On November 15, 2014, an Mw4.3 earthquake occurred 2 km west of Mihoub village, 60 km SE of Algiers. In this study, we retrieve the relative source-time functions of the mainshock and largest aftershock (Mw3.9) for rupture analysis using the empirical Green’s function method. The two events are nearly colocated with a smaller aftershock (Mw3.5), which is treated as the empirical Green’s function. Moreover, these three events have similar focal mechanisms, suggesting that deconvolution is well posed in this case. The three events were recorded by nine stations of the Algerian permanent network. We use mainly P-wave data. The focal mechanism solution shows dominant reverse faulting with a strong strike-slip component. The two nodal planes align almost E-W, dipping to the south, and NNE-SSW, dipping to the NW, respectively; the fault and auxiliary planes cannot be resolved from hypocenter locations alone because too few aftershocks were recorded by the permanent network. The results show unilateral rupture propagation to the ENE and complex rupture with multiple episodes for the mainshock. The largest aftershock shows similar behavior with slightly less pronounced directivity at some sites. The rupture directivity for the mainshock is estimated at about N66° E, and the rupture velocity is Vr = 0.66β. The E-W nodal plane of the best-fit focal mechanism is the preferred fault plane because it best agrees with the directivity direction and is consistent with the E-W faulting that dominates in the region.

The North Africa passive margin is affected by the ongoing convergence between the African and Eurasian plates. This convergence is responsible for coastal uplift, folding, and reverse faulting on new and reactivated faults on the margin. The active deformation is diffuse and thus rather difficult to locate precisely. We aim to determine how a coastal landscape evolve in this geodynamic setting and gain insights into active tectonics. More particularly, we evidence and quantify coastal uplift pattern of the Chenoua, Sahel, and Algiers reliefs (Algeria), using sequences of marine terraces and rasas and computing several morphometric indices from the drainage pattern. Upper and Middle Pleistocene uplift rates are obtained by fossil shoreline mapping and preliminary U/Th dating of associated coastal deposits. Extrapolation of these rates combined to analyses of sea-level referential data and spatial relationships between marine terraces/rasas and other geological markers lead us to tentatively propose an age for the highest coastal indicators (purported the oldest). Values of morphometric indices showing correlations with uplift rate allow us to analyze uplift variation on area devoid of coastal sequence. Geological and geomorphological data suggest that coastal uplift probably occurred since the Middle Miocene. It resulted in the emergence of the Algiers massif, followed by the Sahel ridge massif. The Sahel ridge has asymmetrically grown by folding from west to east and was affected by temporal variation of uplift. Compared to previous study, the location of the Sahel fold axis has been shifted offshore, near the coast. The Chenoua fault vertical motion does not offset significantly the coastal sequence. Mean apparent uplift rates and corrected uplift rates since 120 ka are globally steady all along the coast with a mean value of 0.055 ± 0.015 mm/year (apparent) and of 0.005 ± 0.045 mm/year (corrected for eustasy). Mean apparent coastal uplift rates between 120 and 400 ka increase eastward from 0.045 ± 0.025 to 0.19 ± 0.12 mm/year (without correction for eustasy) or from 0.06 ± 0.06 to 0.2 ± 0.15 mm/year (with correction for eustasy). In addition, the combination of structural and geomorphic data suggests a low uplift rate for the southern part of the Algiers massif.

In this study, we applied the environmental seismic intensity (ESI-2007) scale to a major recent Algerian earthquake. The ESI-2007 scale is an effective tool to assess the seismic hazard and has been applied to onshore earthquakes. Here we applied the scale to a recent earthquake (Mw 6.8, 2003) that took place offshore in the province of Boumerdès in the north of Algeria along the boundary between African and Eurasian plates. The main shock was associated to an unknown submarine structure. No surface ruptures were observed on the onshore domain, but many earthquake environmental effects (EEEs) were reported during several field investigations. In addition to onshore ground effects, this event triggered turbidity currents responsible for 29 submarine cable breaks. Mapping and describing coseismic ground effects allowed us to distinguish primary and secondary effects like coastal uplifts, liquefaction phenomena, tsunami waves, turbidity currents, cracks, rock falls, slope movements and hydrological anomalies. Considering the total area affected and the distribution of ground effects, we suggest intensity X that appears in agreement with intensity calculated in previous study with the EMS-98 scale. Thus, this method is validated even in the case of a coastal earthquake, and could be applied in the future to Algerian historical earthquakes that have affected scarcely inhabited zones but where EEEs were listed and located.

article i nfo Based on geomorphologic analyses and leveling survey of Quaternary coastal indicators (i.e. marine terraces and notches) along of a 50-km-long coastal stretch of the Algerian coast west of Algiers, Maouche et al. (2011) interpret the coastal segment to have undergone high uplift rates, i.e. 0.84-1.19 mm/yr since last in- terglacial maximum (MIS 5e, 122±6 ka in Table 1, ~140 ka in Maouche et al., 2011) and ~2.5 mm/yr for the last 31 ka. This uplift was said to be due to repeated seismic events that would have occurred during the last ~140 ka, and more particularly during the late Pleistocene.

