This study presents a comparative assessment of potential economic losses caused by seismic events in two high-risk Mediterranean urban centers: downtown Blida (Algeria) and the municipality of Orihuela (Spain). Both regions face serious seismic threats due to their proximity to active fault systems, dense populations, and aging building inventories that remain highly vulnerable to ground shaking. The main goal of this research is to bridge the gap in current risk assessments by estimating economic losses for Blida (Algeria) and the Mean Damage Ratio for Orihuela (Spain) using different approaches to accounting for local site effects and different ground motion prediction equations (GMPEs). Applying a scenario-based framework via the Seismic Loss Estimation using a Logic Tree Approach (SELENA) software, the study modeled four credible earthquake scenarios for Blida (MW 6.5–7.1) and a simulated repetition of the historic 1829 Torrevieja earthquake (MW 6.3–6.9) for Orihuela. The methodology employed a logic-tree approach to manage epistemic uncertainties, incorporating regionally validated Ground-Motion Prediction Equations (GMPEs) and the Euro-Mediterranean RISK-UE building taxonomy to classify thousands of residential and historical structures. The findings reveal critical vulnerabilities in both urban contexts. In Blida, near-fault scenarios (MW 7.1) yield a global Mean Damage Ratio (MDR) of approximately 53

The Soummam Basin, in the central Tell Atlas (Algeria), is a tectonically active region shaped by the ongoing convergence of the African and Eurasian plates. This study integrates morphometric analysis, structural mapping, and field investigations to evaluate the role of neotectonics and active crustal deformation in shaping the landscape. Using 30 m resolution SRTM/DEM data and TopoToolbox in a GIS environment, we extracted and analyzed key geomorphic indices, including the hypsometric integral (HI), normalized channel steepness (Ksn) index, and Chi (chi) index. These analyses were complemented by longitudinal profile interpretation and knickpoint mapping. The results reveal significant spatial variations in morphometric indices that closely correlate with major fault systems, such as the North Tell Fault and the South Kabyle Major Fault. High Ksn values and lithologically independent knickpoints, point to active incision driven by ongoing tectonic uplift. Chi (chi) mapping and divide migration vectors indicate pronounced drainage disequilibrium, particularly across the Djurdjura and Biban Chains, suggesting a segmented and evolving crustal framework. Field observations confirm tectonically influenced landforms, including offset alluvial fans and fault-aligned escarpments. Collectively, these findings indicate that the present-day morphology of the Soummam Basin results from a dynamic interplay between inherited structural segmentation and ongoing deformation under NW-SE compression. This study underscores the importance of integrating morphometric tools with geological and geomorphological data to evaluate neotectonic activity, providing valuable insights for seismic hazard assessment and regional landscape evolution.

Certain regions of Algeria, particularly in the Northeast, are currently facing heightened seismic activity alongside considerable social and economic challenges. Should a seismic event akin to the Djidjelli (now Jijel) earthquake of August 21 and 22, 1856, strike again, numerous coastal cities may suffer significant damage. This study is part of a broader project aimed at estimating seismic risk and damage levels following seismic events, with a particular focus on initial acceleration computation, which serves as a crucial tool for our modeling. Given the significance of conducting studies that enable the estimation of seismic risk and potential damage in urban agglomerations, the overall goal of this work is to assess seismic risk in an urban agglomeration using a deterministic scenario to estimate the risk, seismic vulnerability and damage potential. We provide a seismic risk scenario for Jijel city, with a particular focus on the susceptibility of its historically significant districts: Bourmel-Ben Achour, Ouled Aissa–Camp Chevalier, and the Old City. Using a Ground Motion Prediction Equation, we calculated the maximum expected ground acceleration based on the following considerations: (a) the 1856 Jijel seismic event as a reference; (b) site impacts associated with the area’s geological characteristics; (c) building damage; and (d) seismic vulnerability. This research presents a Peak Ground Acceleration (PGA) map that incorporates the influence of site lithology (Avib). The highest acceleration was recorded in the city center, with EC8 offering a reliable estimate of acceleration across all three examined areas: Bourmel-Ben Achour, Ouled Aissa–Camp Chevalier, and the Old City. The strongest tremors are felt in Jijel’s city center and eastern regions. Correlation with the geological features reveals an estimated PGA of 0.28 g in the Old Town area. This estimate closely aligns with the PGA of 0.52 g obtained from our independent analysis, which accounts for local lithology and site conditions. Furthermore, according to the RPA (Algerian earthquake engineering code) the Jijel province is classified as Zone IIa (medium seismicity), with an acceleration data of 0.25 g. This study integrates Geographic Information Systems (GIS) data into risk models.

