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Invention Of Richter Scale | The Dr. Binocs Show | Best Learning Video for Kids | Preschool Learning

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A look at the worst earthquakes in recorded history, in loss of human life. (The March 11, 2011, earthquake and tsumani that affected eastern Japan is not included because the fatalities caused, about 15,000, are fewer than those resulting from the temblors listed below.) Sources: United States Geological Survey, Encyclopedia Britannica

2: Tangshan, China, July 27, 1976
Magnitude 7.5. Official casualty figure is 255,000 deaths. Estimated death toll as high as 655,000.
Damage extended as far as Beijing. This is probably the greatest death toll from an earthquake in the last four centuries, and the second greatest in recorded history.

4: Sumatra, Indonesia, Dec. 26, 2004
Magnitude 9.1, 227,898 deaths.
This was the third largest earthquake in the world since 1900 and the largest since the 1964 Prince William Sound, Alaska temblor. In total, 227,898 people were killed or were missing and presumed dead and about 1.7 million people were displaced by the earthquake and subsequent tsunami in 14 countries in South Asia and East Africa. (In January 2005, the death toll was 286,000. In April 2005, Indonesia reduced its estimate for the number missing by over 50,000.)

Magnitude 7.0. According to official estimates, 222,570 people killed.

According to official estimates, 300,000 were also injured, 1.3 million displaced, 97,294 houses destroyed and 188,383 damaged in the Port-au-Prince area and in much of southern Haiti. This includes at least 4 people killed by a local tsunami in the Petit Paradis area near Leogane. Tsunami waves were also reported at Jacmel, Les Cayes, Petit Goave, Leogane, Luly and Anse a Galets.

8: Ardabil, Iran, March. 23, 893
Magnitude not known, about 150,000 deaths
The memories of the massive Damghan earthquake (see above) had barely faded when only 37 years later, Iran was again hit by a huge earthquake. This time it cost 150,000 lives and destroyed the largest city in the northwestern section of the country. The area was again hit by a fatal earthquake in 1997.

9: Kanto, Japan, Sept. 1, 1923
7.9 magnitude, 142,800 deaths.
This earthquake brought extreme destruction in the Tokyo-Yokohama area, both from the temblor and subsequent firestorms, which burned about 381,000 of the more than 694,000 houses that were partially or completely destroyed. Although often known as the Great Tokyo Earthquake (or the Great Tokyo Fire), the damage was most severe in Yokohama. Nearly 6 feet of permanent uplift was observed on the north shore of Sagami Bay and horizontal displacements of as much as 15 feet were measured on the Boso Peninsula.

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The top 10 deadliest earthquakes in history

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JavaScript is required to view our full story experience. Please enable JavaScript in your browser preferences. A look at the worst earthquakes in recorded history, in loss of human life. (The March 11, 2011, earthquake and tsumani that affected eastern Japan is not included because the fatalities caused, about 15,000, are fewer than those resulting from the temblors listed below.)

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Kids Earthquake Safety - Disaster Dodgers

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What Is An Earthquake? | The Dr. Binocs Show | Educational Videos For Kids

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The Ring of Fire | Nat Geo Kids Volcano Playlist

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Teaching Tools | Resources for Teachers from Scholastic

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Earthquakes are the result of plate tectonics, or shifting plates in the crust of Earth, and quakes occur when the frictional stress of gliding plate boundaries builds and causes failure at a fault line. In an earthquake, elastic strain energy is released and waves radiate, shaking the ground. Scientists can predict where major temblors might occur in a general sense, but research does not yet allow forecasts for specific locations or accurate predictions of timing. Major earthquakes, some generating tsunamis, have leveled entire cities and affected whole countries. Relatively minor earthquakes can also be induced, or caused by human activity, including extraction of minerals from Earth and the collapse of large buildings.

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Read the latest news and articles about earthquakes. Earthquakes are the result of plate tectonics, or shifting plates in the crust of Earth.