The similar to 60 km-long Sahel ridge west of Algiers (Tell Atlas, north Algeria) is considered as an ENE-WSW fault-propagation fold running along the Mediterranean coast and associated with a north-west dipping thrust. Its proximity with Algiers makes this structure a potential source of destructive earthquakes that could hit the capital city, as occurred in 1365 AD and 1716 AD. The first paleoseismologic investigation on the Sahel ridge was conducted in order to detect paleo-ruptures related to active faulting and to date them. From the first investigations in the area, a first trench was excavated across bending-moment normal faults induced by flexural slip folding in the hanging wall of the Sahel anticline thrust ramp. Paleoseismological analyses recognize eight rupture events affecting colluvial deposits. C-14 dating indicates that these events are very young, six of them being younger than 778 AD. The first sedimentary record indicates two ruptures before 1211 AD, i.e. older than the first historical earthquake documented in the region. Three events have age ranges compatible with the 1365, 1673 and 1716 Algiers earthquakes, whereas three other ones depict very recent ages, i.e. younger than 1700 AD. Potential of these secondary extrados faults for determining paleoseismic events and thrust behaviour is discussed. (c) 2012 Elsevier Ltd and INQUA. All rights reserved.

Based on geomorphologic analyses and leveling survey of Quaternary coastal indicators (i.e. marine terraces and notches) along of a 50-km-long coastal stretch of the Algerian coast west of Algiers, Maouche et al. (2011) interpret the coastal segment to have undergone high uplift rates, i.e. 0.84–1.19mm/yr since last interglacial maximum (MIS 5e, 122±6ka in Table 1, ~140ka in Maouche et al., 2011) and ~2.5mm/yr for the last 31ka. This uplift was said to be due to repeated seismic events that would have occurred during the last ~140ka, and more particularly during the late Pleistocene.

The Cheliff region has experienced some significant earthquakes in the last century (1937, 1954, and 1980). The most destructive one is that of El Asnam on October 10, 1980, Ms = 7.3 (Io = IX), which destroyed the Chlef city (formerly El Asnam) and its surrounding villages. On December 16, 2006 a moderate earthquake (Mw = 5.0) hit the Cheliff region. The maximum observed intensity (Io = V: MSK-scale) was observed at Abou El Hassen, Benaria, Bouzghaïa and Tadjena. No damages or human losses were recorded. Nevertheless, minor cracks on walls of the old school at Tadjena were observed. The point source focal mechanism of the event was determined by inverting the waveforms of three regional broadband stations of the ADSN (Algerian Digital Seismic Network). It corresponds to thrust-reverse faulting with a strike-slip component. The stress tensor obtained by the inversion of the 15 focal mechanisms available in the Cheliff region exhibits a well constrained compression axis σ1 horizontal and trending N145°. The NW dipping nodal plane indicating a NE–SW thrust fault with a right-lateral component (strike, dip, rake = 249, 38, 137) is more compatible with the regional stress tensor than the steep dipping NNE-SSW nodal plane showing reverse faulting with a left-lateral component (strike, dip, rake = 15, 65, 60). Accordingly, the Tadjena moderate size earthquake can be related to the Boukadir active fault bordering the lower Cheliff basin to the north, a situation similar to that of the El Asnam fault bordering the middle Cheliff basin to the north.

The 21 May 2003 Zemmouri earthquake ( Mw =6.8), which killed 2,278 people, injured 11,450, made 250,000 homeless, and destroyed or seriously damaged 6,000 buildings and 20,800 housing units, is the most significant earthquake to affect Algeria since the 1980 El Asnam earthquake ( Ms =7.3). This paper presents the report of the macroseismic survey conducted by the Centre of Research in Astronomy, Astrophysics, and Geophysics (CRAAG, Algeria) immediately after the earthquake. The collected data set has led to a comprehensive evaluation of damage and estimation of intensity at about 600 sites, a number never reached in previous earthquake damage surveys. The produced isoseismal map portrays the spatial distribution of intensities from III to X EMS. A map highlighting the damage distribution, where various geological and hydrological phenomena are reported, is also presented. The extent of the socioeconomic impact of this event confirmed that Algerian buildings are highly vulnerable to the recurrence of destructive earthquakes.

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