[doldge]

Cross-posting from my FB feed:

Here's some of the interesting stuff I've found on the internet about today's earthquake (that they're now calling a 7.8):

1) real-time Buoy data, for helping to determine the likelihood of a Tsunami: http://www.ndbc.noaa.gov/ Interestingly, the quake only caused a tiny change in the sea level (in the region of 5 cm's) but the expected swells on land are in the region of 3-5 meters. I believe this is because as the wave gets closer to land, it get's funneled into a smaller area, meaning the 5cm change in sea level gets amplified. Which is why it's hard for the civil service to accurately predict whether a tsunami is likely when these events occur (That, and the nearest working buoy is in Tonga), which would by why they almost always say yes, and then retract the warning later.

2) the USGS science-y explanation for what actually happened. The take-away seems to be that this may have increased the stress on the primary fault in NZ. Interestingly, their's a a suggestion that the rupture was across the hope fault, rather than along it, which helps to explain why the after shocks have been so varied (by location): http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#...

3) also from USGS, a map indicating affected regions, with town populations, and the likely economic impact of the quake: http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#...

4) The Canterbury Police shared a link earlier that indicated 3-5 meter swells is around the maximum we should expect from a locally generated earthquake (due to the nature of fault lines in NZ), that's not to say we can't experience a larger tsunami, but that said tsunami would have to be generated externally (like say, south america), which should in theory give us more time to prepare. But like all things, this isn't a hard and fast rule.

5) there's a pretty cool video of what purports to be lights in the sky over wellington during the earthquake (probably has something to do with magnetic interference from the energy released by the quake): https://www.facebook.com/plugins/video.php?href=https%3A%2F%...

6) stuff have had pretty good live coverage here: http://www.stuff.co.nz/national/86416304/live-north-canterbu...

7) The USGS website indicated that the quake lasted around 2 minutes, with the highest intensity coming around 50 seconds into the quake.

[DanBC]

There are some videos on Youtube of tsunami from various places.

Here's one from Japan: https://www.youtube.com/watch?v=j0YOXVlPUu4

https://www.youtube.com/watch?v=5IKIazZc-a8

It doesn't look like much is happening at the beginning. It doesn't look like a wave, or a front of water. But it's a lot of water, and it's fast.

[Freestyler_3]

1) I think it was because the 5cm height is backed by a huge width, when crawling towards the land slope creates a very strong (not necessary high) wave that just keeps pushing forward.

[snowwindwaves]

Tsunami waves have an extremely long period. A good surfing wave forms when a swell 2-5 m amplitude with period 13-24s when it starts to feel the bottom of the ocean.

The amplitude of the tsunami wave in the open ocean is much smaller than wind-generated swells but they can have periods of 60-70 minutes so they are more of a surge that just keeps coming when they hit land, and as you say when they start to feel the bottom they stand up and the large volume of water in the wave makes it stand up larger and more powerful than you would expect for a smaller amplitude swell.

Every wave has a peak and a trough and the trough of the tsunami wave is what causes the water levels to recede so drastically before the wave hits.

Geographic features like valleys that get narrower and narrower will cause the same volume of water hitting the coast to make a much more drastic change in water level

[snovv_crash]

Imagine the energy stored by lifting a kilometre-high column of water 5cm. Now imagine how high that energy can lift a 5m column of water once it reaches the coast. Obviously there is the 1/r dissipation because the circumference increases, but still, deep water lifts like this can cause a massive surge at the coast.