Question

The given beach-ball figure denotes the focal mechanism corresponding to which one of the following faults? \includegraphics[width=0.5\linewidth]{16.png}

• A. oblique slip normal
• B. thrust
• C. strike-slip
• D. normal

Hint:

Remember: - Strike-slip = quadrants in checkerboard pattern (alternating). - Normal = dark on sides. - Thrust = dark on top and bottom. This helps in quick identification of focal mechanisms.

Answer 1

The Correct Option is C

Step 1: Understanding the beach-ball (focal mechanism).
A beach-ball diagram represents the fault-plane solution of an earthquake using seismic wave first-motion patterns. The shaded quadrants indicate compression, while the unshaded quadrants represent dilation. Step 2: Identifying the pattern.
The given beach-ball diagram shows alternating quadrants shaded and unshaded in a cross-like symmetry. This pattern is characteristic of strike-slip faulting, where the motion is dominantly horizontal. Step 3: Eliminating incorrect options.
- Oblique slip normal: Involves both dip-slip and strike-slip; its focal mechanism would not show perfect quadrant symmetry.
- Thrust: Produces two opposite shaded quadrants on top and bottom, unlike the given pattern.
- Normal: Produces two opposite shaded quadrants on left and right, also not matching the figure.
Thus, the alternating quadrant pattern uniquely corresponds to a strike-slip fault. \[ \boxed{\text{Hence, the focal mechanism corresponds to a strike-slip fault.}} \]