The statement true about the Mercalli scale is "The scale rates an earthquake according to how much damage it causes."
Explanation:
The Mercalli Scale is a way to rate the earthquakes according to the level of damage at a given place. It got its name after the Italian seismologist Giuseppe Mercalli . The scale has 12 divisions. Lower numbers indicate intensity that is likely felt by people where as the higher numbers indicates the damage to structures and buildings. The ratings are given in Roman numerals. This scale is presently called as the MMI scale, or the Modified Mercalli scale.