Seismic Velocity Values Research Articles

Classifying Ground Rippability and Weathering Grades in a Sedimentary Rock Geological Environment Using Seismic Refraction Survey

Introduction An in-depth understanding of the ground subsurface is crucial for foundation design and excavation works and for avoiding potential hazards during land development.In this regard, the ground rippability and weathering grades are some of the ground information needed. While geotechnical works are preferred, their limited horizontal coverage and high cost are often constraints that limit their use. Aims To counter this, a geophysical survey is employed for its wider area coverage and cost-efficiency. Therefore, this study used the seismic refraction method to assess the rippability and weathering grades in a sedimentary rock geological setting (interbedded sandstone, siltstone, and shale) as a preliminary ground assessment. Methods A seismic refraction survey was carried out using Aktiebolaget Elektrisk Malmletning (ABEM) Terraloc Pro 2, where the survey line was 115m long. Rippability was obtained by correlating seismic values with the Caterpillar D10R rippability table. Meanwhile, the weathering grades of the ground were determined by correlating the study area with another study area of a similar geological setting. Results Within the 39m penetration depth, three layers can be classified from the ground’s P-wave velocity values and D10R Caterpillar rippability chart, which include rippable, marginal, and non-rippable layers. A break in the continuous ground layers could be seen, causing lower velocity values to be sandwiched between high velocities, which signified the presence of fracture. The weathering grades were also successfully classified from the seismic velocity values. Conclusion Using seismic refraction method, this study successfully employed seismic velocity values in determining the rippability and weathering grades of interbedded sedimentary rock without borehole record.

Characterizing mudstones and fault structure in Bumita Quarry, Perlis through integrated geophysical techniques

The parameters of seismic refraction and electrical resistivity play a crucial role in geological studies, as they provide insights into the composition of rocks or soil beneath the Earth’s surface. Previous researchers have established reference ranges for seismic velocity and resistivity values based on different rock types, which are presented in tabulated forms. However, the wide variability in these values sometimes leads to challenges in interpretation due to overlapping ranges. In the region of Perlis, Malaysia, a comprehensive geophysical investigation involving seismic refraction and electrical resistivity methods was conducted within the Chepor Member of the Kubang Pasu Formation at the Bumita Quarry and Utan Aji. The results were then correlated with porosity and permeability data. The Chepor Member primarily comprises both red mudstone and grey mudstone. Interestingly, the seismic velocities of these two mudstone types are quite similar, differing only by a small margin of approximately 200 m/s. The resistivity method employed utilized a pole-dipole array configuration. In terms of resistivity values, the red mudstone exhibited lower readings (ranging from 15 to 100 Ωm) compared to the grey mudstone (ranging from 120 to 500 Ωm). Assessing porosity, the red mudstone displayed a value of 0.95%, alongside a permeability of 5.58×10-5 μd, while the grey mudstone indicated a slightly higher porosity value of 1.9% and a permeability of 2.06×10-5 μd. Consequently, the study successfully established seismic velocity and resistivity benchmarks for the mudstones within the Chepor Member geological unit.

Coastal Groundwater Bodies Modelling Using Geophysical Surveys: The Reconstruction of the Geometry of Alluvial Plains in the North-Eastern Sicily (Italy)

The integration of various geophysical methodologies is considered a fundamental tool for accurately reconstructing the extent and shape of a groundwater body and for estimating the physical parameters that characterize it. This is often essential for the management of water resources in areas affected by geological and environmental hazards. This work aims to reconstruct the pattern and extent of two groundwater bodies, located in the coastal sectors of the North-Eastern Sicily, through the integrated analysis and interpretation of several geoelectrical, seismic and geological data. These are the Sant’Agata-Capo D’Orlando (SCGWB) and the Barcelona-Milazzo (BMGWB) Groundwater Bodies, located at the two ends of the northern sector of the Peloritani geological complex. These two studied coastal plains represent densely populated and industrialized areas, in which the quantity and quality of the groundwater bodies are under constant threat. At first, the resistivity models of the two groundwater bodies were realized through the inversion of a dataset of Vertical Electrical Soundings (VES), constrained by stratigraphic well logs data and other geophysical data. The 3D resistivity models obtained by spatially interpolating 1D inverse VES models have allowed for an initial recognition of the distribution of groundwater, as well as a rough geological framework of the subsoil. Subsequently, these models were implemented by integrating results from active and passive seismic data to determine the seismic P and S wave velocities of the main lithotypes. Simultaneous acquisition and interpretation of seismic and electrical tomographies along identical profiles allowed to determine the specific values of seismic velocity, electrical resistivity and chargeability of the alluvial sediments, and to use these values to constrain the HVSR inversion. All this allowed us to recognize the areal extension and thickness of the various lithotypes in the two investigated areas and, finally, to define the depth and the morphology of the base of the groundwater bodies and the thickness of the filling deposits.

