A numerical scale for measuring the destructive power and major physical effects of an earthquake based on direct observation, modified for North American conditions. The Mercalli scale was first formulated by Giuseppe Mercalli in 1897.

Compare: Richter scale
Number   Typical Results in an Urban Area                                                 
I        hardly noticed by anyone including sensitive animals like birds
II       suspended objects may swing slightly
III      a slight rumble noticed by some people, especially if they are in a tall building
IV       a noticeable vibration that rocks objects slightly
V        felt by most people; small objects may fall
VI       felt by everyone; windows and plaster may break; trees and furniture move
VII      slight to moderate building damage; people knocked down; minor landslides
VIII     moderate to severe damage to buildings; walls fall; trees break; some panic
IX       extensive damage to buildings, foundations, and pipes; general panic
X        roads crack; severe landslides; dams and bridges are severely damaged
XI       major surface changes and collapse of roads, buildings, etc.
XII      total damage to all roads, buildings, etc.; major changes to lakes, rivers, etc.