Magnitude just part of equation An earthquake that measures above 7.0 in magnitude is considered a major quake, but weaker earthquakes can be devastating. The amount of damage depends on a variety of factors, including how far below ground the quake is focused and the type of construction above ground. Friday's earthquake in Iran had a magnitude 6.6. The deadliest USA earthquake was the 7.7 quake that hit San Francisco in , killing at least 700. The USA's strongest quake hit Prince William Sound, Alaska, in with magnitude 9.2, killing 125 people. The quake in California during the World Series registered 6.9 and caused 67 deaths. On Dec. 22, a magnitude-6.5 quake in California caused two deaths. Source: USA TODAY research.   Major Iran quakes Significant temblors during the past 30 years: April 10, , southern Iran. 5,374 deaths. Magnitude: 7.1, considered a major earthquake. Sept. 16, , east-central Iran. 15,000 deaths. Magnitude: 7.5 to 7.9. It leveled many towns and villages. June 21, , Caspian region, northern Iran. 35,000 deaths and 100,000 injuries in the worst recorded disaster in Iran. Magnitude: 7.7. Feb. 28, , northwest Iran. 1,000 deaths. Magnitude: 5.5. May 10, , eastern Iran near the Afghan border. 1,560 deaths. Magnitude: 7.1. Friday, southern city of Bam. More than 20,000 deaths. Magnitude: 6.6. Source: Reuters Recent major world quakes Major earthquakes around the world in recent years: Dec. 12, , Indonesia. 2,200 deaths. Magnitude: 6.8. Sept. 30, , India. 10,000 deaths from series of quakes. Magnitude of first: 6.4. Jan. 17, , Japan. 6,430 deaths. Magnitude: 7.2. Feb. 4, , Afghanistan. 4,500 deaths. Magnitude: 6.1. May 30, , Afghanistan. 4,000 deaths. Magnitude: 6.9. July 17, , Papua New Guinea. 2,100 deaths. Magnitude: 7.1. Aug. 17, , Turkey. 17,800 deaths. Magnitude: 7.4. Jan. 26, , India. 19,700 deaths. Magnitude: 7.7. May 21, , Algeria. 2,251 deaths. Magnitude: 6.7. Friday, Iran. More than 20,000 deaths. Magnitude: 6.6. Source: Reuters   Other natural disasters with great loss of life Catastrophes of the past several decades in which many thousands of people have died An earthquake with a magnitude of 7.8 on the Richter scale at Mount Huascaran, in Peru, triggers a rock and snow avalanche that buries the towns of Yungay and Ranrahirca, killing 67,000 people. In Bangladesh, between 300,000 and 500,000 people die in cyclone-induced flooding, as do more than 130,000 people in . Heavy rains cause severe flooding in northern Vietnam, killing 100,000 people. The deadliest earthquake of the 20th century, with a magnitude of eight, strikes Tianjin (formerly Tangshan), in China. The official casualty figure issued by the Chinese government is 255,000 but unofficial estimates of the death toll are as high as 655,000. Famine kills more than 900,000 people in Ethiopia. An earthquake in Armenia, measuring 6.9, kills nearly 25,000 people, injures 15,000 and leaves at least 400,000 homeless. An earthquake measuring 7.7 destroys cities and villages in the Caspian Sea area of north-western Iran. At least 50,000 people are killed, more than 60,000 injured and 400,000 left homeless. A tsunami wave kills 138,000 people in Bangladesh. An estimated 11,000 people are killed in an earthquake in Latur, India. An earthquake measuring 7.7 rocks the western Indian state of Gujarat, killing more than 20,000 people and leaving 600,000 homeless. A heatwave leaves 15,000 mainly elderly people dead in France. An earthquake measuring 6.3 kills as many as 50,000 people in the city of Bam, in south-eastern Iran. Source: © Guardian Newspapers by Linda MacDonald, Tuesday December 30,