What is Seismic Imaging?

Jason C. Chavis
Jason C. Chavis
Scientist with beakers
Scientist with beakers

Seismic imaging is the process of investigating the physical characteristics underneath the surface of the earth. The technique, also known as geophysical imaging, uses the process of revealing sections of the Earth with a wave of energy. In order for a researcher to perform a seismic image, a geophysical tomograph must be utilized. The image is referred to as a tomogram. Since seismic imaging is considered an applied science, the information gathered through the procedure generally has a practical use.

The activity of performing a geophysical image uses projection tomographs from multiple directions. Each of these angles takes a slice of the Earth's appearance and feeds the data into some sort of processor. Modern techniques use a computer to process the seismic image using tomographic reconstruction software algorithms, essentially placing each slice into one large image. This presents a definitive image of what lies below the earth's surface.

One of the most common forms of seismic imaging is known as electrical resistivity tomography. Electrical measurements are taken from the surface by boring holes into the ground and placing electrodes inside. The method utilizes a direct current that makes an image from the information.

Ground-penetrating radar is also a heavily-used technique to analyze the geophysical information under the surface. This method sends radar pulses into the ground and reflects signals from the various structures in the ground. Usually, the UHF or VHF frequencies of the radio spectrum are used. This is a non-invasive method of detecting various things like rock, structures, openings and water.

The best way to isolate metallic materials such as ores underneath the surface is the concept of induced polarization. Similar to electrical resistivity tomography, an electrical current is sent into the ground and monitored via electrodes to identify voltage. The different resistive frequencies can be measured over a specific time frame. Unlike the other method, however, alternating current is used to provide the seismic image.

Reflection seismology is another form of performing seismic imaging. This allows researchers to send controlled seismic energy into the earth's surface using specialized vibration tools. Once the wave is reflected from an object, it travels back to a receiver, giving the analyst an understanding of the exact depth of the feature in question.

Seismic imaging has a number of different applications. When engineers are looking to construct a building, the presence of underground objects must be ascertained. Also, mineral and oil mining utilize the techniques to help locate resources. The practice is also used for general geological analysis in an effort to study underground features.

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