Search

The establishment of a unified earthquake catalog is a basic requirement for attaining a detailed seismological analysis and an improved seismic hazard assessment. Accordingly, the current research paper aims to present a reliable instrumental unified earthquake catalog for the northern part of Algeria. This unified catalog is compiled using regional empirical relationships derived from converting different magnitude scales to an advanced physical-based moment magnitude scale suggested in the recent literature and denoted by Mwg. The regression methodology used in this study is called the New General Orthogonal Regression approach (N.GOR), which was selected since it is the most trustworthy procedure for scaling the magnitudes to Mwg. To highlight the significance of using the N.GOR, the obtained outcomes of the scaling relations were compared with those issued from the conventional general orthogonal regression (GOR) method, which is deemed to be the most dependable methodology used worldwide for magnitude conversion problems. The unified earthquake catalog was assembled from 1954 to 2022. Reliably converting the original magnitudes into homogenized moment magnitude leads to a complete and consistent unified earthquake catalog. Indeed, the unified moment magnitude catalog presented in this paper could provide reliable data for studying earthquakes distribution and the assessment of seismic hazards in the north of Algeria. [ABSTRACT FROM AUTHOR]

A great number of local newspapers and periodicals of the nineteenth and twentieth centuries contributed to the survival of information related to the earthquakes that occurred in Algeria during those periods. These documents which often relay the information from official institutions provide fruitful seismological accounts allowing a sound reappraisal of Algeria seismicity in terms of the estimation of macroseismic parameters. A recent systematic documentation on the Algeria seismicity revealed the occurrence of more than 650 earthquakes that were not reported in the previous seismological compilations, from 1844 onward, despite their significant number. In this paper we provide a quick overview on the newspapers and periodicals that existed at that time and from which fruitful information were retrieved and focus on the most significant events that we newly found. A careful analysis of the historical records allowed the estimation of the intensity of these earthquakes, which globally ranges from V to VIII EMS. These new results augment the seismological knowledge in Algeria and will certainly have implications for seismic hazard assessment. [ABSTRACT FROM AUTHOR]

Seismic hazard in terms of spectral acceleration ( SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration ( PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra ( UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 ( M S 6.8), and October 10, 1980 ( M S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively. [ABSTRACT FROM AUTHOR]

The occurrence of the Algiers earthquake ( M 6.8) of May 21, 2003, has motivated the necessity to reassess the probabilistic seismic hazard of northern Algeria. The fact that this destructive earthquake took place in an area where there was no evidence of previous significant earthquakes, neither instrumental nor historical, strongly encourages us to review the seismic hazard map of this region. Recently, the probabilistic seismic hazard of northern Algeria was computed using the spatially smoothed seismicity methodology. The catalog used in the previous computation was updated for this review, and not only includes information until June 2003, but also considers a recent re-evaluation of several historical earthquakes. In this paper, the same methodology and seismicity models are utilized in an effort to compare this methodology against an improved and updated seismic catalog. The largest mean peak ground acceleration (PGA) values are obtained in northernmost Algeria, specifically in the central area of the Tell Atlas. These values are of the order of 0.48 g for a return period of 475 years. In the City of Algiers, the capital of Algeria, and approximately 50 km from the reported epicenter of this latest destructive earthquake, a new mean PGA value of 0.23 g is obtained for the same return period. This value is 0.07 g greater than that obtained in the previous computation. In general, we receive greater seismic hazard results in the surrounding area of Algiers, especially to the southwest. The main reason is not this recent earthquake by itself, but the significant increase in the mmax magnitude in the seismic source where the city and the epicenter are included. [ABSTRACT FROM AUTHOR]

Seismic vulnerability analysis of historical masonry buildings, addressed to earthquake emergency management and protection strategy planning, requires large-scale vulnerability and damage assessment. In this sense, two seismic vulnerability index methods and damage estimation have been adapted and applied to a pilot-scale urban area located in Annaba city (Algeria). The first method is based on the EMS-98 building typologies, and the second is based on the Italian GNDT approach. To accomplish this task, the authors employed an existing data survey, which, however, was not originally developed for seismic purposes. It was used herein to provide input to the vulnerability methods. The main goal of this research is not only to assess the seismic vulnerability and expected damage within Annaba, but also to adapt the two mentioned approaches to the existing data survey, aiming to use such nonspecific building database and to study the possibility of its application for seismic risk estimation in similar regions. The results obtained from the application of these two methods were integrated and compared using a geographic information system, proving that the vulnerability of the buildings surveyed in Annaba is significant, and therefore risk mitigation efforts and public awareness are required. [ABSTRACT FROM AUTHOR]

