Complex deformation is observed along the plate boundary between the Africa and Eurasia plates, this complexity is highlighted by the faulting mechanism changing from normal faulting at the Mid-Atlantic Ridge to thrust and strike-slip faulting in the Ibero-Maghreb region (Iberia, Morocco, Algeria and Tunisia). The geodynamics of the study area shows the occurrence of NW‒SE convergence between the two plates, with anticlockwise rotation. An updated scheme of the pattern of the tectonic stress direction from the Azores Archipelago to the Tunisian Atlas is presented, along with the analysis of the principal stress axis orientations (Shmax = σ1, Shmin = σ3) from the inversion of fault plane solutions. We used a catalogue of 557 fault plane solutions with only main shocks without considering the related aftershock solutions for the period from 1931 to 2020. This study complements previous work limited to Algeria and eastern Morocco by inverting earthquake mechanisms of aftershock sequences of strong events that occurred in Al Hoceima (Morocco), El Asnam, Chenoua-Tipasa, Zemmouri and Constantine (Algeria). The present work includes the area from Tunisia to the Mid-Atlantic Ridge. The inversion considers only the earthquake mechanisms of events 4.0≤M≤8.4, excluding the aftershocks of strong events. We used the Slickenside analysis package of Michael’s method. The stress field we obtained shows an extensional regime in the Mid-Atlantic Ridge, Terceira Ridge and Azores Islands and a strike-slip regime along the Gloria Fault, Gorringe Bank, and Gulf of Cadiz, to southern Spain. The same regime is also observed in the Rif and Alboran Sea. The stress regime becomes compressional in western Algeria, with strike-slip in eastern and southern Tunisia and an exception in northern Tunisia, where the stress exhibits a reverse rupture process. This study leads us to propose a new sketch of the present stress field along the western part of the Eurasia–Africa plate boundary.

The Tell Atlas of Algeria is an earthquake-prone area, which experienced many strong earthquakes induced by the collision between the African and Eurasian plates. The “Centre de Recherche en Astronomie Astrophysique et Géophysique” (CRAAG), in charge of the Algerian Seismological Survey, provides, for each earthquake, the parameters of the macroseismic intensity ( I 0 ), the epicenter location and the duration magnitude ( M d ). The catalog of Algerian earthquakes contains data represented mainly by maximum intensity I 0 (for historical seismicity and mostly pre-instrumental earthquakes era) and duration magnitude M d for most of the instrumental seismicity. A previous study by Hamdache et al. (Hamdache et al., Seismol Res Lett 81:732–739, 2010) produced a unified catalog of the main seismic event in Algeria. This study aims to homogenize the Algerian seismic catalog and to achieve its completeness by determining empirical relations converting M d and I 0 (given by CRAAG) to M w , M s , m b (given by international seismological agencies). To compute the relationship between intensity and magnitudes, we adopted Linear Orthogonal Regression applied to the dataset we selected. Our catalog is now complete and homogeneous, and M w , M s and m b were assigned for historical earthquakes. This will be useful for earthquake engineering and for those dealing with seismic hazard assessment in the Tell Atlas (Algeria), where several urbanized large cities are under the threat of strong earthquake, as is the case for Algiers capital city. The recent urban development in countries with catalogs limited primarily to macroseismic data increased the need for useable relations to convert epicentral intensities to instrumental magnitude m b , M s or M w .

For any seismic hazard study, a reliable, homogenized and complete seismic catalogue is required. The Algerian seismicity catalogue has been recently updated by retrieving and reappraising many historical events. The Algerian seismic network has also been densified up to about 80 seismic stations covering the Tell Atlas which is the most active area of northern Algeria for monitoring of the seismic activity reducing the magnitude threshold. Recently, we have launched archeoseismological studies to retrieve past strong earthquakes that have affected Roman sites located along the Tell Atlas. Here, we proceed with tectonic investigations around selected sites where significant observed damage was identified. On the other hand, paleoseismological investigations were conducted along the El Asnam fault (now Chlef) following the large Ms 7.3 earthquake of 1980. Paleoseismic studies combined with archeoseismological results provide the dating of past earthquakes and contribute to the completeness of the seismicity catalogue.

