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?

Question

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

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Answer 1 · 2018-01-31T07:41:30

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

Apply the equation

$v_{p} = \sqrt{\frac{M}{ρ}}$ $v_p=sqrt(M/rho)$

Here,

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

The speed of the $P-wave$ $"P-wave"$ is $v_{p} = 6 k m s^{- 1} = 6000 m s^{- 1}$ $v_p=6kms^-1=6000ms^-1$

Therefore,

$M = ρ v_{p}^{2} = 2400 \cdot 6000^{2} \frac{k g}{m^{3}} \cdot \frac{m^{2}}{s^{2}}$ $M=rhov_p^2=2400*6000^2 (kg)/m^3*m^2/s^2$

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

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