A report on NHK’s morning news show today introduced new research on the earthquake that hit Nagomi-machi in Kumamoto Prefecture on January 3rd. The rating on the Japanese seismic intensity scale was “lower 6” – quite high on a scale that tops out at 7. The amount of damage, however, was surprisingly low given that rating. Well, the NHK report said that, according to researchers at Tokyo University, the relatively high intensity scale number was caused by the “period” (shuki; the time that one back and forth movement takes) of the quake: 0.5 seconds (fairly slow). Apparently, this kind of shaking is what people can feel most easily and the Japanese scale tends to respond more to this type. The slower rate of shaking seems to be related to the softness of the ground there.
I guess the amount of energy was low enough that, even with this kind of shaking, the damage wasn’t that great. I wonder, though, if this means that Nagomi could have suffered a fate like that of Mashiki if the energy of the quake had been significantly higher. As I recall, Mashiki also had a fairly slow “period” that resulted from its own soft ground.
– Kirk
