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The site characterization process is vital for the engineering structures and earthworks. In the current study, a Multi-Channel Analysis of Surface Waves (MASW) was carried out in western Riyadh City, Saudi Arabia. This aimed to determine subsurface geology, material stiffness, and potential weak zones approximately down to a depth of 30 m, and to propose the suitable seismic site characterization for precise foundation design. A total of 30 MASW lines were executed utilizing the Geode digital seismograph equipped with a 24geophone array of 4.5 Hz. The data acquisition, processing, and inversion were meticulously calibrated to derive shear velocities representing subsurface geological conditions. The Vs30 map, based on estimated values ranging from 443.71 m/s to 639.78 m/s for soil, was prepared for the area. The results of the 1D and 2D Vs profiles tinted small Vs values at shallow depths. The resulting geological model is composed of sand, gravel, moderately weathered limestone, and hard limestone sequence. Analysis of shear wave velocities shows variations, indicating low shear velocity (representing sediments or rocks of low stiffness) juxtaposed with higher velocity layers (indicating rocks of higher stiffness) at depths greater than 10 m. This could imply the presence of a cavity or weak zone. The topmost shear wave velocity zone indicated materials with low Vs values (ranging from 180 m/s to 360 m/s), predominantly associated with stiff materials such as silty sand, gravel, and sandy deposits. The subsequent zone, with 3 to about 10 m depth, was characterized by medium to very dense soil with shear wave velocity values ranging from 360 m/s to 760 m/s, attributed to layers of silty clay and silty sand. At approximately 12 m, a high shear velocity layer (ranging from 760 m/s to 1,500 m/s) was identified, extending to a maximum depth of 22 m, potentially indicative of less weathered or fractured bedrock associated with limestone. While the deepest layer, with very high shear velocity (exceeding 1,500 m/s) beyond 22 m, indicated bedrock associated with hard limestone. The average Shear-wave velocity of soil for the whole study area (Vs30 = 551.2 m/s) suggests that the site can be classified as Class C (Very Dense Soil and Soft Rock) according to the National Earthquake Hazard Reeducation Program NEHRP (National earthquake hazards reduction program, 2001). These results will support, to a great extent, the design of engineering structures in the area of study. [ABSTRACT FROM AUTHOR]

This article aims to aid in exploring and forecasting hydrothermal minerals and gold deposits in Central Saudi Arabia (SA), with a focus on structural contexts. Remote sensing (RS) and satellite-based Bouguer gravity (SBG) data were integrated in order to create a mineral prediction map for the researched location. Data from the Landsat Operational Land Imager (OLI) and Shuttle Radar Topography Mission (SRTM) were transformed and enhanced using a variety of approaches. The delineation of hydrothermal alteration zones (HAZs) and highlighting of structural discontinuities in the OLI data were made possible using band ratios and oriented principal component analysis (PCA). Additionally, the underlying structural features were successfully exposed by processing the SBG using a variety of edge detection techniques, like the analytical signal (AS), total horizontal derivative (THD), tilt angle (TA), horizontal tilt angle (TDX), theta map (TM), horizontal derivative of the tilt derivative (HD_TDR), horizontal gradient of the tilt angle (HGTA), tilt angle of the analytical signal (TAAS), and soft sign function (SF). As a result, more prominent lineaments were found in the NW–SE, NNW–SSE, NE–SW, and NNE–SSW directions than in the N–S and E–W directions. The GIS incorporated surface/subsurface geological structure density maps with zones of hydrothermal alteration. It was found that the lineaments derived from the analysis of the RS and SBG data were more in line with the HAZs, which demonstrated the common connection between alteration zones and deep lineaments. The findings revealed a mineral prediction map with extremely low to extremely high probabilities. Overall, combining RS and SBG data effectively identified probable mineralization sites associated with hydrothermal processes and made it easier to create this study's final predictive mineralization map. [ABSTRACT FROM AUTHOR]

