Algeria has experienced several seismic events, particularly in the northern part of the country. Historical and cultural heritage cities especially are facing increasing risks due to population growth, urbanization and public awareness. A method for assessing seismic risk mitigation priorities for building structures on a city or regional scale is needed. For this purpose, a proposed Scenario-based seismic damage prediction code named PBESP (proposed Blida earthquake scenario program) is built, using vulnerability curves drawn up for Algerian structural context, as a function of building vulnerability index and macroseismic intensity. In-field Building inventory data base is carried out and integrated in GIS (geographic information system) tool, considering structural parameters of 370 buildings in Blida city. PBESP and RADIUS methodologies (risk assessment tools for the diagnosis of urban areas against seismic disasters) are compiled assuming the Blida fault, to assess potential damage. The resulting seismic risk maps from the two methods, illustrating the spatial damage distribution reveal the high level of Blida city vulnerability, mainly regarding the old masonry structures that make up the city’s heritage. According to the damage rates estimated in previous studies ( 40

After a natural disaster occurrence, such as earthquakes, the remote sensing often remains a substantial way to detect the extent of disaster. It allows the implementation of a real time post-disaster management plans, mobilization of emergency, coordination of seeking, rescue and mapping the damage spatial distribution.With the advent of the very high resolution satellites, the opportunities to improve the frequency and quality of urban data have emerged. The very high resolution satellites, whose discrimination power of objects on the ground can help to quickly develop useful tools to various stakeholders in post disaster crisis.This paper aims to develop an automatic process for detecting buildings height, throughits shadow form Quick Bird images analysis. The extraction of the building shadow is performed through a panchromatic channel, the size of the shadow and the height of the building are then extracted from a developed program under Matlab software. This method has the main advantage of being independent of time and season and the skill of the photo interpreter.The method is used for the detection of post-earthquake construction damages that occurred after Boumerdes earthquake of May 21 st 2003. Six buildings are considered and the results show a good agreement with the in situ observations.

On 25th April 2012, a moderate Mw4.9 earthquake, followed by an aftershock sequence (0.6 ≤ ML ≤ 4.3), occurred in Beni Haoua, northern Algeria. To reveal the fault responsible for this earthquake and the likely associated subsurface deformation, a detailed study of the weak seismicity based on spectral modelling of source parameters has been performed. The earthquake affected the area located in the north-eastern extend of the El Asnam seismic zone and it appears likely related to the reactivation of a segment of the fault zone that caused the El Asnam Mw7.1 earthquake on 10th October 1980, one of the most destructive earthquakes recorded in northern Africa and western Mediterranean. The determination of the source parameters of these earthquakes is important because they are too small to be reported in a global catalogue. In this study, source parameters are determined for 35 associated aftershocks using spectral modelling of three components P and S waves, assuming the Madariaga 1976 model. This model is one of the most widely used for a singular crack, radially expanding at a constant rupture speed. In this study, we estimated the source parameters (seismic moment, size of the seismic source, source dislocation and stress drop) from data in the frequency domain and we show how the results depend on the model assumptions. The Q attenuation factors for P and S waves are estimated to be 97 (50–170) and 153 (73–242), respectively, with a ratio of Qs/Qp = 1.62. We analysed source spectra and stress drops of 35 micro-earthquakes and resolved significant variations in earthquake stress drop and apparent average source dimension Rp and Rs of about 17 and 75 m, respectively. From the local magnitude calculated for the studied aftershock sequence, we highlighted similar relationship between the moment magnitude and the local magnitude, Mwp = 0.62 ML + 0.86 and Mws = 0.63 ML + 0.81, for P and S waves, respectively. This type of study is very important since we have exploited low magnitude earthquakes to obtain information that can contribute to the seismotectonic analysis of active seismic zone.

The fusion and analysis of multiple criteria is a critical step in increasing the precision of the location of areas of mineral potential during the mineral discovery phase. The study aims to provide a potential map of the hydrothermal alteration zones responsible for the formation of antimony mineralisation in the Guelma region, based on criteria derived from geological and remote sensing data. Remote sensing and GIS techniques were jointly applied to prepare and integrate several factors contributing to the mineralisation occurrences. Remote sensing techniques such as Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), Band Ratio (BR), False Color Composite (FCC) and were used to define the geological characteristics of the study area including lithological units, structural features and hydrothermal alteration zones. The thematic layers extracted from each criterion were evaluated using a hybrid fuzzy _AHP model. The results of the applications in this study provide an acceptable map defining the areas that may contain antimony mineralisation in the Guelma region.The results of the method were in good agreement with known mineralisation in the area and could be used as a means of exploring for future deposits.

