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What is an Earthquake?

This is how large earthquakes occurs.

The mechanics behind the Tokai Earthquake
The surface of the Earth is made up of tens of hard, flat blocks known as plates. The points at which different plates are connected sometimes hit each other or are pushed under one another due to slight movements caused by the movement of the mantle found beneath them. This has led to the formation of mountain ranges and sea trenches, and also leads to earthquakes and volcanic activity. The Philippine Sea Plate, located in the seabed to the south of Shizuoka Prefecture, has been moving from the south, levering itself under the Continental Eurasia Plate and dragging the tip of the Eurasia Plate down with it. When the strain caused by this reaches its limit, the Eurasia Plate will bounce back causing an earthquake. This will be the Tokai Earthquake. The Tokai Earthquake Theory was announced in 1976. The last occurrence, the Ansei Tokai Earthquake, was in 1854. If you consider that large earthquakes tend to occur in the same locations in cycles of 100 to 150 years, the "next biggie" is without doubt on its way.

Table of Japan Meteorological Agency's (JMA) Seismic Intensity Scale and Related Explanations.

Richter Scale	JMA Seismic Intensity Scale	How humans are affected	Situation inside	Situation outside
0.5	0	Unable to feel any tremors.
1.5	1	Some people inside buildings may feel slight tremors.
2.5	2	The majority of people inside buildings feel slight tremors. Some people who are asleep may wake up.	Items that are hanging such as lights begin to swing slightly.
3.5	3	The majority of people inside buildings feel slight tremors. There will be some people who become scared.	Crockery on shelves may begin to make noise.	Power lines will swing slightly.
4.5	4	There will be considerable fear and some people may start thinking about getting to safety. The majority of sleeping people will wake up.	Hanging items swing a lot and crockery on shelves make noise. Items not positioned firmly may fall.	Power lines will swing a lot. People walking will feel tremors. Some people riding bicycles will feel tremors.
	5 Weak	The majority of people will begin to act to ensure their own safety. Some people will have difficulty moving.	Hanging items shake and swing violently; crockery on shelves and books on bookcases may fall.	Glass windows may shatter. The shaking of telegraph poles can be seen. Non-reinforced concrete walls may fall apart. There will be some damage on roads.
5.0	5 Strong	Feeling of extreme fear. Most people have difficulty moving.	The majority of crockery and books will fall. Television may fall from their stands. Heavy furniture such as cupboards may topple. Doors may no longer open due to their shapes contorting. Some doors may fall off.	Non-reinforced concrete walls will fall. Vending machines not properly fastened in position may topple. The majority of gravestones will topple. It becomes difficult to ride a bicycle and there will be some cars that stop.
6.0	6 Weak	It becomes difficult to remain standing.	The majority of unfixed, heavy furniture will move and topple. There will be many doors that no longer open.	In a large number of buildings window glass and tiling will be damaged and fall.
6.5	6 Strong	It becomes impossible to stand. Movement is restricted to crawling.	The majority of unfixed, heavy furniture will move and topple. There will be doors that slip out of their holding and fly off.	In the majority of buildings' window glass and tiling will be damaged and fall. Nearly all non-reinforced concrete walls will collapse.
	7	Totally at the mercy of the tremors; unable to move according to your own will.	The majority of furniture moves a lot and there will be many items flying about	Almost all building will have falling tiles and glass. There will be some reinforced concrete walls that are also damaged.

The seismic intensity scale shows the magnitude of an earthquake and is measured using seismic sensory equipment. This "Table of Japan Meteorological Agency's Earthquake Seismic Intensity and Related Explanations" shows the phenomena and damage that actually occurred in the area where an earthquake and was subsequently measured, took place.

What is an Earthquake?

The mechanics behind the Tokai Earthquake