Question

Choose the CORRECT statement(s) on the phenomenon of spatial aliasing of seismic data.

• A. Spatial aliasing can be reduced by increasing the geophone (group) spacing
• B. Spatial aliasing is more likely to occur for higher temporal frequencies in the data
• C. Subsurface formations with higher interval velocities increase the likelihood of spatial aliasing
• D. Reflections from steep dips are more likely to be spatially aliased

Hint:

Spatial aliasing worsens with high frequencies and steep dips. To reduce aliasing, use smaller geophone spacing or apply anti-alias filters.

Answer 1

The Correct Option is B, D

Step 1: Concept of spatial aliasing.
Spatial aliasing occurs when seismic data is sampled too sparsely in space, causing different dips or wavenumbers to become indistinguishable. It is similar to temporal aliasing but applies in the spatial domain. The Nyquist criterion requires that the spatial sampling interval $\Delta x$ must satisfy: \[ \Delta x \leq \frac{v}{2 f \sin\theta} \] where $v$ = velocity, $f$ = temporal frequency, and $\theta$ = dip angle. Step 2: Checking each option.
- (A) Spatial aliasing can be reduced by increasing the geophone spacing.
This is incorrect. Increasing spacing worsens aliasing because fewer samples are taken. To reduce aliasing, spacing must be decreased. - (B) Spatial aliasing is more likely for higher temporal frequencies.
Correct. From the formula above, higher $f$ reduces the allowed spacing, so aliasing is more likely. - (C) Higher interval velocities increase likelihood of aliasing.
Incorrect. Higher velocity actually reduces aliasing because the allowable spacing ($v / 2f \sin\theta$) increases. - (D) Reflections from steep dips are more likely to be aliased.
Correct. Larger $\sin\theta$ (steeper dips) makes the denominator larger, reducing the allowable spacing and increasing aliasing risk. Step 3: Final Answer.
Thus, the correct statements are (B) and (D). \[ \boxed{\text{Correct Answer: (B), (D)}} \]