How strong is an intensity?

震度を知る

JMA intensity scale · select a level

1
Felt by a few people at rest
2
Felt by many people indoors at rest
3
Felt by almost everyone indoors
4
Most people are startled
5−
Most people want to hold on to something
5+
Walking becomes difficult
6−
Standing becomes difficult
6+
Impossible to stand; you can only crawl
7
People are thrown by the shaking
5−
What happens

Dishes and books may fall; unsecured furniture may move.

What to do

Protect your head and get under a table. Don’t rush outside; check for fire once shaking stops.

Intensity ≠ Magnitude

M7.0 Epicenter 6+ Near 4 Mid 2 Far
One M7.0 earthquake — a different intensity at each place

Intensity (Shindo)

How strongly the ground shakes where you are. One earthquake has a different intensity at every place. JMA scale: 0–7, ten levels.

Magnitude (M)

How much energy the earthquake itself released. One earthquake, one number — with no upper limit.

Think of a light bulb: magnitude is its wattage; intensity is how bright it looks from where you stand.
Energy compared with M5
M5
×1
M6
×32
M7
×1,000
M8
×32,000
M9
×1,000,000
FAQ

Why is there no intensity 8?

Intensity 7 is open-ended: it covers every measured intensity of 6.5 and above. At that level, poorly resistant buildings can collapse and people cannot move, so the right action is the same however much stronger it gets — protect your life first. Splitting it further would not change what you should do.

Example: the 2011 Great East Japan Earthquake was M9.0, with a maximum intensity of 7.