Question

The average density of Earth's crust $10km$ beneath the surface is $2.7gm/c{m}^3$. The speed of longitudinal seismic waves at that depth is $5.4km/s$. The bulk modulus of Earth's crust considering its behaviour as fluid at that depth is:

• A. $7.9\times {10}^{7}Pa$
• B. $5.6\times {10}^{10}Pa$
• C. $1.46\times {10}^{7}Pa$
• D. $7.9\times {10}^{10}Pa$

Answer 1

The correct option is D $7.9\times {10}^{10}Pa$

Given, average density of the Earth's crust.

$\rho =2.7gm/c{m}^3=2.7\times {10}^{3}kg/m^3$

Speed of the waves,

$v=5.4km/s=5.4\times {10}^{3}m/s$

From Newton's formula,

$v=\sqrt{\frac{B}{\rho }}$

$B=v^2\rho$

$B=(5.4\times {10}^3{)}^2(2.7\times {10}^3)$

$B=7.9\times {10}^{10}Pa$

Final answer : (a)