Seismic Refraction Techniques Research Articles

Application of seismic refraction tomography for detecting a hidden potential fault

Seismic refraction technique is an increasingly useful geophysical tool for geotechnical studies in civil engineering work including the mapping of different soil formation of subsoil and detection of the bed rock. Additionally, wave velocity is a key parameter which correlates directly with significant geotechnical parameters of soils and rocks. Today, the evolution of the measurement technique in the field and the data processing allows to obtain tomographic images which increases its potential for applications to evaluate structuration of rock mass. This work describes the basic principles of seismic tomography and a case history of an application in civil works used to evaluate the foundation conditions of a site were a new structure for a spillway for the Gatun lake, north Panama, was projected. The study allowed to detect a destructured band sector in the bedrock which was covered by more modern sediments and vegetation just in the site of interest for the foundation of a project. The magnitude of the destructured bedrock forced to relocate the structure.

INTEGRATION OF SEISMIC REFRACTION AND LABORATORY TEST TECHNIQUES FOR SLOPE STABILITY ANALYSIS, SOUTH-SOUTH, NIGERIA

This study integrates seismic refraction technique (SRT) and laboratory test technique (LTT) methods in order to evaluates the slope stability characteristics of the sedimentary rocks at Mary-Slessor Secondary School, South-South, Nigeria. The integrated approach was adopted to investigate the material strength, soil resistivity and delineate optimal slopes with regards to the factor of safety (FOS). Three layers were delineated in the field analysis, the velocity and resistivity of the first, second and third layers range from (460.5 – 1050) m/s and (850 – 1220) Ωm at 5.61 m depth, (1705 – 2100) m/s, (560 – 650) Ωm at 7.20 m, and (2000 – 2500) m/s, (330 – 450) Ωm at 13.3 m respectively. The elastic parameters obtained from SRT and LTT ranged from (1.1 – 2021.1) kN/m2 and (1.2 – 2270) kN/m2. The result revealed the material’s strengths of the third layer formation with a high velocity and low resistivity being optimally stable with regards to FOS.

Preliminary Assessment of the Soil Foundation Characteristics Utilizing the 2D Resistivity Imaging and Down-Hole Seismic Refraction Techniques: A Case Study in Tenth of Ramadan City, Egypt

Two-dimensional electrical resistivity imaging and seismic refraction, in the form of down-hole survey, were applied to delineate the subsurface section and elastic moduli and identify geotechnical characteristics of subsurface materials in the 10th of Ramadan industrial area, Cairo, Egypt. The results of four 2-D profiles of electrical resistivity, in the form of dipole–dipole and Wenner configurations, revealed that the subsurface section contains two main geo-electrical layers; the first is made of sand, some silt, and gravels, reflecting low resistivity values ranging from 25 to 65.5 ohm m. This layer is overlying a high resistivity layer (65.5 to135 ohm m), corresponding to medium to coarse sand, with gravel and calcareous materials. It is worth noting that that the down-hole technique was used to measure velocities of P and S waves in order to derive the low strain dynamic elastic properties, such as Poisson’s ratio, Shear modulus, stress ratio, concentration index, N-value, and the ultimate and allowable bearing capacities of the subsurface soil, down to an approximate depth of 30 m in the borehole at the site. In addition, the Vs30 value was calculated and revealed that the soil is categorized as a NEHRP class (D). Furthermore, the results of geotechnical parameters and elastic moduli were found to be realistic and sensible for the purposes of engineering constructions and imply that the soil in the study area is characterized by fairly to moderately competent quality. A new empirical correlation is proposed between the obtained Vs and resistivity values, where Vs = 1.0302 ρ + 172.74.

