The extensive records of the United States Geological Service (USGS) show that the biggest earthquake since 1900 occurred near the cities of Valdivia and Puerto Montt, Chile, in 1960. Known as the Great Chilean Earthquake, the quake measured 9.5 on the Richter scale. The death toll is not known, although the USGS estimates that about 1,655 people died, and the earthquake may have caused as much as $800 billion US Dollars (USD) in damage. It is possible, however, that some earlier events that occurred before accurate measurements could be made may have been even more powerful. The number of fatalities and the amount of damage depend not only on the magnitude of the quake, but also on where it occurs, with those that are close to heavily populated areas being the deadliest.
The Richter Scale
Earthquakes have been recorded on seismographs as wavy lines on graph paper since the late 19th century. In 1935, the physicist and seismologist Charles F. Richter developed a scale for measuring their strength, based on seismograph recordings. The scale is exponential, meaning that each whole value represents a shock with ten times the magnitude of the preceding whole value. For example, an earthquake that measures 8.0 on the Richter scale has ten times the magnitude of one that measures 7.0. There is no upper limit to the scale, but 9.5, for the Great Chilean Earthquake, is the highest measurement ever recorded. This is equivalent to the detonation of 2.7 gigatons (billion tons) of TNT.
The Great Chilean Earthquake
The Earth’s crust is made up of “plates” that float on denser magma below, and move relative to one another. Sometimes two continental plates will crash into one another, and sometimes an oceanic plate will move under a continental one. This is happening off the west coast of South America, which is known as a subduction zone. On 22 May 1960, part of the oceanic plate near the coat of Chile moved under the South American continental plate. This disturbance caused land along the Chilean coast to suddenly drop by about ten feet (three meters), and ground further inland to rise by about twenty feet (six meters).
This abrupt shift caused the biggest earthquake ever recorded, and a major tsunami. Many of the buildings in the affected cities had been designed to withstand earthquakes, and a number of smaller quakes in the months leading up to this disaster had given some warning. This lessened the impact of the earthquake itself, but it was the tsunami that was responsible for most of the casualties and damage. The massive wave affected not only Chile, but also caused deaths and damage as far away as Hawaii, Japan, and the Philippines.
Other Big Earthquakes in Modern Times
In terms of events that were studied, measured, and recorded on the Richter scale, the Great Chilean Earthquake was far and away the biggest ever. Keeping in mind that the Richter scale runs along an exponential progression, the next largest was at Prince William Sound, Alaska in 1964, which measured 9.2. The third biggest earthquake ever recorded, was under the Indian Ocean in 2004, clocking in at 9.1 on the Richter scale and generating a formidable tsunami that devastated much of the coastline of Southeast Asia, and killed nearly 228,000 people.
It is highly probable that some ancient earthquakes were of an even higher magnitude than the 1960 Chile disaster, but because the Richter scale was not developed until the 1930s, it is difficult to quantitatively compare them. Retrospective examination of seismograph records dating back to around 1900 allows estimates to be made, but for earlier events, any assessment of the severity can only be based on eyewitness accounts, and the amount of damage done. For example, the Lisbon earthquake of 1755 was by all accounts very severe, and it generated a massive tsunami which magnified the death toll. The Shaanxi earthquake which occurred in China in the 1500s was the deadliest known to history, killing almost one million people. This event may also have been the biggest known to man, but there is simply no way to tell.