Jebha (ENE-WSW) left strike slip faults. This zone is subjected to the influence of
the faults in “crustal” scale of the Alboran ridges, which corresponds to a structure of kilometric scale
(fold fault) which absorbed a great part of the Africa-Europe convergence (Ait Brahim 2002; Azzouzi
et al. 2005). In this zone occurred the 26/05/1994 Mw 6.7 and the destructive 24/02/2004, Mw 6.4,
Al Hoceima earthquakes (Çakir et al. 2006).
Zone 4: The western Rif zone
This zone includes the western Rif, its overlapping boundary on the Gharb basin and the
Gibraltar straight. It is the seat of significant earthquakes like that of the 27/12/1722, with magnitude
Mw 6.9; the 21/01/1909 (Mw 6.4, I0 IX), and that of Tangiers on 12/04/1773 with magnitude Mw 6.7
(I0 VII) (El Mrabet 2005). The focal mechanism of the 15/03/1964 earthquake, with magnitude mbLg
6.2, provide a reverse fault plane with orientation ENE-WSW (Buforn et al. 1988).
Zone 5: The west Alboran zone
This zone corresponds to the Western part of the Alboran Sea characterized by intermediate
depth earthquakes. The Ms 5.2 (Mw 4.0) earthquake on 07/08/1975 was characterized by reverse
with strike slip component focal mechanism (Coca and Buforn 1994).
Zone 6: The Atlantic-Gulf of Cadiz zone
This zone is located in the Atlantic at the boundary of Iberian and African plates and extends
from the Azores to the Gulf of Cadiz including the western part of Gloria and Gorringe transforming
faults. Eastward, this contact is strongly affected by transversal faults, which are responsible of the
01/11/1755 Lisbon earthquake, with macroseismic magnitude M 8.7 (Pereira de Sousa 1919; Abe
1979; Johnston 1996; Martínez-Solares and Lopez-Arroyo 2004). This event involved significant
damage on the Moroccan territory and a tsunami on the Atlantic coast (Levret. 1991). It was followed
by many aftershocks, including that of November 18, the most strongly felt in the North of Morocco
(Tangier, Tétouan) (Levret et al. 1991). This zone also generated on 28/02/1969 a strong earthquake
with magnitude Mw 7.9 (e.g. Gracia et al. 2003; Grandin et al. 2007).
Zone 7: Cheliff
The Cheliff basin is one of the well-known and most studied areas in the Tell Atlas (Yielding et
al., 1989). It was the site of destructive and large to moderate earthquakes such as the 1954
Orléansville Ms = 6.7 and the El Asnam, Ms = 7.3 earthquake (Ouyed et al., 1981), the Tadjenna
earthquake, Mw 5.0 (Beldjoudi et al. 2012). The 1980 earthquake is the best instrumentally and
geologically documented seismic event in the western Mediterranean area and is very representative
of the neotectonics in the Tell Atlas. The associated coseismic surface ruptures exhibited 36 km of
segmented NE-SW striking thrust faulting, showing 2m of average vertical displacement (Philip and
Meghraoui 1983). Paleoseismic studies along the El Asnam fault related fold have produced a wealth
of information on its late Quaternary activity (Meghraoui et al. 1988a;b; Meyer et al. 1990).
Significant progress has been made on the resolution of the recurrence interval and slip rates
through a detailed analysis of earthquake-induced flood deposits and leveling profiles across the
main thrust fault and secondary faulting by Meghraoui and Doumaz (1996). An average recurrence
interval is calculated to be 720 years during the Holocene time. During periods of high seismic rate,
this recurrence time may reduce to 300 to 500 years. The minimum uplift rate is 0.6 mm/y and with
coseismic slip variation, it may range from 0.25 mm/y to 1.6mm/y from which Meghraoui and
Doumaz (1996) estimated a shortening rate ranging between 0.17 mm/y to 1.2 mm/y. The El Asnam
fault zone offers the necessary elements to understand the thrust fault behavior and the related
folding (King and Vita Finzi 1981; Meghraoui 1988) and is taken as a reference example for the
identification of other active geological structures in northern Algeria. The Tenes-Abou El Hassan
active fold, comparable to the one of El Asnam and situated 50 km to the North, displays on his
southern flank a 23 km long reverse faulting with flexural slip (Aoudia and Meghraoui 1995). Three
segments were identified along strike, indicating some evidence for the occurrence of possible large
earthquakes in the past. The 1922 moderate sized earthquake (Mw = 6.0) was probably the result of
a rupture displacing about 13 km of the central segment. Morphological evidences such as steep fold
scarp, tilted young quaternary deposits, uplifted alluvial terraces, southward progressive migration of
meanders and the impressive graben-like structure on the top of the anticline refer to fold growth
process by successive coseismic movements and yield 0.5 mm/y of uplift rate. The Boukadir active
fold (30 km) located between the El Asnam structure and the one of Tenes-Abou El Hassan, displays a
N065 trending thrust fault (Meghraoui 1988). Another structure, corresponding to the eastern edge
of the Chelif basin, is the Dahra active broken fold. South of the Dahra range Anderson (1936)
describes several asymmetrical anticlinal ridges with a transport direction to the southeast. South
and southwest of the Tenes-Abou El Hassan region, flexures are juxtaposed to flat-lying young
deposits where the maximum thickness of Neogene and Quaternary formations may reach 5000 m
(Perrodon 1957). Meghraoui (1982) and Thomas (1985), in their neotectonic analysis of the oriental
and occidental parts of the basin, respectively, determined N-S to NNW-SSE shortening directions. In
the western Cheliff basin, Thomas (1985) points-out the existence of E-W trending folds with NE-SW
striking axes controlled by inferred E-W striking deep-seated dextral faults. We believe that each of
these structures can be associated with parallel thrust and reverse faults and each of them shows a
similar behaviour as that of the El Asnam fault.
