The largest earthquakes in Algeria in the modern period: the El Asnam and Zemmouri-Boumerd s faults

Algeria has experienced many destructive earthquakes during the last few centuries (e.g., Ayadi and Bezzeghoud, 2015). The city of El Asnam (formerly Orléanville, today Chlef) was severely damaged in 1954 and 1980 by magnitude 6.7 and 7.3 earthquakes, respectively. On October 10, 1989, a magnitude 5.9 earthquake struck the Mont Chenoua-Tipasa coastal area approximately 150 km west of Zemmouri, which is where the May 21, 2003 earthquake occurred (Mw6.8). Many other large historical and instrumental earthquakes have severely damaged the coastal cities of Algeria over the last few centuries (i.e., around Algiers, Oran, Mascara, Djidjelli, Constantine and Bejaia). These earthquakes suggest active deformation of the margin in conjunction with the clear offshore extent of active coastal faults. According to several studies, the main active geological structures around El Asnam, Algiers, Zemmouri and Boumerdès have experienced several disastrous earthquakes. Many other earthquakes have occurred in and around the Chlef and Mitidja Basins, underlining the seismic activity in the area. In this chapter, we highlight the main characteristics of the two largest earthquakes that have occurred in Algeria in the modern period: the El Asnam earthquakes of September 9 (Mw6.7) and October 10 1980 (Mw7.3), and the Zemmouri-Boumerdès earthquake of May 21, 2003, (Mw6.8)

Stress transfer among en echelon and opposing thrusts and tear faults : triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B03305, doi:10.1029/2010JB007654.The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 Mw = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ∼2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ∼0.25 m slip, were brought >2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ∼2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a Mw = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history.Funding by the U.S. Office of Foreign Disaster Assistance of the U.S. Agency for International Development is gratefully acknowledged. Additional funding was provided by the INSU research project ACI Cat‐Nat Risque Sismique de la Région d’Alger. S. Belabbes was supported by the Algerian Ministry of Higher Education and Research

The history of seismology and historical seismicity in Algeria: an overview

Algeria is one of the most seismically active areas along the Nubia-Eurasia convergent plates boundary. It is well known that the instrumental records of seismic events are incomplete because of inadequate instrumentation and the poor coverage of seismogenic areas from 1900 until the installation in 1992 of the Algerian Telemetered Seismological Network. The available catalogues of the seismicity of Algeria, including several published research papers on the same topic, reported numerous destructive earthquakes striking several regions, particularly along the coast [Oran, Mascara, Chlef (Former Orléansville and El Asnam), Tipasa-Chenoua, Algiers, Zemmouri, Constantine, Béjaia, Djidjelli (5.9 < M < 7.3; IX < Io < X]. This seismicity is the result of the collision between the Nubia and Eurasian plates and is located within the Algerian Tell Atlas. To properly study the seismicity of Algeria, we must consider three periods in relation to the installation of the seismic instrumentation over the Algerian territory: (1) the pre-1910 period with the first published seismic catalogues, (2) the post-1910 period with the beginning of the instrumental seismicity and, finally, (3) the post-1980 period with the installation of the Algerian Teleseismic Network in 1990 and its upgrade following the Zemmouri earthquake of May 21st 2003

Étude du site archéologique romain de Tipasa par la méthode électrique

Since the last decades, the geophysical methods, applied to archaeological research, has known a very large success. In Algeria, we have just began to apply these techniques in order to investigate archaeological sites. This paper gives the results of the first temptation in this domain using electrical method. This latter, in our case, was the most adequate one, which can give us good results because we have a high resistivity contrast between the structures we look for and the medium containing it, using the Wenner array. In order to control our results we have excavated two of the areas where anomalies occurred.Depuis quelques décennies, les méthodes géophysiques appliquées à la recherche archéologique ont eu un large succès. En Algérie, cette nouvelle approche en recherche archéologique se trouve encore à ses débuts. Ce sont les résultats de la première tentative d'application de l'une de ces méthodes - la prospection électrique en l'occurence - que nous allons exposer. Cette technique se trouvait être, dans notre cas, la plus indiquée, car nous avions un bon contraste de résistivité entre les structures archéologiques et l'encaissant. Le dispositif utilisé est le quadripole Wenner. Ce travail étant le premier du genre en Algérie, nous avons eu recours à la fouille, d'une part, pour vérifier que les anomalies sont réellement dues à des structures archéologiques et, d'autre part, les résultats de la fouille serviront à l'étude sur modèle réduit. Le bilan de la prospection était très satisfaisant, car les anomalies révélées par la prospection électrique ont été confirmées par la fouille, et ce, sur deux zones d'anomalie d'une aire d'étude qui en compte trois. La troisième reste encore à vérifier. Les vestiges que nous avons découverts seraient les annexes de l'amphithéâtre romain. Signalons que la fouille n'a mis en évidence que le haut des structures.Ayadi Abdelhakim, Laouici Djamel, Idjeraoui Fariza. Étude du site archéologique romain de Tipasa par la méthode électrique. In: Revue d'Archéométrie, n°16, 1992. pp. 13-19

