Problems with the Richter scale

The major problem with Richter magnitude is that it is not easily related to physical characteristics of the earthquake source. Furthermore,there is a saturation effect near 8.3-8.5, owing to the scaling law of earthquake spectra, that causes traditional magnitude methods to yield the same magnitude estimate for events that are clearly of different size. By the beginning of the 21st century, most seismologists considered the traditional magnitude scales to be largely obsolete, being replaced by a more physically meaningful measurement called the seismic moment which is more directly relatable to the physical parameters, such as the dimension of the earthquake rupture, and the energy released from the earthquake. In 1979 seismologists Tom Hanks and Hiroo Kanamori, also of the California Institute of Technology, proposed the moment magnitude scale , which provides a way of expressing seismic moments in a form that can be approximately related to traditional seismic magnitude measurements.