Nowadays the salinization of freshwater resources due to seawater intrusion represent a worldwide issue. Accordingly, this study aims to identify and locate the freshwater-saltwater interface in the downstream part of the Nador wadi plain (Algeria), a coastal area characterized by a semi-arid mediterranean climate using a multi-methodologies approach including geophysical methods, hydrostatics approach, hydrochemical method, and piezometry situation. The investigation was carried out by the electrical survey and refraction seismic methods in the period of April-May 2018. Moreover, the hydrochemical and piezometry methods were used to confirm the results of the geophysical technique. The results of the present study case showed that the seawater intrusion interface is located at 420–1380 m from the shoreline. Additionally, the presence of the bedrock bulge (clay formation) at a distance ranging between 550 and 1050 m from the shoreline, plays the role of the natural hydraulic barrier for the seawater advance. The findings indicate that the identified seawater intrusion interface and the natural hydraulic barrier formed by the bedrock bulge are critical for managing groundwater resources in the Nador wadi plain. This methodology can be applied to other coastal plains worldwide to address the challenges of seawater intrusion and groundwater salinization.

This work aims to determine the present-day in-situ stress and pore pressure in the Ahnet Basin, Algeria, through a 1D geomechanical approach. We investigated the drilling-induced fracture (DIF) from FMI log data to ascertain the direction of maximum horizontal stress (SHmax) from the Ahnet Field. A mean orientation of N140 ( & PLUSMN; 10) has been interpreted, which is NW-SE (N140-N320), with a local variation of ( & PLUSMN; 20) compared to fields such as Illizi, Hassi Messaoud, and North Algeria, which can be explained by depth variation and intrinsic rock properties. A 1.05 psi/ft gradient of overburden stress (Sv) has been obtained from density. Pore pressure has been estimated from the sonic log by a normal compaction trend, indicates a hydrostatic regime from the surface to the top of the Silurian unit with an average pore pressure gradient of 0.43 psi/ft and an overpressure regime against the hot shale unit with a gradient of 0.58 psi/ft caused by the high in situ temperature in the study area and possible activity of the mega-shear zone. The poroelastic approach under transverse isotropic vertical conditions (VTI) has been used to calculate the minimum and maximum horizontal stress magnitudes. The outlines indicate a high-stress gradient close to 0.82 psi/ft, for Shmin calibrated with MDT stress points and 1.10 psi/ft for SHmax. The stress magnitudes results, suggest a present-day normal to strike-slip stress regime in the Ahnet Basin. Fault reactivation potential at two Silurian units has been inferred from the frictional theory analysis. The results indicate that increased pore pressure in hot shale formations due to by fluid injection and hydraulic fracturing causing shear slippage of the pre-existing faults, resulting in induced seismicity. Our study has contributed to the understanding of stress state origin in Ahnet Basin, the relationship between in situ temperature and pore pressure, and the fault stability analysis in such unconventional reservoir development.

The northern Algeria forms the southern edge of the Western Mediterranean Sea that formed within the zone of convergence between the African and Eurasian plates. It is one of the poorest studied areas in the western Mediterranean region, mainly due to the lack of data. The current structure of northern Algeria is the result of the geodynamic evolution that occurred in the western Mediterranean. The few tomographic studies revealed the presence of velocity anomalies beneath the south of the western Mediterranean region. These anomalies suggest the existence of abnormally cold material in the asthenosphere, interpreted as the trace of subducted plunging panels (slab). During the recent decades, the seismological network in northern Algeria has significantly developed, giving rise to a significant increase in the amount of information given by the network database. This development motivated us to investigate the crust and the upper mantle structure beneath the northern Algeria using a non-linear teleseismic tomography method. An overall of 29 stations distributed along the northern part of Algeria have been used to collect 11018 P-waves from 2847 earthquakes recorded over ten years. The proposed model suggests the presence of high-velocity anomalies along of the northern Algeria. We interpreted these abnormal anomalies as a slab teared into two panels. A central segment bending along the Atlasic massif of Hodna and plunging under the Lesser Kabylia. The second segment at the North-East, shifted to the north plunging towards the North-East. A series of Tellian high-velocity anomalies axes mark the limit between the African and the Eurasian plate. The south eastern region covered by our model (Aurès massif) is characterized by a low-velocity anomaly potentially linked to the remnant of the Mesozoic rifting.