Empirical Relationship between Three Geotechnical Properties Obtained in Three Sites in Kerbala City, Iraq

The material index (Im), concentration index (Ic ), and Coefficient of Lateral earth pressure at res (Ko ) are important geotechnical properties, which are determined in seismic cross holes depending on wave velocities. These three geotechnical properties were determined in three sites in Kerbala City, Iraq. These geotechnical properties are determined depending on the cross-hole survey achieved at Al-Abbas holy shrine, the pure water p, project and the Al-Khiam hotel sites. From a comparison of of the values of these properties in the three sites, three empirical relations were found between them, these are Im = - Ko, Ic = 4 – Ko, and Ic = 4 + Im. the author believed that these relations are usfule in determine these properties. In this research, it was reached to find new equations or relationships through which these three properties can be calculated by calculating one of them, and then finding the values of the other properties ia n short time, and with high accuracy. These new equations or relations I called Al-Kafeel equaions. Im , ,Ic and Ko have been calculated for more than 2034 samples from the surface of tearthths to up 15 m. These parameters have been calculated for more than 2034 samples from the earth's surface and up to 15 m, which used seismic velocity values in calculating these properties by the international old equations. This paper used new equations which are called Al-Kafeel geotechnical equations. The results were compared using the two equations, and it was very successful, and the error rate was between 1%–2%. These simple equations or relations, Al-Kafeel Equations, have been reached and used for the first time since 2017 and have given excellent results in terms of time, and accuracy.

Approximation of seismic velocities from the spectrum of weighted graphs

Extracting seismic velocities from recorded seismic data requires converting the shot gathers to mid-point gathers, calculating the velocity spectrum, and picking the velocity values. In this paper, we propose to use graph theory to extract the seismic velocity values directly from the mid-point gathers. We use spectral data of a weighted graph model for approximating the seismic velocity. We develop a regression model to predict the seismic velocity from the largest eigenvalue of the graph representing the physical system. The approach is tested on a synthetic seismic data that represent a typical near-surface geological situation. The method was able to predict the seismic velocity of the second layer with 99.4% accuracy.

Determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities

Objective. The purpose of the study is to determine the coordinates of the earthquake hypocenter with the simultaneous determination of the seismic wave velocity.Method. The study is based on the use of figures of the fourth and second order - the Cassini oval and hyperbola, figures of the second order - ellipse and hyperbola and combined methods that allow, at given seismic wave velocities, according to three seismic sensors, to determine the coordinates of the earthquake hypocenter. In this case, the velocities are assumed to be known a priori. According to the readings of the fourth seismic sensor, and for given seismic wave velocities, the distance from the fourth seismic sensor to the hypocenter is determined. Again, according to the coordinates of the fourth seismic sensor and the hypocenter coordinates calculated from the three seismic sensors, the distance between them is calculated. If the seismic wave velocities do not correspond to the true ones, a discrepancy will appear between the two calculated values of the distances from the hypocenter to the fourth seismic sensor. By varying the velocities of seismic waves when calculating the coordinates of the hypocenter, we achieve a minimum discrepancy.Result. The problem of determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities is solved. The error distribution densities in determining the coordinates of the earthquake hypocenter and seismic wave velocities are obtained.Conclusion. The proposed method makes it possible to increase the accuracy of determining the coordinates of the earthquake source, as well as to refine the values of seismic wave velocities.

