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HVSR and Polarization Analysis of Ambient Vibration Noise to Identify and Characterize the Western Thénia Fault Segmen...
21/09/2025



HVSR and Polarization Analysis of Ambient Vibration Noise to Identify and Characterize the Western Thénia Fault Segment (Algeria)

AUTEURS
Nour El Houda Boudjenana (USTHB Alger, Algérie)
Rabah Bensalem (USTHB Alger, Algérie ; CGS Alger, Algérie)
Fares Ouzzani (CRAAG Alger, Algérie)
El Hadi Oubaiche (CGS Alger, Algérie)
Mohamed Yacine Tebbouche (USTHB Alger, Algérie)
Djamel Machane (USTHB Alger, Algérie ; CGS Alger, Algérie)

R***E
Pure and Applied Geophysics
Sous presse
https://link.springer.com/article/10.1007/s00024-025-03792-1

RESUME
[en] Abstract
Thénia fault is well characterized in its eastern part whereas in its western part, between Cap-Matifou and Boumerdes, the fault trace, although invisible, is marked by a Plio-quaternary scarp with a direction N110°. Questions persist regarding its existence, its continuity and its exact position in its western segment which remains poorly documented. In this work, we study the spectral ratios (HVSR) and horizontal polarization of ground motion using ambient vibration noise recordings made in the western part of the Thénia fault, with the objective of asserting or not its continuity. Clustering of HVSR curves based on their trends, their frequency peaks and their amplitudes highlighted three distinct zones: both the plateau area north of the scarp and the lower part of the plain to the south are characterized by high frequency curves while the scarp area is characterized by a mix of low and high frequencies. Moreover, polarization analysis of the ambient vibration noise recordings, carried out by the covariance matrix method, indicates well-polarized signals on the scarp and weak ones on the northern and southern parts. This analysis also made it possible to highlight a mean direction of predominant polarization between 10° and 30°, whose transverse projection coincides perfectly with the direction of the scarp which is N110°. This polarization direction is observed for low and high frequencies which represent the same soil response for different depths. All of these results support the hypothesis of the extension of the Thénia strike-slip fault in its western part, which until now only showed a banal escarpment. The results obtained will make it possible to refine the mapping of the Thénia fault zone at the seismic microzoning scale and to have a better assessment of the regional seismic hazard and good management of the seismic risk, particularly in urbanized areas.

Seismic microzonation of urban site using the target spectral ratio method (THVSR): a case study of Algiers cityAUTEURS...
21/09/2025



Seismic microzonation of urban site using the target spectral ratio method (THVSR): a case study of Algiers city

AUTEURS
Linda Chibane (USTHB Alger, Algérie)
Nasser Laouami (CGS Alger, Algérie)
Mustapha Hellel (USTHB Alger, Algérie)
Mohamed Yacine (USTHB Alger, Algérie)

R***E
Environmental Earth Sciences
Vol. 84 ; article n° 131
https://link.springer.com/article/10.1007/s12665-025-12133-3

RESUME
[en] Abstract
This paper presents a seismic microzonation study of the urban area of Algiers city in Algeria, using 640 microtremor measurements and site classification based on target horizontal over vertical spectral ratios (THVSR) approach. Northern Algeria lies along the Africa-Eurasia plate boundary, and the Algiers city is located in one of the most seismically active areas in the western Mediterranean. The area's geological context suggests the prevalence of alluvial soils, especially in its central part, which undergoes significant site amplification. The seismic design codes use the concept of soil class to categorize common-soil conditions into broad classes bounded by typical average shear wave velocities in the top 30 m (Vs30). Geophysical methods involving boreholes are required for the measurement of Vs30, however, their prohibitive cost makes them unappealing. In order to prepare a first order seismic microzonation map for the urban area of Algiers city, an alternative new classification scheme based on THVSR is performed over 640 microtremor measurements. The results of the classification of sites based on THVSR consist of providing the site class according to the recent updated version of Algerian Seismic Code (RPA, 2024), the main frequency of the site, and an average estimate of Vs30. To assess the reliability of the THVSR approach, microtremor measurements were compared with shear-wave velocity profiles at 29 sites where Vs30 data were available. In the absence of extensive geophysical surveys, the proposed technique provides a cost-effective and efficient tool for seismic microzonation, with direct applications to urban planning.

