Earthquakes measuring 6 or above on the Richter scale are frequent in Southern Iceland. They occur due to fault movements in a narrow belt stretching east from Ölfus to Hekla. This fault separates the North American Plate to the north from the Eurasian Plate to the south and spreads about 1.8 cm a year. The earthquakes are caused by horizontal movements along faults in a north-south direction and extend through the entire crust, up to 10 kilometres below the surface.
The last major earthquake in Southern Iceland occurred on 28 May 2008 along a fault stretching south from Hveragerði to Eyrarbakki. It measured 6.3 on the Richter scale. In June 2000 there were two earthquakes four days apart, measuring 6.5 and 6.6. These were the first large earthquakes in Southern Iceland since 1912 when an earthquake measuring 7 shook the area. Prior to that, there were 5 quakes in 1896 measuring 6.5-6.9. The Richter scale is a logarithmic scale, meaning that an earthquake measuring 7 is 10 times more powerful than one that measures 6 and 100 times more powerful than one that measures 5. It hardly needs to be said that these earthquakes all caused damage. The earliest recorded earthquake in Southern Iceland was in 1013.