Which of the following sources is/are used in land seismic surveys?
Show Hint
- Vibrosis
- Dynamite
- Airgun
- Thumper
The Correct Option is A, B, D
Solution and Explanation
A seismic source is the device used to send energy, in the form of vibrations, into the ground. The waves that bounce back off rock layers are picked up by receivers called geophones, and this data is used to map the subsurface. Different sources work in different settings. Some only work on land, some only work in water.
Step 2: Check option (A), Vibrosis.
This refers to the Vibroseis method, where a heavy truck fitted with a vibrating plate presses onto the ground and sends a long, controlled sweep of vibrations into the earth. It is one of the most common sources for land seismic surveys, especially in areas where explosives cannot be used, such as near towns. So option (A) is correct.
Step 3: Check option (B), Dynamite.
Dynamite, or other explosive charges, is placed in a shallow drilled hole and set off to create a sharp, strong burst of seismic energy. This has been used in land seismic surveys for many decades and is still used where the terrain allows shot holes to be drilled. So option (B) is correct.
Step 4: Check option (C), Airgun.
An airgun releases a burst of compressed air into water, which makes a sharp pressure pulse. It only works underwater since it needs water around it to transmit the pulse well, so it is used in marine seismic surveys, not on land. Option (C) does not belong here.
Step 5: Check option (D), Thumper.
A thumper, also called a weight drop source, is a truck mounted heavy weight that is lifted and dropped onto a steel plate on the ground, sending a sharp impact into the earth. This is a classic land seismic source, used where vibroseis trucks or explosives are not practical. So option (D) is correct.
Step 6: Final answer.
The vibrator truck, dynamite and the thumper all generate seismic waves through direct contact with the ground, while the airgun needs a body of water to work and belongs to marine surveys.
\[ \boxed{\text{(A), (B) and (D)}} \]
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