Geological evidence of extreme high-energy sea wave events can be preserved in coastal areas as depositional and/or erosional deposits. In this work we present field evidence for the existence of high energy sea wave depositional features, in the Mostaganem region, northwestern Algeria, which include: (i) unusual marine sedimentary features trapped in a waterway valley, in an old coastal notch, and in low-lying parts of the coastal zone, (ii) carried, imbricate and oriented large boulders of weight ranging between 1.2- 32.6 tons. Both the boulders and the sedimentary deposits fit the characteristics of high energy waves deposits while at least some of them fit the tsunamis waves ones. Hydrodynamic analysis of the joint bound and the submerged boulders, considered in this study, yield values ranging between 0.40m to 29.24m for storm waves height (Hs) and 0.10m to 7.31m for tsunamis waves height (Ht). The threshold minimum velocity ranges between 1.91m/s-17.14m/s. Therefore, the majority of the boulders may have both storm and/or tsunami origin while some of them (weight exceeding 25 tons) requires very high storm waves unlikely to occur in the study area; Consequently, the tsunami origin is the most possible for this case. On the other hand, tsunami modeling, considering near shore active faults, has shown that the maximum heights of 1.21m, 0.81m, 0.35m, 0.41m and 0.34m can be expected at Stidia (where the boulders are described), Les Andalouse, AinTurck (north-west Algeria), Almeria and Cartagena (Southern Spain), respectively. these heights are comparable to the ones described during the Oran October 9th, (I0 = IX) historical earthquake in northwestern Algeria and Southern Spain. Nevertheless, the maximum wave height needed to move some of the very big boulders found in the study area exceeds 7 m, possible likely, not from near shore earthquakes, but from Iberian or Mediterranean offshore earthquakes considered in previous study as a possible source for northern Algerian tsunamis. This work should encourage further research in the prevention of tsunami hazards along the Algerian coast, densely populated and where important economic infrastructures are located, which is insufficiently studied compared to other Mediterranean regions.

This study employs the classical approach of Probabilistic Seismic Hazard Analysis (PSHA) to explore the potential regional seismic hazard in Bejaia City and its surrounding regions in Algeria. The analysis explicitly focuses on individual active faults by integrating the fundamental concepts of the characteristic earthquake model. The research unfolds in three key phases: First, a comprehensive and homogeneous earthquake catalog was compiled and updated, following the methodology of the Unified Moment Magnitude (MW) parametric earthquake catalog for Algeria and adjacent regions (PECAAR). This updated catalog forms a consistent and a reliable basis for estimating the Gutenberg-Richter parameters. Second, active and potentially active fault networks were identified and characterized using seismotectonic data. Critical earthquake hazard parameters, such as the expected maximum magnitude ( m_max ), slip rate along the fault ( ṡ ), and rupture area ( A_f ), were estimated for each fault. These parameters provide a deeper insight into the region’s earthquake potential. Third, ground motion models (GMMs) were selected for the Bejaia region. The PSHA was conducted using these GMMs, and the results are presented as Peak Ground Acceleration (PGA) seismic hazard maps illustrating the spatial distribution of expected seismic hazard levels for two key return periods 475 years (10

Blida (Algeria) is characterized by a high level of seismic exposure and vulnerability due to its dense population and the presence of aging buildings. The historical earthquake that occurred in 1825, with a moment magnitude (Mw7.1), underscored the urgent need for a thorough assessment of seismic risk in the area. Here, an extensive study conducted in downtown of the city of Blida to evaluate seismic risk and its consequences is presented. Geounits 141 and 148 emerged as the most severely affected in all the simulated earthquake scenarios indicating severe damage and casualties mainly for closest earthquakes (Blida and Bounaian, both with moment magnitude Mw7.1) but also for furthest earthquakes as Mouzaia El Affroun (Mw6.6), and Hammam Melouane (Mw6.5). The sensitivity analysis demonstrated the importance of the selection of the performance point computation method (improved displacement coefficient method -IDCM, modified capacity spectrum-MADRS, and nonlinear analysis method -N2) and the choice of the ground motion prediction equation. IDCM results are less influenced by the choice of the GMPE, but they provide higher damage results expressed as a mean damage ratio. Moreover, the study estimated potential human impacts in the Blida region, highlighting varying levels of impact on different geounits under different earthquake scenarios. The study's primary findings from seismic risk assessments in the studied region highlight its high susceptibility to earthquakes and can be summarized as follows: The mean damage ratio will be 52.6% +/- 1.4%, 50.9% +/- 1.6%; 31.8% +/- 3.4% and 21.4% +/- 3.1% for the Blida, Bounaian, Mouzaia El Affroun and Hammam Melouane earthquakes respectively.