Combination of ground penetrating radar and seismic surveys of the tailings dam

Identification of water-saturated zones in the tailings dams is an actual scientific and practical task in terms of providing, first of all, their mechanical strength and filtration stability. Use of active sounding geophysical study methods allows obtaining sufficiently detailed information about the peculiarities of the internal structure of the tailings dam and the degree of water saturation of the composing soils. The paper presents the results of in-situ experiments on the study of the tailings dam of the mining enterprise by ground penetrating radar (GPR) and seismic methods. A comparative analysis of the conducted studies has allowed clarifying the internal structure and assessing the dam’s condition, paying special attention to the identification of local zones of increased water saturation and filtration. Based on the calculated correlation coefficient of electromagnetic and seismic wave velocity values, it was revealed that synchronization of geophysical surveys allows significantly increasing the reliability of in-situ determinations, as well as obtaining more reliable data. The results of the studies are the basis for predicting the most vulnerable places (zones) of a bulk ground hydraulic facility, as well as the localization of water-saturated areas in the body of the ground structures with greater reliability and performance.

Composition of the lunar mantle for lower mantle high-velocity seismic model

We investigated models of the internal structure of initially homogeneous Moon differentiated as a result of partial melting, using data on seismic velocities according to the seismic models assume the zonal structure of the lunar mantle is a model of the Moon which was obtained with using the array processing methods of high velocities in the lower mantle. As a result of inversion of gravity (mass, moment of inertia), seismic (P- and S-waves velocities) and petrological (balance ratios) data, the Monte Carlo method was used to reconstruct the chemical composition and internal structure of the Moon. The phase composition and physical properties of the mantle were obtained with Gibbs free energy minimization method and equations of state in the five-component system CaO-FeO-MgO-Al2O3-SiO2. For all models, possible values of seismic velocities and concentrations of the main oxides in three zones of the mantle were obtained, satisfying the geochemical and geophysical constraints and the possible sizes of the Fe-10%S core were determined. It was found that the lunar mantle chemical composition (concentration of FeO, Al2O3 and CaO) differs depending on the mantle zone. Constraints on the values of seismic velocities in the lower mantle and the most probable size of the lunar core were determined: VP ≤ 8.45 km/s; Fe-10%S core radius is ∼360 km.

Interpretasi Tingkat Kekerasan Batuan Bawah Permukaan di Daerah Rawan Gempa Bumi Kota Bengkulu

<p class="AbstractText">Bengkulu City is located in the subduction zone of the Indo-Australian and Eurasian plates, so it is prone to earthquake. To anticipate the impact of earthquake, disaster mitigation can be carried out, one of which is a study of the level of rock hardness in the area. This study aims to determine the level of rock hardness based on seismic wave velocity in several rock formations and to determine which rock formations have the potential to cause vulnerability to earthquakes. Field data acquisition uses the seismic refraction method with time-term inversion technique. The data obtained in the field are processed to obtain a 2-D cross-section of the subsurface seismic wave velocity values. The study results show that the level of rock hardness depends on the type of rock formation. The Andesite Rock Formation Unit (Tpan) has the highest level of hardness, while the transitional area between the Alluvium Rock Formation Unit (Qa) and the Swamp Sedimentary Rock Formation Unit (Qs) has the lowest level of hardness.</p>

Heat Flow in SW of Galicia And NW of Portugal. The Interpretation of a Seismic Anomaly

