Aeromagnetic data over Harrat Lunayyir and surrounding areas,western Saudi Arabia

Harrat Lunayyir is one of the smaller lava fields in western Saudi Arabia that is of current interest due to a dike intrusion episode in 2009, an ongoing swarm of earthquakes and the possible hazard that pose. In addition to seismology, other geophysical data have been used to study the structure of the area, and the available aeromagnetic information is shown and discussed here. The reduced to the pole (RTP) magnetic grid and its enhancements have been used to define some of the main anomalies, and these have been correlated with the known geology, including the Red Sea coastal dike system. There are numerous linear features that are possibly related to the dikes or faulting, but within the area of the harrat, details due to the underlying structure are largely obscured by the magnetic surface lavas. Northeasterly trends in the magnetic data may indicate old zones of weakness that intersect one of the main coastal dikes at the location of the recent seismic activity and surface fissure, suggesting that this is a point of weakness resulting in the volcanism and seismicity that also appears to be largely limited to two of the NE trends. The association of the recent seismicity with a known geological and aeromagnetic feature is important in determining the seismic hazard for the region, especially if the location of future activity can be used to reduce overall uncertainty in the analysis by identifying potential fault sources. Here, the seismicity appears to lie on one of the NNW-trending coastal dikes that have been reactivated recently along a section between two NE-trending older faults.     

Universal model forms for predicting the shear modulus and material damping of soils

Numerous model forms have been used to predict the dynamic behaviours of soils, mainly the shear modulus and material damping. These models are used to represent normalised shear modulus reduction and material damping curves. The majority of the existing models are empirical and were proposed for specific soil types, strain ranges, etc. Some are limited to the data used in fitting, but fail to provide a good fit to other sets of data. The available model functions are not universal, which means that a model developed for one soil type may not be applicable for use with other soil types. In this paper, two universal mathematical models were proposed to predict the normalised shear modulus reduction and material damping curves. The mathematical model forms are sufficiently flexible to be widely used with different soil types. The models were evaluated using verification data of eight different soil types, i.e., data that were not used to fit the model parameters. The results indicate that the proposed model forms can accurately model the dynamic soil properties within the typical earthquake range. The advantage of developing the two universal models are two-fold, first the forms are applicable for sand, clay, and fibre-soil composite and second with further testing of soils, the model coefficients could ultimately be used to further understand the physical processes in soil behaviour, especially damping.     

Heating–freezing effects on the pore size distribution of a kaolinite clay

This study aims to quantify the effect of heating and freezing temperatures on the pore size distribution of saturated clays. Three kaolinite clay specimens were subjected to different temperatures: 20, 70, and ? 10 °C. Upon achieving the desired temperature for each specimen, the specimens were flash frozen in liquid nitrogen to preserve their microstructure. Each specimen was, then, freeze-dried for 24 h after which consecutive two-dimensional (2-D) SEM images were taken using a dual focused ion beam/scanning electron microscope. The produced 2-D images of each specimen were used to reconstruct three-dimensional tomographies of the specimens, which were analyzed to determine the pore size distribution at each temperature. Compared to the specimen at room temperature, the pores in the specimen subjected to ? 10 °C were larger; this is believed to be due to the formation of ice lenses inside the pores upon freezing and potential merging between initial pores to form larger pores. On the other hand, the heated specimen showed an increase in the volume of the smaller pores and a decrease in the volume of the larger pores compared to the specimen at room temperature. This opposite behavior between the small and large pores in the heated specimen is justified considering (1) the easier flow of water out of the larger pores compared to that in the smaller pores and (2) the anisotropic nature of the thermal expansion of the clay particles.     

