Our Methods
Geophysical Methods
Seismic P- and S-wave Reflection
The principles of seismic P-wave reflection for the near surface involve using primary waves (P-waves) to study shallow subsurface geological formations. This method involves generating P-waves artificially, which then travel through the subsurface and reflect off interfaces between different geological materials. The travel times and amplitudes of these reflected waves can be analyzed to determine the depth, thickness, and composition of the subsurface layers. This technique is widely used in applications such as civil engineering, hydrogeology, and archaeology, where understanding near-surface geology is essential. The principles of seismic S-wave reflection method uses artificially generated S-waves, which are slower than primary waves (P-waves) and can only propagate through solid media. This method is particularly effective for detecting variations in shear strength, which can be vital for construction projects, landslide prediction, and studying shallow geological phenomena. As S-waves are less affected by water saturation than P-waves, their use in near-surface applications often provides more accurate subsurface images, especially in wet or fluid-saturated environments.
Seismic Refraction
The seismic refraction method is a geophysical technique used for investigating subsurface geological structures and layers. It is based on the principle that seismic waves change speed when they pass through different types of materials or layers in the Earth’s subsurface. This speed change often leads to refraction, or a bending of the seismic wave’s path. By measuring the travel times of seismic waves from a source to various detectors or geophones, it’s possible to calculate the velocities of the waves in different layers. This allows us to map the subsurface structures based on variations in seismic velocity. The method is particularly effective for delineating geologic layers and identifying features such as the depth to bedrock or the water table.
Downhole Seismic
Downhole seismic surveys for the near surface involve the use of seismic waves, primarily P-waves and S-waves, to characterize the subsurface geological formations from within a borehole. In this method, a seismic source is placed on the ground surface or in a shallow borehole, while the receivers (geophones or accelerometers) are deployed in the same or another borehole. The source generates seismic waves that travel downward through the subsurface and are recorded by the downhole receivers. By measuring the time it takes for these waves to travel from the source to the receivers, the seismic velocity of the intervening geological layers can be determined. This method is often used to measure the velocity of P-waves and S-waves in the near surface, providing valuable information about the mechanical properties of the rock or soil, such as stiffness and strength. These measurements can be used in a variety of applications including site characterization for construction, assessing the stability of slopes, earthquake site response analysis, and locating subsurface geological features.
Multichannel Analysis of Surface Waves (MASW)
Multichannel Analysis of Surface Waves (MASW) is a non-invasive geophysical method employed to determine the shear-wave velocity profile of the near-surface subsurface. The fundamental principle behind MASW involves recording and analyzing surface waves, specifically Rayleigh waves, which are seismic waves that travel along the surface of the Earth. A seismic source generates these surface waves, which then propagate through the subsurface and are recorded by an array of geophones positioned on the ground surface. The geophones record the ground motion caused by the passing surface waves, and the collected data is then processed and analyzed to create dispersion curves that show the variation of wave velocity with frequency. These dispersion curves are then inverted to obtain a shear-wave velocity profile of the subsurface. This profile provides critical information about the elastic properties of the subsurface layers, helping to evaluate the mechanical properties of the near surface, and hence, the site’s suitability for construction, its seismic risk, and other geotechnical aspects.
Refraction Microtremor (ReMi)
The Refraction Microtremor (ReMi) method is a geophysical technique used for assessing the near-surface shear-wave velocity. The key principle of ReMi involves utilizing ambient seismic noise, or “microtremors,” as the seismic source instead of actively generated waves. This method records the naturally occurring surface waves (Rayleigh waves) using an array of seismometers or geophones. Through analysis of these recordings, the method generates a dispersion curve representing the relationship between wave velocity and frequency. This dispersion curve is subsequently inverted to obtain a shear-wave velocity profile of the near surface. ReMi is particularly useful for determining the average shear-wave velocity down to a depth of 30 meters (Vs30), a key parameter for site-specific seismic hazard analyses and ground motion prediction. The technique offers an efficient and less intrusive alternative to active source methods, particularly in urban or sensitive environments.
Electrical Resistivity & IP
Electrical resistivity and induced polarization (IP) are geophysical methods used to probe the near-surface subsurface by investigating its electrical properties. In the electrical resistivity method, an electrical current is introduced into the ground through a pair of electrodes, and the resulting potential difference is measured through another pair of electrodes. The degree to which the subsurface resists the flow of this current is known as its resistivity, which varies with the type and condition of the material, including its porosity, saturation, salinity, and temperature. In the induced polarization method, a primary electric current is applied, and after it is switched off, the decay of the voltage is measured. This response provides information about the subsurface’s ability to polarize under an applied electric field, which is influenced by factors such as mineral content, grain size, and the presence of fluids. These methods are particularly useful in applications like groundwater exploration, mineral prospecting, and environmental surveys, providing a non-invasive means to identify and map variations in subsurface properties.