Role of Fluid on Earthquake Occurrence: Example of the 2019 Ridgecrest and the 1997, 2009 and 2016 Central Apennines Se...
20/09/2025



Role of Fluid on Earthquake Occurrence: Example of the 2019 Ridgecrest and the 1997, 2009 and 2016 Central Apennines Sequences

AUTEUR
Jugurtha Kariche (USTHB Alger, Algérie)

R***E
Pure and Applied Geophysics
Sous presse
https://link.springer.com/article/10.1007/s00024-025-03833-9

RESUME
[en] Abstract
This paper focuses on the study of the temporal evolution of seismicity and the role of fluids during major earthquake sequences that occurred in the Central Apennines and Southern Walker Lane belt-Eastern California Shear Zone over the last two decades: the 1997 Colfiorito, the 2009 L’Aquila, the 2016 Amatrice-Norcia, and the 2019 Ridgecrest sequences. The availability of high-quality earthquakes catalogs offers the opportunity to evaluate in detail the temporal evolution of the earthquake's size distribution (or b-value) and propose a physical explanation based on the effect of the fluid flow process in triggering seismicity. For all seismic sequences, the b-value time series show a gradual decrease from a few months to one year before mainshocks. The gradual decrease in the b-value is interpreted as a gradual increase in earthquake activity due essentially to the short-term to intermediate-term pore-fluid fluctuations. The temporal variation of the b-value during Amatrice-Norcia and Ridgecrest foreshock sequences is characterized by a double b-value minimum separated by a short-lived b-value increase as observed in laboratory experiments on water-saturated rocks. The observed fluctuation of the b-value is presented here as an accelerating crack growth due essentially to the fluid flow instability. Even though seismic precursors could have been predictable in areas with high dense seismic networks, the different b-value time series reveal the difficulty in establishing a correspondence between the duration of the foreshock activity and the magnitude of the next largest expected earthquake. This may suggest that the fluid migration controls the size of the ruptures.

Some Tortonian ostracods from the Oued Bir Moka section (Tafna Basin, NW Algeria)AUTHORSAbdelhakim Benkheda (ENS Ouargl...
20/09/2025



Some Tortonian ostracods from the Oued Bir Moka section (Tafna Basin, NW Algeria)

AUTHORS
Abdelhakim Benkheda (ENS Ouargla, Algérie)
Francesco Sciuto (University of Catania, Italie)
Mostapha Benzina (Université de Ouargla, Algérie)
Abdelmalik Draoui (Université de Ouargla, Algérie)
Hakim Hebib (Université de Tlemcen, Algérie)

R***E
R***e de Micropaléontologie
Vol. 89 ; article n° 100866
https://www.sciencedirect.com/science/article/pii/S0035159825000340

RESUME
[en] Abstract
Ostracod species, some new, others little known, belonging to the family Trachyleberididae are described, figured and commented in this paper. The specimens come from Tortonian sediments outcropping along a stratigraphic section located in the Tafna Basin (NW Algeria).

HIGHLIGHTS
• A stratigraphic section located in the Tafna Basin (NW Algeria) was sampled.
• Ostracod species belonging to Trachyleberididae (Sylvester-Bradley, 1948) are analyzed.
• Two ostracod species, new to the science, have been described, figured and commented.

Identifying pre-seismic ionospheric disturbances using space geodesy: A case study of the 2011 Lorca earthquake (Mw 5.1...
13/09/2025



Identifying pre-seismic ionospheric disturbances using space geodesy: A case study of the 2011 Lorca earthquake (Mw 5.1), Spain

AUTEUR
Abdennasser Tachema (Université de Tlemcen, Algérie)

R***E
Earth Science Informatics
Voume : 17 ; pages : 2055–2071
https://link.springer.com/article/10.1007/s12145-024-01272-z

RESUME
[en] Abstract
This research work examines earthquake-induced ionospheric anomalies through an in-depth analysis of Total Electron Content (TEC) parameter. It involves modeling the ionospheric F2-layer by processing geodetic and geophysical data to generate regional TEC maps. Additionally, a geodetic approach is developed for short-term seismic hazard prediction, grounded in seismo-ionospheric interactions. This study supports the concept that the occupied space between the lithosphere and ionosphere forms a coherent structure of electrons and protons, ensuring the transmission of electromagnetic waves generated during the seismic nucleation of rocks at depths. Therefore, the analysis of GPS-TEC signals using both wavelet-based and statistical techniques is crucial for detecting the arrival time of pre-earthquake ionospheric anomalies. The study assesses the effectiveness of the applied geodetic approach, using datasets from ground-based GPS/GNSS stations in an area proportional to seismic wave propagation. In-depth investigation of the Mw 5.1 shallow-moderate earthquake, that shook the Spanish city of Lorca on May 11th, 2011, revealed consistent outcomes in short-term seismic prediction. The forecasts indicated a lead time ranging from hours to days prior to the occurrence of the mainshock. These findings affirm the coupling hypothesis between the lithospheric and ionospheric envelopes allowing the prediction of imminent earthquakes over seismogenic regions.

