The Mercalli scale is a seismic scale used to measure the intensity of an earthquake. The measurement is based on observations and experiences, and it is currently measured on a scale of 12 degrees of intensity, indicated by Roman numerals I through XII.
The original Mercalli scale was formulated in the late 1800s and early 1900s as a 10-degree scale. It was later modified several times, and its current form is known as the Modified Mercalli scale. The lower end of the scale is based on reports from people regarding the intensity of the effects they experienced, and the data is collected to form maps of intensity. The upper levels are generally based on observations of destruction caused by an earthquake, such as structural damage. The Mercalli scale differs from the Richter scale, which measures the magnitude of earthquakes.