In this study the seismic hazard in Northern Algeria is analyzed by using a probabilistic approach, and specifically the parametric-historic method. This method enables the incorporation of the entire accessible seismic history into the analysis and effectively addresses both the spatial heterogeneity and temporal variability of the seismicity parameters. The recently compiled earthquake catalog covering the region and spanning the period from 1658 to 2018 was used for estimating the seismicity parameters. The seismic hazard maps in terms of peak ground acceleration (PGA) were calculated for return period of 475 years for rock, stiff soil, and soft soil conditions. The uniform hazard spectra (UHS) for the major cities in Northern Algeria were calculated for the same conditions. The largest PGA values are observed near the cities of Chlef, Algiers, Blida, Medea, and Tipasa. Arguably the most important obtained result is evident in the seismic hazard estimates for the capital city of Algiers, which significantly exceed previously published estimates.

The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8, 2023, was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity. This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar (InSAR) observations from both ascending and descending orbits. Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km, exceeding the typical range for crustal earthquakes. This result suggests the presence of cooler temperatures in the lower crust, which facilitates the accumulation of tectonic stress. The earthquake exhibited a steep reverse mechanism, dipping at 70°, accompanied by minor strike-slip motion. Within the geotectonic framework of the High Atlas, known for its volcanic legacy and resulting thermal irregularities, we investigated the potential contributions of these factors to the initiation of the Adassil earthquake. Deep seismicity within the lower crust, away from plate boundaries, calls for extensive research to elucidate its implications for regional seismic hazard assessment. Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings, which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms.

In order to better constrain the Mesozoic-Cenozoic evolution of the Precambrian Hoggar shield, a paleomagnetic study, combined with detailed fieldwork, was carried out to date its detrital local cover, the Serouenout Formation. Thermal demagnetization yields, only in a few samples, the characteristic remanent magnetization carried by hematite. Post-tilting remagnetization was obtained in sites located along a fault affected by intense fluids circulation. The paleomagnetic directions recorded at seven widespread other sites are on the contrary associated with a positive fold test. It provides a relatively well-defined paleomagnetic pole (A95 = 4.1°), sufficient to estimate the age of the Serouenout Formation. The comparison of this pole with the reference curve of Africa suggests two possible age windows, Triassic and Upper Cretaceous-Lower Paleocene, while the discovery in the uppermost levels of the Serouenout Formation of a fern-rich level with Weichselia reticulata (Bathonian to Cenomanian; Blanco-Moreno et al., 2018) imposes a deposition during the Cenomanian. The presence of a detrital formation at least 350 m thick, with a basal conglomerate containing large pebbles, implies the existence, during this time period, of a tectonic event that generated differential uplift. In addition, structural observations indicate that the Serouenout Formation recorded later brittle tectonics, dominated by a network of vertical N–S dextral faults. The horizontal displacement generated by one well-developed fault has been estimated to be at least 1 km. This activity is related to the known Alpine reactivations of the N–S Pan-African mega-structures, which are still at the origin of the current intraplate seismicity.