During the 2013 to 2016 period, the Hammam Melouane region was the theatre of three recorded earthquakes, highlighting persistent seismic activity and suggesting the presence of asperities likely to trigger significant earthquakes. The purpose of this work is to map lineaments in order to isolate main fault of Hammam Melouane based on remote sensing images processing of the southern edge of the Mitidja basin. The obtained map shows areas of high structural density trended toward the N-S, NE-SW and NW-SE overlap and confirm the directions of all the events of the recorded seismic sequence, and as well as those of the focal mechanisms of the three main shocks recorded in the region from 2013 to 2016.

A strong offshore earthquake (Mw6.0) struck Be ' jaia city (eastern Algeria) on March 18th, 2021. This earthquake was followed by several aftershocks among the Mw5.2 that occurred 13 min after the main shock. Moreover, another earthquake (Mw5.0) occurred in the same zone one year later on March 19th, 2022. Near-field digital accelerograph records were used to study the earthquake and its related aftershocks. First, the March 2021 (Mw6.0) main shock, six of its main aftershocks, and the March 19th, 2022 (Mw5.0) earthquake were located. These epicentres are distributed in a 10 km-long and 2 to 3 km-wide NE-SW-trending area, with depths ranging between 8 km and 14 km. Second, using waveform inversion, the seismic moment and the focal mechanism of the three events (the March 18th, 2021, main shock and its strongest aftershock (Mw5.2) that occurred 13 min after the main shock and the March 19th, 2022 (Mw5.0) earthquake) were determined. These focal mechanisms exhibit reverse faulting with a short lateral component. Third, the source rupture process of the March 18th, 2021 (Mw6.0), earthquake was calculated from waveform inversion to obtain the moment-release distribution on a finite fault. The nodal plane oriented N74E seems to be associated with the activated fault plane. Considering the seismotectonic framework of the region, the fault that activated during the 2021 earthquake sequence is offshore. This fault, called the Western Segment, which is situated in the western part of the reverse fault system, is also at the origin of the Djidjelli historical earthquakes of August 21st, and 22nd, 1856 (Io = VIII-IX, M >= 6.6).

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, respectively, 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 ΔCFF 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.

A single backscattering method is used to estimate coda quality factor functions (Qc) from coda-wave attenuation for the Algiers vicinity and eastern part of the Mitidja Basin. The frequency-dependent Qc relation is determined using a high-quality data set with good signal-to-noise ratios (SNR > 5) of 228 accelerogram waveforms of local earthquakes in the magnitude range 2.3–5.3, with focal depth varying from 1.3 to 31 km and epicentral distances less than 65 km. We studied the frequency and lapse time dependence of coda-wave attenuation through the variation of coda window length of 20, 30 and 35 s for seven frequency bands in the range of 1.5–24 Hz. The obtained average Qc increases with increasing coda window length, implying an increase in sampled depth. The Qc of horizontal components (N and E) are slightly lower than the Qc of the vertical component (Z). The obtained low values of Qc and high values of frequency-dependent parameter n indicate that the penetration depth that consists of the crust and part of the upper mantle beneath the Algiers region is seismically active with a high level of heterogeneity. The average frequency-dependent Qc values in the three directions are QcZ = (69.76 ± 2.98)f(0.82 ± 0.01), QcN = (60.2 ± 4.86)f(0.88 ± 0.03) and QcE = (59.63 ± 5.07)f(0.88 ± 0.03) with a coda window length of 20 s in which the penetration depth is 56.2 km and the covered area is 8141 km2.

