Receiver function studies of crustal structure, composition, and evolution beneath the Afar Depression, Ethiopia

The dissertation utilizes a set of sophisticated computer programs developed at the Geophysics group at Missouri S&T to characterize crustal properties beneath the Afar Depression in Ethiopia where extensional tectonics dominates. In this study, measurements of crustal thickness (H), crustal mean Vp/Vs [which is related to Poisson\u27s ratio (Σ)], and the sharpness of the Moho (R) were determined using teleseismic data from 18 broadband seismic sensors that we deployed along a profile of 250 km long with a station spacing of ~ 10 km. The stations had been recording continuously for an entire year from December 2009 until December 2010. The measurements were determined by stacking P-to-S converted waves (PmS) and their multiples (PPmS and PSmS). Results suggest that the average crustal thickness beneath the Afar Depression is about 28.56±0.28 km and the crust is characterized by large Vp/Vs of 1.93±0.017 and smaller-than-normal overall stacking amplitude of the P-to-S converted phases beneath most stations. Our results suggest that the crust beneath the entire study area is significantly thinned and extensively intruded by mafic dikes, representing a transitional stage between continental and ocean crust. The Tendaho Graben has the thinnest and most mafic crust, which is also supported by the observation of gravity data which suggest that the active magmatic areas are characterized by higher gravity anomalies while the thicker crusts have smaller and negative anomalies. Thus, the crust beneath the center of the Tendaho Graben is likely to be oceanic-type, and becomes progressively more continental away from the center --Abstract, page iii

Receiver Function Constraints on Crustal Seismic Velocities and Partial Melting beneath the Red Sea Rift and Adjacent Regions, Afar Depression

The Afar Depression is an ideal locale for the investigation of crustal processes involved in the transition from continental rifting to oceanic spreading. To provide relatively high resolution images of the crust beneath the Red Sea rift (RSR) represented by the Tendaho graben in the Afar Depression, we deployed an array of 18 broadband seismic stations in 2010 and 2011. Stacking of about 2300 receiver functions from the 18 and several nearby stations along the ~200 km long array reveals an average crustal thickness of 22 ± 4 km, ranging from ~17 km near the RSR axis to 30 km within the overlap zone between the Red Sea and Gulf of Aden rifts. The resulting anomalously high Vp/Vs ratios decrease from 2.40 in the southwest to 1.85 within the overlap zone. We utilize theoretical Vp and melt fraction relationships to obtain an overall highly reduced average crustal Vp of ~5.1 km/s. The melt percentage is about 10% beneath the RSR while the overlap zone contains minor quantities of partial melt. The observed high Vp/Vs values beneath most of the study area indicate widespread partial melting beneath the southwest half of the profile, probably as a result of gradual eastward migration of the RSR axis. Our results also suggest that the current extensional strain in the lower crust beneath the region is diffuse, while the strain field in the upper crust is localized along narrow volcanic segments. These disparate styles of deformation imply a high degree of decoupling between the upper and lower crust

Groundwater quality assessment in western Saudi Arabia using GIS and multivariate analysis

In arid and semi-arid regions, assessment of groundwater quality and potentially toxic elements is essential issue for health of the human being. Groundwaters were collected from sixty-eight wells in Harrat Khaybar, Saudi Arabia to evaluate their suitability for drinking and irrigation purposes and to document the potential sources of contamination. Several contamination indices and inverse distance weighted technique were applied for assessing contamination and generate spatial maps for the potentially toxic elements (PTEs). The results showed that the average values of the ions, Cl–, SO42–, HCO3–, NO3–, Na+, Ca2+, Mg2+, and the total dissolved solids (TDS) were greater than the permissible limit for drinking water while the average values of PTEs were less than the permissible limit, with exceeding limits of Cr, Se, As, Zn, and Pb in some individual samples. Piper diagram indicated that 47.10% of the water samples are of Na-K-SO4-Cl type, 23.51% of Ca-Mg-CO3-HCO3 type, 23.51% of Ca-Mg-SO4-Cl type, and 5.88% of Na-K-CO3-HCO3 type. Based on the groundwater quality index (GWQI), 29 of the groundwater wells were categorized as excellent and good water for drinking purposes, while 29 wells fell under poor, very poor water, and unsuitable for drinking. Additionally, results of heavy metal pollution index (HPI) indicated that all waters fell within the low pollution category, while results of the metal index (MI) indicated that 35 wells fell within very pure, pure, and slightly affected categories, while 33 wells fell in the moderately, strongly, and seriously affected categories. Results of sodium adsorption ratio (SAR), sodium percentage (%Na), and magnesium ratio (MR) revealed that 33.82–98.5 % of the water samples are suitable for irrigation depending on the parameter type. Ions exchange reactions and dissolution of rock forming minerals, as well as industrial and domestic effluents and intensive use of fertilizers and pesticides were the natural and anthropogenic factors controlling the groundwater geochemistry in the study area and PTE contamination in some wells

