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Algiers, Algeria

Sardou M.,University Sidi Mohammed Ben Abdellah | Maouche S.,CRAAG | Missoum H.,University Sidi Mohammed Ben Abdellah
Arabian Journal of Geosciences

Floods are among the significant natural hazards in Algeria. They cause severe casualties, damage to building and destruction of roads, public works, and infrastructures. Northwestern Algeria has experienced devastating floods in the past that caused considerable damage, e.g., Mohammadia 1881, Mostaganem 1927, and El Asnam 1966. Analysis of historical floods is one of the major tools in flood hazard assessment that enables predicting future flood events. One of the objectives of this work is to address the gap of available information regarding the floods that happened in Algeria, particularly during historical times. The first historical data analysis that we performed on the basis of an intensive survey shows that the study area is subject to flooding. This inventory is the first step towards flood zonation and construction of an atlas of extreme floods in northwestern Algeria. The catalog of historical floods contains more than 127 documented events. As results, this paper presents a method of compiling historical flooding data and the analysis of the obtained database which represents a major contribution to flood risk assessment. © 2016, Saudi Society for Geosciences. Source

Maouche S.,CRAAG | Maouche S.,University of Science and Technology Houari Boumediene | Meghraoui M.,Institute Of Physique Du Globe | Morhange C.,CEREGE | And 3 more authors.

Major uplifts of late Quaternary marine terraces are visible along the coastline of the Tell Atlas of Algeria located along the Africa-Eurasia convergent plate boundary. The active tectonics of this region is associated with large shallow earthquakes (M ≥ 6.5), numerous thrust mechanisms and surface fault-related fold. We conducted a detailed levelling survey of late Pleistocene and Holocene marine notches in the Algiers region that experienced 0.50. m coastal uplift during the 2003 Zemmouri earthquake (Mw 6.8). East of Algiers, Holocene marine indicators show three pre-2003 main notch levels formed in the last 21.9. ka. West of Algiers on the Sahel anticline, the levelling of uplifted marine terraces shows a distinct staircase morphology with successive notches that document the incremental folding uplift during the late Pleistocene and Holocene. The timing of successive uplifts related to past coseismic movements along this coastal region indicates episodic activity during the late Holocene. Modelling of surface deformation in the Zemmouri earthquake area implies a 50-km-long, 20-km-wide, NE-SW trending, SE dipping fault rupture and an average 1.3 m coseismic slip at depth. Further west, the 70-km-long Sahel fold is subdivided in 3 sub-segments and shows ~0.84-1.2 mm/yr uplift rate in the last 120-140. ka. The homogeneous Holocene uplift of marine terraces and the anticline dimensions imply the possible occurrence of large earthquakes with Mw ≥ 7 in the past. The surface deformation and related successive uplifts are modelled to infer the size and characteristics of probable future earthquakes and their seismic hazard implications for the Algiers region. © 2011 Elsevier B.V. Source

Giresse P.,CNRS Training and Research Center on Mediterranean Environments | Bassetti M.-A.,CNRS Training and Research Center on Mediterranean Environments | Pauc H.,CNRS Training and Research Center on Mediterranean Environments | Gaullier V.,CNRS Training and Research Center on Mediterranean Environments | And 3 more authors.
Sedimentary Geology

From the analysis of seven new sediment piston-cores sampled in 2005 (MARADJA-2 French-Algerian cruise), this study aims to identify for the first time possible late Pleistocene to recent sedimentary instabilities controlled by seismicity off or close to the eastern coast of Algeria. The detailed lithologic study allows us to identify the frequency of the gravity events (turbidites, debrites) and to discuss their geographical sources and triggering mechanisms. Based on a chronostratigraphy of 24 14C AMS datings, sediment accumulation rates in zones extending off Bejaia and Annaba and, in particular, semi-quantitative analysis of the microfossils and lithogenic tracers of the origin of gravity flows was discussed. Two sediment cores, here considered as reference cores, enabled the estimation of palaeoenvironmental parameters that controlled sedimentation: (1) in the prodelta of Soummam Oued, after 2215calyrBP, floods were less frequent and sediment accumulation rates decreased because of a drier climate; (2) in the middle slope to the NE of Annaba, a location shielded from gravity flows, an increased sedimentation rate coincided with the passage of warmer waters leading to maxima of carbonate biogenic fluxes (particularly pteropods). Off Bejaia, two deep sediment cores show a spectacular increase in sediment accumulation rate between 2200 and 1000calyrBP while turbidites become more frequent. According to the eustatic and climatic stability of this interval, an episode of strong slope instability of the slope is suggested. Both sediment cores on the slope of Annaba indicate an increase in gravity flows during the same last thousand years, which is tentatively related to a regional increase of seismicity during this interval. This spatial distribution of gravity events is clearly different to that of the western margin where the sedimentation is less perturbed.© 2013 Elsevier B.V. Source

Naitamor S.,CRAAG | Cohen M.B.,Stanford University | Cotts B.R.T.,Exponent, Inc. | Ghalila H.,University of Tunis | And 2 more authors.
Journal of Geophysical Research: Space Physics

Lightning strokes are capable of initiating disturbances in the lower ionosphere, whose recoveries persist for many minutes. These events are remotely sensed via monitoring subionospherically propagating very low frequency (VLF) transmitter signals, which are perturbed as they pass through the region above the lightning stroke. In this paper we describe the properties and characteristics of the early VLF signal perturbations, which exhibit long recovery times using subionospheric VLF transmitter data from three identical receivers located at Algiers (Algeria), Tunis (Tunisia), and Sebha (Libya). The results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations. Comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties (e.g., peak current and polarity), or that of transient luminous events may be much less important. The dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric VLF probe signal at the ionospheric disturbance, where scattering occurs, and the subsequent modal structure that propagates to the receiver location. Key Points Signal Mode Composition Long Recovery Early events Lightning peak current role ©2013. American Geophysical Union. All Rights Reserved. Source

Sawires R.,Assiut University | Sawires R.,University of Jaen | Pelaez J.A.,University of Jaen | Ibrahim H.A.,Assiut University | And 3 more authors.
Natural Hazards

In the present study, a new seismic source model for the Egyptian territory and its surroundings is proposed. This model can be readily used for seismic hazard assessment and seismic forecasting studies. Seismicity data, focal mechanism solutions, as well as all available geological and tectonic information (e.g. active faults) were taken into account during the definition of this model, in an attempt to define zones which do not show only a rather homogeneous seismicity release, but also exhibit similar seismotectonic characteristics. This work presents a comprehensive description of the different tectonic features and their associated seismicity to define the possible seismic sources in and around Egypt. The proposed seismic source model comprises 28 seismic sources covering the shallow seismicity (h ≤ 35 km) for the Egyptian territory and its surroundings. In addition, for the Eastern Mediterranean region, we considered the shallow seismic source zones (h ≤ 20 km), used in the SHARE project for estimating the seismic hazard for Europe. Furthermore, to cover the intermediate-depth seismicity (20 ≤ h ≤ 100 km), seven intermediate seismic source zones were delineated in the Eastern Mediterranean region. Following the determination of zone boundaries, a separate earthquake and focal mechanism sub-catalogue for each seismic zone was created. Seismicity parameters (b-value, activity “a-value” and maximum expected magnitude) have been computed for each source. In addition, the predominant focal mechanism solution was assigned for each source zone using the stress field inversion approach. The proposed seismic source model and its related seismicity parameters can be employed directly in seismic hazard assessment studies for Egypt. © 2015, Springer Science+Business Media Dordrecht. Source

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