The Japanese seismic intensity scale “shindo” is a measure of the effects of an earthquake. It is more meaningful for what is happening at the surface and at various locations away from the epicentre. In general, a higher Magnitude means a higher shindo, but there can be circumstances where the effects are concentrated or dissipated. Consider that when you read, ” the probability of a strong quake of “lower 6” or more on the Japanese seismic intensity scale to 7 occurring in the next 30 years had climbed 31 points from 2010 to an estimated 62.3 percent for Mito, Ibaraki Prefecture, 90 km north-east of Tokyo” and “The probabilities for some locations were underestimated before the [March 2011 Great East Japan Earthquake].”
Oddly, Tokyo’s probably increased to only 23.2, much lower than neighbouring Yokohama (71.0) and Chiba (75.7). (Yoshiko-chan, you can go to work as normal.)
[Table from wikipedia – Japan Meteorological Agency seismic intensity scale – retrieved 2012-12-22]
|Magnitude-Shindo Number / Meter reading||Effects on people||Indoor situations||Outdoor situations||Residences||Other buildings||Lifelines||Ground and slopes||Peak ground acceleration|
|0 (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|
|1 (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|
|2 (2) / 1.5–2.4||Felt by many to most people indoors. Some people awake.||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|
|3 (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|
|4 (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|
|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|
|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|
|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 other.||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|
|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|
|7 (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|
Here’s a map of Japan with satellite imagery of earthquakes and tsunami.
The Newcastle Earthquake of 1989 was Magnitude 5.6 with an MMI of VIII Destructive. If the peak acceleration figure of 1m/s^2 is correct, its shindo number would be 5-lower; but from personal experience it was probably closer to a 4. And for further comparison, Newcastle was at the lowest probability level for an earthquake (despite its history of 1 every 50 years) but since 1989 has been put in the top level. There’s still no special building code requirement, but I’d be slightly over-engineering to be safe.