Zone 8: Gouraya
The Gouraya zone is between the Mitidja and Cheliff basins. In this area Glangeaud (1932)
and Perrodon (1957) reported the existence of thrusts with a strike slip component affecting
Cretaceous napes that are unconformably covered by folded Neogene and Quaternary deposits.
However, in contrast to the previous zones, the quaternary basins of this province are very squeezed
making the tectonics more complex. The peculiar distribution among pre-Noegene, Neogene and
recent formations shows that considerable strike-slip motion is required to explain stratigraphic
mismatches across individual basins. It is rather difficult to single out the seismogenic sources,
because of the intricate and puzzling tectonic fabric accompanied by very fast erosional processes
emphasized by regional landslides. The retrospective study and related reconstruction of the
macroseismic field of the second largest seismic event (I0 IX EMS) which occurred on 15 January
1891, at Larhat in the coastal area of north central Algeria, coupled with a morphological analysis,
allowed a better understanding of the seismotectonic framework of this zone (Maouche et al. 2008).
These authors present an aerial photo which shows the landslide on which the city of Larhat (ex
Villebourg) is constructed today. This landslide was reactivated during the earthquake and is
characterized by the presence of 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 geological structure
(Maouche et al. 2008).
Zone 9: Mitidja basin
Like in the Cheliff zone, the Mitidja zone shows the same features of active deformation. The
Mitidja region, in terms of seismic history as reported by Harbi et al. (2007) has experienced several
destructive earthquakes in the past, like the earthquakes of January 2, 1365 (X, EMS); February 3,
1716 (IX, EMS); April 14, 1839 (VIII, EMS); June 18, 1847 (VI, MSK) and November 5, 1924 (VIII, MSK).
These events were followed by a long sequence of aftershocks suggesting a high magnitude for the
main shocks. The strongest seismic event recorded in the coastal region of Algiers is the ChenouaTipaza earthquake of October 1989 (Ms = 6.1). Meghraoui (1991) associated this event to a blind
reverse faulting related to the Sahel anticline. The focal mechanism solution yielded a reverse fault
striking ENE-WSW that is in good agreement with the western segment of the active Sahel folding
structure delineated from geology. Two other segments can be observed along strike, yielding in
total 70 km of folded structure. The northern flanks of this coastal structure show a step like
morphology of marine terraces reflecting recent uplift movements. Recently, Maouche et al. (2011)
estimated two periods of uplift indicating 0.9 mm/year and 2.1 mm/year post 45ka and prior 45 ka,
respectively, by using
14
C and dating inferred from SPECMAP curves. The 70 km Sahel anticline
constitutes the most striking feature from the seismic hazard point of view. This basin clearly
highlights the important issue of blind faulting that remains one of the main problems to be faced
from the seismic hazard point of view. However, the north-eastern part of the Mitidja basin deserves
more attention. This area is nowadays better known, from a seismotectonic point of view, since it
experienced, on 21 May 2003, the most destructive shock (Mw 6.8, I0 X EMS) in its seismic history.
This event, associated to offshore reverse faulting, occurred on the northeastern continuation of the
en-echelon fault system bordering the Mitidja basin to the south (see Figure 1b in Ayadi et al. 2008).
