70,000 people were killed or presumed dead on May 31, 1970, when a 7.9 earthquake hit Chimbote, Peru.
70,000 people were killed or presumed dead on May 31, 1970, when a 7.9 earthquake hit Chimbote, Peru.
AFP/Getty Images
When 72,000 people were killed by a magnitude-7.2 earthquake in Messina, Italy, more than 40% of the city's population was killed. The December 28, 1908, quake caused a tsunami and was felt throughout Sicily.
When 72,000 people were killed by a magnitude-7.2 earthquake in Messina, Italy, more than 40% of the city's population was killed. The December 28, 1908, quake caused a tsunami and was felt throughout Sicily.
FPG/Hulton Archive/Getty Images
86,000 people were killed on October 8, 2005, when a magnitude-7.6 earthquake slammed northern Pakistan. The heaviest damage occurred in parts of Kashmir, where entire villages were destroyed.
86,000 people were killed on October 8, 2005, when a magnitude-7.6 earthquake slammed northern Pakistan. The heaviest damage occurred in parts of Kashmir, where entire villages were destroyed.
ARIF ALI/AFP/Getty Images
The magnitude-7.9 earthquake that struck eastern Sichuan, China on May 12, 2008, killed 87,587 people and was felt in parts of Bangladesh, Taiwan, Thailand and Vietnam.
The magnitude-7.9 earthquake that struck eastern Sichuan, China on May 12, 2008, killed 87,587 people and was felt in parts of Bangladesh, Taiwan, Thailand and Vietnam.
TEH ENG KOON/AFP/Getty Images
A statue of Turkmenistan's former President Saparmurad Niyazov sits in front of the earthquake memorial in Ashgabat, 13 February 2007. Almost all the brick buildings in Ashgabat, collapsed and 110,000 people were killed when a magnitude-7.3 earthquake struck October 5, 1948.
A statue of Turkmenistan's former President Saparmurad Niyazov sits in front of the earthquake memorial in Ashgabat, 13 February 2007. Almost all the brick buildings in Ashgabat, collapsed and 110,000 people were killed when a magnitude-7.3 earthquake struck October 5, 1948.
MUSTAFA OZER/AFP/Getty Images
A 7.9 earthquake in the Tokyo-Yokohama area of Japan killed 142,800. The quake, which took place on September 1, 1923, caused firestorms and generated a tsunami.
A 7.9 earthquake in the Tokyo-Yokohama area of Japan killed 142,800. The quake, which took place on September 1, 1923, caused firestorms and generated a tsunami.
Topical Press Agency/Getty Images
An estimated 200,000 people were killed when a 7.8-magnitude earthquake hit Haiyuan County, China, on December 16, 1920. Here, Muslims pray outside a mosque in Haiyuan in 2007.
An estimated 200,000 people were killed when a 7.8-magnitude earthquake hit Haiyuan County, China, on December 16, 1920. Here, Muslims pray outside a mosque in Haiyuan in 2007.
Reuters/Landov/File
227,898 people were killed on December 26, 2004, when a magnitude-9.1. quake hit Sumatra. This was the third-largest earthquake measured since 1900. Almost 2 million people were displaced by the earthquake and resulting tsunami.
227,898 people were killed on December 26, 2004, when a magnitude-9.1. quake hit Sumatra. This was the third-largest earthquake measured since 1900. Almost 2 million people were displaced by the earthquake and resulting tsunami.
INOONG/AFP/Getty Images
On July 27, 1976, a magnitude-7.5 earthquake killed an estimated 242,769 people in Tangshan, China. Unofficial estimates put the toll at much higher, perhaps 655,000 deaths.
On July 27, 1976, a magnitude-7.5 earthquake killed an estimated 242,769 people in Tangshan, China. Unofficial estimates put the toll at much higher, perhaps 655,000 deaths.
U.S. Geological Survey
A magnitude-7.0 earthquake struck Haiti on January 12, 2010. Official estimates put the death toll at 316,000 people, but other estimates suggest substantially lower casualties -- perhaps 230,000 or lower. More than 1 million people were displaced.
A magnitude-7.0 earthquake struck Haiti on January 12, 2010. Official estimates put the death toll at 316,000 people, but other estimates suggest substantially lower casualties -- perhaps 230,000 or lower. More than 1 million people were displaced.
JEAN-PHILIPPE KSIAZEK/AFP/Getty Images
10 deadliest earthquakes
CNN  — 

Earthquakes are measured using seismographs, which monitor the seismic waves that travel through the Earth after an earthquake strikes.

Scientists used the Richter Scale for many years but now largely follow the “moment magnitude scale,” which the U.S. Geological Survey says is a more accurate measure of size.

Here are the magnitude classes:

Microearthquake:

– Magnitude: Less than 3.0

– Damage: Little to none

Minor earthquake:

– Magnitude: 3.0 - 3.9

– Damage: Little to none

Light earthquake:

– Magnitude: 4.0 - 4.9

– Damage: Moderate

Moderate earthquake:

– Magnitude: 5.0 - 5.9

– Damage: Considerable

Strong earthquake:

– Magnitude: 6.0 - 6.9

– Damage: Severe

Major earthquake:

– Magnitude: 7.0 - 7.9

– Damage: Widespread, heavy

Great earthquake:

– Magnitude: 8.0 and up

– Damage: Tremendous