Attenuation characteristics of coda wave in southern Arabian Shield

This study aims to estimate regional attenuation of coda wave in the southernmost part of the Arabian Shield. The decay rate of the time-domain coda envelope was analyzed and used for the estimation of coda wave quality factor (Qc) following the single isotropic-scattering model. The dataset comprises of a total number of 78 earthquakes of magnitude ranges from 1.5 to 4.5 recorded by 13 seismic stations within a hypocentral distance of 11 to 205 km and a lapse time between 10 and 40 s. Seismograms from vertical and two horizontal components have been analyzed at central frequencies of 3, 6, 9, 12, 18, 21, and 24 Hz, obtaining frequency-dependent attenuation relationships in the form of Qc=(36 ± 10)f(0.98±0.1), Qc=(53 ± 13)f(0.89±0.1), Qc=(63 ± 12)f(0.86±0.1), and Qc=(75 ± 13)f(0.81±0.14) at lapse time 10, 20, 30, and 40 s respectively. The regional frequency-dependent relationship is approximated by the power law of Qc=57±11f0.88±0.1 for the study area. For 10 sec lapse time, the average Qc ranges between 124 ± 41 at 3 Hz and 890 ± 193 at 24 Hz, while for 40 sec lapse time it varies from 200 ± 51 at 3 Hz to 1077 ± 130 at 24 Hz, implying a continuous increase in Qc with lapse time as a consequence of subsurface homogeneity with depth. The relationship between Qc and frequency shows that the coda quality factor is frequency dependent. The low attenuation characteristics can be attributed to the geodynamic process that causes a thin lithosphere beneath the study area due to active rifting in the Red Sea combined with magma flow and migration into the Arabian Shield

Assessment and Spatiotemporal Variability of Heavy Metals Pollution in Water and Sediments of a Coastal Landscape at the Nile Delta

This study assessed the spatiotemporal variability and pollution grades of heavy metals in water and sediments of Bahr El-Baqar drain, Eastern Nile Delta, Egypt, by integration of geochemical analysis, metal pollution indices, correlation, and multivariate statistical analyses. Twenty samples of water and sediments were collected during 2018 and analyzed for heavy metal concentrations using ICP-OES. Heavy metal contents in the water samples followed the order: Fe > Zn > Al > Pb > Mn > Cu > Ni. The drain sediments were highly contaminated with heavy metals that followed the order: Fe > Al > Mn > V > Zn > Cu > Cr > Ba > Ni > Pb > As. Spatiotemporally, most metals in the drain sediments showed a decreasing trend from upstream (south) to downstream sites (north). Results of principal component analysis (PCA) supported those from the Pearson correlation between investigated heavy metals. In water, Mn, Ni, Pb, Zn, Cu, and Fe showed highly significant correlations. In sediments, Ba, Ni, Zn, Fe, Al, Mn, and V showed strong positive correlations indicating that these metals were derived from similar anthropogenic sources. The calculated metal pollution indices: enrichment factor (EF), contamination factor (CF), pollution load index (PLI), degree of contamination (DC), and index of geo-accumulation (Igeo) indicated high loadings of heavy metals in the drain sediments. EFs revealed low, moderate to significant enrichment, whereas CFs showed low, moderate, and considerable contamination. PLI indicated low, baseline, and progressive contamination, while DC indicated low, moderate, and considerable degree of contamination. Igeo of all investigated metals (except for As; class 1) indicated extremely contaminated sediments (class 7)

Crustal Thickness, Poisson\u27s Ratio, and Moho Sharpness beneath Central Tien Shan: Constraints from Receiver Function Stacking

The Tien Shan is an approximately 2500-km long, 300-500-km wide chain of mountains located in central Asia. It is considered as one of the most tectonically active mountain ranges in the world and is a classic example of intraplate mountain building. Previous seismic and potential field studies were mostly concerned with lateral variations of crustal thickness, and systematic determinations of crustal Poisson\u27s ratio (which can be computed uniquely from Vp/Vs, the ratio of the P- and S-wave velocities) and Moho sharpness beneath Tien Shan have not be performed. Here we report preliminary results of such determinations using all the broadband seismic data archived at the IRIS Data Management Center, and use potential field data to constrain the interpretations of the seismic data. Results to date suggest that the average crustal thickness beneath Tien Shan from stacking of receiver functions is about 53 km which is consistent with previous geophysical determinations. The study area is characterized by a large Vp/Vs of 1.81±0.025 and a large overall stacking amplitude of the P-to-S converted phases beneath most stations, suggesting a mafic crust which is separated from the mantle by a sharp Moho. The thickest crust (about 68 km) is found beneath the northwestern corner of the Tarim basin. Distribution of earthquakes suggests that this area is among the seismically most active in Tien Shan. Stations in the vicinity of the Naryn Basin east of the Talas-Fergana strike-slip fault show low Vp/Vs ratios and anomalously thin crust of about 42 km, probably suggesting delamination of the lower crust. This interpretation is consistent with the positive regional Bouguer gravity anomalies which suggest a thinned crust beneath the area