Non-invasive geophysical imaging and facies analysis in mining tailings

Stratigraphy and facies analysis in a mining waste domain such as in tailings storage facilities (TSFs) is still a complex task due to sparsely distributed field data. Geophysical techniques and the interpretation of geophysical data in terms of stratigraphy and facies get relevance for integrating geophysics with other models investigating mining waste domains (e.g., hydrogeological-geochemical).In this paper, we introduce a conventional application of differential operators for interpreting geophysical data in terms of stratigraphy and facies analysis in TSFs. The geophysical data is acquired in a tailings area in the Pyhäsalmi mine, Finland, using seismic refraction (SR) and electric resistivity imaging (ERI) techniques. The SR inversion model constrained by a geological model approximated the ground and bedrock layers by delineating P-wave velocities (Vp). The SR layered model served as a constraint for the electrical resistivity (ρ) model in the ERI method. ERI inversion model data was used for facies analysis and interpretation in terms of other subsurface variables (e.g., water saturation, salinity). For this, a first-order derivative (gradient approach) and a second-order derivative combined with a Gaussian filter (Laplacian approach) were applied to highlight facies and transition zones. The approach embeds the data as scalar functions within a space domain defined by the model local structure. When applied to the ERI data, the gradient and the Laplacian functions captured the local extrema and the minimum threshold crossings respectively enhancing local geoelectric zones and layered contacts in line with field observations. This paper demonstrated that such image analysis can be proposed for interpretation of geophysical data in terms of segmentation and analysis of local facies, relevant in model conceptualization and parameterization of hydrogeological models.

Shear wave velocity profiling by inverse analysis of array microtremors for two cities in Iran: conventional derivative-based versus genetic algorithm inversion methods

GA-based and conventional derivative-based inversion methods were employed to determine Vs profile of subsurface soil layers from array microtremors for two cities in Iran. The applied methods were verified against geotechnical and geophysical data. The results obtained by both GA-based and conventional inversions were in acceptable agreement with results of other Vs profiling techniques. However, the variability of obtained Vs data was smaller at deeper depths indicating more reliability of predictions. Comparison between seismic ground response based on Vs profiles of different methods showed that both GA-based and conventional inversion methods agree more with the seismic downhole method than the seismic refraction technique.

Delineation of shallow structures in the vicinity of Ulu Slim hot spring using seismic refraction and MASW techniques

ABSTRACT Ulu Slim hot spring possesses the highest surface temperature with a reported temperature of 104° C. Hence, the site may be suitable for electric power generation from the geothermal aquifer. In the present work, two seismic techniques are used for shallow structures investigation. The methods are the seismic refraction and the Multi-Channel Analysis of Surface Waves (MASW). The delineation of superficial structures will aid in developing the area without affecting the geothermal system. The instrumentation used for both is similar to a large extent. The main differences are the natural frequencies of geophones used. MASW requires a low natural frequency geophone, whereas seismic refraction uses high-frequency ones. Both techniques are applied at five locations distributed in the 5 km x 5km area. The results obtained from both methods are also tending to confirm with each other. From all profiles, three layers are delineated in the vicinity of the hot spring. The top layer is impermeable clay with an average Vp of 500 m/s and Vs <200 m/s. Underneath this surface layer, the possible aquifer unit characterised by sand, with Vp in the range of 1000 to 2800 m/s and Vs between 200 m/s and 300 m/s. The final layer is the bedrock characterised by a Vp higher than 3700 m/s and Vs greater than 300 m/s. A particularly striking feature of the bedrock structure obtained from our results shows that the bedrock is relatively close to the surface of the vicinity of the hot spring, with a depth of about 5 m. These results confirm the conceptual model proposed for the Ulu Slim hot springs as of granitic origin. Moreover, a plot of the Poisson ratio indicated regions of high water saturation that may represent the hot water pathway to the surface.