Positive and negative magnetic anomalies occupied the total aeromagnetic (TM) map of the Harrat ad Danun area, Saudi Arabia. Reduction to the pole (RTP) maps display the range of magnetic values (−312.4 to 209.4 nT) that vary in shape, size, and magnitude. These anomalies generally follow the NNW–SSE (Red Sea axis trend), NE–SW, and NNE–SSW trends. The NNW-SSE linear negative and positive magnetic anomalies could be brought on by buried faults, shear zones, or subsurface dikes. In the central part, the position of Au and Ba mineralization was connected to this trend. It is concluded that the principal structures are represented by the NNW–SSE, NE–SW, and NNE–SSW tendencies. Based on gridded RTP magnetic data, the 2-D power spectrum was computed and revealed the frequency of the near-surface and deep magnetic components. It is believed that the depths of the shallow and deep magnetic sources are typically 80 m and 570 m, respectively. Additional negative and positive magnetic anomalies with varied amplitudes and frequencies, trending in the NNW–SSE, ENE–WSW, and NE–SW directions, are seen when the high-pass and low-pass maps are closely examined. Many faults in various directions cut into these anomalies. The occurrence of negative linear magnetic anomalies (−36.6 nT to −137.3 nT) at this depth (80 m) is also confirmed by this map. The TDR filter and the Euler deconvolution method were used to identify the horizontal variations in magnetic susceptibility as well as the source position and depth of magnetic sources. The linear clustering rings are thought to be caused by contacts or faults with depths between 1 m to 474 m that are oriented WNW–ESE, NNE–SSW, and NNW–SSE. These faults or contacts are thought to be particularly prominent in the western, eastern, southern, northern, and central zones. The majority of felsic and mafic dikes are found to be connected to subsurface structures, showing that three structural trends—WNW–ESE, NNE–SSW, and NNW–SSE—affect the studied area. This demonstrates that important features and shear zones control the majority of Saudi Arabia's gold deposits. A negative magnetic anomaly that is centered in the area, trending NNW–SSE and crossing the NNE–SSW fault, is connected to the plotted gold and barite mineralization in the study area. This may imply that these two tendencies are responsible for mineralization. This result raises the possibility of mineralization in the NNW negative magnetic feature located in the western part of the area. The occurrence of gold and barite was significantly impacted by the NNW–SSE and NNE–SSW structural lineaments. [ABSTRACT FROM AUTHOR]

In the current study, the geotechnical properties of the near-surface geological units are collected, tested, correlated, evaluated, and then mapped. In addition, the groundwater level is estimated through comprehensive geotechnical investigations conducted in and around the entire Holy city of Makkah Al-Mukarramah. Based on the measured standard penetration test (SPT), the soil materials vary from soft to very dense materials where SPT ranges from 4 to >50 and increases with depth. On the other hand, the calculated rock quality designation (RQD), the rock quality spans from very poor to good where RQD changes from 0 to 80%. Accordingly, the ground conditions of Makkah can de differentiated into eight subsoil and rock units with various geotechnical properties. Moreover, it is indicated that the physical and chemical nature of these sub-soil and rock units have a considerable effect on the foundations of the constructions that may be risky in the future. The continuous evaluation of the geotechnical and chemical properties for the future projects on these soils and even rock units is highly recommended. These results will greatly support civil engineers and urban designers in the Makkah Al-Mukarramah municipality. [ABSTRACT FROM AUTHOR]

