# The P-waves have a speed of about 6 km/s. How do you estimate the average bulk modulus of Earth's crust given that the density of rock is about 2400 kg/m3. Answer the question in Pa?

## Earthquakes at fault lines in Earths crust create seismic waves, which are longitudinal (P-waves) or transverse (S-waves).

Jan 31, 2018

The bulk modulus is $= 8.64 \cdot {10}^{4} M P a$

#### Explanation:

Apply the equation

${v}_{p} = \sqrt{\frac{M}{\rho}}$

Here,

The density of the rock is $\rho = 2400 k g {m}^{-} 3$

The speed of the $\text{P-wave}$ is ${v}_{p} = 6 k m {s}^{-} 1 = 6000 m {s}^{-} 1$

Therefore,

$M = \rho {v}_{p}^{2} = 2400 \cdot {6000}^{2} \frac{k g}{m} ^ 3 \cdot {m}^{2} / {s}^{2}$

$= 8.64 \cdot {10}^{10} P a$

$= 8.64 \cdot {10}^{4} M P a$