Calcareous nannofossil biostratigraphy of the Paleocene at the Misheiti section,East Central Sinai,Egypt

Integration of calcareous nannofossil data, δ¹³C and δ¹⁸O values, and carbonate contents of the lower Paleocene–upper Paleocene sequence that crops out at the Misheiti section, East Central Sinai, Egypt, were used to denote the Danian/Selandian (D/S) and Selandian/Thanetian (S/T) stage boundaries. The study interval belongs to the Dakhla and Tarawan formations. Four calcareous nannofossil zones (NP4, NP5, NP6, and NP7/8) were recognized. The base of the Selandian Stage is tentatively placed at the lowest occurrences (LOs) of taxa ascribable to the second radiation of fasciculiths (i.e., Lithoptychius janii). This level is marked by a sudden drop of δ¹³C and δ¹⁸O values and carbonate content. No distinctive lithological changes were observed across the D/S boundary at the study section. A hiatus at the NP5/NP6 zonal boundary is indicated by the condensation of zones NP5 and NP6.The base of the Thanetian is placed at the base of Zone NP7/8 at the lithological change observed in correspondence to the boundary between the Dakhla and Tarawan formations. The δ¹³C and δ¹⁸O values abruptly decrease slightly above the base of Zone NP7/8. No consistent variations in the carbonate contents were recorded within Zone NP6 or across the NP6/NP7/8 zonal boundary.     

High resolution spatiotemporal analysis of erosion risk per land cover category in Korçe region,Albania

Some recent land use changes in Albania, such as deforestation, cropland abandonment, and urban sprawl, have caused serious increase of erosion risk. The main objective of this study was to map erosion risk in Korçe region and assess the degree at which every land use is concerned. The G2 erosion model was applied, which can provide erosion maps and statistical figures at month-time intervals using input from free European and global geodatabases. The mapping results in Korçe region were derived at a 30-m cell size, which is an innovation for G2. Autumn-winter months were found to be the most erosive, with average erosion rates reaching the maximum in November and December, i.e. 2.62 and 2.36 t/ha, respectively, while the annual rate was estimated at 10.25 t/ha/yr. Natural grasslands, shurblands, mixed forests, and vineyards showed to exhibit the highest mean erosion rates, while shrublands, broad-leaved forests and natural grasslands were found to be the most extended land covers risky for non-sustainable erosion rates (i.e. >10 t/ha/yr). A detailed examination of the detected hot spots is now necessary by the competent authorities, in order to apply appropriate, site-specific conservation measures. Notably, use of SPOT VGT data did not prevent the maps from having extended gaps due to cloudiness. Sentinel-2 time series, freely available by the European Space Agency (ESA), have the potential to improve spatiotemporal coverage of V-factor, thus further empowering the G2 model, in the near future.     

A geoelectrical and hydrogeological study for the assessment of groundwater resources in Wadi Al Bih, UAE

Drilling information, historical water table levels, groundwater salinity records of the existing water wells in Wadi Al Bih area, United Arab Emirates, were stored in a geodatabase and used to characterize the geological and hydrogeological settings of this area. A 2D earth resistivity imaging survey was conducted for the first time in the Northern UAE to determine the potential of the Quaternary aquifer and its groundwater quality in the areas where there are no monitoring wells. The results of the chemical analyses of the collected groundwater samples together with the inversion results of the resistivity data were used to draw a total salinity map and determine the spatial variations in groundwater quality. The inversion results of the 2D earth resistivity imaging data indicated that the Quaternary aquifer in the study area is in a good connection with the underlying carbonate aquifer. It also indicated that the carbonate aquifer is of major regional and vertical extension and it contains the fresh water in this area. The data stored in the developed database were used to produce different types of geopotential maps.     

A regional stratigraphic correlation for the upper Campanian phosphorites and associated rocks in Egypt and Jordan

Facies analyses and a sequence stratigraphical framework with regional correlation of the upper Campanian phosphate province are presented, based on three main sections located in Egypt (Gebel Duwi and Abu Tartur sections) and north Jordan (Umm Qais section). Fifteen facies types were grouped into: phosphate (FT1–5), carbonate (FT6–11) and siliciclastic (FT12–15) facies associations. The main component of phosphate rocks is pellets in situ and common reworked biogenic debris, especially in the upper phosphate beds (e.g. fish teeth and bones), which along with abundant Thalassinoides burrows suggests that the skeletal material was the main source for phosphates in Egypt; in contrast the common authigenic phosphatic grains (pristine) in Jordan reflect an upwelling regime. Based on age assignment as well as stratigraphical position, the phosphorite beds show great similarity that may suggests a similar origin and proximity during the period of deposition of the Duwi Formation of the Red Sea coast of Egypt and its equivalent, the Al-Hisa Phosphorite Formation in Jordan, which represents an early transgressive system tract of a depositional sequence. On the Abu Tartur plateau, the presence of sandy pyritic phosphatic grainstone (FT1) and glauconitic quartz arenite (FT12) in the middle part of the studied section, along with the absence of chert facies (FT14), reflects a more shallow marine depositional environment with increased fluvial sediment supply compared to those along the Red Sea coast and north Jordan.     