The 4 degrees 50'Shear zone (SZ), one of the major structures of western Gondwana, formed in Hoggar during the PanAfrican orogeny is still poorly studied; especially ages and deformation characteristics are lacking. We performed microstructural analysis and EBSD measurements on nine selected mylonites from the 4 degrees 50'SZ, and zircon U-Pb dating on two granitoid samples. The protolith of these mylonites are granitoids. Most samples display segregation of dominant feldspar and minor quartz in separate layers that underline the N-S subvertical mylonitic foliation. Feldspar grains display evidence of intracrystalline deformation, supporting dextral shear-sense. Plagioclase and K-feldspar are frequently corroded with embayments infilled by secondary K-feldspar and plagioclase respectively. Interstitial quartz grains disseminated in feldspar aggregates may infill fractures in feldspar grains. Quartz ribbons, usually parallel to the foliation, locally crosscut feldspar layers. Quartz is partially recrystallized and elongate crystals form a secondary foliation at similar to 30 degrees to the main foliation, supporting a later sinistral shearing. In some samples, amphibole is associated with quartz and oriented parallel to the foliation. In all samples, quartz CPO suggests a dominant prism- slip-system, activated at medium/high temperature (similar to 500-700 degrees c), but stress-induced oriented crystallization may have contributed to this CPO. K-feldspar CPO supports the activation of the [100](010) slip system while the plagioclase CPO points to activation of [100](001) system. These CPO support dislocation creep under amphibolite facies conditions. These new data, in addition to U-Pb dating, suggest the following evolution: 1) successive intrusions of granitoids in the SZ (similar to 661-similar to 639 Ma) due to partial-melting of the lower-crust and, possibly also of the lithospheric-mantle, 2) the 4 degrees 50' SZ was rooted in the lower-crust or the upper-mantle, and 3) dextral shearing lasted over >= 20My. This was followed by successive magma batches that intruded these rocks during a late migmatitic episode (similar to 623-similar to 609 Ma). After similar to 609 Ma, a moderate sinistral reactivation of the 4 degrees 50' SZ occurred and was accommodated through dislocation creep mainly localized in quartz ribbons. During accretion of the Western Gondwana, the 4 degrees 50' SZ was active during subduction. During >= 20My, it was successively intruded by granitoids that cooled down slowly, and have been deformed in the submagmatic state then in the solid-state.

It is well known that seismic hazard studies are very sensitive to the maximum possible magnitude estimate which is a critical key parameter used in the establishment of building codes. This study focuses on the analysis of space–time variations of seismic hazard parameters in northern Algeria with a special emphasis on maximum possible magnitude M max . Namely, seismic hazard parameters include the seismic activity rate λ , the Gutenberg–Richter b -value in addition to M max . The analysis is applied to Bellalem et al. (2022)’s Parametric Earthquake Catalog for Algeria and Adjacent Regions (PECAAR) which includes events with magnitudes M W ≥ 2.8 occurred during the time period 1658–2018. Background seismicity distribution is identified using Gardner and Knopoff (1974)’s windowing method, and then it is plotted together with the seismic hazard parameters distributions to study their space–time variability. The results show the overall statistical properties of the PECAAR newly compiled catalog. The last two decades are characterized by a mean seismicity rate concentrated along the coastal active faults band with the highest seismicity rate registered south of Algiers city and in the western region of Cheliff. Similarly, the highest M max estimates, which exceed 7.5, are observed in Blida south of Algiers city and the Cheliff region, thus pointing to a high hazard potential in these two densely populated cities. The obtained results describe northern Algeria's seismic hazard potential quite well, especially the maximum possible magnitude in each location.

The Tell Atlas of Algeria has a huge potential for hydrothermal energy from over 240 thermal springs with temperatures up to 98^∘ C in the Guelma area. The most exciting region is situated in the northeastern part which is known to have the hottest hydrothermal systems. In this work, we use a high-resolution gravity study to identify the location and origin of the hot water, and how it reaches the surface. Gravimetric data analysis shows the shapes of the anomalies arising due to structures at different subsurface depths. The calculation of the energy spectrum for the data also showcases the depths of the bodies causing anomalies. 3D-Euler deconvolution is applied to estimate the depths of preexisting tectonic structures (faults). These preprocessing steps assist with assessing signal attenuation that impacts the Bouguer anomaly map. The residual anomaly is used in a three-dimensional inversion to provide a subsurface density distribution model that illustrates the locations of the origin of the dominant subsurface thermal systems. Overall, the combination of these standard processing steps applied to the measurements of gravity data at the surface provides new insights about the sources of the hydrothermal systems in the Hammam Debagh and Hammam Ouled Ali regions. Faults that are key to the water infiltrating from depth to the surface are also identified. These represent the pathway of the hot water in the study area.

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).

For any seismic hazard study, a reliable, homogenized and complete seismic catalogue is required. The Algerian seismicity catalogue has been recently updated by retrieving and reappraising many historical events. The Algerian seismic network has also been densified up to about 80 seismic stations covering the Tell Atlas which is the most active area of northern Algeria for monitoring of the seismic activity reducing the magnitude threshold. Recently, we have launched archeoseismological studies to retrieve past strong earthquakes that have affected Roman sites located along the Tell Atlas. Here, we proceed with tectonic investigations around selected sites where significant observed damage was identified. On the other hand, paleoseismological investigations were conducted along the El Asnam fault (now Chlef) following the large Ms 7.3 earthquake of 1980. Paleoseismic studies combined with archeoseismological results provide the dating of past earthquakes and contribute to the completeness of the seismicity catalogue.

