Japan Meteorological Agency seismic intensity scale
The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan to measure the intensity of earthquakes. It is measured in units of shindo (震度, seismic intensity, "degree of shaking"). Unlike magnitude measures such as the moment magnitude scale (Mw), and the earlier Richter magnitude scale, which attempt to describe the energy released by the earthquake, the JMA scale describes the degree of shaking at various points on the Earth's surface, and is analogous to the Mercalli intensity scale. The intensity of an earthquake is not totally determined by its magnitude, but varies with event's depth, and distance from the event; for example, a quake may be described as "shindo 4 in Tokyo, shindo 3 in Yokohama, shindo 2 in Shizuoka".
Japan experiences about 400 earthquakes every day, although the vast majority are shindo scale "0" or less and detectable only using specialist apparatus.
The Japan Meteorological Agency (JMA) first assigned a four-stage Shindo in 1884, with the levels: 微 (faint), 弱 (weak), 強 (strong), and 烈 (violent).
In 1898 this scale was changed to a numerical system, assigning earthquakes levels 0–7.
In 1908, the levels on this scale were given descriptions, and earthquakes were assigned levels based on their perceived effect on people. This scale was widely used during the Meiji period, and revised during the Shōwa period with the descriptions seeing an overhaul.
Following the Great Hanshin earthquake in 1995, the first time an earthquake had received the highest rating of 7 on the scale, levels 5 and 6 were divided in two, giving a total of 10 levels of earthquake: 0–4, lower/upper 5 (５弱、５強, "weak 5"/"strong 5"), lower/upper 6 (６弱、６強, "weak 6"/"strong 6") and 7.
The JMA Scale runs from 0 to 7, with 7 being the strongest. The Mercalli intensity scale is sometimes used together with the Shindo; however this is not usual practice in Japan. Real-time earthquake reports are calculated automatically from measurements of ground acceleration. The JMA reports the earthquake level based on the ground acceleration, measured automatically with seismic intensity meters. There is no simple and linear relationship between Shindo Number and peak ground acceleration as Shindo Number also depends on duration, so the values of the table below should only be regarded as an approximate orientation.
|Magnitude-Shindo Number (Shindo Number in Japanese) / Meter reading||Effects on people||Indoor situations||Outdoor situations||Residences||Other buildings||Utilities||Ground and slopes||Peak ground acceleration||Approximate Equivalent Rating on Mercalli Scale|
|0 / 0–0.4||Not felt by all or most people.||Indoor objects will not shake.||Buildings will not receive damage.||Less than 0.008 m/s²||I|
|1 / 0.5–1.4||Felt by only some people indoors.||Objects may swing/rattle very slightly.||Upper sections of multi-story buildings may feel the earthquake.||0.008–0.025 m/s²||I–II|
|2 / 1.5–2.4||Felt by many to most people indoors. Some people awaken||Hanging objects such as lamps swing slightly.||Homes and apartment buildings will shake, but will receive no damage.||No buildings receive damage.||0.025–0.08 m/s²||II–IV|
|3 / 2.5–3.4||Felt by most to all people indoors. Some people are frightened.||Objects inside rattle noticeably and can fall off tables.||Electric wires swing slightly. People can feel it outdoors.||Houses may shake strongly. Less earthquake-resistant houses can receive slight damage.||Buildings may receive slight damage if not earthquake-resistant. None to very light damage to earthquake-resistant and normal buildings.||No services are affected.||0.08–0.25 m/s²||III–IV|
|4 / 3.5–4.4||Many people are frightened. Some people try to escape from danger. Most sleeping people awake.||Hanging objects swing considerably and dishes in a cupboard rattle. Unstable ornaments fall occasionally. Very loud noises.||Electric wires swing considerably. People outside can notice the tremor.||Less earthquake-resistant homes can suffer slight damage. Most homes shake strongly and small cracks may appear. The entirety of apartment buildings will shake.||Other buildings can receive slight damage. Earthquake-resistant structures will survive, most likely without damage.||Electricity may go out shortly.||No landslides or cracks occur.||0.25–0.80 m/s²||V–VII|
