Antarctica has the least earthquakes of any continent, but small earthquakes can occur anywhere in the World. There is no scientific reason for California to fall into the ocean. Magnitude measures the energy released at the source of the earthquake. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded on a seismogram at a certain period. Intensity measures the strength of shaking produced by the earthquake at a certain location.
Intensity is determined from effects on people, human structures, and the natural environment.
Intensity does not have a mathematical basis, but is based on observed effects. The Richter scale is not a physical device, but a mathematical formula. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded on a seismogram at a certain period. Many assumptions have to be made when making these comparisons. Because different researchers can get widely varying magnitudes from using different assumptions on how to make these comparisons, many of the old earthquakes have big differences in the magnitudes assigned to them.