The study of aftershocks and velocity structure associated with the Zemmouri earthquake allowed
Ayadi et al. (2008) to better constrain the fault geometry and structure in the Mitidja basin. These
authors showed that the thrust fault is related to a complex pattern of seismic activity with variable
aftershocks density along strike that defines four main segments (Ayadi et al. 2008). On the other
hand and as mentioned by Belabbès et al. (2009), the western and the eastern edges of the Mitidja
basin were reactivated during the Chenoua mount, 1989 (Mw 5.9) and Zemmouri, 2003 earthquakes
(Mw 6.8), respectively and a reactivation of the southern segment of the basin, i.e the Blida thrust
fault, is expected.
Zone 10: Kabylie
The Kabylie zone is characterized by high alpine mountains within a complex structural
environment. It is represented by thrusts underlined by nape fronts striking roughly east-west with a
vergence to the south involving basement rocks. There are no geological or morphological witnesses
of recent activity in this area. This zone is considered to have a low degree of seismic activity, when
considered independently from the neighboring zones. Nevertheless this seismic zone, particularly
the Ain El Hamam-Larbaa Nath Irathen and Tigzirt regions, experienced some damaging or strong
earthquakes like the earthquakes of October 23, 1891 (VII EMS) and April 9, 1927 (V EMS) (Harbi et
al. 2010).
Zone 11: Soumam
The Soummam zone is represented by a Neogene elongated basin clearly observable on
large-scale geological maps. As clearly shown by its geometry, this zone points out two different
structural strikes along its length, corresponding to two sub-basins, one striking almost E–W and the
second striking NE–SW. From the point of view of seismicity, the Soummam valley is characterised by
a moderate and permanent seismic activity. The earthquake catalogue (Harbi et al. 2010) reveals
some seismic crisis, at the beginning of this century, in Mechdallah (formerly Maillot) and El Kseur. By
analysing digital elevation model and aerial photos, Boudiaf (1996) has showed recent tectonic
structures in the Soummam valley. In the Tazmalt-M’chedallah region, alluvial terraces are clearly
deformed by tectonic scarps affecting the Quaternary glacis. These movements are also visible in the
region of Sidi Aich. One should note that Pliocene is largely deformed in the whole Soummam basin.
This zone was on November 16, 2000 the site of the destructive event of Beni Ourtilane (M 5.8)
(Bouhadad et al. 2003).
Zone 12: Jijel-Babor
The Babor ranges is located to the east of the Soummam Valley, and is a prolongation of the
Djurdjura Mesozoic chain. It is a fold belt characterized by deep valleys and high mountain ranges
(2004 m). The Babor mountains correspond to the north-east prolongation of the Biban ranges. The
limestone massif of Kherrata within the Babor zone is also characterised by a moderate and
permanent seismic activity. The seismic history of the region shows that the seismic activity is
relatively moderate and constant. As reported by Benouar (1994) the moderate earthquake of 15
January, 1949 generated surface ruptures striking N070E that are likely associated with an active
asymmetric fold present in the area (Meghraoui 1988). This faulted-fold seems to be responsible of
the constant activity in the Babor zone. The study of the recent earthquake of Laalam of March 20,
2006 (Mw 5.2) shed light on the seismotectonics of the Babor ranges (Beldjoudi et al. 2009;
Guemache et al. 2009; Bouhadad et al. 2010). To the northeast within the same zone lies the town of
Jijel. This coastal city was the site of two destructive earthquakes, on 21 and 22 August 1856,
triggering tsunami at various points of the Algerian and Balearic coasts and producing significant
surface effects and deformation (Harbi et al. 2011). These offshore events (VIII and IX EMS
respectively, Ms 6.6 for the August 22, earthquake) are comparable to the Larhat 1891 and
Zemmouri 2003 earthquakes, respectively (Maouche et al. 2008).
Zone 13: Constantine-Bibans
In contrast to the Central and Western part of Algeria, the Constantine basin is localized at higher
altitudes and exhibits a rather different faulting mechanism from the four above-mentioned zones.