For any seismic hazard study, a reliable, homogenized, and complete seismic catalog is required. The Algerian seismicity catalog has been recently updated by retrieving and reappraising many historical events. The Algerian seismic network has also been densified up to about 80 seismic stations covering the Tell Atlas which is the most active area of northern Algeria for monitoring of the seismic activity reducing the magnitude threshold. Recently, we have launched archeoseismological studies to retrieve past strong earthquakes that have affected Roman sites located along the Tell Atlas. Here, we proceed with tectonic investigations around selected sites where significant observed damage were identified. On the other hand, paleoseismological investigations were conducted along the El Asnam fault (now Chlef) following the large Ms 7.3 earthquake of 1980. Paleoseismic studies combined with archeoseismological results provide the dating of past earthquakes and contribute to the completeness of the seismicity catalog.

The Tell Atlas of Algeria, which experienced several destructive earthquakes in the past, is among the most seismic active zones in the western Mediterranean. The seismicity is not randomly distributed but directly related to active geological structures, which mainly correspond to faulted folds. The comprehensive studies of the El Asnam and Zemmouri faults allowed identifying similar structures distributed all over the Tell Atlas, which generated moderate earthquakes. The available paleoseismic data attest that the recurrence of strong earthquakes (M > 7.0) is about 300-500 years while seismicity data suggest 25-30 years for moderate earthquakes. This paper presents a review of active tectonics and seismic hazard in the Tell Atlas.

The seismicity of the Tell Atlas, which extends from the Algerian margin to the South Atlasic fault system, is related to the dynamics of Quaternary basins under an oblique NW-SE convergent stress regime, including the basins of Mleta and L'Habra in the west, Cheliff and Mitidja in the centre, and Soummam, Hodna and Guelma in the east. This seismicity is characterized by moderate to low magnitudes with strong events occurring generally once a decade. Over the last six decades, several moderate, strong and major events occurred that were associated with extensive and severe damage, such as those of El Asnam (1954, M-s 6.7; 1980, M-s 7.3), Constantine (1985, M-s 6.0), Tipasa-Chenoua (1989, M-s 6.0), Mascara (1994, M-s 6.0), Ain Temouchent (1999, M-s 5.8), Beni Ouartilane (2001, M-s 5.6), Zemmouri-Boumerdes (2003, M-w 6.8) and Laalam (2005, M-s 5.8), in addition to numerous large historical seismic events, including those that occurred in Algiers (1365 and 1716, I-o = X), Oran (1790, I-o = X), Mascara (1819, I-o = X), Djidjelli (1856, I-o = VIII) and M'sila (1885, I-o = IX). This chapter presents a review of the seismicity of North Algeria and a detailed analysis of the main earthquakes that have occurred in the Tell Atlas since 1980. Finally, the impacts of several significant earthquakes that occurred during the period between 1364 and 2015 are presented and discussed in terms of seismic energy.

The recent seismicity of the Blida region could not be assessed without due consideration to its earthquake history. We reexamine the 1867 Mouzaia-El Affroun earthquake, which is one of the largest historical earthquakes that occurred in the region, and use the earthquake history of the last 250 yrs to help decipher the complexity of the active deformation of the Mitidja basin (MB). Newly discovered contemporary accounts are used to assess and discuss the extent and intensity of events considered of particular interest and which occurred before the installation of the Algerian seismic network. The 78 significant earthquakes tabulated with comments, among which are 27 events that were not reported in any previous work or catalog, make it clear that the southern border of the MB has long been markedly more active than the northern border. A main objective of this article is to make available the historical data that can be used in further investigations.

