Question:
Which one among the following events recorded in a land seismic reflection survey using vertical component geophones has the highest apparent slowness?
Which one among the following events recorded in a land seismic reflection survey using vertical component geophones has the highest apparent slowness?
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Always remember: Surface waves (like ground roll) are slower than body waves (P-waves, S-waves). Therefore, they dominate in noise records due to their high apparent slowness.
Updated On: Aug 22, 2025
- Primary P-wave reflection
- Direct wave
- Head wave
- Ground roll
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The Correct Option is D
Solution and Explanation
Step 1: Define apparent slowness.
Apparent slowness is the reciprocal of apparent velocity. A wave with lower velocity will have higher apparent slowness.
Step 2: Compare velocities of given seismic events.
\begin{itemize}
\item Primary P-wave reflection: Travels at the velocity of P-waves, typically the fastest seismic waves in the subsurface (\(\sim 5-8\) km/s). Hence, they have low apparent slowness.
\item Direct wave: Travels along the surface with near-surface P-wave velocity, still faster than surface waves.
\item Head wave: Travels critically refracted along a high-velocity layer, so it appears at high velocity (low slowness).
\item Ground roll: A type of surface wave (Rayleigh/Love wave) that is very slow compared to body waves (velocity \(\sim 0.5-1\) km/s). Because of this very low velocity, it has the highest apparent slowness.
\end{itemize}
Step 3: Conclusion.
Since ground roll has the slowest velocity among the listed events, it corresponds to the highest apparent slowness.
\[
\boxed{\text{Ground roll}}
\]
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