Its geomorphology shows very squeezed and deep valleys with steep slopes. Filed investigations and
conventional geological maps when cleaned up from older structures, show the existence of active
faults. Many of these faults are trending NE-SW in the same direction as the surface ruptures due to
the most significant event that took place in this region, the 1985 Ms = 6.0 (Harbi et al. 2010). The
strike-slip focal mechanism solution is in good agreement with the nature of surface ruptures and
reflects well the squeezed morphology in this uplifted zone, where much of the actual deformation is
more likely to be accommodated by transcurrent motions than by compressional ones. From the
spatial extent of the 1985 aftershock sequence a 30 km maximal fault length is inferred. The largest
events which struck the Constantine basin are the earthquakes of August 4, 1908 (Ms 5.2); August 6,
1947 (Ms 5.0) and October 27, 1985 (Ms 6.0) (Benouar 1994). To the west of the Constantine basin,
Vila (1980) mapped, in the Biban region, a quaternary anticline of Djebel Tella, a fault northern
Djemila and another fault at Djebel Youcef. According to this author, these faults affect the
quaternary deposits and are related to hydrothermal springs. Moreover and in spite of their low
importance, the terraces erected in the Biban ranges by Oued Sellam river in the plateau of Setif, the
network of Guergour near Guenzet and Oued Ksob river are uplifted and tilted. This is a geological
witness of recent activity in this area. The Biban region experienced the largest number of damaging
earthquake in eastern Algeria as reported in Harbi et al. (2010), the most important ones are the
earthquakes of: Mansoura January 8, 1887 (I0 VIII EMS); Mansoura November 24, 1973 (I0 VIII-IX EMS,
Ms 5.1); Bir Haddada September 4, 1963 (I0 VIII-IX EMS, mb 6.3).
Zone 14: Hodna-Biskra
The Hodna basin bounds the Bibans ranges to the south. This Neogene basin is characterised
by relatively high reliefs as Djebel Mâadid (1863 m) (Boudiaf 1996) which corresponds to the western
termination of Hodna mounts, and it is also as well highlighted as the vast depression of Hodna by a
gravimetric study (Zerdazi 1990). The Hodna basin shows similarities with the active Neogene basins
of the Tellian Atlas (Cheliff, Mitidja); in the same way one observe a series of anticlines affecting
recent deposits, oriented in the NE-SW. The tectonics, studied by different authors (Harbi et al.
2003b and references therein) show geometry of fault related fold as the Chott El HammamBoutaleb structure. The reverse fault of Chott El Hammam of 30 km length, which limit the SE side of
the Boutaleb anticline, would have generated the January 1, 1965 M’sila earthquake. Moreover the
presence of folded Pleistocene deposits on this fault related fold is indicative of its recent activity.
The Hodna basin was the site of several damaging events, among which: M'sila January 30, 1885 (I0
VII EMS, Ms 5.6); M'sila December 3, 1885 (I0 IX EMS); Berhoum February 12, 1946 (I0 VIII EMS, mb
6.2); M'sila January 1, 1965 (I0VIII EMS, Ms 5.5) (Harbi et al. 2010). To the east of the Hodna basin,
one observes the Aures region and Biskra oasis to th south, which experienced a damaging
earthquake on November 16, 1869 (I0 VIII EMS) (Harbi et al. 2003a;b). From a tectonic point of view,
the Aures massif is structured into folds and thrust during the Mesozoic and Cainozoic and even till
Pleistocene. The recent tectonic activity is not easily perceptible. Nevertheless, some previous works
confirm the presence of recent tectonics in this southern part of the Tellian Atlas. The most uplifted
alluvial terraces observed are situated along the Oued El Abiod river (in the M’chouneche gorges
near Biskra) give evidence of recent tectonic activity. However, the lack of dating in quaternary
deposits does not permit to specify the continuity of this tectonics until the recent time. Regarding
the south-atlasique flexure which limits the Aurès belt and the Saharan platform, a synthesis of
scientific work (Harbi et al. 2003b and references therein), shows a land strip formed by series of
flexures, faults related folds and reverse faults, relaying from west to east. The last recurrent faulting
observed in the Aurès belt are of post-Pliocene age. Busson (1970) thought of a rejuvenation of the
age of this structure in Biskra zone which could be post-Pliocene confirmed later by Frizon de
Lamotte et al. (1990). Two tectonic phases are distinguished during the structuring of the southatlasic flexure; the first one of upper Eocene age and the second of post-Burdigalian until Pliocene
and even Quaternary ages. This latter observation is attested by the presence of Pliocene
conglomerates, systematically rocked southwards from 40° to 60° and even forming in some places
Pliocene and quaternary folds. Hence the seismic activity in the Saharan Atlas is in favour of a
process of recent tectonic.
The western part of the Zone 14 includes the region of Aumale which experienced one of the largest
shock that occurred in Algeria, that is the Aumale June 24, 1910 Ms = 6.6 event (Benouar 1994).
Zone 15: Guelma
The geological studies carried out in the Guelma basin show a pull-apart basin formed
between two overlapping east-west dextral strike slip faults. Crustal extension occurs in between.