Self-Potential (SP)
The Self-Potential (SP) method, also known as spontaneous potential, is a passive geophysical technique used to measure the natural electric potential differences in the Earth’s subsurface, without the need for an artificial electrical source. These potential differences are primarily generated by electrochemical reactions between different types of soil and rock materials, the flow of groundwater, and variations in temperature or concentration of certain ions. In an SP survey, electrodes are placed on the ground surface to record the variations in the natural electric field. By mapping these potential differences, we can infer the distribution of subsurface properties that influence the electric potential, such as the presence of water, mineral deposits, or hydrocarbon accumulations. The SP method has a wide range of applications, including exploration for mineral and water seepage from dams and leeves, hydrogeological investigations, and geothermal energy exploration.
Electromagnetic (EM)
Electromagnetic (EM) surveys are a type of geophysical method used to investigate the electrical conductivity of the near-surface subsurface. This is accomplished by generating an electromagnetic field using a transmitter coil and measuring the resultant secondary electromagnetic field using a receiver coil. When the primary electromagnetic field interacts with the subsurface, it induces electric currents known as eddy currents, which generate the secondary electromagnetic field. The strength and phase of this secondary field are related to the electrical conductivity of the subsurface. Different materials, including rocks, minerals, water, and contaminants, have different conductivities, and so they generate different secondary electromagnetic responses. By measuring these responses, EM surveys can identify and map variations in subsurface conductivity. This technique is commonly used in mineral exploration, groundwater surveys, and environmental studies.
Ground Penetrating Radar (GPR)
Ground Penetrating Radar (GPR) is a non-invasive geophysical technique used to image the subsurface of the Earth. The method involves transmitting high-frequency radio waves into the ground and recording the reflected signals. When the radar wave encounters a boundary between materials with different electrical properties, a portion of the energy is reflected back to the surface, while the rest continues deeper. The reflected signals are recorded by a receiver, and the travel times of these signals are used to determine the depth of the reflecting boundaries. The strength of the reflection is dependent on the contrast in electrical properties between different materials, allowing GPR to detect changes in material composition and the presence of objects or structures in the subsurface. GPR is widely used in a variety of fields, such as geology, archaeology, environmental studies, and civil engineering, providing a rapid and detailed image of the near-surface subsurface.
Magnetic Surveying
Magnetic surveying is a geophysical method used to measure variations in the Earth’s magnetic field caused by the presence of magnetic minerals in the subsurface. The basic principle involves the detection of anomalies, or differences, in the Earth’s magnetic field that are caused by variations in the magnetization of the subsurface rocks. These anomalies can be measured using a magnetometer, an instrument sensitive to magnetic fields. Depending on the type and concentration of magnetic minerals present, different rocks will produce different magnetic fields. By mapping these magnetic anomalies, we can infer the distribution of magnetic minerals in the subsurface and thus detect geological structures or features. Magnetic surveys are used in various applications including mineral and hydrocarbon exploration, archaeology, and unexploded ordnance detection, providing a non-invasive way to probe the near-surface subsurface.
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Our Very Powerful Proven Tool of Training, the FREE Lunch & Learn where we come to your company to give a FREE Training to your team during their lunch time not to interrupt the work while investing in more educated team.
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We organize a two-day workshop on Near-Surface Geophysics that brings professionals, researchers, students, and enthusiasts in the field of geophysics to gain immersive learning experience. The workshop covers a broad range of near-surface geophysical methods, including Seismic Reflection, Reflection, Ground Penetrating Radar (GPR), Electrical Resistivity, Induced Polarization (IP), and more. We share our knowledge through insightful sessions, hands-on exercises, and real-world case studies. Contact us if you are interested in participating in our near-surface geophysics workshop.
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We can gladly organize or help organize a Geophysics Field Camp about near-surface geophysics, specifically designed to take place at your camp and tailored to meet the needs of your students. Upon your request, our experienced team will create a comprehensive program that covers an array of near-surface geophysical techniques, including Seismic Reflection, and Refraction, MASW Ground Penetrating Radar (GPR), and Electrical Resistivity, among others. The field camp encapsulates the entire geophysical survey process, from initial planning and data acquisition, right through to data processing and final interpretation. Our skilled instructors will be on hand to guide students, fostering not just the technical competencies, but also critical fieldwork skills such as problem-solving, and safety awareness. By bringing the theoretical knowledge to life through practical application, our Geophysics Field Camp delivers an engaging and enriching hands-on learning experience for your students.
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We offer a series of compact yet comprehensive Short Courses on near-surface geophysics, with a focus on both the underlying principles and practical applications. These courses are designed to cater to a wide range of individuals, whether you’re a seasoned professional looking to refresh your skills, a student eager to dive into the field, or someone with a keen interest in geophysics. Each course will cover a specific technique such as Seismic Reflection, Ground Penetrating Radar (GPR), Electrical Resistivity, or Induced Polarization (IP). We delve into the fundamental principles that govern each method, followed by exploring how these techniques are used in real-world scenarios such as mineral exploration, environmental surveys, archaeological investigations, and civil engineering projects. The courses will also include hands-on exercises and case studies to ensure a practical understanding of the techniques. Our experienced instructors will guide you throughout your learning journey, creating an engaging and collaborative learning environment. Enroll in our Short Courses to expand your knowledge and skills in near-surface geophysics.
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