Application of seismic tomography for detecting structural faults in a Tertiary Formation

Seismic refraction technique is an increasingly useful geophysical tool for geotechnical studies in civil engineering work including the mapping of different soil formation of subsoil and detection of the bed rock. Additionally, wave velocity is a key parameter which correlates directly with significant geotechnical parameters of soils and rocks. Today, the evolution of the measurement technique in the field and the data processing allows to obtain tomographic images which increases its potential for applications to evaluate structuration of rock mass. This work describes the basic principles of seismic tomography and a case history of an application in civil works used to detect hidden faults in the sedimentary Gatun formation at the north of Panama. The correlation between the seismic profile and geologic profile obtained from boreholes showed very good agreement. Subsequent directed boreholes performed at the site confirmed the position and nature of the faults detected.

Estimation of Rock Load in Development Workings of Underground Coal Mines – A Modified RMR Approach

Underground coal mining in India contributes to a share of 55 Mt production with more than 500 mines in operation. In spite of using the well-established CMRI-ISM Rock Mass Rating (RMR dyn ) classification system for roof support design successfully in Indian geo-mining conditions, accidents due to roof fall constitute the major challenge. These failures are generally due to the presence of weak beddings and laminations. Seismic refraction technique (for shallow depth) can be useful in detecting the rock mass conditions. Based on the study a modified rock mass classification system (RMR dyn ) was setup by incorporating field P-wave velocity with a view to arrive at a real ground condition of the in situ rock. Rock loads were also determined in the field to develop a relation with RMR dyn . A comparison of rock load estimation by CMRI-ISM RMR, numerical simulation and RMR dyn clearly depicts that the latter approach is more reliable as the results are close to the actual scenario.

Coupled geophysical characterization of shallow fluvio-clastic sediments in Agwagune, southeastern Nigeria

Geophysical investigation performed using electrical resistivity tomography (ERT), vertical electrical sounding (VES), seismic refraction (SRF) and ground penetrating radar (GPR) techniques were used to constrain and characterize shallow lithologic units in the Cross River bank (CRB) in southeastern Nigeria. Results show that the upper layer sediments comprise a 3-5-layered lithostratigraphic sequence with high clayey content. Around the Cross River bank (CRB), the top sediments consist of loose, silty and clayey sands with low resistivities (<150 Ωm) and low P-wave velocities (300–1000 m/s). These attenuating sediments have no reasonable continuity beyond the vicinity of the CRB. The low attenuating indurated silts/sands characterized by low resistivities (<25 Ωm) and high P-wave velocities (1000–2400 m/s) underlie the first layer around in the CRB. Localized microstructures (e.g., fractures) trending east-west, and saturated sand-filled channels truncate their lateral continuities. The lacustrine clays characterized by low resistivities (<15 Ωm) and high P-wave velocities (>2400 m/s) make up the third layer. The clayey sediments impede vertical percolation of groundwater forcing it to accumulate at the bottom of the second layer resulting in high static water levels of <3 m within the CRB and >5 m elsewhere. Hydraulic gradient in the Cross River bed (CRBD) and in the coastal groundwater drives groundwater flow into the CRBD through macropores. The sediments become unstable when these macropores become enlarged as more materials are continuously transmitted through them.

Geotechnical investigation of near-surface structures using seismic refraction techniques in parts of Akwa Ibom State, Southern Nigeria

Seismic refraction survey was carried out using 24 channels enhancement seismograph to measure the refracted travel time of P and S waves. The travel times of refracted waves measured were used to calculate P and S wave velocities employed in determination of elastic and bearing strength properties of the materials. SeisImager packages software comprising of plotrefra and pickwin were used for data processing and interpretation. The result shows that seismic waves penetrate into two layers. The values of the depth and thickness of the bedrock for upper layer ranged from 0.0 to 5.0 and 5.0 m; lower layer: 7.0 to 15.0 and 8.0 m. The elastic parameters; Poisson ratio, young modulus and shear modulus for upper layer ranged from − 11.10 to 0.04, (− 30.17 to 3.25) × 105 N/m2 and (0.70 to 4.23) × 105 N/m2 and lower layer: − 9.92 to 0.08, (− 24.83 to 5.21) × 105 N/m2 and (0.80 to 7.47) × 105 N/m2 respectively. The allowable and ultimate bearing capacity for upper layer ranged from (0.84 to 2.11) × 105 N/m2 and (3.37 to 8.44) × 105 N/m2 and lower layer: (0.87 to 2.17) × 105 N/m2 and (3.50 to 8.69) × 105 N/m2. The upper layer characterized by incompetent soil and rock quality and lower layer characterized by good competent soil and rock quality. The lower layer was delineated as the best layer for foundation and engineering work whose allowable bearing capacity and elastic parameters are better correlated for sand to gravel which is geologic equivalence.

