Who uses the modified Mercalli scale?

The Modified Mercalli Scale shows the intensity of an earthquake.

The scale indicates the perceived intensity of ground shaking based on the damage caused by an earthquake to buildings and infrastructure and the opinions of witnesses as to the severity of the felt ground movement.

In order to attempt to quantify the Mercalli scale and decrease it's reliance on the subjective opinion of witnesses, the USGS also include data of measured ground accelerations taken from seismometers in the formulation of the Mercalli value.

Please see the related questions for further information on the measurement of earthquake strength.