The problem with these measures is that they don't correlate well. For example, we could use values such as the number of fatalities or injuries, the maximum value of shaking intensity, or the area of intense shaking. Early estimates of earthquake size were based on non-instrumental measures of the earthquakes effects.
The magnitude is the most often cited measure of an earthquake's size, but it is not the only measure, and in fact, there are different types of earthquake magnitude.
SLUĮAS-A193 Class NotesĮarthquake Magnitude