Coastal groundwater is the major source of freshwater in coastal areas, due to shortage of the water resource in coastal zones. Groundwater samples were collected from 48 sites along the Saudi Red Sea coast between Rabigh and Yanbu to document the hydrogeochemical characteristics, water quality, and the health risks of nitrate, fluoride, nickel, copper, and zinc on adults and children. Groundwater chemistry indicated neutral to slightly alkaline nature, and the total dissolved salts (TDS) concentrations mainly increase towards the coastal plain. Major cations, major anions, and heavy metals (HMs) were in the order of Cl− > Na+ > SO 4 2− > Ca2+ > HCO 3 − > NO 3 − > Mg2+ > K+, F− > Zn > Cu > Ni. Na-Cl, mixed Ca-Mg-Cl and Na-K-HCO 3 , Ca Cl, and Mg-HCO 3 were the principal hydrochemical water types. Results of heavy metal pollution index (HPI), and water quality index (WQI) showed moderate to heavy pollution and unsuitable groundwater for human consumption mostly in the western side along the coastal plain, which might be influenced by the groundwater salinization. Principal component analysis (PCA) generated four components, which indicated the various sources of contamination. Hazard index (HI) of nitrate and fluoride were above the safety limit of 1, suggesting increase non-cancer health risk issues in both children and adults. • Cl− and Na+ were the highest major anion and cation, in investigated groundwater. • SO 4 2−, HCO 3 −, Ca2+, Cl−, Mg2+, Na+, and Zn exceeded WHO limit for drinking water. • 70.83 % and 89.58 % of the HI in samples were above 1 for adults and children. • The groundwater salinization lead to increase major ions and health risks. [ABSTRACT FROM AUTHOR]

Nine seismic refraction profiles were conducted and processed to study the near-surface sediments in the new urban area of Diriyah. The 2D geoseismic models illustrate two layers: a surface layer of soft sediments and weathered to hard limestone bedrock. Moreover, microtremor measurements were performed at 38 sites for 40 min using three-component seismographs and processed to assess the peak spectral amplitude and the corresponding fundamental resonance frequency. The seismic vulnerability index at each measurement site was estimated. These results correlate well with the geotechnical borehole data. The north-western zone is highly vulnerable due to the great thickness of the soft sediments. [ABSTRACT FROM AUTHOR]

The estimation of local site response and geotechnical properties of near-surface deposits becomes essential for improving the building codes especially in big cities as Riyadh. This study aims to estimate the site response parameters in the northern expansion zone of Riyadh city. Microtremor measurements were recorded at 45 sites at the study area, north of Riyadh, and the resonance frequency and amplification factor were calculated using the H/V spectral ratio approach. The microtremor data has been processed using geopsy software to get the H/V curve and get the value of the resonance frequency (f o) and amplitude (A o). The values of the resonance frequency span from 0.79 to 45 Hz, while the amplification factor ranges from 1.22 to 8.5, indicating the presence of foundation bedrocks at various levels with varying soil thickness. Moreover, the N 60 parameter was calculated to correct the SPT-N uncorrected field readings in order to estimate the shear wave velocity parameter down to 30 m depth (Vs 30). The computed shear wave velocity for a depth of 30 m (Vs 30) ranges from 210 to 630 m/s. Accordingly, the soil at the studied area can be divided into two site soil classes C and D according to the National Earthquake Hazard Reduction Program (NEHRP). The findings of this study should be considered as part of the development of the Saudi Building Code for Riyadh City. [ABSTRACT FROM AUTHOR]

Six profiles of the two-dimensional multi-channel electrical resistivity tomography (ERT) were conducted at the northwest part of Riyadh city using the SYSCAL Pro system with a dipole–dipole configuration to detect the near-surface water-bearing potential zones. The ERT field measurements use a series of regularly placed electrodes to measure the electrical resistivity along the profile. The results of the inverse models are displayed as cross-sections of the true resistivity distribution of the subsurface with depth along with each profile. The two-dimensional (2-D) inversion results of the electrical resistivity data indicate three geoelectric zones; 1st zone of low resistivity values (<100 Ω.m), representing two groundwater-bearing potential zones from top to bottom as follows; the 1st one extends downwards to 10- and 15-meters depth, while the 2nd zone spreads between 15- and 30-meters depth, 2nd zone with resistivities ranging from 100 to 1000 Ω.m, which represent the highly fractures limestone; the 3rd zone with resistivities greater than 1000 Ω.m reflecting compacted limestone rocks. It is noticed also some of the low resistivity pockets are isolated through the subsurface geoelectrical cross-section indicating the presence of voids and/or cavities. Based on these results, the investigated area is considered as one of the promising zones for groundwater supply in Riyadh city and its future urbanization expansion projects. This can be accessed by drilling wells down to a depth of 50 m for groundwater extraction. [ABSTRACT FROM AUTHOR]