When dealing with structural damages, under the effect of natural hazards such as earthquakes, it is still a scientific challenge to predict the potential damages, before occurrence of a given hazard, as well as to evaluate the damages once the earthquake has occurred. In the present study, two distinct methods addressing these topics are developed. Thousands (∼54,000) of existing buildings damaged during the Boumerdes earthquake that occurred in Algeria (M = 6.8, May 21, 2003) are considered in order to study their accuracy and sensitivity. Once an earthquake has occurred, quick evaluations of the damages are required in order to distinguish which structures should be demolished or evacuated immediately from those which can be kept in service without evacuation of its inhabitants. For this purpose, visual inspections are performed by trained and qualified engineers. For the case of Algeria, an evaluation form has been developed and is still in use since the early 80s: Five categories of damages are considered (no damage or very slight, slight, moderate, major, and very severe/collapse). This paper develops a theoretical methodology that processes the observed damages caused to the structural and nonstructural components (foundations, roofs, slabs, walls, beams, columns, fillings, partition walls, stairways, balconies, etc.), in order to help the evaluator to derive the global damage evaluation. This theoretical methodology transforms the damage category into a corresponding 'residual' risk of failure ranging from zero (no damage) to one (complete damage). The global failure risk, in fact its corresponding damage category, is then derived according to given combinations of probabilistic events in order to express the influence of any component on the global damage and behavior. The method is calibrated on a set of ∼54,000 buildings inspected after Boumerdes earthquake. Almost 80 % of accordance (same damage category) is obtained, when comparing the theoretical results to the observed damages. For pre-earthquake analysis, the methodology widely used around the world relies on the prior calibration of the seismic response of the structures under given expected scenarios. As the structural response is governed by the constitutive materials and structural typology as well as the seismic input and soil conditions, the damage prediction depends intimately on the accuracy of the so-called fragility curve and response spectrum established for each type of structure (RC framed structures, confined or unconfined masonry, etc.) and soil (hard rock, soft soil, etc.). In the present study, the adaptation to Algerian buildings concerns the specific soil conditions as well as the structural dynamic response. The theoretical prediction of the expected damages is helpful for the calibration of the methodology. Thousands (∼3,700) of real structures and the damages caused by the earthquake (Algeria, Boumerdes: M = 6.8, May 21, 2003) are considered for the a posteriori calibration and validation process. The theoretical predictions show the importance of the elastic response spectrum, the local soil conditions, and the structural typology. Although the observed and predicted categories of damage are close, it appears that the existing form used for the visual damage inspection would still require further improvements, in order to allow easy evaluation and identification of the damage level. These methods coupled to databases, and GIS tools could be helpful for the local and technical authorities during the post-earthquake evaluation process: real time information on the damage extent at urban or regional scales as well as the extent of losses and the required resources for reconstruction, evacuation, strengthening, etc. [ABSTRACT FROM AUTHOR]

In this study, loss estimation models were developed for reasonably accurate assessment of economic and human losses from seismic events in the Mediterranean region, based on damage assessment at an urban scale. Data were compiled from existing worldwide databases, and completed with earthquake information from regional studies. Economic data were converted to a single common currency unit (2015 USD value) and the wealth of the areas affected by 65 earthquakes of the region from 1900 to 2015 was assessed. Reduced-form models were used to determine economic and human losses, with earthquake magnitude and intensity as hazard-related variables, and gross domestic product of the affected area and the affected population as exposure-related variables. Damage to buildings was also used as a hazard-related variable to predict economic and human losses. Finally, site-specific regression models were proposed for economic and human losses due to earthquakes in the Mediterranean region, and more specifically, in Algeria. We show that by introducing the damage variable into the models, prediction error can be reduced, and that accuracy of loss model estimation is site dependent and requires regional data on earthquake losses to improve. A case study for Constantine, Algeria shows the improvements needed for increased accuracy. [ABSTRACT FROM AUTHOR]

