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Underground Mapping and Technologies: Seismic Imaging with GPR
- Gökçe Bal
- Oct 7, 2025
- 5 min read
Have you ever wondered about the hidden world beneath the streets of a city? Beneath the concrete and soil lie subway tunnels, pipelines, ancient ruins, and groundwater. Exploring this unseen world is like looking at the Earth's crust with an X-ray. Underground mapping is a process developed to pinpoint the location of this invisible infrastructure and geological layers.
Contents:
Ground Penetrating Radar
Subsurface mapping, like surface mapping, reveals subsurface layers and objects in three dimensions. For example, before starting a highway project, they must be able to see beneath the ground to avoid damaging old water pipes or electrical cables. Similarly, geologists use these methods to detect structures below the surface when exploring for oil and minerals. In essence, geophysics helps discover resources such as oil, gas, minerals, and water by measuring the physical properties of the subsurface. In short, in many areas, from infrastructure planning to resource exploration, mapping the invisible world beneath the earth makes projects both safer and more efficient.
Mapping with Ground Penetrating Radar (GPR)
One of the most well-known methods of mapping the subsurface is Ground Penetrating Radar (GPR) . GPR ( Ground Penetrating Radar) is, in practice, a ground-penetrating version of a radar device. High-frequency electromagnetic waves (radio waves) are sent from an antenna attached to the device; these waves hit different layers beneath the soil and are reflected back. When these signals are collected, the arrival time and amplitude of the signals are calculated to create a subsurface map . In other words, it's like scanning beneath the asphalt with an X-ray machine.
In practice, GPR scans are performed with antennas mounted on a vehicle's wheels or back. Their applications are diverse:
Utilities detection: GPR locates buried infrastructure (such as sewer, rainwater, drinking water, natural gas, electricity, fiber-optic communication lines, and underground tanks) without interruption. For example, before a subway tunnel is opened, GPR scans the excavation site to locate old pipes and cables.
Soil survey: Before building road, dam, building, or bridge foundations, GPR measures soil layers, hardness, and moisture content. This allows engineers to make safe designs with advance knowledge of ground conditions.
Tunnel and gallery surveys: Large voids such as underground tunnels or mine galleries can be imaged with GPR, preventing voids from forming beneath new excavations.
Interior scanning: GPR can also map rebar, cracks, or voids in walls, ceilings, and floors of buildings. It is particularly useful for non-destructive inspection of historic structures.
Archaeology and forensic science: GPR allows archaeologists to locate ancient city ruins, tombs, or buried treasure without excavation. It is also used outside of archaeology to locate mass graves at battlefields.
GPR: Arkeolojik Tarama Mining exploration: Operations such as identifying near-surface mineral veins or detecting voids in mine galleries can be performed with GPR.
One of the greatest advantages of using GPR is its trenchless exploration . GPR prevents unnecessary excavations in pre-mapped areas, saving time and money. For example, conducting a GPR scan before laying a new stormwater line prevents damage to underlying infrastructure, such as electricity or natural gas lines, during the excavation. This significantly reduces the risk of malfunctions and outages in urban networks. In short, GPR enables the safe mapping of underground resources and infrastructure, allowing us to anticipate unexpected problems on projects.
Mapping with Seismic Method
Seismic imaging is another fundamental technique for examining the subsurface. We can compare older methods to sound imaging : We create maps by listening to the reflections of vibration waves sent underground. This typically involves creating seismic waves in the field with a vibroseismus or small controlled explosion, then recording the waves that propagate to the surface and bounce back using sensors called geophones. The collected data is then processed by computers to determine the depth of strata and the location of structures.
The application areas of the seismic method are:
Hydrocarbon (oil and natural gas) exploration: Seismic exploration is perhaps the most critical method in the oil and gas industry. As is well known, drilling is very expensive; therefore, seismic scanning is first conducted over a large area. By analyzing the incoming reflections, the geometry of the rock layers underground is understood. These analyses help identify potentially productive oil and gas reservoirs. For geologists, seismic exploration is crucial for locating potential hydrocarbon reserves. For example, in Turkey , seismic research vessels such as the Barbaros Hayrettin Paşa and Oruç Reis are exploring new energy fields by imaging subsea rock structures to depths of 8–15 km in the Black Sea.
Mineral and geothermal exploration: Seismic measurements are also used to locate underlying mineral deposits or geothermal springs. Mining engineers use this data to identify ore-focused drilling locations.
Civil and infrastructure engineering: Before large structures like bridges, dams, or high-rise buildings are built, the ground structure is examined in detail. Seismic data reveals the different layers and cracks within the ground, allowing engineers to predict earthquake and settlement risks. Therefore, seismic imaging is critical for ensuring a building or bridge is placed on solid ground.
Earthquake engineering and risk analysis: Mapping fault lines and block boundaries is as important as the region's earthquake history. Seismic methods (such as seismic tomography) reveal the three-dimensional shape of ground faults, contributing to the design of potentially earthquake-resistant structures.
Groundwater and environmental studies: Groundwater and aquifer basins can be mapped using seismic recordings. This provides answers to environmental questions such as how much groundwater is in each area and how pollution spreads.
In short, seismic imaging offers more effective mapping over large areas or at greater depths. Because it uses waves at the speed of sound over long distances, it can image underground structures even kilometers deep. In the future, new data processing techniques and AI-powered algorithms will make this technology even more powerful.
Its Importance for Infrastructure Planning and Resource Exploration
GPR and seismic methods play critical roles in urban infrastructure and energy and mineral exploration:
Trenchless Work: In major cities like Istanbul, Ankara, and Izmir, GPR allows infrastructure lines to be pre-determined. This prevents unnecessary excavations and traffic disruptions, allowing projects to be completed quickly and safely.
Resource Exploration: Turkey's geothermal, coal, and mineral potential are being revealed through seismic methods. With this data, MTA engineers can produce detailed underground maps of energy and water resources.
Disaster Management: Underground maps reduce earthquake risk by identifying fault lines and contribute to safe construction.
Environmental Sustainability: Sustainable water management and environmental protection are supported by mapping aquifers, water levels and pollution areas.
In short, these technologies not only make projects safer but also enable us to manage natural resources and cities more consciously. Today, maps encompass not only the surface but also the subsurface.
Looking to the Future in Underground Mapping
While GPR and seismic methods currently offer critical advantages in many applications, the technology is rapidly evolving. 3D underground models are now easier to create, and data can be automatically classified using artificial intelligence. Drone or robotic surveying systems can perform precise scanning even in remote areas. In the future, these methods will enable surveyors and geophysicists to obtain much faster and more precise results. This will make underground treasures and risks much more visible.
Ultimately, underground mapping technologies not only reveal the location of new resources; they also make our cities smarter and our plans more secure. Discovering the secrets buried beneath the earth may be an endless endeavor, but each new measurement opens a small window into the darkness. With the tools we have today, we can illuminate the earth's interior as well as its exterior—and with every step we take, we move forward with greater confidence.
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