In the hard rock terrains of southwestern Saudi Arabia, vertical electrical soundings (VES) were used to demarcate groundwater potential zones. To map the groundwater potential zones, 16 VES were done using a Schlumberger electrode array arrangement. Zond-IP computer software was used to analyze and interpret field measurements. The pseudo and resistivity cross-sections have been processed. The evaluation of the 1D geoelectrical curves revealed that the area is characterized by three geoelectrical resistivity layers. The topmost layer of unconsolidated alluvium deposits, which has a wide range of resistivities (42.28 to 297.97 Ω·m) and a thickness of up to 6 m, is the first of these layers. This range of resistivity is linked to changes in the layer's lithology and humidity. The second layer's resistivity values range from 372 to 3625 Ω·m, while the third layer's resistivity values range from 1015.37 to 21113 Ω·m. The second layer's resistivity implies fractured and weathered/jointed basement rocks, and the third layer's resistivity indicates broken to huge basement rocks. According to the findings, the worn and fractured horizons of basement rocks found in the vicinity are acceptable groundwater potential aquifers. The degree of weathering and fracture of the foundation rocks, and thus their water saturation, can be linked to vertical and horizontal variations in resistivity. [ABSTRACT FROM AUTHOR]

This study includes the determination of the engineering physical parameters of a proposed urban expansion site at Khamis Mushait city, SW Saudi Arabia. The seismic refraction survey as a noninvasive seismic technique was used to determine the P wave velocity profile of the soil section in the studied site. This method provides a simplified characterization of subsurface in two-dimensional depth-velocity profiles. Seismic records obtained were processed and analyzed by SeisImager software to obtain one-dimensional P wave velocity (Vp) distribution. The measured P wave velocities were used to estimate relative density, N value, modulus of elasticity, uniaxial compression strength, ultimate tensile strength, ultimate bearing capacity, allowable bearing capacity, Poisson's ratio, and rock quality designation. The results indicate that the investigated site is composed mainly of two soil layers. The top layer is interpreted as loose incompetent soil sediments (alluvial sediments) to the depth of 5 m with V ranging between 300 and 880 m/s. This layer is underlain by the second competent soil layer with thickness reaching 18 m and V ranging between 1,097 and 2,626 m/s. The second layer is considered as the foundation layer, and its determined engineering physical parameters are vital information for the engineers in construction and urban development of this site. [ABSTRACT FROM AUTHOR]

In desert regions like Saudi Arabia, groundwater exploration is critical for drinking, household, and agricultural purposes. The purpose of this study is to use Vertical Electric Sounding (VES) to assign near-surface groundwater sources in the Wadi Nisah area of central Saudi Arabia. Twenty VES stations were installed in the central part of Wadi Nisah, with a maximum half current electrode separation (AB/2) of 100 m, utilizing a Syscal R2 resistivity-meter with Schlumberger electrode design. The interpretation of these VES's revealed five geoelectric layers, the first of which is formed of dry sand with greater resistivity values and has a depth of around 3 m. The groundwater-bearing aquifer is represented by the fifth layer, which is the deepest, with depths ranging from 37.8 to 52.25 m below the surface and resistivities ranging from 47 Ω-m to 115.3 Ω-m. Six geoelectrical cross-sections were also mapped to show the lateral and vertical heterogeneities of the underlying lithology in the study area. These findings suggest that the groundwater bearing layer is a hydrologically promising zone capable of delivering optimal groundwater yield for drinking and agricultural use in the study area; the VES technique is a useful tool for identifying groundwater prospective zones. [ABSTRACT FROM AUTHOR]