A novel interpolation method for InSAR atmospheric wet delay correction

The accuracy and capability of Differential interferometric Synthetic Aperture Radar (DInSAR) depends on the phase errors. In particular, errors associated with Atmospheric Wet Delay (AWD) should be reduced to ensure reliable results from the interferometric process. This paper addresses a new method for AWD estimation based on MEdium Resolution Imaging Spectrometer (MERIS) water vapor image which is used as an auxiliary data to correct AWD effects on ENVIronment SATellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) interferogram. We also explore the possibility of using MERIS data under cloudy conditions and we propose a novel method for the interpolation of water vapor in the presence of clouds using a hybrid technique we name Three Dimensional Inverse Distance Weighted (3D-IDW). It is shown that the proposed method succeeds to provide a quite realistic prediction of MERIS water vapor distribution on cloudy area. Obtained results show that 3D-IDW method succeeds to estimate IWV for each cloudy pixel with RMSE not exceeding 0.094 g/cm2 over area masked by 90% of cloud. The proposed method was tested on Mitidja region (north central Algeria), using a couple of Advanced Synthetic Aperture Radar (ASAR) and MERIS images on the 65 descending track. The results demonstrates an improvement of 15% in the standard deviation of interferogram after ADW correction. Finally, the obtained surface deformation reveals the presence of subsiding districts which may be linked to seasonal water level fluctuation and overdrafting groundwater confirming the results of previous study

Stress Change and Fault Interaction from a Two Century‐Long Earthquake Sequence in the Central Tell Atlas, Algeria

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High-density seismic network for monitoring Alentejo region (Portugal) and Mitidja basin region (Algeria)

The seismic sensor network Alentejo (SSN-Alentejo) brings a new approach in seismological survey based on networked low- cost sensors and acquisition systems. It is developed by the Earth Sciences Institute (Instituto de Ciências da Terra, University of Evora) to bring the most dense seismic sensor network ever deployed in Portugal. By combining high-sensitive sensors with low- cost sensors, this novel network aims to improve the characterisation of seismic activity in the region, by augmenting existing sensing and monitoring capabilities, enabling the opportunity to observe, for the first time in Portuguese territory, real-time monitoring of the seismic activity in high resolution. In this study, we start by describing the seismicity along the occidental border between the Eurasian-Nubian plates, including the two regions of our interest: the Arraiolos region, in Portugal, and the Mitidja basin, in Algeria. We then present our work in designing and implementing a high-density sensor network, including low-cost sensor systems and server platforms. The conducted tests have proven the feasibility of the overall platform, including its detectability capability. Future work includes the deployment of the sensor network in the Alentejo region. Since seismogenic zones such as the Mitidja or Chelif basins in Algeria will also benefit from having a high-density network, we will also seek collaboration with Algerian institutions.Funding: The SSN-Alentejo project is funded by the Science Foundation of Portugal (FCT) under grant number ALT20-03-0145- FEDER- 031260

An update of Algerian’s seismic catalog from historical seismicity, archeoseismological, and paleoseismological studies

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.This work was prepared with the support of UNESCO-IGCP-659 Project “Seismic Hazard and Risk in Africa”

Seismicity and Seismotectonics of the Mitidja Basin Southern Edge (Tell Atlas, Algeria): Case Study of the Hammam Melouane Region

Many moderate to large historical and instrumental events have been documented in the Mitidja basin, affecting in particular the southern edge of the active Quaternary Mitidja basin, which is composed of nearly NE–SW-trending fault system. The earthquake catalogue reports that the Hammam Melouane region has experienced several moderate seismic events such as those of 8 February 1937 (I0 = V), 20 July 1975 (I0 = V–VI), 29 September 1981 (I0 = V) and 17 December 1986 (I0 = V). Recently, between 2013 and 2016, this area experienced three moderate earthquakes with a series of aftershocks. In this paper, we present an analysis of the seismic sequences that occurred in the Hammam Melouane Geothermal Spring area on 17 July 2013 (ML 4.9), 23 December 2014 (ML 5.3) and 10 February 2016 (Mw 4.8), about 3–7 km apart, at hypocentral depths of 11.5 km, 19.0 km and 18.0 km, respec- tively, with centroid depth of 5 km for the first main shock. Ninety- seven events with local magnitude ranging between ML 0.9 and ML 5.3 were recorded and analyzed. The series of aftershocks display two clusters, trending N–S for the 2013 event and NE–SW for the 2014 event, located at shallow depths of 1.5–14 km and 18–28 km, respectively. The event distribution shows variability in faulting, combining strike-slip and thrust focal mechanisms of the main events, leading us to hypothesize a simultaneous interaction between two geological active structures represented by the * N–S- to NE–SW-trending faults belonging to the southern Mitidja fault system. On one hand, the computed DCFF indeed supports and strengthens the fault interaction model between the three events. On the other hand, the analysis of the post-seismic stress distribution caused by fluid circulation reveals that the 2013 and 2014 events seem to have caused a poroelastic stress relaxation and thus influenced the occurrence of the 2016 main shock.The National Earthquake Engineering Research Centre (CGS, Algiers), the Centre de Recherche en Astronomie, Astrophysique et Geophysique (CRAAG, Algiers) and the Instituto de Ciências da Terra (ICT, Univ. of Évora—UID/GEO/04683/2020, Portugal)

The Seismotectonic Map of Africa

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