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Skip to main content Official websites use .gov A.gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock () or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

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(Image: © Giuseppe Bellini/Getty Images)

A magnitude-6.6 earthquake that rocked central Italy on Sunday (Oct. 30) was not only the strongest earthquake to strike the region in 36 years, but it was also the latest in a series of powerful tremors. Those originated Aug. 24, with a magnitude-6.2 temblor, and then ramped up again Oct. 26 with two formidable quakes.

And the shaking didn't end on Oct. 30. Following the earthquake, Italy's geophysics and volcanology institution Istituto Nazionale di Geofisica e Vulcanologia (INGV) reported 560 post-quake tremors, which are typically referred to as aftershocks.

While most aftershocks are minor, some can be as strong as the earthquake that preceded them. So, what distinguishes aftershocks from earthquakes, and how do geologists interpret these events to understand seismic activity in Italy and in other earthquake-prone regions worldwide? [ The 10 Biggest Earthquakes in History]

Earthquakes typically happen in groups, and scientists use the terms earthquake and aftershock to describe when in the sequence a tremor occurred, said Michael L. Blanpied, the associate coordinator of the U.S. Geological Survey (USGS) Earthquake Hazards Program.

Seismologists refer to the biggest quake in a sequence as the "main shock," Blanpied told Live Science. Quakes that precede it are "foreshocks," and quakes that follow the main event are "aftershocks."

Sometimes, however, an aftershock emerges that is more powerful than the main shock that happened earlier.

"Then we shuffle around the names," Blanpied said. "We call the new biggest one the main shock. We call the earlier ones foreshocks, and the ones that come after it are aftershocks.

"It's our way of sorting things out," he explained. "But they're all earthquakes."

Forecasting the swarm

In central Italy, earthquake sequences typically produce lots of tremors. "They tend to come in what we call swarms," Blanpied said. But it's hard for scientists to know if a cluster of aftershocks will produce a powerful event or simply peter out, he said.

"The rate of the earthquakes can rise or fall, and there may be more than one big one in the midst. Trying to forecast the future activity in such a swarm is extremely difficult," he said.

Geologically speaking, the faults that fuel Italy's quakes are young, only about 1 million years old. They run down the spine of the Apennine Mountains and are relatively small, so they can't generate massive quakes like those created by longer and older faults, such as the San Andreas in California.

"In mature faults, once an earthquake gets going, it can race along for long distances -that's where you can get the magnitude-7 to -8 quakes," Blanpied said. "In a more youthful, broken-up mélange of faults like we have in central Italy, one particular piece of fault may only be big enough to host a 5- to 6-magnitude earthquake."

Layers of stress

But in areas veined with shorter faults, like in central Italy, a quake can send a cascade of stresses into faults nearby, pushing them closer to the brink, when they would slip and trigger yet another earthquake, Blanpied said.

According to Blanpied, the recent tremors can be linked back to quakes that visited the region in August. As those faults triggered quakes, they also moved stress onto faults to the south, which are creating the big earthquakes now, Blanpied said. And these recent quakes could in turn shunt stress into more faults, potentially triggering even more earthquakes.

"What we don't know is if additional faults big enough to make magnitude-6 quakes will now be brought closer to failure," Blanpied said.

He explained that Italian seismologists are currently in the field, mapping fault ruptures and closely examining the locations of new earthquakes. The researchers are working to determine which faults have moved and by how much, and how that could increase the stress load in other faults, making them prone to quakes as well.

"We hope that the sequence will die off now," he added. "But we have to see. We have no way to predict that for sure."

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Italy Quakes: What Makes an Earthquake an Aftershock?

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(Image: © Giuseppe Bellini/Getty Images) A magnitude-6.6 earthquake that rocked central Italy on Sunday (Oct. 30) was not only the strongest earthquake to strike the region in 36 years, but it was also the latest in a series of powerful tremors. Those originated Aug. 24, with a magnitude-6.2 temblor, and then ramped up again Oct.

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Learn the science behind how earthquakes happen—and how you can stay safe if one hits.