Hazardous ground deformation and landslides occur frequently in the Mila Basin, Algeria and this problem remains unsolved. However, the historical seismicity in the area indicates no severe damage from past earthquakes. For this reason, studies are needed to monitor the slow ground movements and their triggering factors. Since about two decades ago, satellite observations by interferometric synthetic aperture radar (InSAR) technique and the multi‐temporal (MT‐InSAR) technique have provided a tool for monitoring slow and extremely slow ground displacements. In this study, 2D decomposition of InSAR outputs revealed a sliding surface at two regions located 12 km apart, indicating slow motion rather than fast movement along the damaged area. We concluded that the factors leading to surface displacement in the investigated area include the triggering earthquakes, precipitation, terrain topography and soil moisture. This study contributes to landslide hazard identification and risk assessment in the Mila Basin.

The hyper-arid Saharan desert belt stretching across North Africa is an important part of the global climate system, with dust export shown to influence climate systems such as ENSO and distant monsoon systems. Understanding climate dynamics and potential future changes in this region is however difficult due to a paucity in both instrumental and high-resolution paleoclimate data. There is strong evidence for periods of increased rainfall across large parts of North Africa during the late Quaternary, termed ‘Green Sahara’ periods, which contribute to regional aquifer recharge and improved human population connectivity across the Sahara. There is, however, currently limited evidence regarding: i) precisely where and when rainfall occurred and; ii) the sources of moisture contributing to increased rainfall at the northern-most reaches of the Sahara. In this study, we present new proxy reconstructions from the northern limits of the presently hyper-arid Sahara Desert, to identify moisture sources, timing and latitudinal extent of rainfall change during these so-called Green Sahara periods. We do this using several ancient fossil stalagmites collected from cave sites in the desert foothills of the central Saharan Atlas Mountains, Algeria. High-precision U-Th chronology and stable-isotope measurements on calcite samples from multiple cave sites contribute towards an east-west transect of records. Due to the locations of the caves, stalagmite growth periods and stable isotope records provide direct evidence of where and when there was significantly increased rainfall in this region, and help us to identify potential sources of moisture through time. We present these results, and their implications for a more detailed reconstruction of the occurrence of Green Sahara periods in northwest Africa.

This work aims to analyze flood-related deaths in northwestern Algeria for the period 1966–2019. Devastating and unpredictable floods resulted in more than a thousand deaths in the last two centuries in this area. Despite the severity of the floods in this territory, official databases and studies on flood fatalities are not available. To address this gap, we compile a database consisting of 324 deaths caused by 52 flood events using referenced sources. The data is assessed according to the type of flood event responsible for each death, the temporal and spatial distribution of deaths, and the analysis of victim’s characteristics and incident’s circumstances. The results show that flash floods caused most deaths. There has been a downward trend in the number of flood deaths over the years. A coincidence of high daily rainfall values with high mortality events, as well as increased mortality rates in autumn and during daylight hours. Spatially, flood deaths occurred mainly in sites crossed by rivers and in plain zones with high population density. Analysis indicates that males are more vulnerable to deadly floods than females are; moreover, young children and the elderly are the most exposed age groups. Drowning is the leading fatality cause type, and the fatal incidents occur mostly outdoor among individuals on foot. These results contributed to fill the gaps on flood deaths that reflect the vulnerability of the study area and could help the decision makers to improve the strategy against flood risks.

Previous paleomagnetic studies performed in the central North-Algeria (Chellif and Mitidja basins) on Neogene formations pointed out tectonic clockwise blocks rotations. This deformation pattern was interpreted as resulting from a bookshelf neotectonics, consequence of the Africa-Eurasia plates convergence. A new paleomagnetic study was conducted on the Neogene volcanic rocks outcropping in the northwestern Algeria (Marset Ben Mhidi, Aïn Temouchent, Tifaraouine area). The obtained stable remanent magnetization is mainly carried by Ti-poor titanomagnetite. The paleomagnetic data show that, since the lava emplacement, the northwestern Algeria underwent a mean moderate clockwise block rotation of 9.3° ± 4.5°. For the Algerian margin, this confirms a context of transpression and blocks rotations in a strike-slip tectonic setting. A decreasing deformation gradient from the E to the W affected the different basins of this margin, from strong rotations within the Mitidja, to the moderate ones in the Chellif and to Marset Ben Mhidi, Aïn Temouchent, Tifaraouine area, where rotation magnitudes are significantly lower.