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 is the boundary surface between the Earth's crust and the mantle.

Step 2: Describe how it is identified. 
It is identified by a distinct and rapid increase in the velocity of seismic waves (both P-waves and S-waves). This is because the mantle below is significantly denser and more rigid than the crust above.

Step 3: Quantify the velocity change. 
P-wave (primary wave) velocity in the lower crust is typically 6.7–7.2 km/s. Upon crossing the Moho into the mantle, it abruptly increases to 7.6–8.6 km/s. Therefore, the depth where the P-wave velocity sharply increases to over 7.6 km/s is the defining characteristic of the Moho. 

Conclusion: Option (B) provides the best description of this seismic velocity jump.