Crustal and upper mantle structure beneath the Gulf of Mexico and the Caribbean Sea from Rayleigh‐wave analysis

The elastic structure beneath the Gulf of Mexico and the Caribbean Sea is presented in this paper by means of S‐velocity maps, for depths ranging from 0 to 350 km, determined from Rayleigh‐wave analysis. The S‐velocity mapping, for the depth range from 0 to 5 km, shows clearly the distribution of sedimentary basins of the study area. For the depth range from 5 to 35 km, the higher S‐velocity values are associated to the areas in which the crust is thinner (oceanic crust). For the Caribbean Plate, which consists of the Venezuelan and Colombian basins separated by the Beata Ridge, a differentiation between both basins is possible in terms of S‐velocity. The thickening of the Caribbean crust (observed in the southern part of the study area), due to the Caribbean–South America plate interactions, is confirmed by the S‐velocity mapping; thickened crust is characterized by S‐velocities lower than those for the upper mantle. For depths greater than 35 km, the S‐velocity presents its higher values at the older regions of the study area, while the younger or active regions are imaged with low S‐velocity. Finally, a new and very interesting feature presented in this study is the location and thickness of the lithosphere–asthenosphere system. On the other hand, this study provides the mapping necessary to locate the deep geologic structures, present in the study area, which tectonic and geologic evolution is wished to determine, allowing also to know the nature and type of the crust and upper‐mantle structure beneath this area. Once this knowledge is reached, an evolutionary model can be developed. This study is especially interesting for areas in the Gulf of Mexico that are hidden beneath near‐opaque, complex, and extensive allochthonous salt bodies, which make it difficult to use other seismic exploration techniques such as seismic refraction or reflection techniques.

A multi‐azimuth seismic refraction study for a horizontal transverse isotropic medium: physical modelling results

ABSTRACTTo investigate the characteristics of the anisotropic stratum, a multi‐azimuth seismic refraction technique is proposed in this study since the travel time anomaly of the refraction wave induced by this anisotropic stratum will be large for a far offset receiver. To simplify the problem, a two‐layer (isotropy–horizontal transverse isotropy) model is considered. A new travel time equation of the refracted P‐wave propagation in this two‐layer model is derived, which is the function of the phase and group velocities of the horizontal transverse isotropic stratum. In addition, the measured refraction wave velocity in the physical model experiment is the group velocity. The isotropic intercept time equation of a refraction wave can be directly used to estimate the thickness of the top (isotropic) layer of the two‐layer model because the contrast between the phase and group velocities of the horizontal transverse isotropic medium is seldom greater than 10% in the Earth. If the contrast between the phase and group velocities of an anisotropic medium is small, the approximated travel time equation of a refraction wave is obtained. This equation is only dependent on the group velocity of the horizontal transverse isotropic stratum. The elastic constants A11, A13, and A33 and the Thomsen anisotropic parameter ε of the horizontal transverse isotropic stratum can be estimated using this multi‐azimuth seismic refraction technique. Furthermore, under a condition of weak anisotropy, the Thomsen anisotropic parameter δ of the horizontal transverse isotropic stratum can be estimated by this technique as well.

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.