This study aimed to identify groundwater resources at Harrat Khaybar to meet the increasing demand for groundwater for drinking and other purposes, including agricultural and industrial activities. Aquifers were assigned based on integrated electrical resistivity tomography (ERT) and hydrogeological data. Twenty-three ERT profiles ranging 590–890 m long distributed across Harrat Khaybar were acquired. The ERT data were processed to obtain 2D subsurface geoelectrical sections that indicated a variable depth for groundwater as 6–280 m. To investigate water quality, 69 groundwater samples were collected from intensively pumped wells distributed throughout the Harrat. The depth to groundwater measured in these wells ranged 1.5–80 m. It was concluded that Harrat Khaybar is composed of basaltic lava flows underlain by alluvial deposits, which represent two significant water-bearing formations: sub-basaltic alluvial deposits and basalt flows. The depth to the groundwater abruptly deepened from 1.5 to 80 m in the northeast and southwest directions, which could be due to groundwater-bearing formations dipping in these directions or northwest-orientated tension faults. The groundwater quality was assessed in terms of total dissolved solids (TDS), which ranged from 225 to 8340 mg/l, and a TDS-drilling zone encountered in the western part of the Harrat, the following similar most likely resulted from groundwater mineralization. The concentration of TDS generally decreased toward the east in the groundwater flow direction. The pH (6.5–8.1) of the samples indicated that the groundwater pH meets quality standards for domestic and irrigation purposes. It is concluded that, the application of both methods will be of great benefit to identify the groundwater sources and its quality as well. [ABSTRACT FROM AUTHOR]

Eight time-domain electromagnetic profiles were carried out in Harrat Ithnayn, northwestern Saudi Arabia, to detect potential groundwater-bearing aquifers in the area. The collected data were processed and analyzed, with the results inferred or extrapolated between one-dimensional vertical soundings to obtain two-dimensional resistivity sections of the subsurface geological setting. We found that the resistivity values change laterally and vertically throughout the area. High resistivity values (greater than 100 Ohm-m) occupy most of the sections down to depths of approximately 100–150 m, whereas the low-resistivity regions of the section appear to be shallower than 100 m toward the west in the northern part of Harrat Ithnayn. The high-resistivity regions correspond to the Harrat basalts and are underlain by low resistivity (down to a few Ohm-m) in the saturated zones. There are also localized regions of low resistivity at depths of approximately 20–30 m, indicating shallow local groundwater aquifers. Aquifer thickness varies from approximately 50 to more than 100 m. In the southern part, the resistivity sections indicate that the main aquifer is at a depth of 150–200 m (possibly near 170 m) below the basalt. A saturated zone or shallow aquifer approximately 20–30 m thick also exists at a depth of approximately 15 m. In both the shallow and deep aquifers, the resistivity values indicate that there is good quality fresh water. [ABSTRACT FROM AUTHOR]

A new seismicity map has been developed for Neom megaproject in the north-western zone of Saudi Arabia which has experienced considerable earthquake activity in the historical and recent times. The data used an up-to-date earthquake (M w ≥ 3.0) catalog, major structures and tectonic trends. The majority of earthquake epicenters along the Red Sea rift are clustered in an axial trough, as well as on or nearby the active transform faults within the Red Sea basin. These earthquake activities are produced due to to the geodynamic processes such as continental rift and seafloor spreading prevailing in the area. Ten seismotectonic source zones have been identified in the area under investigation. It is indicated that the Gulf of Aqaba and southern end of the Gulf of Suez seismotectonic source zones are the most hazardous zone for Neom megaproject according to the maximum expected magnitudes where Mw are 7.7 and 6.7 respectively. Based on the magnitude-frequency relationship, the b- value varies from 0.41 to 0.934. The highest b values are related to the northwestern coast of the Red Sea, whereas the lowest b -value are related to the Duba source zone. Consequently, damaging earthquakes could affect Neom megaproject, so earthquake hazard assessment is highly recommended for the minimization and mitigation of earthquake losses in this area. [ABSTRACT FROM AUTHOR]

