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EARTHQUAKES

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 quakes:
            a magnitude 6 quake (no hyphen)
            recording 7.1
            2.5 to 3 magnitude tremor (do not use decimals with round numbers)

Magnitude is abbreviated M:
            an M 7.3 quake

Do not hyphenate P waves and S waves as nouns.