Evaluating the structural model from ambient vibration recordings and shallow seismic refraction techniques. A case study of Zagazig City, Egypt

This study uses the seismic refraction and noise measurements to investigate the velocity structure of the subsurface and emphasize the advantage of ambient vibration over the conventional seismic refraction technique. Field measurements were carried out at nine sites in and around Zagazig city. Shallow seismic refraction data were interpreted using the delay time method to obtain the two-dimension ground model at each site. Ambient vibration arrays are used to infer the one-dimensional compressional and shear wave velocity profiles through two main steps. The first step is to derive the dispersion curve from the recorded signals using the frequency-wavenumber method. The second is to invert the dispersion curve to obtain the site velocity profiles. The results of the compressional wave velocities obtained from seismic refraction technique showed that the subsurface consists of a number of layers ranging from two to four layers and give a good agreement with the results of the seismic wave velocities obtained from the ambient vibration arrays. The ambient vibration arrays gave a deeper depth of penetration than the other method, providing more information on the subsurface structure without any disturbance to the environment. This work provides reliable estimates of the seismic velocity structures of both shallow and deep sedimentary layers within the area of interest.

IMPROVEMENT AND CHARACTERIZATION OF SABKHA SOIL OF SAUDI ARABIA: A REVIEW

Sabkha is an inferior and indigenous type of soil which forms widely in the Arabian Gulf and in many parts of Saudi Arabia, especially in the coastal areas. Several studies over the last 25 years have been conducted to develop a better understanding and characterization of Sabkha soil and to improve its strength and durability. Different studies from different perspectives, different geographical locations, and particular types were discussed with specific treatment for its improvement. The main purpose of this study is to conclude Saudi Arabian Sabkha Soil characteristics, its associated problems, and to recapitulate the current technologies and practices for the improvement of it. The relative advantages and some of the drawbacks of currently available techniques have also been discussed. Scope and future development regarding this field have also been summarized. Preloading technique was found to be effective for stabilization and consolidation of Sabkha soil over longer period of time. Another study revealed characterizing Saudi Arabian Sabkha soil using seismic refraction technique. Other comparative research was studied which focused on the improvement of Sabkha soil for road construction using geotextile and cement additives. The results suggest that both of the techniques have similar effect on the improvement of subgrade but the geotextile application is more economical as compared to others. Geotextile (grade A-400) with greater strength and thickness exhibits higher load carrying capability which leads to less deformation settlement on the subgrade.

Procedure and evidence of seismic research into physical properties of cohesive soils

The article puts forward a procedure to determine structure and physical properties of nearsurface cohesive soil based on seismic surveying. The backbone of the approach is the use of distribution of P- and S-waves obtained from combination of the seismic refraction technique modification and the multichannel surface wave analysis. The recovery of the physical properties uses correlation dependences. The authors give an example of field data processing. The field research covered a section of a motor road where groundwater level is determined and zones subjected to washout and deformation are detected.

Compressive and Shear Wave Velocity Profiles using Seismic Refraction Technique

Seismic refraction measurement is one of the geophysics exploration techniques to determine soil profile. Meanwhile, the borehole technique is an established way to identify the changes of soil layer based on number of blows penetrating the soil. Both techniques are commonly adopted for subsurface investigation. The seismic refraction test is a non-destructive and relatively fast assessment compared to borehole technique. The soil velocities of compressive wave and shear wave derived from the seismic refraction measurements can be directly utilised to calculate soil parameters such as soil modulus and Poisson’s ratio. This study investigates the seismic refraction techniques to obtain compressive and shear wave velocity profile. Using the vertical and horizontal geophones as well as vertical and horizontal strike directions of the transient seismic source, the propagation of compressive wave and shear wave can be examined, respectively. The study was conducted at Sejagung Sri Medan. The seismic velocity profile was obtained at a depth of 20 m. The velocity of the shear wave is about half of the velocity of the compression wave. The soil profiles of compressive and shear wave velocities were verified using the borehole data and showed good agreement with the borehole data.