Four heat flow density values and five temperature-depth profiles were obtained in a heterogeneous region considering heat flow by conduction in the vertical direction, and heat sources in the crust due to radioactivity decay. The heat produced in the upper layers of the crust was obtained based on gamma-ray charts and published data of laboratory radioactivity measurements on samples taken from the region. Seismic data were used to obtain the thickness of the different layers of the upper and middle crust and the depth of the Moho discontinuity considered coincident with the crust/mantle boundary. The heat flow at the surface is obtained by adding the heat flow from the mantle with the heat generated by the radioactive sources in the crust. The method was applied to a region with one measured heat flow density value (Ourense) and four points without any heat flow density measurement. A heat flow value from the mantle was obtained with Ourense data. Special attention was given to a region (A) with a seismic anomaly near the surface. The anomaly was explained by mass deficit near the surface that gives rise to an abnormal density value and an increase in seismic wave velocity values. The decrease in density is due to the presence of water in the region forming an aquifer. Geothermometer values obtained from samples of water in the thermal springs of Tuy (Spain) and Monção (Portugal) were used as the water temperature at the bottom of the aquifer. Isostatic balance in the region was considered to obtain density values and the amount of water in the region. Thermal conductivity and radioactivity heat source values in the region were obtained considering the amount of water in the region. Values from 86 to 97 mW/m2 were obtained using the same value of heat flow from the mantle. This is due to different values of heat produced in the crust due to different thickness layer values or/and to different heat production values.

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

CO2 induced changes in Mount Simon sandstone: Understanding links to post CO2 injection monitoring, seismicity, and reservoir integrity

The purpose of this study is to quantify geochemical reactions of CO2 and brine with subsurface samples taken from the Mt. Simon sandstone and identify any potential alterations of the geomechanical rock properties that could lead to changes observable in seismic monitoring or result in changes of micro seismicity such as those observed at the Illinois Basin-Decatur Project (IBDP) site. Two Mt. Simon sandstone samples from 6919.3 feet (2109.0 m) and 6926.1 feet (2111.1 m) depth were exposed to supercritical CO2 (scCO2) dissolved in brine at in-situ reservoir conditions for one month. Geochemical, spectral, scanning electron microscopy, and petrophysical methods were used to analyze the samples before and after the one-month exposure. Significant changes were observed. Multiple geomechanical properties were chosen to form the framework against which to interrogate the petrophysical data: Young’s modulus (E), Poisson’s ratio (ν), lambda·rho (λρ), and mu·rho (μρ). In this study we conclude that framework composition, porosity, heterogeneities, effective pressure, and reactive geochemistry are first order controls on trends in the E-μ and λρ-μρ cross plot spaces. Changes in porosity, permeability, dynamic moduli, and brittleness with exposure to these fluids were observed. No change in ultrasonic P-wave attenuation (QP) was observed. Geochemical alteration causes a distinct shift in λρ-μρ in both samples as well as changes in E, ν , and P and S wave seismic velocity values. These observations could provide insight into subsurface monitoring using seismic methods including amplitude variation with offset (AVO) classification.

Estimation of near-surface geotechnical parameters using seismic measurements at phase ǀǀ site, Ahmadu Bello University Zaria, North-western Nigeria

Determination of the dynamic geotechnical properties and seismic wave velocities serves as essential inputs for a foundation design cognizant of seismic site response and rock strength. This study evaluates competent zones for construction at Ahmadu Bello University Zaria, Phase II site. Four shallow seismic refraction profiles were carried out using the ABEM Terraloc Pro seismograph. Compressional (P) and shear (S) waves were acquired and the time-term technique, which is a combination of linear least squares and delay time analysis to invert the first arrivals for a velocity section and then to tomography section was adopted. These sections were correlated with a borehole report and a good matching was observed. The result shows that the area consists of three subsurface layers; an overburden with average thickness of about 10.5 m and P- and S-wave velocities (velocities) of about 550 m/s and 345 m/s respectively, the weathered basement with an average thickness of 12.5 m and velocities of 950 m/s and 550 m/s respectively, while the fresh basement was found at a depth of about 24 m with velocities of 1250 m/s and 680 m/s respectively. The Concentration Index, Material Index, Poisson’s Ratio, and Stress Ratio were calculated to be in the range of 4.869 to 6.128, -0.032 to 0.312, 0.172 to 0.258, and 0.267 to 0.346 respectively in the study area. The seismic velocity values, engineering consolidation, and strength parameters showed that the subsurface soil/rock at the eastern parts of the study area is characterized by less competent soil/rock quality while the western parts are characterized by more competent soil/rock quality. Hence, the western and north-western parts are more preferable for the foundation of structures to be erected.

Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. The interpretation of these reflections has been complicated by disparate borehole data, particularly because of the scarce amount of available sonic borehole logs and the varying practices in logging of borehole lithologies. SOM is an unsupervised data mining method based on vector quantization. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion.