C'est avec une profonde tristesse que nous annonçons le décès de Monsieur Kechid Sid Ali, Professeur de géologie à la Fa...
10/09/2025

C'est avec une profonde tristesse que nous annonçons le décès de Monsieur Kechid Sid Ali, Professeur de géologie à la Faculté des Sciences de la Terre de l'USTHB, qui a marqué des générations d'étudiants par son savoir et sa passion dans ce domaine.

Son départ laisse un grand vide dans nos cœurs, mais son souvenir restera vivant à travers ceux qui l'ont connu et estimé.

L'enterrement aura lieu Demain, le 11/09/2025 après Salât Eddohr au cimetière Hasnaoua, Cheraga.

Nous présentons nos sincères condoléances aux familles Kechid et Benkherouf.

إنا لله و إنا إليه راجعون

Australie, un voyage à travers le temps - partie 04 (Cénozoïque)
08/09/2025

Australie, un voyage à travers le temps - partie 04 (Cénozoïque)

Australie, un voyage à travers le temps - partie 03 (Mésozoïque)
08/09/2025

Australie, un voyage à travers le temps - partie 03 (Mésozoïque)

Australie, un voyage à travers le temps - partie 02 (Paléozoïque)
08/09/2025

Australie, un voyage à travers le temps - partie 02 (Paléozoïque)

Australie, un voyage à travers le temps - partie 01 (Précambrien)
08/09/2025

Australie, un voyage à travers le temps - partie 01 (Précambrien)

Caulostrepsis taeniola and other sclerobionts on Crassostrea gryphoides shells from the Middle Miocene transgressive de...
05/09/2025



Caulostrepsis taeniola and other sclerobionts on Crassostrea gryphoides shells from the Middle Miocene transgressive deposits of the Chellala Mountains (Algeria)

AUTEURS
Abdelmounim Mazouzi (Université de Ouargla, Algérie)
Mohammed Nadir Naimi (USTHB Alger, Algérie)
Amine Cherif (Université de Ouargla, Algérie)

R***E
Journal of African Earth Sciences
Sous presse ; article n° 105828
https://www.sciencedirect.com/science/article/abs/pii/S1464343X2500295X

RESUME
[en] Abstract
The ichnological study of the Middle Miocene deposits of the Chellala Mountains (Pre-Atlas domain, Algeria) revealed relatively abundant but less diverse sclerobiont communities that are preserved in Crassostrea gryphoides shells. The most prominent trace fossil found is Caulostrepsis taeniola. Other bioerosive traces are represented by Entobia geometrica, Gastrochaenolites isp., and Trypanites isp.. The four borings consist of dwelling trace fossils (domichnia) produced by polychaete annelids and endolithic bivalves. Among sclerozoans, epibionts are dominated by the two barnacle species Balanus crenatus and B. stellaris. The ichnoassemblage is assigned to the Trypanites ichnofacies, indicating nearshore, high-energy deposition influenced by storm events, and post-mortem bioerosion. The study of the mid-Miocene transgression in this key area of northern Algeria has made it possible to produce a palaeogeographic map corresponding to the period of maximum sea level.

HIGHLIGHTS
• Middle Miocene sclerobiont communities preserved in Crassostrea gryphoides shells are described
• The dominant trace fossil is Caulostrepsis taeniola, with Entobia, Gastrochaenolites, and Trypanites
• Borings represent domichnial components produced by polychaete annelids and endolithic bivalves
• Epibionts are mainly the barnacles Balanus crenatus and B. stellaris
• The ichnoassemblage indicates a nearshore, storm-influenced setting, linked to the mid-Miocene transgression

Geochemistry and economic evaluation of REE + Y potential in the fine-grained matrix of sedimentary phosphorites from t...
02/09/2025



Geochemistry and economic evaluation of REE + Y potential in the fine-grained matrix of sedimentary phosphorites from the Tebessa region, eastern Algeria

AUTEURS
Riadh Aouachria (Université de Ouargla, Algérie)
Rabah Kechiched (Université de Ouargla, Algérie)
Roberto Buccione (University of Basilicata, Italie)
Giovanni Mongelli (University of Basilicata, Italie)
Ouafi Ameur-Zaimeche (Université de Ouargla, Algérie)
Olivier Bruguier (Université de Montpellier, France)
Laszlo Kocsis (University of Lausanne, Suisse)
Rabah Laouar (Université d'Annaba, Algérie)

R***E
Journal of Geochemical Exploration
Sous presse ; article n° 107889
https://www.sciencedirect.com/science/article/abs/pii/S0375674225002213

RESUME
[en] Abstract
The Algerian phosphorites, deposited during the Paleocene-Eocene, are part of the Tethyan phosphogenesis along the southern paleo-Tethys margin. Located primarily in the Tebessa region, these deposits hold reserves exceeding 2 billion metric tons. Recent interest has grown due to their enrichment in rare earth elements plus yttrium (REY). While previous studies have examined whole-rock and grain-size fractions, the fine-grained matrix (

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