Some ways to record earthquakes (ground velocity or acceleration), there is a particular range of frequencies with the most energy, and only tiny earthquakes have these peaks in the audible range. The attenuation during wave propagation usually means there is little energy above 20 Hz or so in the motion at the surface. Sensors deep in the ground can record motions up to 100 Hz if the earthquakes are close enough.

The scaling is generally that if the seismic moment is 1000 times greater, the duration of the earthquake is ten (cube root) times longer, and the pitch is ten times lower frequency. A difference of a factor of 1000 in moment translates to 2 magnitude units. I think M4 events are roughly 1 Hz, so M6s would be 0.1 Hz, and M2s 10 Hz.