Earthquakes have been occurring on Earth since its formation. They occur when tectonic plates that are sliding against or past each other build up enough tension to slip, causing the rock to settle into a new position and the ground to shake. The United States Geological Survey predicts that 500,000 earthquakes happen every year, although most go undetected because they are so small or so far away from populated areas. 10,000 of them can be felt by humans and 100 of them cause damage. Unfortunately, scientists have not yet discovered a reliably precise way to predict earthquakes, and there is debate over whether such a thing is even possible. Current prediction methods involve measuring the tension that has been bled off by past earthquakes and how often earthquakes have occurred at that location before. Due to the fact that the instruments that can measure tension and accurate seismographs are a recent invention, earthquake prediction continues to be inaccurate and imprecise.
This presents a problem when it comes to the construction of nuclear power plants. It is estimated by the World Nuclear Association that 20% of the world's nuclear reactors are operating in "areas of significant seismic activity" - earthquake danger zones. Consequently, nuclear plants are designed to withstand seismic activity. A system called Probabilistic Seismic Hazard Analysis is used when nuclear plants are designed, to make sure the facilities are capable of withstanding earthquakes beyond the magnitude of the strongest earthquake recorded at that site. When an earthquake is detected, a nuclear reactor will shut down.
However, this system is not foolproof. For example, on March 11, 2011, a magnitude 9 undersea earthquake hit T?hoku, Japan, triggering a 40-foot tsunami that then swept over the Japanese city of Fukushima. The six reactors located in the Fukushima Daiichi plant did shut down in response to the earthquake and emergency diesel generators started as expected, but when the tsunami hit an hour later, the generators failed. Three reactors suffered a major accident sequence. Hydrogen created by the reaction of zirconium and water in the plant's cooling apparatus caused two explosions, and water contaminated by radioactive material was leaked into the seawater and groundwater surrounding the plant. Although the Fukushima Daiichi disaster is one of only two Level 7 nuclear disasters in world history on the INES scale (the other being the Chernobyl disaster in 1986), close calls and smaller accidents are far more common.
This dataset shows earthquakes that have occurred over the past 4,000 years, shown in layers of 200 years each. It also shows the location of all active nuclear power plants across the world. Earthquake location data and intensity was drawn from NOAA's Significant Earthquake database. For more information on the Modified Mercalli Intensity Scale used, visit this USGS page. Nuclear plant location data was taken from the World Nuclear Organization. Both the nuclear power plant locations layer and the layer of cumulative earthquake data are set to transparent, so that viewers can turn them on and off at will.
This dataset was created using Quantum GIS (or QGIS, or Quantum Geographic Information System), which is a "free, open source geographic information system." A tutorial is available that will walk you through the basics of using QGIS to create SOS-formatted maps, including this one. In addition to this dataset, the tutorial also walks through the creation of the Marine Life Tracking dataset and the Global Statistics dataset.