Abstract The present study aims to charcaterize, by geophysical methods (electrical sounding and seismic refraction), the downstream part of the Oued Nador alluvial layer or deposits (Tipaza, Algeria) and the morphology of its bedrock to better locate the freshwater-saltwater limit. This will allow to better understand the marine intrusion.Indeed, the aquifer is defined by a clay and marl substratum of middle to lower Pliocene Piacenzian age rich in recent Neogene and Quaternary filling (Quaternary alluvium composed of sand, gravel and pebbles). During Spring of 2015, 2016, and 2017 three electrical surveys were conducted. The results indicate that the origin of the salinity is due to progressive marine intrusion inside the aquifer (Bechkit et al, 2017; Bechkit et al, 2018a; Bechkit et al, 2018b). However the presence of clay makes the contrast between the saltwater and the clays less important so that it is difficult distinguish electrically the two mediums. In May 2018, we combined both electrical survey and a refraction seismic acquisition on the area of study. This work was carried out in order to separate, through the ranges of wave propagation velocity, the saltwater formations from the clay ones. The presence at a certain distance from the coast of an elevation of the clay bedrock has an advantage. Indeed, it acts as a natural barrier against any intrusion on a large scale of saltwater at depth. The study carried out in this context showed that the combination of two geophysical methods is very useful in environmental study for the evaluation of the salt water intrusion in an alluvial ground in the presence of clay formations.

The Tuareg Shield, to which Hoggar (southern Algeria) belongs, has a swell-shaped morphology of lithospheric scale of ~1000 km in diameter linked to Cenozoic volcanism occurring in several regions, including Atakor, the center of the swell, which reaches nearly 3000 m in altitude. The lack of high-resolution geophysical data for constraining its deep structure is at the origin of a controversy about its innermost nature and about the origin of the Cenozoic volcanism. During the course of this study, magnetotelluric (MT) broadband data were collected at 18 sites forming a northeast-southwest profile 170 km long within the Atakor region. The electrical resistivity model obtained by inverting the magnetotelluric data reveals lithospheric structure down to a depth of ~100 km. From this depth to the surface, the model does not show any regional anomaly that may result from a metasomatized lithosphere or from an asthenospheric upwelling, including a mantle plume. MT data reveal rather a lithosphere affected by a set of rather thin subvertical conductors that can be attributed to the electrical signature of some known shear zones resulting from the Pan-African evolution of the LATEA metacraton, which globally corresponds to the uplifted Central Hoggar swell. The main anomaly is deeply rooted in the lithosphere and underlies the Atakor-Manzaz volcanic districts. As a whole, MT data are therefore properly integrated within the hypothesis of the reactivation of shear zones due the intraplate deformation related to the collision between Africa and Europe since the Eocene, applied onto the metacratonic region.