Potential Effects of Climate Change on Agricultural Water Resources in Riyadh Region, Saudi Arabia

The water supply in Saudi Arabia is already depleted. Climate change will exacerbate the demand for these resources. This paper examines how climate change affects the water demands of Saudi Arabia’s most important food crops: wheat, clover, vegetables, and dates. To reduce the adverse climate change impacts on these crops’ productivity, as well as their irrigation water requirements (IWR), a number of adaptation techniques were investigated. The study was carried out for the Ar Riyadh region, Saudi Arabia, with a cultivated area of 179,730 ha. In this study, five climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) for two Shared Socio-economic Pathways (SSPs), SSP2-4.5 and SSP5-8.5, were used to forecast and investigate the potential impacts of climate change on agricultural water resources in the Al-Riyadh Region of Saudi Arabia. To simulate IWRs under the present and projected climate change scenarios, CROPWAT8.0 was used. The results showed that the maximum increase ratio in 2100 under SSP2-4.5 and SSP5-8.5, respectively, will be 4.46% and 12.11% higher than in the current case (2020). The results showed that the projected maximum temperatures in 2100 will be increased by 4.46% and 12.11%, respectively, under SSP2-4.5 and SSP5-8.5, compared to the current case (2020), supporting past research on the Arabian Peninsula that revealed that both short- and long-term temperature increases are anticipated to be considerable. Under SSP2-4.5 and SSP5-8.5, the projected ETo was found to be increased by 2.18% and 6.35% in 2100, respectively. Given that evapotranspiration closely mirrors the temperature behavior in the study region from June to August, our data suggest that crop and irrigation demand may increase in the mid to long term. The findings indicate that Riyadh, Saudi Arabia’s capital and commercial hub, will require more water to irrigate agricultural land because of the expanding ETo trend. Under SSP2-4.5 and SSP5-8.5, the projected growth irrigation water requirement (GIWR) will be increased by 3.1% and 6.7% in 2100, respectively. Under SSP5-8.5, crop areas of wheat, clover, dates, maize, citrus, tomato, potato, and other vegetables in Ar Riyadh will decrease by 6.56%, 7.17%, 5.90%, 6.43%, 5.47%, 6.99%, 5.21%, and 5.5%, respectively, in 2100. Conversely, under SSP2-4.5, the crop areas will decrease by 3.10%, 3.67%, 2.35%, 3.83%, 2.32%, 4.18%, 1.72%, and 2.38% in 2100, respectively. This research could aid in clarifying the adverse climate change impacts on GIWR in Ar Riyad, as well as improving water resource management planning

Mapping Leachate Pathways in Aging Mining Tailings Pond Using Electrical Resistivity Tomography

Mining activities often leave behind a legacy of environmental challenges, with aging tailings ponds representing a significant concern due to their potential for leachate formation and subsequent contaminant release. Thus, this study employs Electrical Resistivity Tomography (ERT) to investigate the intricate pathways of leachate within an aging mining tailings pond, addressing the pressing environmental and human health concerns associated with potential contaminant release. Ten 2D ERT profiles were acquired at the El Mochito mine waste site, covering an area of approximately half a square kilometer. These profiles, ranging in length from 104 to 363 m, provided insights into subsurface conditions down to a maximum depth of 60 m. The subsurface mapping of the ERT data showed three different geoelectric layers. The uppermost layer, with a thickness of approximately 2.5 m and resistivity values ranging from 60 to 100 Ohm.m, was identified as a dry tailing/soil zone. Beneath it, the second layer exhibited moderately resistive values (30–60 Ohm.m) with varying thicknesses of 10–20 m, signifying a percolation/leaching zone (semi-saturated zone). The third layer, characterized by substantially low resistivity (1–30 Ohm.m), indicated saturation and the presence of conductive materials, strongly suggesting active leaching. Based on these findings, this study recommends further investigation through geochemical analysis of subsurface samples and more advanced geophysical imaging techniques to validate the distribution of anomalous zones and delineate remediation pathways. This study lays the foundation for future comprehensive research that will integrate geophysical surveys with geochemical analysis and establish 4D modeling techniques to monitor pollutant penetration over time, with a particular focus on mine waste tailings mapping. Plus, this study contributes valuable insights into the characterization of leachate pathways within mining tailings ponds, offering a foundation for informed environmental management and remediation strategies