We’ve been feeling a lot of earthquakes lately here in Uenohara, nothing consequential, they’re really just barely strong enough to even be noticed, but they freak me out. I don’t understand them, I don’t have any idea what to do in the event of a bad earthquake, and they are unpredictable.
At home when I would watch TV, there would be severe weather warnings that would scroll under what ever I was watching, usually it was just a thunderstorm, but sometimes it would be a fire or severe winds. Here in Japan you will see earthquake notices, with the location and strength of the earthquake.
Japan uses a different scale for measuring the strength of earthquakes. Most countries report earthquakes on the Moment Magnitude Scale (MMS) which is the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. Earthquakes between 3.0 and 3.9 are noticeable but not damaging on this scale. The Great Japan Earthquake was a 9.3.
Japan uses the Japan Meteorological Agency seismic intensity scale (JMA) which measures earthquakes in units of shindo (amount of shaking). The strength of an earthquake is referred to by it’s shindo number and can range from 1-7 shindo. Earthquake measurements are usually stated in whole numbers (an earthquake measurement of 2.5 up to 3.4 would be 3 shindo intensity). 3 shindo intensity earthquakes are noticeable but not damaging on this scale. The Great Japan Earthquakes was a 7 on this scale.
A magnitude scale like MMS is more useful scientifically, because it can easily give and indication of epicenter, and area affected. But I believe an intensity scale, like JMA, is more useful for human safety. Intensity can be roughly converted to peak ground acceleration, which give a good indication of how much damage is done by the earthquake. Earthquakes below 4 shindo do no damage, and are unlikely to harm anyone (peak ground acceleration of 0.80 m/s). 4 and 5 shindo earthquakes are somewhat damaging, though very few people are likely to be hurt (between 0.80 and 2.50 m/s). 6 shindo earthquakes are very damaging, and likely to result in severe property damage, bodily harm, and death (between 2.5 and 4.0 m/s). 7 shindo earthquakes are devastating, and will likely result in catastrophic infrastructural damage, and many injuries and deaths (anything about 4.0 m/s).
I have not yet experienced an earthquake over a 3 shindo level, and hope I never will. I would rather have raging skies, and stable grounds, than the other way around.