Kirk here with some notes on the tidal surge warnings we had here in Kumamoto and throughout Japan’s Pacific coastline.
It turns out that this was a new sort of phenomenon and that even the pros in the JMA (Japan Meteorological Agency) were caught off guard.
The illustration you see with this post is the same as what I saw on NHK’s 7 PM news program. It seems that the surges that occurred in Japan were mostly the result of atmosphereic pressure waves (waves that travel OVER the ocean), not of waves that were tranmitted directly THROUGH the water, as is normal. This confused the experts because it is the first recorded instance of the phenomenon occurring.
Normally, waves transmitted through the water will be bigger at points closer to the source. In this case, however, Japan had some surges that were considerably larger than those observed at the Pacific islands located between Japan and Tonga. The reason for this is that the effects of atmospheric pressure waves on the water tend to accumulate.
Another point that confused the experts was that atmospheric pressure waves propagate more quickly than waves that move though the water. So, the normal predictions about when waves might arrive were way off.
Confusion about these issues led the JMA to issue “no big deal” statements early on and then have to scramble to call for national tsunami warnings later as the actual messurements started to come in.
(This summary is based primarily on my understanding of what I saw on TV. I hope I got it basically right.)
P.S. Despite the warnings, there wasn’t any damage in Kumamoto as far as I know. I think, though, that surges caused some relatively minor problems in other parts of Japan.