The ambient vibration horizontal-to-vertical spectrum method (HVSR) is widely used in microzonation and structural studies, assuming stability and reproducibility of HVSR frequency peaks. A 35-day continuous HVSR monitoring performed in the suburbs of Algiers (Algeria) reveals that HVSR peaks are not always stable and reproducible both in frequency and amplitude. HVSR curves show a first peak, which varies from 0.9 to 1.8 Hz with amplitudes from 0.9 to 3.3, and a second peak from 5 to 7.7 Hz with amplitudes from 1.4 to 4. These results show that HVSR peak frequencies and amplitudes are highly sensitive to nearby anthropogenic sources.

Periurbanization dynamics phenomenon causes significant damages to Mitidja plain, which is the agricultural land around Algiers (capital of Algeria). Hence, a cover land monitoring is performed on this paper to delineate, follow, and draw the changes. The proposed methodology is based, on one hand, on the multi-temporal supervised Landsat satellite images classification (1987 to 2017), in order to map soil occupation. On the other hand, a two-dimensional simulation (space time) is developed using cellular automata, which represents landscape mutation process from rural to urban. This simulation allows the implementation of qualitative rules of space evolution. It mainly identifies process changes as well as their rates. The delineation of a such complex periurban space of a large city like Algiers can be expressed in terms of fairly “natural” spatial transition rules. The results of this study are interesting and show that more than 80% of urbanization, during the period 1987–2017, was done on agricultural land.

The Oran region (Western Tell Atlas) was hit by two earthquakes on January 9th, 2008 (Mw = 4.7) and on June 6th, 2008 (Mw = 5.4). The two events were recorded by the national accelerographs network maintained by National Center of Applied Research in Earthquakes Engineering (CGS, Algiers). This work aims to characterize these two earthquakes in order to contribute to understand the seismotectonic context of the study region. We located the events using Grid Search Method based on P and S waves arrival time differences. The obtained hypocenter locations are, respectively, (0.457 degrees W, 35.689 degrees N, 11 km) and (0.576 degrees W, 35.689 degrees N, 8 km). We perform waveforms inversion to estimate the moment magnitudes and the seismic moments which are, respectively, Mw = 4.7, M-0 = 0.13 E+17 N m and Mw = 5.4, M-0 = 0.18 10 E+18 N m for the two events. Concerning the focal mechanism solutions both earthquakes yield reverse faulting with a compressional axes oriented NW-SE which is consistent with the active fault system trend in the study region. These two events occurred in an area which has been seismically quiet, since the event of December 1959 (Ms 4.7) and the historical major event of October 9th, 1790 (I-0= IX-X; likely Ms >= 6.0).

Most of the housing stock of the old cities in the north of Algeria is on masonry and reinforced concrete. These agglomerations are located in the coastal strip, which are precisely exposed to a high seismic hazard. As a reminder, the north of Algeria has been shaken by several major and moderate seismic events. In the case of Algiers, for the greatest part of the area the buildings were constructed during the 1871–1936 period, so bearing the traces of several earthquakes since no major reinforcement campaign was undertaken. This paper reported the analysis results of the impact of a seismic event by considering the fundamental period of the reinforced concrete buildings identified before and after the earthquake. A comparison between the obtained results with the site conditions were operated using a non-destructive technique, that of background noise.

Hypocenters of main shock and aftershocks of the March 20, 2006 Laalam earthquake are relocated using HypoDD double-difference technique. We combined accelerogram and seismogram data of the National Center of Applied Research in Earthquake Engineering (CGS). Among about 191 aftershocks, recorded at least by 4 stations, 141 aftershocks of Md 1.2–2.7 were relocated using HypoDD. The obtained swarm of epicenters occupying a crustal volume of 5 km × 3 km × 5 km and the focal mechanism corresponds to an unknown pure left lateral strike slip, trending N174°E. We were able to calculate focal mechanisms for only seven aftershocks with more than seven polarity readings, which give a P axis oriented NNW–SSE. The waveform inversion also provided values of Mw 5.1, M0 5.9 10−16 Nm and the depth 4.9 km. The dislocation and the stress drop were estimated to 90 cm and 16.5 bars, respectively.

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.

