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GEOPHYSICAL METHOD - Coggle Diagram
GEOPHYSICAL METHOD
SEISMIC METHOD
Principle
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Reflection is seismic signal reflected back to the surface at layer interfaces. The recorded at distance less than depth of investigation.
Refraction is the signals returns to the surface by refraction at subsurface interfaces. The recorded at distance is more than depth
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Instrument
Geophone
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More Info
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Main application for reflection is basin application while for refraction is basin application, crustal study and plate tectonics
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GRAVITY METHOD
Principle
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The gravimeter used in relative measurement is a mass loaded spring or acceleration and the gradient
The gravity is influenced positively if causative body is heavier, larger and occur at shallow depth
If subsurface has heavier body, the gravity pull more (+g) and
spring extends longer
If surface bodies that has different density from surrounding, the gravity deviates from the normal value
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Instrument
Gravimeter
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More Info
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Main application are mining, hydrology, plate tectonics, mantle dynamics and core dynamics
Survey method can be performed by on the land, airborne or spaceborn
Main obstacle is the relatively small variations in densities of rock. Due to this, the gravimeter is super sensitive with gal unit
Procedure
- Determine the location of latitude, longitude and elevation of the gravity stations
- One station act as local base station) must be located and has to be reoccupied every half to 1 hour or so to obtain the natural drift of the instrument
- Take gravity readings at regular intervals along a traverse that crosses the expected location of the target
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