Assia Harbi

Coastal uplift and thrust faulting associated with the Mw = 6.8 Zemmouri (Algeria) earthquake of 21 May, 2003

[1] A shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 May 2003 earthquake (Mw 6.8) in northern Algeria. We measured the amount of coastal uplift on a white band (emerged algae) and harbors quays between Boumerdes and Dellys. Most of measured points were collected using tape and differential GPS on rocky headlands with σ ± 0.15 m error bar (tidal prism). Leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area. The uplift distribution shows an average 0.55 m along the shoreline with a maximum 0.75 m east of Boumerdes and a minimum close to 0 near Cap Djinet. The active deformation related to a thrust fault is modeled along the ∼55 km coastline. The dislocation model predicts surface slip on a N 54°E trending reverse fault, dipping 50° SE in agreement with CMT solution and coastal uplift. The faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore.

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part I: Review of historical seismicity

As large destructive seismic events are not frequent in Algeria, anexhaustive knowledge of the historical seismicity is required to have arealistic view of seismic hazard in this part of the world. This research workpresents a critical reappraisal of seismicity in the north-eastern Algeria forseismotectonic and seismic hazard purposes. This part of work focuses onthe seismicity of pre-1900 period for the area under consideration[33°N-38°N, 4°E-9.5°E]. By going back tothe available documentary sources and evaluating and analysing the eventsin geographical, cultural and historical context, it has been possible toidentify 111 events, from 1850–1899, which are not reported in therecent Algerian catalogue. Several spurious events, reported in standardlistings, have been deleted and nine unknown events have been discovered.It is quite clear that macroseismic information derived from press reportsand published documents in Algeria, under certain conditions, is veryincomplete, even for destructive earthquakes, located in the countrysideaway from communication centres. One of the reasons for this iscensorship, noticeable during the colonisation period. Critical analysis ofnewly collected information has allowed the determination and/or theimprovement of the macroseismic parameters of each event, such aslocation, maximum epicentral intensity and magnitude to produce anearthquake catalogue as homogeneous and complete as the available data,for the zone under study. The criteria used in this research are explainedand eight historical earthquakes have been the subject of retrospectivemacroseismic field construction.The investigation of historical earthquakes is one of the most important taskin studying seismotectonic for seismic hazard evaluation purposes.

Neotectonics and associate seismicity in the Eastern Tellian Atlas of Algeria

Seismicity in the Eastern Tellian Atlas of Algeria is active of moderate to low magnitude. The direct identification of active fault is often a difficult task. In fact, in this region, despite the intense seismicity, only the Constantine earthquake of 27 October, 1985 ( M s = 5.7) and the Kherrata earthquake of 17 February, 1949 ( M s = 4.7), have generated surface ruptures. Hence, the integration of both geological, historical and instrumental seismic data are important in order to characterise the most important seismogenic structures. This paper presents a preliminary overview of the identified neotectonic faults that we consider active in the Eastern Tellian Atlas of Algeria. Thus, seismicity and neotectonic maps are presented and the faults which are active or potentially active from a neotectonic point of view are shown in relation with the main seismic groupings. This study based mainly on available seismic and bibliographic data and several unpublished marine seismic data enable us to suspect a fault as the eventual source of the Jijeli earthquake of 21 August 1856 that destroyed the Jijeli town and its surroundings. The results inferred from this work represent a starting point for more detailed studies in seismogenic areas.

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part II: 20th century seismicity and seismotectonics analysis

The main objective of the research work isthe homogenisation of the two recentAlgerian earthquake catalogues for thecommon covered period of time, from 1900 to1990, for the region under considerationlimited by [33°N–38°N,4°E-9.5°E] and the updatingof the catalogue for the twentieth century(1900–2000). To mitigate the deficiencyof the incompleteness of catalogue, aneffort was made to establish a correlationbetween surface-wave magnitude Ms andbody-wave magnitude mb in the form ofMs = a + b (mb). A complete, exact andhomogeneous earthquake catalogue as much aspossible, comprising 870 seismic events,has been compiled. Seismicity analysis ofthe region shows a strong concentration ofseismicity along a band of no more than400 km width oriented mainly in theeast-west direction parallel to the coast.Moreover, earthquakes in this zone arerather associated to strike-slip mechanism.The focal mechanism show a regional stressregime that corresponds to horizontalcompression in NW-SE to N-S direction. As aresult of the review of the seismicity ofnorth-eastern Algeria from the compilationof checked and corrected data and itscorrelation with other geologic andgeophysical investigations based ondocumentary sources, it was possible toconstruct a most complete seismotectonicmap. It leads also to delineate fourseismogenic zones in the Tellian Atlas, aless important zone in the Saharan Atlas, asixth zone at the boundary of both Atlasand finally, a seventh one along thecoastal zone. The seismicity-active faultscorrelation of some of these defined zonesis examined in details with a specialattention to the Saharan Atlas zone, theHodna and Biban zone as well as Soummam andBabor zone where further research workallowed to find some neotectonic featuresconsidered as a significant sign of recenttectonic activity.

Macroseismic study of the Zemmouri earthquake of 21 May 2003 (Mw 6.8, Algeria)

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.

Reappraisal of the Seismicity of the Southern Edge of the Mitidja Basin (Blida Region, North‐Central Algeria)

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.

Roman literary and epigraphic sources for the study of historical seismicity in Algeria circa 42–420 ad

The seismicity of Algeria since the nineteenth century is relatively well documented. However, compared with the numerous damaging earthquakes that are documented since 1850, fewer than a dozen reports of earthquakes are listed for the pre-1850 ad period, suggesting that the historical record is missing a substantial number of earthquakes. This paper examines the use of literary and epigraphic sources relevant to the investigation of seismicity in Algeria during Roman times. We provide examples where the meager written literary record may be supplemented with appropriate archaeological and epigraphic data describing damage to ancient Roman sites. The examples show that collaboration between earth scientists and archeologists is of utility in improving the seismic record and highlights the need for further study of data sources and repositories located both inside and outside of Algeria.

Active Tectonics and Seismic Hazard in the Tell Atlas (Northern Algeria): A Review

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.

A Glimpse at the History of Seismology in Algeria

Seismology has a long tradition stretching back over three centuries in Algeria since the country is an earthquake-prone area. This paper presents a quick overview on the development of seismology in Algeria from the first written records of seismic events in the fourteenth century up to the monitoring of earthquakes and modern, and historical seismological studies nowadays. We particularly focus on the important milestones on the way of progress of seismology in Algeria and present a summary on what has been achieved so far in seismology research and education.

Characterizing the active tectonics in the Oran region (Algeria) and recasting the 1790 earthquake

In this work, we reappraise the seismogenic potential of the geologic structures in the western Tell Atlas of Algeria, considered active host to moderate to low magnitude earthquakes. The direct identification of active faults is generally a difficult task in northern Algeria. The active tectonics in the Oran Plio-Quaternary age basin (Northwestern Algeria) is analyzed and characterized through a morpho-structural study combining topographic, geomorphologic, geological, and neotectonic data. Folds and fault scarps affecting Quaternary deposits show that the region is affected by compressional deformation still active nowadays, as shown by the recorded seismic activity. Our new observations enable a better understanding of the present seismotectonic context of the Oran region, particularly with regard to the magnitude and source of the 1790 Oran damaging event. The obtained result helps to shed some light on the elusive active tectonics characterizing this coastal area, and to assess regional seismic hazard, particularly in coastal zones where large seismogenic areas straddle the onshore–offshore zones.