Research Article| September 30, 2015 The Algerian Homogenized Macroseismic Database (267–1989): A Deeper Insight into the Algerian Historical Seismicity Assia Harbi; Assia Harbi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Amal Sebaï; Amal Sebaï aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Manel Benmedjber; Manel Benmedjber aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Farida Ousadou; Farida Ousadou aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Yasmina Rouchiche; Yasmina Rouchiche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Ahmed Grigahcene; Ahmed Grigahcene aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Djamel Aïni; Djamel Aïni bIbn Badis Mostaganem University, Avenue Hamadou Hossine, 27000 Mostaganem, Algeriadjamel.aini@gmail.com Search for other works by this author on: GSW Google Scholar Seid Bourouis; Seid Bourouis aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Said Maouche; Said Maouche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Abdelhakim Ayadi Abdelhakim Ayadi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Search for other works by this author on: GSW Google Scholar Author and Article Information Assia Harbi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Amal Sebaï aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Manel Benmedjber aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Farida Ousadou aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Yasmina Rouchiche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Ahmed Grigahcene aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Djamel Aïni bIbn Badis Mostaganem University, Avenue Hamadou Hossine, 27000 Mostaganem, Algeriadjamel.aini@gmail.com Seid Bourouis aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Said Maouche aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Abdelhakim Ayadi aCentre de Recherche en Astronomie, Astrophysique et Géophysique, BP 63, Bouzaréah, 16340, Algiers, Algeriaharbi.assia@gmail.comaharbi@ictp.itsebai_amal@yahoo.frm.benmedjber@gmail.comf.ousadou@gmail.comyasrou@gmail.comahmedgrig@hotmail.comsaid.maouche@gmail.comabdelhakim.ayadi@gmail.com Publisher: Seismological Society of America First Online: 14 Jul 2017 Online Issn: 1938-2057 Print Issn: 0895-0695 © 2015 by the Seismological Society of America Seismological Research Letters (2015) 86 (6): 1705–1716. https://doi.org/10.1785/0220150092 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Assia Harbi, Amal Sebaï, Manel Benmedjber, Farida Ousadou, Yasmina Rouchiche, Ahmed Grigahcene, Djamel Aïni, Seid Bourouis, Said Maouche, Abdelhakim Ayadi; The Algerian Homogenized Macroseismic Database (267–1989): A Deeper Insight into the Algerian Historical Seismicity. Seismological Research Letters 2015;; 86 (6): 1705–1716. doi: https://doi.org/10.1785/0220150092 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Studying the effects of past earthquakes is an important component of predicting the effects of future earthquakes, and knowledge of historic earthquakes is important for understanding future earthquakes. The revision of the historical seismicity of Algeria started at the beginning of this century and is still going on (e.g., Harbi, Benouar, and Benhallou, 2003; Sebaï and Bernard, 2008). The final objective of this reappraisal is to produce an earthquake catalog for Algeria that is as homogeneous as possible, compiled in a unique format, and covering a period of time going back as far as the existing data allow.... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The data of the known field experiment on water injection in the borehole were analyzed. Parameters of self-similarity of seismicity were estimated in comparison with the changes of water pressure. Changes of seismicity parameters that indicate the redistribution of the failure from lower scales to upper are revealed. The total number of earthquakes per series of the water initiation found to be depended exponentially on the water pressure and seismic activity maximum is delayed gradually relative to beginning of initiation. The growth of induced seismicity zone in time differs from diffusion model for water flow in the porous medium. Analysis carried out from laboratory data indicates that diffusion growth of the failure area may be realized in the dry specimen, without fluid. It could be assumed that both kinetic processes - water and the failure diffusion - can be significant for the development of seismicity induced by the water injection.

We analysed the triggered seismicity recorded near 3 km in depth within granite during the 1993 water injection experiment at Soultz (France). We selected all large multiplets associated with the largest dislocated fault identified on the borehole logging (4.3 cm slip), and showed that each one consisted of the repeated rupture of a single asperity. These asperities were forced to rupture due to fault creep around them, so that their growing, cumulative slip history reveals the creep history on the fault, with a mean slip rate and a seismicity rate both decaying approximately as 1/t. This is consistent with a rate-strengthening friction law on the creeping faults, and differs from the interpretation of Omori type 1/t seismicity rates in terms of a weakening friction control of the unstable fault surfaces. This model of asperity rupture forced by relaxation creep is easily generalized in seismogenic regions, even for single ruptures of asperities on small creeping faults, showing that a significant part of aftershock rates can be controlled by the strengthening friction properties and the creep of faults at all scales. This lead us to introduce the concept of a critical asperity density, above which dynamic interaction between neighbouring asperities can initiate large seismic ruptures. At Soultz, the asperity density is subcritical, but the neighbouring asperities nonetheless interact, at distances up to a few source dimensions, as revealed by their delayed cross-triggering. Considering the seismic cloud in Soultz at a global scale, the strain produced by the injection experiment was mostly aseismic, related to creep on major faults, and causing large permeability changes - influencing in turn the pore pressure diffusion and the creeping process. Our observations demonstrate that the identification and analysis of multiplets can provide accurate images of the geometry and kinematics of transient slip patches, and indirectly detect pore pressure changes, which should contribute to a better understanding of the coupling between transient fluid flow, creep and microseismic activity in seismogenic regions.