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Abbes K.,Center National Of Recherche Appliquee En Genie Parasismique | Abbes K.,University of Science and Technology Houari Boumediene | Dorbath L.,University of Strasbourg | Dorbath C.,University of Strasbourg | And 5 more authors.
Journal of Seismology | Year: 2016

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. © 2015, Springer Science+Business Media Dordrecht.

Louadj S.,Mouloud Mammeri University | Bahar R.,Mouloud Mammeri University | Vincens E.,École Centrale Lyon | Laouami N.,Center National Of Recherche Appliquee En Genie Parasismique
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 | Year: 2014

Northern Algeria is a highly seismic area. During the last two decades, it experienced several moderate to strong destructive earthquakes. On May 21, 2003, Algiers-Boumerdes region was struck by a destructive magnitude 6.8 (Mw) earthquake. Keddara dam is a rockfill dam in Boumerdes region. The present study concerns analysis of the seismic response of this dam during Boumerdes main shock event.The acceleration records of the main shock were recorded at the stations of the national accelerograph network, which furnishes the records on the rock, and crest near the maximum section of the dam. The behavior of both rockfill and core of the dam is described using Ramberg-Osgood nonlinear relationship.A comparison with real earthquake records reveals that uniform motions overestimate the accelerations at the crest and underestimate the shear stress at the base. The effects of spatial varying of ground motion on dynamic response of such structure must be considered. © 2014 Taylor & Francis Group, London.

Senouci A.,University of Science and Technology of Oran | Bard P.Y.,Joseph Fourier University | Farsi M.N.,Center National Of Recherche Appliquee En Genie Parasismique | Beck E.,Joseph Fourier University | Cartier S.,Joseph Fourier University
Bulletin of Earthquake Engineering | Year: 2013

The city of Oran is exposed to a significant seismic hazard, as almost all the northern Algeria territory, where numerous casualties and severe damage occurred in the last decades due to several moderate to large earthquakes. A mitigation policy should include the establishment of priorities to reduce the vulnerability of existing buildings based on the knowledge of the actual urban fabrics. The complexity of vulnerability assessment requires a gradual approach from the urban scale to the building scale. The study reported in this paper corresponds to the first step of such an approach, i.e., a preliminary study of the seismic vulnerability and expected damage within an urban district of the city of Oran, based on a non-dedicated data base from a building survey previously performed for other purposes. The main goals of this study are twofold: (1) an assessment of the degree of uncertainty and robustness of such results through a comparison of the results derived from different urban vulnerability methods (GNDT 2; RISK-UE LM1; and VULNERALP 2.0) and (2) an assessment of the actual level of seismic risk in the city of Oran. Cross-method comparisons and correlations highlight a satisfactory agreement between mean damage estimates at the urban scale, despite significant scattering at the single building scale, and uncertainty levels which vary significantly from one method to the other. For a given scenario, the three methods provide damage estimates lying within half an EMS damage degree of one another, with some systematic positive bias for VULNERALP and negative bias for RISK-UE LM1, especially for masonry buildings. The expected mean damage is very important for intensities 9 and 10, with an average damage grade around 3-4 for intensity 9 and 4-5 for intensity 10. The spatial distribution of damage systematically exhibits larger values in the northern, older, commercial area, than in the southern, more recent and more residential area, in relation to the building typology and the existence of several aggravating factors. Some areas of higher vulnerability / damage can be distinguished, which should receive particular attention for retrofitting priorities or urban planning decisions, also taking into account their cultural heritage value. © 2012 Springer Science+Business Media Dordrecht.

Moulouel H.,Center National Of Recherche Appliquee En Genie Parasismique | Micarelli L.,Beicip Franlab | Moretti I.,GDF SUEZ | Machane D.,Center National Of Recherche Appliquee En Genie Parasismique
Bulletin de la Societe Geologique de France | Year: 2015

The Aigion active fault belongs to a system of north-dipping normal faults that affect the southern shore of the gulf of Corinth. Cores of AIG-10 well crossed the Aigion active fault show the usual presence of a damage zone and a gouge. This work presents a thin section analysis under optical and cathodoluminescence microscopy. It confirms the zonation in terms of fracturing next to the fault zone. Away from the fault zone, fracturing inherited from the Hellenic compressive phase is dominant, even though E-W fractures related to the current extension are observed. All these fractures are sealed and the filling is similar to the limestone host-rock in terms of luminescence. Close to the fault, the number of fault-related fractures increases. Under cathodoluminescence analysis, the fracture filling indicates the passage of several fluids that would be external, and the latest generation of fractures is still open. Beneath 5 m thick of cataclasite and ultracataclasite in limestone and radiolarite (fault core) and 13 m thick of gouge in radiolarite, in the footwall, observations are limited, because the presence of karst has restricted coring opportunities. Nevertheless we can see that the filling of the extension related fractures is different from what has been revealed in the hanging wall fault zone. This suggests that Aigion active fault plane acts as a local transverse seal and has always been. Analysis of cement sequences highlights longitudinal permeability; also, we discussed the role, in terms of fluid transfer, of fault propagation induced features.

Laouami N.,Center National Of Recherche Appliquee En Genie Parasismique | Slimani A.,Center National Of Recherche Appliquee En Genie Parasismique
Pure and Applied Geophysics | Year: 2013

The Algiers-Boumerdes regions were hit by an M w 6.8 destructive earthquake on May 21, 2003. The accelerometric and seismometric networks successfully recorded the main shock and many aftershocks at some locations where the damage was most extensive. A microtremor measurement was performed in the same locations; some of them are localized on the Mitidja basin. In this paper, we propose to analyze earthquake-induced site effect derived from horizontal to vertical spectral ratio from ambient noise (noise horizontal to vertical-NHV), or from very weak, weak, moderate and strong (peak ground acceleration-PGA >10 % g) seismic motions (EHV), and transfer function evaluation from soil velocity profile data at four sites. H/V spectral ratios are computed by using both Fourier and response spectra. Compared to the transfer function, the obtained results show that in the case of soft soils, NHV as well as EHV give a good estimation of the soil's fundamental frequency, whereas the NHV underestimate the H/V amplitude and the EHV amplitude increase with the seismic motion intensity. In the case of firm soils, whereas the NHV gives flat curves synonymous for a rock site or a bump, the EHV is more appropriate as seen by identifying clear peaks with non negligible amplitude. In the case of soft sites as well as in the case of firm sites, strong peaks at frequencies higher than the fundamental one are found from EHV curves. Those peaks would not be found when looking at NHV ratios alone, are evidenced by the computed transfer function as well as by an analytical formulation, and are in agreement with the observed distribution of damage during the M w 6.8 2003 Boumerdes earthquake. Finally, the same analysis is performed by using response spectra rather than Fourier spectra and leads to the same conclusions. Moreover, the calculation of the response spectra is more easily compared with the smoothing operation of the Fourier spectra. © 2012 Springer Basel.

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