Earthquake Magnitude Scale Magnitude Earthquake Effects Estimated Number Each Year 2.5 or less Usually not felt, but can be recorded by seismograph. Millions 2.5 to 5.4 Often felt, but only causes ...

Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number ... think of it in terms of the energy released by explosives: a magnitude 1 seismic wave releases ...