The size of the pull-apart is quite important and this is linked to the amount of overlap (25 km) and
distance between overlapping segments. In this basin two particular faults are observed which are
Bouchegouf and Hammam N’Bailis faults. These faults, affecting the quaternary deposits and related
to hydrothermal springs (Vila 1980), are potentially active and could be in relation with the damaging
earthquakes of the Guelma basin: Héliopolis on December, 17, 1850 (I0 VI EMS); Guelma on February
10, 1937 (I0 VIII EMS, mb 5.4) and recently Hamam Debbagh on September 20, 2003 (mb 5.2) with a
strike slip source mechanism. The seismicity south of Guelma basin is also present, even of it is of low
magnitude (Harbi et al. 2011). Based on aeromagnetic studies, Zerdazi (1990) displayed to the northeast of Saharan Atlas, a NE-SW fault extending from Khenchela anticline to north of Ouenza and
going through the south of Mesloula. This fault could have been active since the Turonian till the
Quaternary (Vila 1980). Additionally, the residual gravimetric map allowed this author to point out
the Terraguelt fault trough and to specify its outlines.
Zone 16: Annaba
The Annaba zone is the easternmost zone in the Tell Atlas of Algeria and extends to Tunisia.
The outcrops in this area are mainly basement Palaeozoic rocks. The most recent faulting system is
striking NE-SW. Like in the Kabylie zone, there are no witnesses of recent tectonic activity. The only
seismic event strongly felt in the region, on a quite large area of perceptibility, is the offshore
earthquake of Herbillon which occurred on September 19, 1935 (Harbi and Maouche 2009).
Zone 17: Sahara Atlas
This is the only zone that does not belong to the Tell Atlas chain. The Sahara Atlas is
considered as another structural domain made of thrust and folded structures (Vila 1980; Wildi
1983), defined as being active until at least the beginning of the middle Pleistocene (Outtani et al.
1995). Unfortunately there is no knowledge of whether there are evidences of more recent activity
or not. This zone is separated from the active Tell Atlas Mountains by the stable High Plateaux zone.
Therefore it is not within the plate boundary zone, and consequently the seismic activity is low.
However, the few events that took place in the area were strong enough to cause damage and loss of
lives, mainly due to the low quality of building materials (Benouar 1994). We would not describe this
zone as being stable or tectonically inactive, but it simply behaves differently from marginal active
orogens. This zone requires more investigations in historical seismicity.
Zone 18: Tunis-Bizerte
This is the zone where had occurred the strongest historical event between 410-412 known
as Utique event mentioned in several catalogues with intensity I0 = X. This event was at the origin of
the total destruction of Utique City and its hardboard in the Punic epoch. Several seismotectonic
studies (Hfaiedh 1983; Hfaiedh et al. 1985, Ben Ayed 1986; Kacem 2004) have identified a weak
tectonic structure showing a sort of mosaic of blocs cute by the main fault system trending NE-SW,
NW-SE faults and East –West faults acting as strike slip. The NE-SW fault system known also as the
atlasic trending faults are in fact old faults reactivated during the most orogenic phases as reverse
faults sometime with a strike slip component as shown by the focal mechanism of the most recent
5.6 magnitude event in Sidi Thabet region Northwestern of Tunis (Hfaiedh 1983). In the recent
period, this zone was shaken by several events: 1 December 1970 Sidi Thabet earthquake (M 5.6), 9
April 1979 Ras Jebel earthquake (M 4.9) to the East of Bizerte. Micro tectonic measurements and
focal mechanism solutions show the persistence of NNW- SSE stress field in conformity with the
African-Eurasian plates convergence. Using the conversion formula M = 0.6 I0 + 0.78 (Hfaiedh 1983),
the Utique historical event magnitude is estimated at 6.78. Based on the compilation of historical and
instrumental seismicity the maximum expected magnitude in this zone is estimated at 7.0. This zone
could be extended to the south–east to overlap the zones 15 and 16 since the most important
tectonic structures are oriented NE-SW which is a characteristic of the Tunisian Atlas.
Zone 19: Cap Bon and Sahel Zone
This zone is part of the eastern Tunisia and pelagean platform extending to the offshore
domain. It is limited to the West and NW by the North – South Axis important feature of the Tunisian
geology that was interpreted as deep and old structure considered as barrier separating the Tunisian
Atlas to the West from the Sahel and pelagean domain to the East. The main active area within the
current zone is the golf of Hammamet and Monastir and Mahdia region. Historical and spectacular
Neotectonic prove was discovered in Monastir area where a roman mosaic showing strike slip fault
and centimetric fold was discovered during archeological investigations (Kamoun et al. 1980). The
maximum observed magnitude in the recent time was known in the gulf of Hammamet (M 5.6), in
Jammal 1977 (M 4.7) and in Mahdia coastal belt extending to the offshore east-west grabens. Other
archeological and neotectonic investigations carried out in Sidi Khalifa region prove that tectonic
instability has witness of earthquake occurrence during the historical time mainly roman epoch
(Kacem et al. 1997).
