Richter Magnitude In 1935 Charles Richter of the California Institute of Technology developed the first magnitude scale using seismic records. As shown in Figure 8 (top), the Richter scale is based on the amplitude of the largest seismic wave (P S, or surface wave) recorded on seismic waves weaken as the distance between the focus and the seismograph increases, Richter developed a method that accounts for the decrease in wave amplitude with increasing distance. Theoretically, as long as equivalent instruments are used, monitoring stations at various locations will obtain the same Richter magnitude for each recorded earthquake. In practice, however, different recording stations often obtain slightly different Richter magnitudes for the same earthquake-a consequence of the variations in rock types through which the waves travel.