An earthquake is a violent shaking of the ground that is usually caused by a sudden motion on a geological fault.

(Columbia University)

The energy released in an earthquake registering 6.7 on the Richter scale is roughly equal to the energy contained in a one megaton hydrogen bomb. (Washington Post)

And who figured that out?

The cause of earthquakes was stated correctly in 1760 by British engineer John Michell, one of the first fathers of seismology, in a memoir in which he wrote that earthquakes — and the waves of energy that they make — are caused by "shifting masses of rock miles below the surface."

(U.S. Geological Survey)

How is the strength of earthquakes measured?

The Richter scale — developed in 1935 by American seismologist Charles Richter — measures the ground vibration produced by earthquakes as a way of quantifying their magnitude.

(Columbia University)

What is the strongest earthquake ever recorded?

On May 22, 1960, the strongest earthquake ever recorded — with a magnitude of 9.5 on the Richter scale — occurred along the coast of southern Chile.

(U.S. Geological Survey)

Which quake is the deadliest in recorded history?

The deadliest earthquake in recorded history struck Shensi province in China in 1556 — killing about 830,000 people.

(U.S. Geological Survey)

Japan is the target of 20% of all quakes that rate a six or higher on the Richter scale. (Discover)

What about in recent years?

The December 26, 2004 earthquake off the coast of Sumatra, Indonesia — and a subsequent tsunami — killed more than 283,100 people in ten countries in South Asia and East Africa and displaced 1.1 million.

(U.S. Geological Survey)

Just how powerful is a strong earthquake?

The energy released in an earthquake registering 6.7 on the Richter scale — the same intensity as the December 2003 earthquake that hit the Iranian city of Bam — is roughly equal to the energy contained in a one megaton hydrogen bomb.

(Washington Post)

Which nation is particularly at risk?

Japan is the target of 20% of all quakes that rate a six or higher on the Richter scale.

(Discover)

Why is Japan so quake-prone?

Japan is located atop four tectonic plates — making it exceptionally prone to earthquakes.

(New York Times)

What’s the worst case scenario?

Scientists estimate a magnitude 7.3 earthquake directly under the northern part of Tokyo Bay would cause $955 billion worth of damage — and as many as 11,000 deaths.

(Government of Japan)

Each year, the southern California area has about 10,000 earthquakes — or more than 27 each day. Most of them are so small that they are not felt. (U.S. Geological Survey)

When was the last time an earthquake caused major devastation in Japan?

In 1995, a 7.2 magnitude earthquake in Kobe killed over 6,000 people — and caused damage of about $114 billion, or more than 2% of Japan's GDP at the time.

(Wall Street Journal)

How long was the impact felt?

More than 300,000 Japanese were left homeless by the Kobe earthquake in 1995 — and some were still in makeshift camps eight years later.

(The Guardian)

Why else are quakes so troublesome?

A magnitude 6.8 earthquake in July 2007 severely damaged Japan's Kashiwazaki-Kariwa nuclear plant —the world's largest nuclear power plant in terms of capacity.

(Associated Press)

What other recent quake made headlines?

The earthquake that struck Pakistan in October 2005 was South Asia's strongest in 100 years.

(Daily Telegraph)

Why do experts think that the region is overdue for more quakes?

Historical records show that at least as far back as the early 1800s, sizeable quakes have erupted every few decades in the Himalaya region. But since 1920, the Himalaya have remained quiet — with some areas having been spared a major earthquake for the past 500 years.

(Scientific American)

The deadliest earthquake in recorded history struck Shensi province in China in 1556 — killing about 830,000 people. (U.S. Geological Survey)

What is the expected result?

A magnitude 8.1 to 8.3 quake in the Himalaya region could kill as many as 200,000 people.

(Scientific American)

What other region is at risk?

Iran's capital city Tehran lies on a major geological fault line. An earthquake of the same intensity that hit the Iranian city of Bam in 2003 could kill about one million of the city's 12 million people.

(Financial Times)

And finally, what about earthquakes in California?

Each year, the southern California area has about 10,000 earthquakes — or more than 27 each day. Most of them are so small that they are not felt. Only several hundred are greater than magnitude 3.0 — and only about 15-20 are greater than magnitude 4.0.

(U.S. Geological Survey)