<P> The instrumental scales used to describe the size of an earthquake began with the Richter magnitude scale in the 1930s . It is a relatively simple measurement of an event's amplitude, and its use has become minimal in the 21st century . Seismic waves travel through the Earth's interior and can be recorded by seismometers at great distances . The surface wave magnitude was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events . The moment magnitude scale measures the amplitude of the shock, but also takes into account the seismic moment (total rupture area, average slip of the fault, and rigidity of the rock). The Japan Meteorological Agency seismic intensity scale, the Medvedev--Sponheuer--Karnik scale, and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking . </P> <P> Every tremor produces different types of seismic waves, which travel through rock with different velocities: </P> <Ul> <Li> Longitudinal P - waves (shock - or pressure waves) </Li> <Li> Transverse S - waves (both body waves) </Li> <Li> Surface waves--(Rayleigh and Love waves) </Li> </Ul> <Li> Longitudinal P - waves (shock - or pressure waves) </Li>

The point of origin of an earthquake is its