Considering the maximum observed magnitude, within this zone, maximum magnitude of M
= 6.0 should be expected.
Zone 20: Gabes and Gulf of Gabes
This zone is stretching West-East and is covering the golf of Gabes (offshore domain) and
to the Western part is on land (shore). This last part could overlap the extension of Gafsa fault
system near Gabes. Gafsa fault system (Zone 21) is stretching almost NW-SE from the Algerian
border to the plain of Jeffara south of Gabes. This SE extremity of Gafsa fault system could be linked
to the in-land part of zone 20 since there are similarities of geology and tectonics in this area. This
region is known by frequent and low seismicity since the installation of the local seismic array in
1989. However, the historical seismicity catalogue mentions a 5.6 magnitude event. The second
region within Gabes zone is the Gulf of Gabes which is the domain of moderate seismicity with
magnitude around 5. The active structures are normal faults separating grabens trenching N130 –
N140. The maximum expected earthquake within this zone could reach magnitude of 6.0.
Zone 21: Kasserine – Gafsa
The northern branch of this zone is covering the Kasserine region which belongs to the
Tunisian Atlas with grabens. The major tectonic structure is represented by Kasserine fault stretching
almost East–West. The displacement process initiates occurrence of events with magnitudes M= 4.4 4.9. Within the Kasserine depression area, besides the peripheral faults stretching in North West –
south east direction, there are also transverse active faults stretching in north east–south west, and
north-south direction. The intersections of the two systems are an area with increased potential of
occurrence of stronger earthquakes. The maximum expected magnitude that could occur within this
zone is around 5.5. The southern branch of this zone is covering the Gafsa region and part of the
Southern Atlas. The main tectonic structure into this zone is represented by Gafsa regional fault
running from the Algerian border to the south of Gabes and may extend through Jeffara fault to the
Libyan border in the south east. This zone was shaken by several moderate events with magnitudes
varying from 4.7 to 5.6. The central part of Gafsa fault, which runs through Gafsa City could generate
a maximum earthquake of magnitude M = 6.0.
Zone 22: Hun graben:
This zone coincides with the NW-SE trending Hun graben, the westernmost tectonic element
of the Sirt basin rift system. The Hun graben area was the site of several earthquakes through history.
In April 19 -1935 a great earthquake (mb=7.1) hit the Hun graben area near the city of Al Qadahiah,
followed by a very large number of aftershocks including two of magnitudes 6.0 and 6.5 on the
Richter scale (Suleiman and Doser 1995). In 1941 a major earthquake of magnitude 5.6 hit the Hun
graben area. This zone was the sight of a large number of earthquakes; of noticeable magnitude
were those events that hit in 1983, 1992, 2000 and 2001 with magnitudes 4.4, 4.3, 3.7 and 3.4
respectively. The seismicity in this zone seems to concentrate at the eastern boarder of the graben
(Suleman 2007).
Zone 23: Western Gulf of Sirt
This zone was the site of the 1939 earthquake sequence. The 1939 main shock was of
magnitude 5.6 and was followed by a number of aftershocks. Other earthquakes hit the area and
seem to align in a NE-SW trending fashion. First motion results suggest strike-slip and normal faulting
occurring through the zone. (Suleman 2007).
Zone 24: Offshore Tripoli
The offshore Tripoli area continued to be seismically active. This cluster of seismicity was
concentrated in an offshore area located 80 km northeast of Tripoli. In 1974 an earthquake (Ms=5.6)
whose epicenter is in this offshore seismically active area shook Tripoli and its environs area.
Earthquakes reported to hit the same area in 1975, 1976, 1981, 1988, 1990, and 1999, which
confirms the seismic activity of this area (Suleiman and Doser 1995
Zone 25: Al-Marj
This zone represents the coastal regions of the NE part of the country. This zone continues to
be seismically active area. The city of Al-Maraj was heavily damaged by an m=5.3 earthquake in 1963.
The seismic activity in this zone extends to the north as far as Greece. In April of 2008 the same was
hit by an earthquake of magnitude 4.1. This earthquake was felt by most of the people and cause
some damage to certain buildings (Suleman 2007).
Zone 26- Eastern Sirt Basin
Although this zone is less active comparing to the other zones, a number of earthquakes
were reported to hit this region. This zone coincides with the eastern boarder of Sirt basin refit
system (Suleman 2007).
