Échanges du phosphore à l'interface eau-sédiment dans un bassin de maturation (lagunage de Boujaad) et un étang d'alevinage (station de pisciculture Deroua, Béni-Mellal), Maroc

Les sédiments utilisés dans cette étude sont prélevés dans deux milieux différents (bassin de maturation du lagunage de Boujaad et étang d'alevinage de la station Deroua, Béni-Mellal) dans le but de comprendre les conditions du milieu qui provoquent les échanges du phosphore à l'interface eau-sédiment et de comparer les échanges du phosphore à ce niveau.Cette étude a montré une différence dans la composition chimique des deux sédiments. En effet, au niveau de l'étang d'alevinage, le phosphore inorganique représente une part majoritaire (92,5%) surtout liée au calcium. En revanche, le phosphore total est réparti en phosphore organique (49,2%) et inorganique (49,8%) au niveau du bassin de maturation.Dans le bassin de maturation, le relargage du phosphore est plus important et il est sous forme inorganique lié essentiellement aux hydroxydes de fer. La fixation du phosphore par les sédiments est importante particulièrement en conditions aérobies, aussi bien dans le bassin de maturation que dans l'étang d'alevinage.Sediment samples used in this work were taken from two different sites (maturation pond of Boujaad lagunage and fry pond of the Deroua fish farm) in order to understand and compare the conditions affecting phosphate exchanges across water-sediment interface.This study showed a difference in the chemical composition of the two sediments. In the fry pond, the majority of the phosphate was present as inorganic phosphate (92.5%), especially in forms bound to calcium. On the other hand, total phosphate was divided equally into organic (49.2%) and inorganic (49.8%) phosphorus in the maturation pond. In this pond, phosphate solubility increased in the interstitial water under anoxic conditions. The phosphate released came principally from the inorganic fraction, particularly from Fe(OOH)-P. The maturation pond sediments, which had accumulated much organic matter, liberated more orthophosphate than did the fry pond sediments. Under air flushing, phosphate adsorption is significant particularly in the maturation and fry pond sediments

Apport du SIG et de la télédétection dans la modélisation spatiale de la susceptibilité aux mouvements de terrain dans la région d’Al Hoceima, Rif Oriental, Maroc

L’évaluation du degré de susceptibilité aux mouvements de terrains est devenue une préoccupation majeure dans les terrains montagneux, elle oriente les efforts à entreprendre pour prévenir les catastrophes, minimiser les risques et gérer les conséquences. Les techniques d’analyse spatialisée par le système d'information géographique (SIG) et télédétection sont de plus en plus utilisées pour évaluer la susceptibilité des versants aux mouvements de terrain. Dans cette étude, la modélisation par un modèle probabiliste bivarié (théorie d’évidence) a été utilisé pour cartographier les zones susceptibles aux mouvements de terrains dans la région d’Al Hoceima (NE du Maroc). Le SIG est également utilisé pour apprécier la relation entre : (i) les mouvements des terrains et (ii) la distribution spatiale des facteurs causatifs, l’information relative à ces deux composantes a été dérivée des données de terrain, traitements d’imageries satellitaires et les documents cartographiques disponibles. Ces données ont été intégrées dans une base de données SIG avec d’autres paramètres issus des cartes géologiques, topographiques et des stations météorologiques. Cette phase de préparation a été suivie par un test de l’indépendance conditionnelle des facteurs causatifs par rapport aux mouvements de terrain survenus dans la zone. Les paramètres indépendants ont servi aux calculs des poids positifs, négatifs (W+,W-), et leurs contrastes (C). Finalement, les cartes de pondérations obtenues des différentes combinaisons ont été évaluées pour retenir la meilleur simulation des facteurs causatifs, sur ce, une série des tests de validation des résultats obtenus par l’analyse de la courbe ROC a été effectuée. Les résultats ont montrés que la combinaison qui regroupe les facteurs prédictifs : pente, exposition des versants, lithologie et densité de fracturation s’avère être la meilleure combinaison possible. Cette combinaison permet de prédire environ 70% des instabilités existants.Mots-clés: mouvement de terrain, théorie de l’évidence, la région d’Al Hoceima, SIG et télédétection. The use of GIS and remote sensing in spatial modeling of susceptibility to landslides in the region of Al Hoceima (Eastern Rif, Morocco)The evaluation of the degree of susceptibility to landslides has become a major concern in mountainous terrain, it directs the efforts to be undertaken to prevent disasters, mitigate risk and manage the consequences. The spatial analysis using Geographic Information System (GIS) and remote sensing techniques are increasingly used to assess the susceptibility to landslides. In this study, a bivariate probability model (theory of evidence or 'weights of evidence') coupled with GIS for mapping areas susceptible to landslides in the region of Al Hoceima (NE of Morocco) was used. GIS is also used to assess the relationship between the landslides and the spatial distribution of causative factors. The Information on these factors was derived from observational field data and available cartographic and remote sensed data. These data were integrated in a GIS database with other parameters derived from geological maps, topographical and climate measures stations of the study area. This preparation stage was followed by a test of conditional independence of the causative factors in relation to landslides occurred in the study area. Independent parameters were used for calculations of positive weight, negative weight (W +, W -), and contrast (C). Finally, the maps obtained from different combinations were evaluated in order to retain the best simulation of causative factors, for this, a series of tests to validate the results obtained by the ROC curve analysis was performed. The results showed that the following combination of predictive factors: slope, exposure, lithology and density prove the best combination. This combination predicts about 70% of existing instabilities.Keywords: landslides, weights of evidence, region of Al Hoceima, GIS and remote sensing

