The Richter scale measures the magnitude of an earthquake; the Mercalli scale measures the intensity.
The magnitude is a measure of the amount of energy released at the source of the earthquake, and is determined from measurements on seismographs. The intensity is a measure of the effects of the earthquake on people, man–made structures, and the natural environment, at a given location.
The Richter scale is more correctly known as the local magnitude scale (ML). It has various shortcomings, on account of which most authorities now use other scales, such as the moment magnitude scale (MW), to report earthquake magnitudes. Much of the news media however still refers to these as "Richter" magnitudes. In fact this is not so far from the truth, as all magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values.
© Haydn Thompson 2018