Zone 27: Southern Gulf of Suez
This seismic zone represents a broad area of active tectonics as evidenced by the high level
of seismicity and the generally high heat flow, where small cells of magmatic activity are just
beginning to nucleate (Cochran 2005). The fault pattern in the Gulf of Suez consists of two major
sets: (1) the main clysmic fault trend (N 40°–30° W), that contains normal faults parallel to the rift
axis and created during Neogene times in a pure extensional regime (Said 1962; Bartov et al. 1980;
Jarrige et al. 1986; Colleta et al. 1988), (2) Transfer faults with NNE, WNW and ENE trends (Patton et
al. 1994). The southern Gulf of Suez is the site of the magnitude 7.2 Ms earthquake on March 31,
1969. The focal mechanism solution of this earthquake indicates that, the southern part of the Gulf
of Suez is dominated by active extensional stress regime. The mechanism of this event corresponds
to nearly pure dip-slip movement along the NE dipping fault (Huang and Solomon, 1987; Jackson et
al. 1988; Figure 2). The Stress inversion for the high quality focal mechanisms in this zone reflects a
relatively homogeneous stress pattern dominated by ENE-WSW (N52°E) extension regime (σ1 axis
have steepest plunge) which is perpendicular to the rift trend (Hussein et al. 2008). The composite
mechanisms of the events located at the southern part of the Gulf of Suez show that the activity took
place along both longitudinal and transverse fault planes inherited from the basement tectonics
(Hussein et al. 2006).
Zone 28: Central Gulf of Suez zone
This zone is separated from the southern Gulf of Suez zone by WNW trending
accommodation zone (Meshref 1990). On the other sides of this accommodation zone, the direction
of the tilt is reversed. The central tectonic province is characterized by a regional NE dip while the
southern tectonic province is characterized by a regional SW dip. The central zone is dominated by
the two major sets of fault pattern existing in the southern Gulf zone. It is also characterized by the
occurrence of shallow, micro earthquakes. The seismic activity in this part of the gulf is low to
moderate compared to the southern Gulf zone. In this zone, the largest instrumentally earthquake is
Shukeir earthquake of 12 June, 1983 with Mw = 5.2. The most representative focal mechanism
solution of this zone obtained from the stress tensor inversion shows pure normal faulting
mechanism along a NW-SE trending fault plane and dipping to the NW (Abdel Rahman and El Etr
1978, Figure 2).
Zone 29: The Cairo-Suez zone
This zone extends from Gharandl accommodation zone, which separates the northern part of
the Gulf of Suez from the central Suez rift to the Nile Delta. Generally, the Cairo-Suez area of this
zone is characterized by the existence of three fault trends; ENE, EW, and NW (Abdel-Rahman and ElEtr 1978). These structures are assigned to an Oligocene age with Post-Miocene rejuvenation (Farag
and Ismail 1959). Moustafa and Abdallah (1991) argue a post Early Miocene age for this structural
deformation, where the Late Oligocene-Early Miocene basalts are affected by such faults.
Instrumental seismicity from 1900 to 2004 shows few small-moderate sizes events with magnitudes
≤ 5 in this source area. The majority of them overlie a well defined EW to WNW surface faults. The
largest instrumental earthquake in this zone are the 29 April, 1974 and 2 January, 1987 of Mw 5.2.
The most representative focal mechanism solution of this region is the event of 24 August, 2002
which shows normal faulting with two nodal planes tending E-W to WNW-ESE (Figure 2), in good
agreement with the observed surface faults based on the detailed field geology studies of Moustafa
and Abd-Allah (1992).
Zone 30: Southwest Cairo Zone
This zone is characterized by the existence of two main systems of normal faulting (Sehim et
al. 1992). The first trends WNW to E-W while the second trends NW-SE. The WNW to E-W trending
faults are of diagonal slip movement where the horizontal sense of dislocation is always of right-later
type motion, while the vertical displacement are of normal sense. The NW striking faults are of
normal type. This zone was struck by the 12 October 1992 Cairo earthquake, which is the largest
instrumentally recorded earthquake in this zone (Mw=5.8). The fault plane solutions of this
earthquake are compatible with the E-W to WNW striking normal faults with a dextral strike slip
motion (Abou Elenean et al. 2000, Figure 2). This zone is considered as important as it is close to the
highly populated Cairo City.
