Earthquake Magnitude

Earthquake magnitude is a logarithmic measure of the energy released at an earthquake source. The modern standard is the moment magnitude Mw, derived from the seismic moment (rupture area times slip times rock rigidity), which does not saturate for great earthquakes the way the older Richter local magnitude ML does. Each whole-number step is about 32 times more energy, so Mw 8 releases roughly 1,000 times the energy of Mw 6. The largest recorded was the 1960 Chile earthquake at Mw 9.5, on a subduction megathrust. Such trench earthquakes displace the seafloor and generate tsunamis, the link to navigation and coastal hazard.