Seismotectonics zoning of Morocco and adjacent region

In the present work, a new seismotectonics zoning of the Morocco and adjacent region is proposed. It is supported on a new database including recent geological (active faults, slip rates, geometrical characteristics, chronology of some recent tectonic phases) and geophysical (both instrumental and historical seismicity, focal mechanisms, nature of the crust) studies. In addition, the geodynamic context of the convergence of the Africa-Europe plates in the area, going from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar, has been taken into account. The newly suggested seismotectonics zoning is not limited to the borders of northern Morocco. It considers all the seismic sources (up to 400 km of distance) able to generate large and destructive earthquakes, such as the 1755 Lisbon earthquake, located in the Azores-Gibraltar transforming fault. New catalogues including the historical and instrumental seismicity since 1045 to 2005, and active faults were elaborated and used in this work. The most influential parameters having effects on the definition of the source area characteristics were determined with a suitable accuracy. The new performed zoning includes 12 shallow seismotectonics sources, each one corresponding to a certain volume of the Earth’s crust, whose known data were used to determine its static and dynamic conditions. Each seismotectonics zone has been analysed and interpreted, presenting certain homogeneity in the seismic potential and mode of deformation, obtained from the seismicity data, the strain and the stresses. For zones including faults, we have specified the geometrical characteristics, the chronology of the different movements corresponding to the successive tectonic episodes, and the associated seismicity. This new zoning will provide an improved contribution for both future probabilistic studies on seismic hazard, determining the ground acceleration, and seismic risk in the north of Morocco

Seismic risk in the city of Al Hoceima (north of Morocco) using the vulnerability index method, applied in Risk-UE project

The final publication is available at Springer via http://dx.doi.org/10.1007/s11069-016-2566-8Al Hoceima is one of the most seismic active regions in north of Morocco. It is demonstrated by the large seismic episodes reported in seismic catalogs and research studies. However, seismic risk is relatively high due to vulnerable buildings that are either old or don’t respect seismic standards. Our aim is to present a study about seismic risk and seismic scenarios for the city of Al Hoceima. The seismic vulnerability of the existing residential buildings was evaluated using the vulnerability index method (Risk-UE). It was chosen to be adapted and applied to the Moroccan constructions for its practicality and simple methodology. A visual inspection of 1102 buildings was carried out to assess the vulnerability factors. As for seismic hazard, it was evaluated in terms of macroseismic intensity for two scenarios (a deterministic and probabilistic scenario). The maps of seismic risk are represented by direct damage on buildings, damage to population and economic cost. According to the results, the main vulnerability index of the city is equal to 0.49 and the seismic risk is estimated as Slight (main damage grade equal to 0.9 for the deterministic scenario and 0.7 for the probabilistic scenario). However, Moderate to heavy damage is expected in areas located in the newer extensions, in both the east and west of the city. Important economic losses and damage to the population are expected in these areas as well. The maps elaborated can be a potential guide to the decision making in the field of seismic risk prevention and mitigation strategies in Al Hoceima.Peer ReviewedPostprint (author's final draft

Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta

Application Of Logistic Regression Method To Produce Landslide Susceptibility Map: A Case Study Of Tetouan Mazari, Morocco

The main purpose of this study is to use logistic regression (RL) model to map landslide susceptibility in and around the area of Tetouan Mazari in the Northern Morocco. Parameters, such as lithology, slope gradient, slope aspect, faults, drainage lines, and hillshade, were considered. Landslide susceptibility map was produced using RL method and then compared and validated. Before the modeling and validation, the observed landslides were separated into two groups. The first group was for training, and the other group was for validation steps. The accuracy of the model was measured by fitting them to a validation set of observed landslides. For validation process, the half landslides remaining was used. The final map was classified into five classes: Very High (32%), High (40%), Medium (7%), Low (7%) and Nil (15%). According to these values logistic regression was determined to be one of the most accurate method to generate landslide susceptibility map. Last but not least, logistic regression model can be used to manage and mitigate hazards related to landslides and to aid in land-use planning for the city of Tetouan

Mass movement susceptibility mapping - A comparison of logistic regression and Weight of evidence methods in Taounate-Ain Aicha region (Central Rif, Morocco)

Taounate region is known by a high density of mass movements which cause several human and economic losses. The goal of this paper is to assess the landslide susceptibility of Taounate using the Weight of Evidence method (WofE) and the Logistic Regression method (LR). Seven conditioning factors were used in this study: lithology, fault, drainage, slope, elevation, exposure and land use. Over the years, this site and its surroundings have experienced repeated landslides. For this reason, landslide susceptibility mapping is mandatory for risk prevention and land-use management. In this study, we have focused on recent large-scale mass movements. Finally, the ROC curves were established to evaluate the degree of fit of the model and to choose the best landslide susceptibility zonation. A total mass movements location were detected; 50% were randomly selected as input data for the entire process using the Spatial Data Model (SDM) and the remaining locations were used for validation purposes. The obtained WofE’s landslide susceptibility map shows that high to very high susceptibility zones contain 62% of the total of inventoried landslides, while the same zones contain only 47% of landslides in the map obtained by the LR method. This landslide susceptibility map obtained is a major contribution to various urban and regional development plans under the Taounate Region National Development Program

Analysis of the recent Plio-Quaternary deformation and the correlation with the focal mechanisms of the significant earthquakes in the Bokoya, Ras Tarf (Eastern Rif)

Relative movements of microplates developed between the African and Eurasian plate characterize the continuity of the tectonic movements in Westerner of the Mediterranean Sea. The convergence movements between these plates, at the origin of the current structuring in oriental Rif. The recent tectonics in the south ripple of Alboran Sea, translated by an important seismic activity, In the North of Morocco, exactly in the Al Hoceima region, considered as zone of plates border with important seismicity. The structural analysis made in this paper and the interpretation of focals mechanisms earthquakes characteristics in the Al Hoceima region, has allows to deduct the main directions of faults, which we compared with the results of the satellite images. This study we has provides to demonstrate the directions of faults which are able to generate earthquakes in the future. The direction NE-SW represents the overall faults dominant in oriental Rif, this major direction coincides with the breaks of surface. A reduced number of faults shows a generall direction NNE-SSO to N-S through the Quaternary formations in the NO of Al Hoceima city, the direction NO does not show a good correlation with the directions of surface rupture, as well as with the deducted directions from focals mechanisms. This study drives us to propose that faults of direction NNE-SSO to NE-SO, represent the major directions of the faults in the Al Hoceima region, which represents the main cause of the seismic activity in the region