Saudi Arabia covers most of the Arabian Peninsula and is characterized by tectonic regimes ranging from Precambrian to Recent. Using gravity data to produce the lateral boundaries of subsurface density bodies, and edge detection of potential field data, a new subsurface structural map was created to decipher the structural framework controls on the distribution of gold deposits in Saudi Arabia. Moreover, we detected the relationships between major structures and mineral accumulations, thereby simultaneously solving the problem of edge detectors over complex tectonic patterns for both deeper and shallower origins. Analytic signal (ASg), theta map (TM), TDX, and softsign function (SF) filters were applied to gravity data of Saudi Arabia. The results unveil low connectivity along the Najd fault system (NFS) with depth, except perhaps for the central zones along each segment. The central zones are the location of significant gold mineralization, i.e., Fawarah, Gariat Avala, Hamdah, and Ghadarah. Moreover, major fault zones parallel to the Red Sea extend northward from the south, and their connectivity increases with depth and controls numerous gold mines, i.e., Jadmah, Wadi Bidah, Mamilah, and Wadi Leif. These fault zones intersect the NFS in the Midyan Terrane at the northern part of the AS, and their conjugation is suggested to be favorable for gold mineralization. The SF maps revealed the boundary between the Arabian Shield and Arabian Shelf, which comprises major shear zones, implying that most known mineralization sites are linked to post-accretionary structures and are not limited to the Najd fault system (NFS). [ABSTRACT FROM AUTHOR]

Shear-wave velocity profiles are the main site-specific data for site classification, which are commonly used for the purposes of seismic microzonation and hazard assessment. The controlled-source spectral analysis of surface wave (CSSASW) dispersion measurements have been successfully performed to characterize seismic sites up to 30-m depths. This study utilizes the CSSASW application in Jizan City to obtain shear-wave velocity profiling at 14 sites distributed throughout the city using an electromagnetic vibrator. The recorded Rayleigh wave phase velocity dispersion curves are transformed to calculate the apparent velocity distribution in depth. Shear-wave velocities, calculated using theoretical relationships, can then be utilized to obtain design parameters for the soil strata. Shear-wave velocity varies from 216.97 to 829.59 m/s through Jizan City indicating the remarkable change of the near-surface sediments. The hard soil profiles of soft rock that were revealed by V s values in this terrain (sites No. 7, 8, and 13) can be attributed to the existence of a dense layer of salt rock. Construction in such areas is prohibited due to the high susceptibility of large settlements in foundations as a consequence of salt dissolution. In the Sabkha terrains, all soil profiles were related to V s , defined as stiff soils that were then modified to a softer class owing to their high liquefaction potential. These results should be considered before establishing important and strategic projects in the city. [ABSTRACT FROM AUTHOR]

Vertical electrical soundings, seismic refraction tomography, and ground magnetic measurements were taken or conducted close to an open dumpsite near Khamis Mushait, southwestern Saudi Arabia, which is characterized by shallow groundwater conditions. Structurally, intersected series of north- to northwest-trending faults affect the area. A new urban expansion and the Khamis Mushait industrial zone are close to the open dumpsite. This study evaluates the potential for leachate intrusion into groundwater aquifers. The results of electrical soundings reveal four geoelectric units: the topsoil, weathered layer, partly weathered/fractured basement, and fresh basement bedrock. At the dumpsite, relatively low resistivity values that are less than 30 Ωm characterize the topsoil, weathered layer, and partly weathered/fractured basement because of conductive leachate from the dumpsite. Besides, the results of ground magnetic data indicate that the deformation of varying intensities affects the dumpsite area, resulting in fractures developing in the N–S, NE–SW, NW–SE, and, to a lesser extent, E–W directions. Moreover, geoseismic tomographic models illustrate a low P-wave velocity zone corresponding to a low resistivity zone, and a NE–SW fault was identified from geoseismic cross-sections. Finally, these fractures and faults could become contaminant pathways for shallow aquifers around the dumpsite. To minimize the impact of such leachate, from a dumpsite, on groundwater quality and the environment in general, the dumpsite must be properly designed, constructed, and managed using engineering principles. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) electrical resistivity tomography (ERT) survey has been conducted in the Harrat Khaybar volcanic field, northeast of Al Madinah Al Munawwarah, Saudi Arabia, to assess the presence of groundwater resources. For this purpose, eleven ERT profiles were generated at six sites oriented north–south and east–west at various lengths between 590 m and 890 m. The ERT data were collected using the Syscal Pro multinode resistivity imaging system with a dipole–dipole array and 5 m of electrode separation. Then, these data have been processed using RES2DINV software to get 2D geoelectric cross-sections. The interpreted 2D geoelectric cross-sections clarified that the Harrat Khaybar occupied by sheets of lava flows underlain by alluvial deposits of gravelly sand and clay. These deposits rest on a Precambrian crystalline rock configuration that has the potential to provide groundwater to the region. Promising water-bearing formations were detected within sub-basaltic alluvial sediments and basaltic flows as well. Moreover, the reported water table in the area has 47 m depth in average with thickness varies between 6 and 200 m. These results correlate well with those of previous hydrogeological studies conducted in Harrat Khaybar. These results are very important for the residents in Harat Khaybar, where enables them to benefit from the groundwater resources in the area for domestic and agricultural purposes. [ABSTRACT FROM AUTHOR]

