Lowercase earthquake in a name:
Loma Prieta earthquake.
In recent years seismologists have abandoned the familiar Richter
scale for measuring earthquakes and now use the more precise
moment-magnitude scale, which measures the total energy released by
a magnitude 6 quake (no hyphen)
2.5 to 3
magnitude tremor (do not use decimals with round numbers)
an M 7.3 quake
Do not hyphenate P waves and S waves as nouns.