The Seismic Refraction Survey to Determine the Depth of Bedrock at the Damansara Area for Horizontal Directional Drilling Method Application

The seismic reflection survey conducted along the road at Damansara to determine the depth of bedrock in order to justify whether HDD method can be utilize to store the fiber optic cable. 10 line seismic survey performed along 1.2 km roadside. The result show that the subsurface profile represent by two layer of earth materials that is topsoil and bedrock granite. Determination between topsoil and granite based on the values of seismic velocity. The boundary between granite and soil interpreted by a velocity value 1,200 m/s. If the velocity values is less than 1,200 m/s, it interpreted as soil or highly weathered rock. Meanwhile the velocity value more than 1,200 m/s is refer as rock and hard to excavate especially using HDD method. The study shows that the general thickness of topsoil along the road in Damansara is around 2.0 to 4.0 m. The minimum thickness of topsoil is 1.0 m and maximum found around 6.0 m. The bedrock observed very shallow and not suitable for HDD method to implement.

Comprehensive Correlations Between the Geotechnical and Seismic Data Conducted via Bender Element

Bender element (BE) is a useful seismic tool to predict the geotechnical soil properties using empirical correlations. However, there were uncertainties in the correlation equations which were not discussed in detail. In this study, the seismic data was thoroughly investigated to improve the correlations with the physical soil properties. Several proportions of sand–kaolin mixtures were compacted, sheared, as well as BE tested. The results showed curve relationships whereas the highest seismic wave velocity and the highest shear strength were attained at the proportion of 40% fine content. At this point, the void ratio, intergranular void ratio, maximum dry density, and specific gravity were 0.43, 1.43, 1.79 g/cm3, and 2.585 respectively. In addition, a direct positive linear relationship between the seismic wave velocity with cohesion (c) and shear strength (τ) provided highest values of seismic velocities at 53.7 kPa and 81.7 kPa of c and τ respectively. However, the seismic wave velocity less significant effected by the friction angle. The paper presented 68 empirical correlation equations between the previous parameters. The comparison with previous researchers indicated that the application of the empirical correlation equations was limited to the material type (clay and sand), fine content range (20–70%), void ratio range (> 0.43), and condition of the samples.

Subsurface Soil Evaluation using Seismic Refraction Tomography and Standard Penetration Test at Bukit Bunuh Impact Crater Area

Subsurface soil varies from place to place due to the rock type, its mineral constituents, the climate
 of the area, time and other geological activities such as meteorite impact. The process that leads to
 the formation of impact crater can cause great variation in the subsurface soil characteristics, which
 may have an effect on civil engineering structures. Hence, the need to evaluate the subsurface soil
 of the impacted area. In this study, Seismic refraction and borehole data were used to achieve the
 aim. The result revealed that the overburden layer inside the crater is dominated by low-velocity
 values (< 750 m/s) which correspond with low N-values. Moderate seismic velocity values (750 –
 1400 m/s) with moderate to high N-values were predominant for overburden soil within the crater
 rim and outside the crater. Slightly, moderately and highly weathered granite was observed at all
 survey lines with velocity values ranging from 1200 - 3450 m/s. The low N-values with lowvelocity values obtained inside the crater are indications that the subsurface soil inside the impact
 crater area has been deformed and weakened as evident by the presence of brecciation which
 occurred during the impact process.

Utilizing shallow seismic refraction in defining the geotechnical properties of the foundation materials: A case study at New Minia City, Nile Valley, Egypt