On August 1st, 2014, a moderate-sized earthquake struck the capital city of Algiers at 05:11:17.6 (GMT+1). The earthquake caused the death of six peoples and injured 420, mainly following a panic movement among the population. Following the main shock, we surveyed the aftershock activity using a portable seismological network (short period), installed from August 2nd, 2014 to August 21st, 2015. In this work, first, we determined the main shock epicenter using the accelerograms recorded by the Algerian accelerograph network (under the coordination of the National Center of Applied Research in Earthquake Engineering–CGS). We calculated the focal mechanism of the main shock, using the inversion of the accelerograph waveforms in displacement that provides a reverse fault with a slight right-lateral component of slip and a compression axis striking NNW–SSE. The obtained scalar seismic moment (M o = 1.25 × 1017 Nm) corresponds to a moment magnitude of M w = 5.3. Second, the analysis of the obtained aftershock swarm, of the survey, suggests an offshore ENE–WSW, trending and NNW dipping, causative active fault in the bay of Algiers, which may likely correspond to an offshore unknown segment of the Sahel active fault.

PreviousNext No AccessInternational Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015The 25 April 2012 Beni Haoua earthquake: instrumental intensity and consistency of ground motion modelingAuthors: Khadidja. AbbesNacima BenkaciAbdennasser SlimaniFaouzi GherboudjMohamed DjeddiKhadidja. AbbesCentre National de Recherche Appliquée en Génie Parasismique Rue Kaddour Rahim Prolongée, Hussein Dey, Alger;Search for more papers by this author, Nacima BenkaciCentre National de Recherche Appliquée en Génie Parasismique Rue Kaddour Rahim Prolongée, Hussein Dey, Alger;Search for more papers by this author, Abdennasser SlimaniCentre National de Recherche Appliquée en Génie Parasismique Rue Kaddour Rahim Prolongée, Hussein Dey, Alger;Search for more papers by this author, Faouzi GherboudjCentre National de Recherche Appliquée en Génie Parasismique Rue Kaddour Rahim Prolongée, Hussein Dey, Alger;Search for more papers by this author, and Mohamed DjeddiUniversité des Sciences et de la Technologie Houari Boumediene Bp 32 El Alia 16111 Bab Ezzouar AlgerSearch for more papers by this authorhttps://doi.org/10.1190/iceg2015-047 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract This paper analyzes the instrumental intensity and examines the consistency of ground motion models, used for seismic hazard analysis in Algeria, with the Beni Haoua earthquake. The accelerograms recorded at 11triaxial stations following the April 25, 2012, are used in the evaluation of intensity based on a combined regression of peak ground acceleration (PGA) and velocity (PGV) amplitudes of the horizontal components provided by Tselentis and Danciu (2008). The Arias intensity is computed and compared with the instrumental intensity. To define how the structures react to ground motions, spectral acceleration is presented for a range of periods. The observed PGA of the Beni Haoua earthquake compared to the empirical ground motion prediction (GMPEs) Ambraseys (2005) show an overestimated model. Keywords: modeling, earthquake, riskPermalink: https://doi.org/10.1190/iceg2015-047FiguresReferencesRelatedDetails International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015ISSN (online):2159-6832Copyright: 2015 Pages: 309 publication data© 2015 Published in electronic format with permission by Society of Exploration Geophysicists (SEG)Publisher:Society of Exploration Geophysicists HistoryPublished Online: 18 Nov 2015 CITATION INFORMATION Khadidja. Abbes, Nacima Benkaci, Abdennasser Slimani, Faouzi Gherboudj, and Mohamed Djeddi, (2015), "The 25 April 2012 Beni Haoua earthquake: instrumental intensity and consistency of ground motion modeling," SEG Global Meeting Abstracts : 168-171. https://doi.org/10.1190/iceg2015-047 Plain-Language Summary KeywordsmodelingearthquakeriskPDF DownloadLoading ...

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.

We present three geomorphologic and geological phenomena that have occurred in Algeria in recent years: (i) the Bab El Oued mudflow on 11 November 2001, which claimed several hundred lives, (ii) a soil collapse induced by sand liquefaction triggered by the Boumerdes earthquake (M-w = 6.8) on 21 May 2003, and (iii) landslides that are threatening Constantine city, for which a hazard map is presented using a qualitative approach. We briefly describe and analyze these natural disasters, and in the first two cases propose the application of geophysical techniques such as ambient noise recordings and electrical imagery to help evaluate their extent and potential threat. Finally a landslide hazard map of Constantine is proposed.