Landslide hazard mapping in the Constantine city,Northeast Algeria using frequency ratio,weighting factor,logistic regression,weights of evidence,and analytical hierarchy process methods

Landslides constitute the most widespread and damaging natural hazards in the Constantine city. They represent a significant constraint to development and urban planning. In order to reduce the risk related to potential landslide, there is a need to develop a comprehensive landslide hazard map (LHM) of the area for an efficient disaster management and for planning development activities. The purpose of this research is to prepare and compare the LHMs of the Constantine city, by applying frequency ratio (FR), weighting factor (Wf), logistic regression (LR), weights of evidence (WOE), and analytical hierarchy process (AHP) methods used in a framework of the geographical information system (GIS). Firstly, a landslide inventory map has been prepared based on the interpretation of aerial photographs, high resolution satellite images, fieldwork, and available literature. Secondly, eight landslide-conditioning factors such as lithology, slope, exposure, rainfall, land use, distance to drainage, distance to road, and distance to fault have been considered to establish LHMs using the FR, Wf, LR, WOE, and AHP models in GIS. For verification, the obtained LHMs have been validated comparing the LHMs with the known landslide locations using the receiver operating characteristics curves (ROC). The validated results indicate that the FR method provides more accurate prediction (86.59 %) of LHMs than the WOE (82.38 %), AHP (77.86 %), Wf (77.58 %), and LR (70.45 %) models. On the other hand, the obtained results showed that all the used models in this study provided a good accuracy in predicting landslide hazard in Constantine city. The established maps can be used as useful tools for risk prevention and land use planning in the Constantine region.     

Subsurface DC resistivity mapping: approximate 1-D interpretation

Resistivity prospecting is the main tool used to investigate the shallow structure of the ground. A series of new techniques for determining the 2-D and 3-D geometry of the ground is now finding increasing use, but the light and simple Wenner prospecting technique remains a practical and efficient tool for rapidly mapping lateral variations in resistivity. When the resistivity changes are smooth, 1-D modelling can be used to interpret the data, and the criteria governing this approximation can be defined from synthetic data generated by a 3-D slab-model. For a Wenner array, two quadripole configurations can be used, Normal and Dipole-Dipole. For these two configurations the width of the transition zone, the apparent anisotropy effect and the precision of the resistivity values recovered from 1-D inversion differ. However the simultaneous inversion of both sets of data gives better results than for either configuration by itself. Two examples illustrate that in geological contexts where the thickness of the weathered zone causes the changes in the apparent resistivity value, this parameter can be recovered from 1-D inversion.     

Effects of hydrocarbon contamination on a free living marine nematode community: results from microcosm experiments

Anthropogenic inputs of crude and refined petroleum hydrocarbons into the sea require knowledge of the effects of these contaminants on the receiving assemblages of organisms. A microcosm experiment was carried out to study the influence of diesel on a free living nematode community of a Tunisian lagoon. Sediments were contaminated by diesel that ranged in concentration from 0.5 to 20 mg diesel kg⁻¹ dry weight (dw), and effects were examined after 90 days. Gradual changes in community structure were revealed depending on the quantity of diesel administrated. In the medium (1 mg diesel kg⁻¹ and 5 mg diesel kg⁻¹ (dw)) and high (10 mg diesel kg⁻¹, 15 mg diesel kg⁻¹ and 20 mg kg⁻¹ (dw)) treated microcosms, most univariate measures, including diversity and species richness, decreased significantly with increasing level of diesel contamination whereas nematode assemblage from the low treated microcosm (0.5 mg diesel kg⁻¹ (dw)) remained unaffected. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the diesel treatments were varied: Chaetonema sp. was eliminated at all doses tested and seemed to be intolerant species to diesel contamination; Pomponema sp. and Oncholaimus campylocercoïdes were significantly affected at all diesel contamination levels but they were not eliminated, these species were categorized as “diesel-sensitive”; Hypodontolaimus colesi, Daptonema trabeculosum and Daptonema fallax which significantly increased respectively at 0.5, 1 and 5 mg diesel kg⁻¹ (dw) concentrations and appeared to be “opportunistic” species at these doses whereas Marylynnia stekhoveni which increased at all high doses (10, 15 and 20 mg diesel kg⁻¹ (dw)) seemed to be a “diesel-resistant” species.     

Phase equilibria and P-T-t path of metapelitic rocks in SE-Hamedan,Sanandaj-Sirjan Zone,Iran

Mineralogy and Petrology - In the southeast of Hamedan, in the Sanandaj-Sirjan Zone of Iran, metamorphic rocks display different metamorphic assemblages formed during dynamothermal and contact...     