Soil Velocity Profile on Soft Soil Using Seismic Refraction

Soil velocity profile often used as subsurface characterization by using geophysical technic. Seismic refraction is one of geophysical technique to determine primary wave (p-wave) velocity of soil profile. In this paper, seismic refraction technique has been performed on two different types of soft soil (peat soil and RECESS clay) for comparison of its p-wave velocity soil profile. From p-wave velocity soil profile comparison, its show the peat soil has soil velocity range from 211 m/s – 534 m/s at depth of 0 – 4 m while the soft clay show soil velocity range from 248 m/s – 1842 m/s at depth of 0 – 5.5 m. The profiles of peat soils and RECESS clay have been verified using peat samplers and existing borehole data. Both of velocity soil profiles, indicated that peat soil have lower velocity compare with soft clay due to its unique and soft soil characteristics. The difference of p-wave velocity soil profile between peat soil and soft clay are clearly showed both soils have different soil p-wave velocity with different soils characteristics.

Subsurface investigation on Quarter 27 of May 15th city, Cairo, Egypt using electrical resistivity tomography and shallow seismic refraction techniques

Geophysical tools such as electrical resistivity tomography (ERT) and shallow seismic (both P-wave seismic refraction and Multi-channel Analysis of Surface Waves (MASW)) are interesting techniques for delineating the subsurface configurations as stratigraphy, structural elements, caves and water saturated zones. The ERT technique is used to delineate the contamination, to detect the buried objects, and to quantify some aquifer properties. Eight 2-D (two dimensional) electrical resistivity sections were measured using two different configurations (dipole–dipole and Wenner). The spread length is of 96m and the electrodes spacing are 2, 4 and 6m, respectively to reach a depth ranging from 13 to 17m. The results indicate that, the subsurface section is divided into main three geo-electrical units, the first is fractured marl and limestone which exhibits high resistivity values ranging from 40 to 300ohmm. The second unit is corresponding to marl of moderate resistivity values and the third unit, which is the deeper unit, exhibits very low resistivity values corresponding to clayey marl. The fourth layer is marly clay with water. The presence of clay causes the most geotechnical problems. Fourteen shallow seismic sections (both for P-wave and MASW) were carried out using spread of 94m and geophone spacing of 2m for each P-wave section. The results demonstrate that the deduced subsurface section consists of four layers, the first layer exhibits very low P-wave velocity ranging from 280 to 420m/s, the second layer reveals P-wave velocity ranging from 400 to 1200m/s, the third layer has P-wave velocity ranging from 970 to 2000m/s and the fourth layer exhibits high velocity ranging from 1900 to 3600m/s. The ERT and shallow seismic results, reflect the presence of two parallel faults passing through Quarter 27 and trending NW-SE.

Constraints on the shallow velocity structure of the Lucky Strike Volcano, Mid-Atlantic Ridge, from downward continued multichannel streamer data

The shallow velocity structure of the Lucky Strike segment of the Mid-Atlantic Ridge is investigated using seismic refraction and reflection techniques applied to downward continued multichannel streamer data. We present a three-dimensional velocity model beneath the Lucky Strike Volcano with unprecedented spatial resolutions of a few hundred meters. These new constraints reveal large lateral variations in P wave velocity structure beneath this feature. Throughout the study area, uppermost crustal velocities are significantly lower than those inferred from lower resolution ocean bottom seismometer studies, with the lowest values (1.8–2.2 km/s) found beneath the three central volcanic cones. Within the central volcano, distinct shallow units are mapped that likely represent a systematic process such as burial of older altered surfaces. We infer that the entire upper part of the central volcano is young relative to the underlying median valley floor and that there has been little increase in the layer 2A velocities since emplacement. Layer 2A thins significantly across the axial valley bounding faults likely as the result of footwall uplift. The upper crustal velocities increase with age, on average, at a rate of ~0.875 km/s/Myr, similar to previous measurements at fast-spreading ridges, suggesting hydrothermal sealing of small-scale porosity is progressing at normal to enhanced rates.