|5-lower (5弱) / 4.5–4.9||Most people try to escape from danger by running outside. Some people find it difficult to move.||Hanging objects swing violently. Most unstable items fall. Dishes in a cupboard and books fall and furniture moves.||People notice electric-light poles swing. Occasionally, windowpanes are broken and fall, unreinforced concrete-block walls collapse, and roads suffer damage.||Less earthquake-resistant homes and apartments suffer damage to walls and pillars.||Cracks are formed in walls of less earthquake-resistant buildings. Normal and earthquake-resistant structures receive slight damage.||A safety device can cut off the gas service in some residences. Sometimes, water pipes are damaged and water service is interrupted. Electricity can be interrupted.||Cracks may appear in soft ground, and rockfalls and small slope failures take place.||0.80–1.40 m/s²||V–VIII|
|5-upper (5強) / 5.0–5.4||Many people are considerably frightened and find it difficult to move.||Most dishes in a cupboard and most books on a bookshelf fall. Occasionally, a TV set on a rack falls, heavy furniture such as a chest of drawers fall, sliding doors slip out of their groove and the deformation of door frames makes it impossible to open doors.||Unreinforced concrete-block walls can collapse and tombstones overturn. Many automobiles stop because it becomes difficult to drive from the shaking. Poorly installed vending machines can fall.||Less earthquake-resistant homes and apartments suffer heavy/significant damage to walls and pillars and can lean.||Medium to large cracks are formed in walls. Crossbeams and pillars of less earthquake-resistant buildings and even highly earthquake-resistant buildings also have cracks.||Gas pipes and water mains are damaged. (Gas service and/or water service are interrupted in some regions.)||Cracks may appear in soft ground. Rockfalls and small slope failures would take place.||1.40–2.50 m/s²||VI–IX|
|6-lower (6弱) / 5.5–5.9||Difficult to keep standing.||A lot of heavy and unfixed furniture moves and falls. It is impossible to open the door in many cases. All objects will shake violently.||Strongly and severely felt outside. Light posts swing, and electric poles can fall down, causing fires.||Less earthquake-resistant houses collapse and even walls and pillars of other homes are damaged. Apartment buildings can collapse by floors falling down onto each others.||Less earthquake-resistant buildings easily receive heavy damage and may be destroyed. Even highly earthquake-resistant buildings have large cracks in walls and will be moderately damaged, at least. In some buildings, wall tiles and windowpanes are damaged and fall.||Gas pipes and/or water mains will be damaged. Gas, water and electricity are interrupted.||Small to medium cracks appear in the ground, and larger landslides take place.||2.50–3.15 m/s²||VIII–X|
|6-upper (6強) / 6.0–6.4||Impossible to keep standing and to move without crawling.||Most heavy and unfixed furniture moves and becomes displaced.||Trees can fall down due to violent shaking. Bridges and roads suffer moderate to severe damage.||Less earthquake-resistant houses will collapse or be severely damaged. In some cases, highly earthquake-resistant residences are heavily damaged. Multi-story apartment buildings will fall down partially or completely.||Many walls collapse, or at least are severely damaged. Some less earthquake-resistant buildings collapse. Even highly earthquake-resistant buildings suffer severe damage.||Occasionally, gas and water mains are damaged. (Electrical service is interrupted. Occasionally, gas and water service are interrupted over a large area.)||Cracks can appear in the ground, and landslides take place.||3.15–4.00 m/s²||IX–X|
|7 / 6.5 and up||Thrown by the shaking and impossible to move at will.||Most furniture moves to a large extent and some jumps up.||In most buildings, wall tiles and windowpanes are damaged and fall. In some cases, reinforced concrete-block walls collapse.||Most or all residences collapse or receive severe damage, no matter how earthquake-resistant they are.||Most or all buildings (even earthquake-resistant ones) suffer severe damage.||Electrical, gas and water service are interrupted.||The ground is considerably distorted by large cracks and fissures, and slope failures and landslides take place, which can change topographic features.||Greater than 4 m/s²||X–XII|
Comparison with other seismic scales
A 1971 study that collected intensities in both the JMA Shindo scale and Medvedev–Sponheuer–Karnik scale (MSK scale). showed that the Shindo scale is more suitable for smaller earthquakes, whereas the MSK scale is more suitable for larger earthquakes. The research also suggested that, for small earthquakes up to Shindo scale 3, the MSK value is correlated with the Shindo value ("J") by the formula MSK = 1.5J + 1.5, whereas for larger earthquakes the correlation is MSK = 1.5J + 0.75.
- Earthquake engineering
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