Snipfact:

  Most earthquakes last only a minute or two, but the Alaska earthquake of 27 March 1964 continued for at least five minutes and registered 8.6 on the Richter scale. It killed 131 people but caused more than $450 million worth of damage.

  An earthquakes in Tang-shan, China, on 28 July 1976, killed 242,419. The Kashmir quake of 8 October 2005 officially killed 87,350 people, but it may have been more than 100,000.

  The worst  earthquake affecting an inhabited area was in Assam, India on 12 June 1987. It is reckoned to have reached 8.7, killing about 1,500. The Colombia/Ecuador earthquake of 31 January 1906 was 8.9 on the Richter scale. Fortunately, it was 300 km off the coast, and so resulted in fewer than 1,000 deaths on land.

  An earthquake affecting the Middle East and North Africa on 20 ,May 1202 may have been the worst in human history. Up to 1,000,000 people were killed, 110,000 in Cairo, Egypt alone.

    0 Detected by sensitive seismographs (some can detect magnitudes of less than zero!) 1 Detected by instruments 2 Lowest felt by humans 3 Slight vibration; more than 100,000 a year around the world 4 Up to 15,000 a year; at 4.5, would be detected by seismographs worldwide, but cause little damage. 5 3,000 a year; that 1960 earthquake in Agadir, Moroco was 5.6 6 100 a year worldwide 7 20 a year; the 1995 earthquake in kobe, Japan was 7.2 8 Major destructive earthquakes; average two a year; the 1904 San Francisco earthquake was probably 8.25 9 No quake higher than 8.9 has been recorded, but 9.0 or even higher is theoretically possible

  Seismic waves are vibrations from earthquakes that travel through the Earth. Sensitive instruments called seismographs can record the waves, even at great distances, and calculate their strength and location. The Richter scale indicates the magnitude of the strength of an earthquake based on the size of the seismic waves. The biggest earthquake is a billion times greater than the smallest.

  Chinese astronomer Chan Heng (AD 78-139) invented an earthquake detector made of a vase adorned with dragons’ heads and surrounded by metal frogs. In each of the dragons’ jaws was a carefully balanced ball. When the first tremors of an earthquake made the device vibrate, the balls fell into the frogs’ mouths, making a noise of warn of the coming danger.

  Earthquakes are movements of the Earth’s surface, often as a result of a fault, or fracture, in the crust. They happen more often in some parts of the world than others. In heavily populated areas,  they cause great damage to buildings and loss of life.