Question

Mohorovicic discontinuity is commonly defined as the depth at which \(\underline{\hspace{1cm}}\).

• A. the p-wave velocity decreases to 5.6 km/sec
• B. the p-wave velocity exceeds 7.6 km/sec
• C. the s-wave velocity exceeds 3.57 km/sec
• D. the p and s waves exceed 5.6 km/sec and 3.57 km/sec respectively

Hint:

Moho = Boundary between Crust and Mantle. It's defined by seismic waves suddenly speeding up. Specifically, P-waves jump from \(\sim\)7 km/s to \(\sim\)8 km/s.

Answer 1

The Correct Option is B

Step 1: Define the Mohorovičić Discontinuity (Moho). The Moho marks the boundary between the Earth's crust and mantle.

Step 2: Explain how it's found. The Moho is identified by a sudden increase in seismic wave speed (P-waves and S-waves). This speed increase happens because the mantle is denser and more solid than the crust.

Step 3: Detail the velocity change. P-wave velocity in the lower crust is usually 6.7–7.2 km/s. Crossing into the mantle, it jumps to 7.6–8.6 km/s. Thus, the Moho is characterized by a sharp P-wave velocity increase to over 7.6 km/s.

Conclusion: Option (B) best describes this seismic velocity change.