The main objective of this paper aims to estimate the geotechnical parameters necessary for engineering constructions. For this purpose, thirty flat seismic refraction profiles were carried out in the study area northeast of New Minia City to describe the geotechnical properties of the subsoil for construction purposes. Both compressional (P) and shear (S) waves were detected and interpreted. The results show that the near surface section of the study area consists of two layers, the first layer of soil (sand from recent deposits), traversed by the second layer (sand and fragments of limestone) and changed laterally into fossiliferous limestone layer. Additionally, a number of engineering parameters for the second layer, such as elastic moduli (Poisson's ratio, bulk's modulus, rigidity modulus and Young's modulus), competence scales (material index, concentration index, stress ratio, and density gradient) and bearing capacity (ultimate and allowable) are determined. It was found that, the P-wave seismic velocities range from 2800 to 4500 m/s and the S-wave seismic velocities range from 1600 to 2750 m/s. Also, concluded that the values of Concentration Index, Material Index, Density Gradient, and Stress Ratio are ranging from 4.8 to 11.1, −0.053 to 0.603, −0.819 to −0.59, and 0.11 to 0.357, respectively. High difference between these two values reflects lithological, structural and textural variations occurred in rocks existed in the investigated area.The seismic velocity values and engineering parameters indicate that the bedrock at northwest and southeast of the study area have low competent rock quality, while the rest of the area have high competent rock quality. So, the suggested area for construction activities was about 9,489,876 m2 from total area 11,770,966 m2.

Geographic variations in lowermost mantle structure from the ray parameters and decay constants of core‐diffracted waves

AbstractWe introduce an array‐based approach for constraining seismic velocity structure in the lowermost mantle by measuring the frequency dependence of the ray parameter p and decay constant γ for core‐diffracted waves (Pdiff and SHdiff). The approach uses an iterative multichannel cross‐correlation algorithm that solves for relative arrival times and amplitudes of core‐diffracted waveforms from multiple peaks in normalized correlograms from pairs of coazimuthal stations. The approach is applied to 60 mb ≥ 5.8 earthquakes for Pdiff and 36 for SHdiff during 2001–2002, with nearly 50,000 unique profile station pairs with epicentral‐distance differences of Δd ≥ 10° and azimuth differences of Δφ ≤ 10°, sampling a significant portion of the lowermost mantle. Cap‐averaging the resulting ray parameter estimates produces geographic variations that are largely consistent with the distribution of lowermost mantle large low‐velocity provinces and seismically fast slab‐accumulation regions seen in seismic tomography models, whose locations also strongly influence the geographic distribution of heat flow out of the core. Geographic variations in station‐pair diffracted‐wave decay constants differ from those of the ray parameters, suggesting that variations in the decay of core‐diffracted waves are more linked to lowermost mantle seismic velocity gradients than absolute values of seismic velocity. The ray parameters and decay constants of core‐diffracted waves are strongly frequency‐dependent, and these frequency variations also vary significantly with geographic location. Combining lateral and vertical seismic‐velocity variations with mineral‐physics data on elasticity and conductivity of lowermost mantle species can provide constraints on D″ composition and CMB heat flux.

Dynamic geotechnical properties evaluation of a candidate nuclear power plant site (NPP): P- and S-waves seismic refraction technique, North Western Coast, Egypt

Determination of the dynamic geotechnical properties and Vs30 of soil and rocks from seismic wave velocities serves as essential inputs for a foundation design cognizant of seismic site response and rock strength. This study evaluates a site which was suggested for a Nuclear Power Plant (NPP) in El-Dabaa area, north western coast of Egypt. On the near subsurface geology is made up of a thick succession of limestone overlain by a thin layer of soft soil. Assessment of geotechnical materials and Vs30 of the near sub-surface lithological layers are required for design of the foundation of critical structures like turbo-generator and reactor buildings. Interpretation of ninety one shallow P-waves and S-waves seismic refraction profiles distributed within the study area in conjunction with data of 76 boreholes were undertaken to delineate the dynamic properties of shallow soil for construction NPP. The velocity of the P- and S-waves were acquired and interpreted using SeisImager Software Package, then the results were used to build a velocity-depth model to estimate the depth to the bedrock and the thicknesses of overburden layers. This model was verified using boreholes data dissected the seismic profiles to improve the final velocity depth model. The depth to bedrock was determined from both shallow seismic refraction profiles and boreholes. Vs30, elastic moduli and dynamic geotechnical parameters were calculated and the site was classified as a National Earthquake Hazard Reduction Program (NEHRP) class “B”. The values of seismic velocities, the engineering consolidations, and the strength parameters showed that the bedrock in the study area is characterized by more competent rock quality.