The seismic phenomenon is the most damaging natural hazard known in the Mediterranean area. The western part of the Eurasia–Nubia plate boundary extends from the Azores to the Mediterranean region. The oceanic part of the plate boundary is well delimited from the Azores Islands, along the Azores-Gibraltar fault to approximately 12◦W (west of the Strait of Gibraltar). From 12◦W to 3.5◦E, including the Iberia–Nubia region and extending to the western part of Algeria, the boundary is more diffuse and forms a wider area of deformation. The boundary between the Iberia and Nubia plates is the most complex part of the margin. This region corresponds to the transition from an oceanic boundary to a continental boundary, where Iberia and Nubia collide. Although most earthquakes along this plate boundary are shallow and generally have magnitudes less than 5.5, there have been several high-magnitude events. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss and considerable economic damage to the region. From 1920 to present, three earthquakes with magnitudes of about 8.0 (Mw 8.2, 25 November 1941; Ms 8.0, 25 February 1969; and Mw 7.9, 26 May 1975) occurred in the oceanic region, and four earthquakes with magnitudes of about 7.0 (Mw 7.1, 8 May 1939, Santa Maria Island and Mw 7.1, January 1980, Terceira and Graciosa Islands, both in the Azores; Ms 7.1, 20 May 1931, Azores-Gibraltar fracture zone; and Mw 7.3, 10 October 1980, El Asnam, Algeria) occurred along the western part of the Eurasia–Nubia plate boundary. In general, large earthquakes (M ≥7) occur within the oceanic region, with the exception of the El Asnam (Algeria) earthquakes. Some of these events caused extensive damage. The 1755 Lisbon earthquake (∼Mw 9) on the Portugal Atlantic margin, about 200 km W–SW of Cape St. Vincent, was followed by a tsunami and fires that caused the near-total destruction of Lisbon and adjacent areas. Estimates of the death toll in Lisbon alone (∼70,000) make it one of the deadliest earthquakes in history. Measured in lives lost, the 1926, 1980 and 1998 Azores earthquakes (Portugal), the 1954 and 1980 El Asnam earthquakes (North Algeria), the 1994 and 2004 Alhoceima earthquakes (North Morocco), and the 2003 Boumerdes earthquakes (North Algeria) were the worst earthquakes in the past 120 years in the study area. Hence, this region has experienced many large and damaging earthquakes. The city of Cairo (Egypt) was struck in October 1992 by an Mw 5.8 magnitude earthquake, which caused large damage. In 1935, the Syrte region in Libya experienced an M6.9 earthquake with severe damage. Generally, North Africa has experienced moderate earthquakes. However, the region remains vulnerable due to the shallow seismicity, the poor mechanical properties of its soil and local site conditions, and the consequent strength of the ground shaking. Knowing the behaviour of a seismogenic area, particularly the fault zone, will lead us to better assess the hazard and risk in and around large urban areas. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using different approaches (ex. deterministic and probabilistic) using historical and instrumental seismicity, earthquake sources, seismotectonic zonation, structural models and attenuation laws. As a result, reliable seismic hazard maps are produced in terms of maximum displacement and in terms of maximum intensity map.

Research Article| September 30, 2015 The Algerian Homogenized Macroseismic Database (267–1989): A Deeper Insight into the Algerian Historical Seismicity Assia Harbi; Assia Harbi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Amal Sebaï; Amal Sebaï aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Manel Benmedjber; Manel Benmedjber aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Farida Ousadou; Farida Ousadou aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Yasmina Rouchiche; Yasmina Rouchiche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Ahmed Grigahcene; Ahmed Grigahcene aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Djamel Aïni; Djamel Aïni bIbn Badis Mostaganem University, Avenue Hamadou Hossine, 27000 Mostaganem, Algeriadjamel.aini@gmail.com Search for other works by this author on: GSW Google Scholar Seid Bourouis; Seid Bourouis aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Said Maouche; Said Maouche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Abdelhakim Ayadi Abdelhakim Ayadi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Author and Article Information Assia Harbi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Amal Sebaï aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Manel Benmedjber aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Farida Ousadou aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Yasmina Rouchiche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Ahmed Grigahcene aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Djamel Aïni bIbn Badis Mostaganem University, Avenue Hamadou Hossine, 27000 Mostaganem, Algeriadjamel.aini@gmail.com Seid Bourouis aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Said Maouche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Abdelhakim Ayadi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Publisher: Seismological Society of America First Online: 14 Jul 2017 Online Issn: 1938-2057 Print Issn: 0895-0695 © 2015 by the Seismological Society of America Seismological Research Letters (2015) 86 (6): 1705–1716. https://doi.org/10.1785/0220150092 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Assia Harbi, Amal Sebaï, Manel Benmedjber, Farida Ousadou, Yasmina Rouchiche, Ahmed Grigahcene, Djamel Aïni, Seid Bourouis, Said Maouche, Abdelhakim Ayadi; The Algerian Homogenized Macroseismic Database (267–1989): A Deeper Insight into the Algerian Historical Seismicity. Seismological Research Letters 2015;; 86 (6): 1705–1716. doi: https://doi.org/10.1785/0220150092 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Studying the effects of past earthquakes is an important component of predicting the effects of future earthquakes, and knowledge of historic earthquakes is important for understanding future earthquakes. The revision of the historical seismicity of Algeria started at the beginning of this century and is still going on (e.g., Harbi, Benouar, and Benhallou, 2003; Sebaï and Bernard, 2008). The final objective of this reappraisal is to produce an earthquake catalog for Algeria that is as homogeneous as possible, compiled in a unique format, and covering a period of time going back as far as the existing data allow.... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquée en Génie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ∼9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8 × 1016 N.m (Mw = 4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3–4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N–S transform zone between two major compressional fault zones oriented NE–SW.