Study of the 26 December 2011 Aswan earthquake,Aswan area,South of Egypt

The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f _o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M _o ) is 4.2?×?10²² Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M _w ) is 4.4.     

Modeling in situ benzene bioremediation in the contaminated Liwa aquifer (UAE) using the slow-release oxygen source technique

Dissolved benzene was detected in the shallow unconfined Liwa aquifer, UAE, which represents the main freshwater source for the nearby residence Bu Hasa camp area. The main source of this contamination is believed to be the rejected water released from Bu Hasa liquid recovery plant. In this paper, a finite element model (METABIOTRANS) is used to simulate the fate and transport of the dissolved benzene plume in Liwa aquifer. Different remediation scenarios were simulated in which the slow-release oxygen source (SOS) technique is utilized to minimize benzene concentrations at the nearest camp supply wells downstream of the contamination zone. Results of the remediation scenarios show that the highest biodegradation rates occur when the oxygen source is placed near the plume center; where higher benzene concentrations exist. The nearest oxygen release source to the contamination zone caused higher stimulation to bacterial growth than further down-gradient oxygen sources. It also exhibited longer resident time of oxygen in the aquifer; and therefore, yielded higher reductions in benzene concentrations. However, using one central SOS proved to be insufficient as contaminant escaped laterally. Additional four transverse oxygen sources were necessary to capture benzene that laterally spread away from the contamination zone. These lateral SOSs were essential to reduce benzene concentrations at the supply wells that are located at the plume fringes. Finally, it was found that increasing oxygen release from one source did not always improve remediation; and that using several SOSs with lower release rates could be a more practical approach to enhance benzene biodegradation in the aquifer.     

Lateral variations of coda Q and attenuation of seismic waves in the Gulf of Suez, Egypt

Gulf of Suez consists mainly of three tectonic provinces that are separated by two accommodation zones. The southern edge of the gulf is bordered by N–S faults which mark the transition between the shallow water, Suez Basin and the deep northern Red Sea Basin. The sensitivity of coda Q measurements with respect to geological differences in the crust is demonstrated in three regions with a large variety of tectonic and geologic properties. The estimation of coda Q (Qc) is performed for 370 local earthquakes recorded at 12 digital seismic stations during the period from 2000 to 2007. The magnitudes of the earthquakes between 1.5 and ~4.5 have been used at central frequencies 1.5, 3, 6, 9, 12, 15, 18, and 24 Hz through three lapse time windows 10, 20, 30 s starting at once and twice the time of the primary S wave from the origin time. The time domain coda decay method of the single isotropic scattering model is employed to calculate frequency-dependent values of coda Q. The Qc values are frequency dependent in the range 1–25 Hz, and are approximated by a least squares fit to the power law [Qc(f) = Qo(f/fo)η]. The observed coda Q indicates that the area is seismically and tectonically active with high heterogeneities. The variation of the quality factor Qc has been estimated at different regions to observe the effect of different tectonic province. The average frequency-dependent estimated relations of Qc vary from 65f1.1 to 96f0.9 at 10 to 30 s window length, respectively. The decreasing value of the frequency parameter with increasing lapse time shows that the crust acquires homogeneity with depth. The variation of Qc with the variations in the geologic and tectonic properties of the crust was investigated. The frequency exponent η might be larger in active tectonic areas and smaller in more stable regions. In the northern region of the Gulf of Suez, the obtained value of η?=?0.8?±?0.011, which might indicate a low level of tectonic activity compared with η?=?1.1?±?0.005 and 1.3?±?0.009 for the central and southern regions of the gulf.