Landslide susceptibility of Makkah Al-Mukarramah has been assessed by collecting microtremor measurements at 277 sites covering the whole area. These data were then processed and analyzed using the horizontal–vertical spectral ratio (HVSR) method to obtain the resonance frequency and H/V amplification factor. The results display that the predominant frequency values range between 0.26 and 17.27 Hz, and the amplification factor varies from 0.87 to 14.68. Then, 34 sites were selected to assess the frequency, amplitude and azimuthal site response where frequency ranges from 0.26 to 13.67 Hz while amplitude varies from 2.0 to 12.2. Moreover, the site response direction was parallel to the landslide directional response in the sliding areas which indicates that the site response direction followed the landslide direction. The results of this study have been approved practically at several sites through field measurements at some of recent landslide occurrence locations in Makkah urban area. These results signifying that microtremor measurements are effective technique in locating the sites suffering landslides, which, in turn, reduce their hazardous impact on either human-life and their beings. Therefore, it is highly recommended to apply this approach in places prone to landslides in southwestern Saudi Arabia. [ABSTRACT FROM AUTHOR]

The upper plutonic rocks in southwestern Saudi Arabia has been mapped through Landsat 8 Operational Land Imager (OLI) data. The gathered field rock samples were subjected to spectral measurements (in the range of 0.4–2.5 µm) in the laboratory using a GER 3700 spectroradiometer. Integrated remote sensing techniques, including the band ratio, principal component analysis (PCA), and Gram-Schmidt spectral sharpening have been applied through this study. The red–greenblue composites of the pan-sharpened original bands (3, 4, and 7), principal components (PC3, PC1, and PC2), and band ratios 5/6 and 5/7 were found to be the most useful to delineate the study area's Upper Proterozoic plutonic rocks. The results of image processing methods, spectral reflectance analyses are in good agreement with the field data. The spectral reflectance curves of the collected samples and the corresponding Landsat 8 pixels match well. It is indicated that Landsat-8 image data has great capability to identify lithological units and could be applicable in several areas in arid and semiarid environments. [ABSTRACT FROM AUTHOR]

Southwestern Saudi Arabia is enriched with fractured and highly-weathered igneous and metamorphic rocks that function as the limited aquifer and supply significant quantities of water for household use and agriculture in this area. Twenty-seven groundwater samples were collected from shallow-dug wells and physio-chemically examined. It is displayed that, however the average value of total dissolved solids (792.67 mg/l) is not curiously high, the ionic component moved toward anthropogenic origin of pollution. The water in the area fits SO4–Cl type facies. The aquifer fractured properties and the existence of groundwater at near-surface depths affecting the groundwater hydrochemistry for the investigated area. Decision and policymakers must consider these results to minimize the environmental impact of local pollutants in the region. [ABSTRACT FROM AUTHOR]