Zone 31: Gulf of Aqaba zone
The Gulf of Aqaba is recognized as an active seismic zone where many destructive
earthquakes have been occurred. The earthquakes of this zone are characterized by shallow foci and
tend to occur along NE trending faults. This zone is considered the sole site within area, well known
by its high seismic activity which occurs as isolated sequences, those are characterized by foreshockmainshock-aftershock, mainshock-aftershock and swarm type activity (Abdel Fattah et al. 1997). The
Gulf of Aqaba transform fault is dominated by a sinistral strike slip with a minor normal component
(Garfunkel 1981). The main fault trends of the Gulf of Aqaba are N-S to NNE-SSW and NW-SE (BenAvraham 1985; Abdel Fattah et al. 1997; Pinar and Türkelli 1997). The largest instrumental event
occurred in this zone is the 22 November, 1995 (Mw = 7.2) which was felt in all countries surrounding
the Levant Fault System. The focal mechanism solution of this event indicates mainly left-lateral
strike-slip with a small component of normal-dip-slip along a NE-SW striking plane (Figure 2). This
sense of motion is consistent with the principal sense of motion recorded in this zone.
Zone 32: Nile cone zone
The largest event in this zone is that of September 12, 1955. This earthquake took place
offshore Alexandria within the Nile Cone, with surface wave magnitude Ms 6.7. The mechanism of
this event corresponds to a reverse faulting with strike slip component on NW/ENE trending planes.
The E–W to ENE trending plane is consistent with the present day tectonics, which might reflect
rejuvenation of the pre-existing E–W to ENE–WSW Mesozoic faults (Korrat et al. 2005). The motion
along this plane is reverse dip slip with a small left lateral component (Figure 2).
Zone 33: Ras El-Hikma zone
This zone was affected in May 28, 1998 by a moderate magnitude earthquake with Mb = 5.5.
The source mechanism of this event shows a high-angle reverse fault mechanism generally trending
NNW–SSE (Abou Elenean and Hussein 2007). The P-axis trends ENE–WSW consistently with the
prevailed compression stress along the southeastern Hellenic arc and southwestern part of the
Cyprean arc. This unexpected mechanism is most probably related to a positive inversion of the NW
trending offshore normal faults (Mosconi et al. 1996) and confirms an extension of the back thrusting
effects towards the African margin.
Zone 34: Levant basin zone
On January 30, 1951, an earthquake with MS = 5.7, was recorded in this zone on the
periphery of the Nile Cone and continental slope. This earthquake corresponds to normal faulting
mechanisms with a slight strike slip component along a NW trending fault plane, dipping NE (Korrat
et al. 2005). The motion is then normal dip slip with a slight right lateral horizontal component. The
mechanism probably shows that the preexisting NW Oligocene-Miocene faults have been
reactivated.
Zone 35: Aswan zone
This zone is the source of Nov.14, 1981 with Ms of 5.4. The majority of the local earthquakes
appear to be concentrated at the intersection points of the E-W and the N-S faults existing in this
zone (Hussein et al. 2008). Generally, the overall faulting displacement exist in this zone is strike slip
with small normal component. The N-S faults have low degree of activity compared with the E-W
faults. The November 14, 1981 earthquake shows strike slip mechanism with a normal component on
a plane trending ENE–WSW to E–W (Figure 2).
Zone 36: Gilf Kebir zone
This zone reflects the instability of the southern part of the western desert where the
December, 9, 1978 earthquake with a magnitude mb = 5.7 took place (Megahed 1987). Most of the
major tectonic elements in this zone strike NE-SW and affect the rocks of Paleozoic to Eocene in age.
The fault plane solution of the Gilf Kebir earthquake shows dextral strike slip movement along a fault
plane striking NE-SW (Maamoun et al. 1980).
Zone 37: Beni Suef zone
This zone was the site of the October 11, 1999 earthquake with a local magnitude of 5.0. The
focal mechanism solution of this event indicates a normal faulting mechanism with a slight shear
component along a true fault plane trending NW and dipping towards SW (Abou Elenean and
Hussein 2008). This result coincides well with the dominant normal faulting structure in this zone.
Zone 38: West Sohag zone
This zone is characterized by the existence of NNW-SSE trending faults. On December 14,
1998 an earthquake of ML 5.4 occurred in this zone. Mechanism of this event indicates normal
faulting mechanism with a slight shear motion along a plane trending NW-SE which is slightly
different from the surface traces (Abou Elenean 2007).
Zone 39: Abou Dabbab zone
This zone is marked by two moderate magnitude earthquakes, the 12 November 1955 Mb
6.1 and the 2 June 1984 Mb 5.1. The source mechanism of this zone is characterized by normal dip
slip motion with a sinistral strike slip component on a plane trending NW-SE. The NW-striking plane
coincides closely with the sinistral strike-slip shears of the Najd fault system.
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