Accurate records of earthquake magnitudes have only been kept for some 100 years since the invention of the seismograph in the 1850s. Recent records of casualties are likely to be more reliable than those of earlier times.
There are estimated to be some 500,000 seismic events each year, of which about 100,000 can be felt and 1,000 cause some form of damage.
Most powerful earthquakes
Each increase of 1 point on the Richter scale represents an increase of x 10 in the disturbance and a release of 30 times more energy. The smallest measurable events release energy in the order of 20J (equivalent to dropping a brick from a table top) - the most powerful recorded earthquake released energy equivalent to the simultaneous detonation of 50 of the most powerful nuclear bombs!
The world's deadliest earthquake may have been the great Honan Shensi province earthquake in China, 1556. Estimates put the total death toll at 830,000.
Similar magnitude earthquakes may result in widely varying casualty rates. The San Francisco Loma Prieta earthquake of 1989, at 6.9 on the Richter scale left 69 people dead whilst the Azerbaijan earthquake, again at 6.9 left some 20,000 killed. The differences are likely, in this case, to be partly explained by the quality of building and civil disaster preparations in the San Francisco area.
Page update: February 1999