Tonight (Saturday), NHK will air a special about mega disasters. One topic will be the threat of “long wave pulse” earthquakes. The wave pattern you see in the image was recorded in Nishihara Mura last year. It took three seconds to complete one cycle in the wave. The quake was devastating for Nishihara Mura but a point to be made in this program (according to previews I’ve seen) is that powerful long wave pulses pose a particular threat to high-rise buildings.
If you feel comfortable with the language and are interested in the topic, you may want to catch tonight’s show.
– Kirk
http://www6.nhk.or.jp/special/detail/index.html?aid=20170902