The Al Hoceima Mw 6.4 earthquake of 24 February 2004 that occurred in the eastern Rif region of Morocco already hit by a large event in May 1994 (Mw 5.9) has been followed by numerous aftershocks in the months following the event. The aftershock sequence has been monitored by a temporary network of 17 autonomous seismic stations during 15 days (28 March-10 April) in addition to 5 permanent stations of the Moroccan seismic network (CNRST, SPG, Rabat). This network allowed locating accurately about 650 aftershocks that are aligned in two directions, about N10-20E and N110-120E, in rough agreement with the two nodal planes of the focal mechanism (Harvard). The aftershock alignments are long enough, about 20 km or more, to correspond both to the main rupture plane. To further constrain the source of the earthquake main shock and aftershocks (mb > 3.5) have been relocated thanks to regional seismic data from Morocco and Spain. While the main shock is located at the intersection of the aftershock clouds, most of the aftershocks are aligned along the N10-20E direction. This direction together with normal sinistral slip implied by the focal mechanism is similar with the direction and mechanisms of active faults in the region, particularly the N10E Trougout oblique normal fault. Indeed, the Al Hoceima region is dominated by an approximate ENE-SSW direction of extension, with oblique normal faults. Three major 10-30 km-long faults, oriented NNE-SSW to NW-SE are particularly clear in the morphology, the Ajdir and Trougout faults, west and east of the Al Hoceima basin, respectively, and the NS Rouadi fault 20 km to the west. These faults show clear evidence of recent vertical displacements during the late Quaternary such as uplifted alluvial terraces along Oued Rihs, offset fan surfaces by the Rouadi fault and also uplifted and tilted abandoned marine terraces on both sides of the Al Hoceima bay.However, the N20E direction is in contrast with seismic sources identified from geodetic inversions, which favour but not exclusively the N110-120E rupture directions, suggesting that the 1994 and 2004 events occurred on conjugate faults. In any event, the recent seismicity is thus concentrated on sinistral N10-20E or N110-120E dextral strike-slip faults, which surface expressions remain hidden below the 3-5 km-thick Rif nappes, as shown by the tomographic images build from the aftershock sequence and the concentration of the seismicity below 3 km. These observations may suggest that strain decoupling between the thrusted cover and the underlying bedrock and highlights the difficulty to determine the source properties of moderate events with blind faults even in the case of good quality recorded data. (C) 2013 Elsevier Ltd. All rights reserved.

This study is devoted to the analysis of the stress state along the Maghreb region based on the inversion of focal solutions. We have inverted the main shock and aftershock focal mechanisms of the strongest seismic events that occurred in five seismogenic zones, from west to east: Al Hoceima (2004), Cheliff (1980), Tipasa–Chenoua (1989), Zemmouri (2003) and Constantine (1985). Most of the focal mechanisms of the aftershock sequences have been constructed within this study. Compressive stress regime is observed in the central part of Algeria between Cheliff and Zemmouri. On both edges of the Maghreb region, the stress regime becomes strike-slip in the Constantine region and in the Moroccan Rift. These different regimes seem to be linked to the free-edge effect (Ionian slab subduction) and to the dynamics of the Alboran Sea in the eastern and western parts of the study area respectively. The σ1 directions experience an anticlockwise rotation of about 20° from eastern to central Algeria. We observe that the direction of σ1 and the direction of convergence are the closest in central Algeria, where the collision is not perturbed by edge effect.