Landslides hazard as one of the major environmental threats of the Neom promising city in northwestern Saudi Arabia has been assessed through data integration of several sources including topographic, geologic, and seismologic data sets. Moreover, Landsat imagery and historical landslide data are introduced in assessing landslide susceptibility of the study area. All these data oriented to generate eight thematic layers representing eight landslide conditioning factors. These factors arranged according to their relative importance for landslide susceptibility mapping as follows: slope angle, elevation, curvature, aspect, earthquake density, fault density, drainage density, and lineaments density. These factors were assessed using GIS through a numerical rating scheme for thematic layers. The ranks and weights were given in association with intensive field studies and authors' experiences. The estimated values of Landslide Potential Index (LPI) varies from 32 up to 107. Then, the resultant landslide susceptibility map classifies the landslide hazards into three relative classes of susceptibility: high, moderate, and low. Furthermore, this map was tested through several field checks and the extracted historical landslides within Neom area as well. This landslide susceptibility map will boost decision-making authority while executing the developing projects throughout the Neom promising area either avoiding strategic facilities or applying corrective geotechnical procedures to minimize the landslide hazardous impact for Neom city. [ABSTRACT FROM AUTHOR]

The environmental threats of soil subsistence in Jeddah city have been assessed using cross-hole seismic testing. These threats affect the state of health of roads, buildings, near-surface foundations ensuring a reliable and economic infrastructure design, as unanticipated site conditions can cause significant traffic problems, soil subsidence, and structural collapse. Cross-hole seismic testing is of utmost importance in determining velocity profiles of P- and S-waves for environmental hazard assessment. These velocity profiles are required to calculate the geotechnical parameters of soil nearby important structures. A cross hole seismic survey was conducted at boreholes close to Jeddah desalination plant. A sledgehammer horizontally striking a wooden plate was used to generate S-waves polarized in the crossline and inline directions. A vertical hammer hitting a metal plate to generate the P-wave then the first break arrival times were inverted for the P- and S-wave velocity structure estimation. The equipment and procedures comply with the American Society for Testing and Materials (ASTM) D 4428/D 4428M-91 standard test method for cross-hole seismic testing. The estimated velocities were utilized to calculate the elastic moduli, geotechnical parameters and density variations within the mapped area. These parameters agree with the lithological variations of near- surface sediments from borehole logs. Finally, the study area illustrated soft, fractured, and poorly graded sediments, which, in turn, require special treatment from engineering point of view before establishing the important facilities in the area. These results are highly recommended and have to be considered to mitigate the environmental hazards in Jeddah city. [ABSTRACT FROM AUTHOR]

To meet the increasing in population, urbanization and public transportation needs of Dammam big city a new transportation infrastructure network is planned and being developed. In the same time, environmental threats of land subsidence on network has been raised and needs to be addressed. Site characterization for designing this transportation lines is crucial to ensure reliable and economic substructure design, because weak site soil conditions may cause land subsidence problems. Downhole seismic (DS) testing is commonly used to determine compression wave (P) and shear wave (S) velocity profiles in geotechnical engineering, which are required in evaluating responses to shaking of geotechnical sites and structures. A DS survey was conducted through boreholes at the center of the Dammam metropolitan city, Saudi Arabia. A sledgehammer horizontally striking a wooden plate generated shear (S) waves polarized in the crossline and inline directions, whereas a vertical hammer hitting a metal plate generated the P wave. Data were obtained using Freedom Data PC, a downhole tool with a triaxle geophone package, and a seismograph. In the downhole technique, the geophones were equestrian on an internal rotating block, and a built-in fluxgate compass as well as servo motor system maintained the orientation of the geophones inside the borehole. The instrumentation and processes complied with the standard test methods for downhole seismic testing (Standard and D7400-08, 2008). This represents, a versatile platform for evaluating structures/infrastructures and geophysical seismic engineering surveys. The estimated seismic velocities were used in estimating the various elastic moduli and density variations within the mapped boreholes. The integrated approach of proper geotechnical characterization and 1D velocity profile proved to be a helpful tool for assessment of subsidence of Dammam city in the future which, in turn, will reduce the environmental threats facing the city. [ABSTRACT FROM AUTHOR]