InSAR analysis of a blind thrust rupture and related active folding: the 1999 Ain Temouchent earthquake (M w 5.7, Algeria) case study

We study the surface deformation associated with the 22 December 1999 earthquake, a moderate sized but damaging event at Ain Temouchent (northwestern Algeria) using Interferometric Satellite Aperture Radar images (InSAR). The mainshock focal mechanism solution indicates reverse faulting with a NE–SW trending rupture comparable to other major seismic events of this section of the Africa–Eurasia plate boundary. Previously, the earthquake fault parameters were, however, poorly known because no aftershocks were precisely determined and no coseismic surface ruptures were observed in the field. Using a pair of ERS data with small baseline and short temporal separation in the ascending orbit we obtained an interferogram that shows the coseismic surface displacement field despite poor coherence. The interferogram measures four fringes and displays an ellipse-shaped lobe with ∼11 cm peak line-of-sight displacement. The elastic modeling using a boundary element method (Poly3Dinv) indicate coseismic slip reaching up to 1 m at 5 km depth on the N 57° E trending, dipping 32° NW Tafna thrust fault. The geodetic estimate of seismic moment is 4.7 × 10¹⁷ N m. (Mw 5.7) in is good agreement with seismological results. The elliptical shape of the surface displacement field coincides with the NE–SW trending Berdani fault-related fold. The consistency between the geological observations and InSAR solution shed light on the precise earthquake location and related Tafna fault parameters.     

Identification and Simultaneous Optimisation of Tunisian Clay Properties: Preliminary Study for the Ceramic Products

The relationship between composition and physical parameters such as specific surface area, cationic exchange capacity and plasticity is studied with the aim of developing regression models that would permit the prediction of clay properties. These models could be useful for mineralogists and industrial applications. Nineteen representative clay samples were collected from Jebel Ressas in north-eastern Tunisia. Mineralogical data show that clay samples cover a very large variety of minerals. The main clay mineral is illite (50–60 wt%), secondary minerals including quartz, calcite and minor amounts of Na-feldspar. This study reveals that the average amount of silica (SiO₂) and alumina (Al₂O₃) are 51.9 and 19.6 wt%, respectively. The contents of lime (CaO) and iron (Fe₂O₃) vary between 4 and 8 wt% whereas the amount of alkalis (Na₂O + K₂O) is on average 4.1 wt%. The grain size data indicates a significant amount of silt fraction, and the fraction <2 µm varies between 23 and 35 wt%. Values for plasticity index range from 16 to 28 wt%. The cation exchange capacity and the specific surface values are 34.1–45.7 meq/100 g of air-dried clay and 302–374 m²/g, respectively. Lastly, regression models are used to correlate the properties with the mineralogical and chemical compositions. The significance and the validity of models were confirmed by statistical analysis and verification experiments. The regression models can be used to select the clay properties (plasticity index, cation exchange capacity and specific surface) in relation with clay minerals proportions and the finer fraction amounts.     

Geoelectrical and hydrogeochemical studies for delineating seawater intrusion in the outlet of Wadi Ham, UAE

The Quaternary aquifer of Wadi Ham, UAE has been overexploited during the last two decades to meet the increasing water demands. As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated. In this paper, a 2D earth resistivity survey was conducted in Wadi Ham in the area between Fujairah and Kalba to delineate the seawater intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data. Results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D resistivity data to identify three zones of water-bearing formation (fresh, brackish, and salt-water zones). Along the four 2D resistivity profiles, the depth to the fresh-brackish interface exceeded 50 m at the western part of the area and was in the order of 10 m or less in the eastern side near the shoreline. Depth to the brackish-saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side. The thickness of the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases.     

Evidence of seismites in coastal Quaternary deposits of western Oranie (northwestern Algeria)

Coastal Quaternary deposits of western Oranie show typical soft-sediment deformations including sedimentary dykes, sand volcanoes, sismoslumps, thixotropic bowls, thixotropic wedges, diapir-like structures, and faults grading. Field observations indicate that these deformations exist at several levels of the studied deposits along the west Oranian coast. This study demonstrated that these structures are earthquakes-related, by analysis of potential trigger sources. Several arguments demonstrate the seismic origin: the depositional environment rich in water that located in an active tectonic region, the thixotropic nature of deformations and their large vertical and horizontal diffusion in the Quaternary series consistent with a seismic recurrence. This allows characterizing these Quaternary soft-sediment deformations as seismites that were triggered by earthquakes.     

The impact of salt diapirs on the quality of carbonate karst waters,Bastak, Iran

The Gavbast karstic aquifer located in southern Iran is in direct contact with an exposed salt diapir. To assess the influence of the diapir on the quality of groundwater in the karstic aquifer, electrical conductivity, total dissolved solids, flow rate, temperature and major ion concentrations were measured at 57 sampling sites, including springs, surface waters and wells. A conceptual model of groundwater flow is proposed for the Gavbast karstic aquifer based on the geological setting, water budget, local base of erosion, and hydrochemistry of the sampling sites. The model suggests two subbasins in the Gavbast Anticline draining into two distinct discharging alluvial sections. Unexpectedly, groundwater discharging from the carbonate Gavbast aquifer is saline or brackish and water is of chloride type. The study indicates that the source of salinity of the Gavbast aquifers is infiltration of surface diapir-derived brine into the aquifer. The contribution of the diapir brine in the Gavbast karst aquifer is calculated about 4 L/s, using chloride mass balance. Construction of salt basins to evaporate brine discharging from the diapir springs is proposed to reduce the salinity of karst water. A row of strategically placed wells in the Gavbast karst aquifer would potentially exploit large volumes of fresh groundwater before it is contaminated by the salt. Such low-cost remediation should allow the agricultural exploitation of 40 km² of currently barren land.