How Earthquakes are Measured in Japan
Created | Updated Dec 16, 2002
The strength of an earthquake is usually reported in terms of its magnitude.
This measure of magnitude, often called the Richter scale for the man who invented it in 1935, was originally a simple logarithmic unit measuring the movement of a particular standardised seismometer1 an idealised distance away from the epicentre.
Today, with vastly improved measuring devices, the scientific community use many different measures of magnitude with subscript letters to indicate which they mean, such as ML2, MS3, mB4 and MW5.
This is all very well for seismologists, but for the general public, these measures can be somewhat misleading. Two quakes of the same magnitude can have very different effects. For example, how worried should we have been about relatives living in Dudley, UK, when we heard reports of a magnitude 5 quake on 23 October 2002?
The Japanese 'Shindo' scale
In Japan, where medium quakes are a weekly occurence, magnitude is quoted in news flashes almost as an afterthought, and often omitted altogether. Instead, a report of the local effects of the quake in a selection of locations is given, using the unique Japanese 'Shindo' (quake level) scale.
| Shindo | People | Indoors | Outdoors | |
| 0 | Feel nothing | |||
| 1 | Some people indoors feel something | |||
| 2 | Most people indoors feel something | Lights hung on wires sway slightly | ||
| 3 | Almost everyone feels something, some people are frightened | Crockery on shelves may rattle | Power and phone lines sway slightly | |
| 4 | Quite frightening, some people fear for their safety | Hanging objects sway a lot, crockery rattles and unstable things may fall over | Power and phone lines sway a lot, people walking feel the quake, people driving cars may feel the quake | |
| Weak 5 | Most people fear for their safety, some people's actions are hindered | Hanging objects sway violently, crockery and books may fall off shelves, most unstable things fall over, furniture may move | Glass windows may break, telegraph poles can be seen to shake, unreinforced brick walls may collapse, roads may be damaged | |
| Strong 5 | Very frightening, most people's actions are hindered | Most crockery and books fall off shelves, TV may fall from its stand, chests of drawers and other heavy furniture may fall over, doors may warp so they cannot be opened, and some sliding doors come away from their tracks | Many unreinforced brick walls collapse, improperly secured vending machines may fall over, many graveyard headstones collapse, hard to drive a car, many cars stop | |
| Weak 6 | Hard to remain standing | Much unfixed heavy furniture moves or falls over, and many doors warp too badly to open | In a fair number of buildings tiled walls and glass windows break and fall | |
| Strong 6 | Impossible to stand, can only move by crawling | Most unfixed heavy furniture moves or falls over, doors may fly off their hinges | In many buildings tiled walls and glass windows break and fall, most unreinforced brick walls collapse | |
| 7 | Impossible to move by one's own volition | Almost all furniture moves greatly, some may fly through the air | Most buildings tiled walls and glass windows break and fall, some reinforced brick walls collapse |
You can see the scale in use at the Japan Weather Association Japan Quake Information page, which keeps information on the 100 most recent offical earthquake reports.
At the left of each map the date and time (year, month, day, hour, minute) of the quake is shown, and the latitude, longitude, depth and magnitude of the epicentre. The epicentre is shown on the map with a small white cross, and each reported 'shindo' is shown as a coloured dot or a coloured region.
You can move back through the earthquake reports using the arrow buttons at the top right (sometimes the same event is reported more than once by different government agencies).
Revised (Vanek, 1962) to be log (A / T) + 1.66 log Δ + 3.3, where T is the period in seconds (valid from 20 to 160 degrees)4Body magnitude: (Gutenberg, 1945) mB = log (A / T) + Q (Δ, h), where A is the peak deviation of the largest of the waves receivbed transmitted through the body of the earth, and Q is a function of the distance Δ and depth h of the epicentre as read from a complicated diagram.
The diagram widely used today was revised by Gutenberg and Richter together in 1956.5Moment magnitude: (Kanamori, 1977) MW = (log M0 - 9.1) / 1.5, where M0 is the moment in Newtons meters measured by a variety of further complicated methods.
