Seismic surface waves travel along the Earth's surface. They can be classified as a form of mechanical surface waves. They are called surface waves, as they diminish as they get further from the surface. They travel more slowly than seismic body waves (P and S). In large earthquakes, surface waves can have an amplitude of several centimeters.
Additional scales were developed – a surface-wave magnitude scale (M s) by Beno Gutenberg in 1945, a body-wave magnitude scale (mB) by Gutenberg and Richter in 1956, and a number of variants – to overcome the deficiencies of the M L scale, but all are subject to saturation.