The basic physical properties that are examined include magnetic, gravity, electrical conductivity, radiation and elastic properties.
Physical laws applied are the same as those of physics such as classical (Newtonian) and quantum (modern) mechanics. Example when gravity is measured, two (2) physical Newton laws are applied such as Newton's second law of motion (F=ma) and Newton universal law of gravitation (F=GMm/r2).
What are geophysical properties utilized in Geophysics?
The physical properties are examined as the results of measure the respective physical parameters such as Magnetic susceptibility, density, electrical conductivity, radiation, elastic parameter at which different Geophysical methods such as,
Magnetic, gravity, electrical resistivity, Electromagnetic, Radiometric and seismic methods can be defined. See the table shown in figure 1.
The Golden Rule is that every Geophysical method is related to each physical parameter. However to obtain the detectable results of the body of interest there must be physical contrast of that measured parameter with respect to the background value.
Example we know that the normal gravity value is 9.8m/s2, if we take measurement and 9.7m/s2 is observed, then the physical contrast for gravity is - 0.1m/s2. So physical contrast gives us the Geophysical anomaly.
It means from the previous example the gravity anomaly is - 0.1m/s2, So the Geophysical anomaly can be positive which indicates that there is an increase in magnitude of such physical parameter, while if it negative means there is decrease in magnitude of such physical parameter.
So the subsurface condition or structure of the body of interest including depth and quality can be revealed.
As it measures physical properties, the acquisition (collection) of geophysical data is done by using specialized instruments and sensors such as magnetometers (for Magnetic), gravimeters (for gravity), radiation counters (for Radiation), geophones/hydrophones (for seismic), and resistivity meters (for resistivity).
Geophysical methods can be implemented (applied) in two (2) ways as described here below,
Active methods: These generate artificial signals and send them into the subsurface and measure the modified signals after being passed through it. Example seismic (refraction and reflection), electromagnetic (EM) such as Ground Penetrating Radar (gpr), electrical resistivity, Induced Polarization.
Passive methods: These measure the natural fields of the Earth, they include Self-Potential, gravity, Magnetic.
Geophysics can be broadly grouped into two (2) branches
Theoretical (Pure) Geophysics: This deals with the theoretical concepts to understand the Earth processes, structures through the use of theory of physics. The main primary objective here is to gain an academic interest on the subject.
Applied Geophysics: It deals with the application of physical laws to the Earth to achieve an economic interest. Such as searching for Mineral, groundwater, energy resources like petroleum, coal, Uranium deposits. Also in engineering projects such as civil, environmental, Mining.
Why do we study geophysics?
As described above most of importance of studying this subject is related to its interests
Academic interest: To get familiarized with Earth physical processes such as dynamics, structure, earthquakes, Volcanic eruptions
Applied interest: To achieve an economic aim such as aiding in engineering projects, like site assessment, environmental contaminant remediation, mining designing. Also in extraction and searching of valuable Earth resources, for example Petroleum (oil and gas), Coal, Uranium, groundwater and Mineral resources.
In order to achieve the desired results the resolution of the sensors of the respective Geophysical instruments is a very important factor to be taken into consideration. However the sound knowledge of knowing which method and where it should be applied including its limitations also adds significant value.
Thank you for your attention!.
The table below shows the relation between measured physical property (parameter) with appropriate geophysical method.
Thanks everyone! For this brief introduction on Geophysics.
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