Natural Disasters
About Earthquakes in Japan
Japan is a country that often experiences earthquakes.
We never know when or where an earthquake will happen.
It is important to learn about earthquakes in advance.
What is an earthquake?
An earthquake is a natural shaking of the ground.
Large earthquakes can have the following effects:
- Buildings may be destroyed
- Objects may fall from high places
- Ground shaking may happen several times after the main earthquake stops
(These are called “aftershocks” (“yoshin” in Japanese)) - The shaking may cause tsunamis and fires
What is meant by the size of an earthquake?
The size of an earthquake is measured using two scales: 1. Magnitude and 2. Seismic Intensity (Shindo)
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Magnitude
This represents the amount of energy released by the earthquake.
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Seismic Intensity (Shindo)
This represents the level of shaking in a particular area.
The levels go from 0 (the weakest) to 7 (the strongest).
Levels 5 and 6 have both “lower” and “upper” levels, making 10 levels in total.
This 10-level seismic intensity scale is only used in Japan.
Seismic Intensity 0
No shaking is felt
Seismic Intensity 1
Shaking may be felt by a small number of people inside buildings in quiet environments.
Seismic Intensity 2
Shaking will be felt by many people inside buildings in quiet environments.
Seismic Intensity 3
Shaking will be felt by most people inside buildings.
Seismic Intensity 4
Most people will experience an alarming level of shaking.
Seismic Intensity 5 Lower
Most people will experience a frightening level of shaking.
Seismic Intensity 5 Upper
Walking without holding onto something becomes difficult.
Seismic Intensity 6 Lower
It becomes difficult to stand.
Seismic Intensity 6 Upper
Standing becomes impossible, and people already standing may fall over.
Seismic Intensity 7
Standing becomes impossible, and people already standing may fall over. Many buildings will start to lean or collapse.
Alert systems for major earthquakes
In Japan, when a major earthquake is about to strike, special sound alerts are played through mobile phones, television and radio. These are called Earthquake Early Warnings.
When these sounds are played, strong shaking will start soon after.
You should act to protect yourself immediately.
Keep away from fallen or falling objects and protect your head.
To hear what the alert sounds like, please visit the links below.
Sound example
| Mobile phones | https://www.youtube.com/watch?v=4gZW7HRHJmM (Japanese) |
|---|---|
| Television/Radio | https://nettv.gov-online.go.jp/prg/prg9152.html (Japanese) |
| Indoor broadcasts | http://www.real-time.jp/?page_id=465 (Japanese) |
Column 1 : Why are earthquakes so common in Japan?
The surface of the earth is covered in hard plates which move slowly. The movement of these plates is what causes earthquakes. Four of these plates meet and collide in the area around Japan. That is why earthquakes are common in Japan.
There are several types of earthquake.
Undersea Earthquakes
When an oceanic plate slides under a continental plate, the edge of the continental plate is also dragged down. When the continental plate tries to return to its original shape, it snaps back.
This causes an earthquake. These earthquakes are called undersea earthquakes.
Inland Earthquakes
When an oceanic plate pushes and pulls a continental plate, energy builds up in the continental plate. This energy makes the ground on top of the continental plate crack and rub together. When this happens, an earthquake occurs. These earthquakes are land earthquakes.
Column 2 : Major Japanese Earthquakes
The following two earthquakes have caused the most damage of any earthquakes from 1990 onwards.
2011 Great East Japan Earthquake
A major earthquake struck the Pacific coast in Japan's Tohoku region.
It was the 4th largest earthquake in the world.
Many people were killed in the tsunami caused by the earthquake.
Over 15,000 deaths were caused, and there are still over 2,500 people missing.
The earthquake was magnitude 9.0, and its highest seismic intensity was 7.
1995 Great Hanshin-Awaji Earthquake
A large earthquake struck which affected the city of Kobe, and its surroundings, in Hyogo Prefecture.
Because it occurred early in the morning, many people were still asleep, and were crushed by heavy objects and killed. Over 6,000 people died.
The earthquake was magnitude 7.3, and its highest seismic intensity was 7.