Question

There is a 9.0 earthquake that just hit San Diego! There have been multiple aftershocks at a 6.0 magnitude. How much weaker are these aftershocks compared to the original earthquake?

a. 3000x weaker
b. 1000x weaker
c. 100x weaker
d. 10x weaker

Answer 1

The magnitude is used to quantify the size of the earthquakes (measures the energy released during the breakdown of a fault) while the intensity is a qualitative description of the effects of the earthquakes (it involves the perception of people as well as damage material and economic suffered due to the event). The relation between intensity and magnitude is

$\frac{I_1}{I_2} =10^{(M1-M2)}$

Here,

M = Magnitude

I = Intensity of each one

Given

$M_1 = 9$

$M_2 =6$

Replacing,

$\frac{I_1}{I_2} =10^{(9-6)}$

$\frac{I_1}{I_2} = 10^3$

$\frac{I_1}{I_2} = 1000$

So the aftershocks are 1000x weaker compared to the original earthquake. The correct answer is B.