Northern Algeria has experienced many destructive earthquakes throughout its history. The largest recent events occurred in El Asnam on October 10, 1980 (moment magnitude; Mw = 7.3), in Constantine on October 27, 1985 (surface-wave magnitude; Ms = 6.0), and in Zemmouri-Boumerdes on May 21, 2003 (Mw = 6.8). Because of the high population density and industrialization in these regions, the earthquakes had disastrous consequences and hence highlighted the vulnerability of Algeria to seismic events. To reduce seismic risk in Constantine, the capital city of East Algeria, we present a seismic risk scenario for this city, focusing on the vulnerability of the key historic areas of Coudia, Bellevue-Ciloc, and the Old City. This scenario allows us to assess the maximum ground acceleration using empirical attenuation laws, based on the following considerations: (a) the 1985 Constantine seismic event as an earthquake reference; (b) site effects related to regional geology; (c) damage to buildings, and (d) seismic vulnerability. This study shows the map of peak ground acceleration taking into account the effects of site lithology (Avib). We observe the strongest vibrations along the two rivers 'Boumerzoug and Rhumel' and also, we note that the EC8 gives a good estimate acceleration in the image of the three studied areas (Bellevue-Ciloc, Coudia, and Old Town). By correlating with the geology, we observe an acceleration of 0.13 g in the neritic limestone of the rock (Old Town) something that fits with the value obtained 0.14 g (PGA) without taking into consideration the lithology. Moreover, according to the Algerian Earthquake Engineering Code (2003) (RPA), the Wilaya of Constantine is classified in the zone IIa (medium seismicity) with an acceleration data of 0.25 g. This study integrates geographic information system (GIS) data into risk models. [ABSTRACT FROM AUTHOR]

Starting on 14 May 2010 and lasting several months, the village of Beni-Ilmane (Msila District, North-Central Algeria) and its surroundings were struck by an important seismic crisis marked by three successive moderate shocks (5.0 ≤ M ≤ 5.2). This sequence of events caused severe damage in the Beni-Ilmane village and in the epicentral area. The poor quality of masonry construction and the cumulative effects of the large number of aftershock events played a key role in the destruction. To follow this earthquake sequence, 11 temporary seismic stations, in addition to the permanent stations of the Algerian seismic network, were deployed in the region. A representative set of well located aftershocks in the period of maximum activity (lasting 18 days) were selected. The horizontal distribution of the aftershocks shows two main earthquake clusters located near Beni-Ilmane village, one cluster oriented E-W and the other oriented NNE-SSW, crossing the first cluster at its eastern tip. The aftershocks distribution suggests that the three main shocks ruptured two distinct and adjacent fault segments of about 8 km length. The focal mechanisms of the first and third events, located in the NNE-SSW cluster, show near-vertical left-lateral strike-slip fault planes. In the second cluster, oriented E-W, focal mechanisms show a high-angle reverse fault. A field survey, initiated immediately after the first main shock, identified surface fissures generated by the three largest events in the sequence. The fissures, concentrated in a narrow area at the western termination of the NE-SW Jebel Choukchot anticline (location of Beni-Ilmane village), showed several orientations which were mainly related to gravity instabilities. The 2010 Beni-Ilmane earthquake sequence, located in the Bibans-Hodna Mountains transition zone, demonstrates that the Tellian Atlas-High Plateaus border region is an active seismic zone marked by moderate and possibly strong earthquakes; thus, a reevaluation of the seismic hazard in the region is needed. [ABSTRACT FROM AUTHOR]

The aim of this study is the comparison between the fundamental periods identified experimentally and those calculated using the formulas given in the Algerian Seismic Code (RPA 99) for vulnerability assessment and for experimental data collection of selected sample of old buildings. The results obtained for vulnerability assessment will then be extrapolated to buildings of the same typology built during the 1949 to 1954 period in the northern part of Algeria. From 1949 to 1954, the reinforced concrete constructions in Algeria were built before the first generation of the Algerian Seismic Code. These buildings being old are certainly weakened by the occupancy activities and seismic event loads. Hence, the evaluation of their vulnerability with respect to the regional seismic hazard requires the knowledge of their structure on a site capacity. The empirical formulas to calculate the fundamental period of a building are based on the Algerian Earthquake Code (RPA 99) .These formulas consider only the geometrical dimension (length, width and height) and the structural design of the buildings. The fundamental periods of vibration of twenty-two buildings, located in Algiers, calculated using the empirical formulas given in the RPA 99 are lower than those identified experimentally. A question then rises, do these tested buildings present any damage or not? As five of these buildings were tested before the 21 May 2003 earthquake, the experimental testing highlighted a decrease in the fundamental frequency which means that these buildings are damaged. Hence, for vulnerability assessment, the empirical formulas given in the Algerian Seismic Code (RPA 99) may not be appropriate for vulnerability assessment of the old buildings built during the 1949 to 1954 period. [ABSTRACT FROM AUTHOR]