Hacker News Reader

Comment by duxup | Hacker News Reader

How do Tsunami Warnings work?

For a Midwesterner a Tornado Warning requires someone to see it, or be be detected by radar. It's usually a good indicator that it is highly likely that the tornado exists and it is actively doing its thing somewhere. Warnings are pretty specific and almost always involve the thing happening.

Tsunami though, would it have to exist as far as seeing it on the coast, or is this more of a "conditions are ripe" kind of event?

I wonder if the Tsunami situation with all the under water variables is a lot more unknown?

View on HN

I am no expert, but I believe they are triggered anytime there is an underwater earthquake. Often these still do not produce any tsunami, but they are issued out of an abundance of caution, there isnt generally a way to see if there really is or isnt until it actually shows up on the coast

It is all 100% automatic based on earthquake data.

We collect a boatload of earthquake data, too. Years ago I subscribed to USGS email alerts for my area as a fun novelty thing, but has to unsubscribe because there were too many of them! (This was in SoCal, so tons of tiny quakes all the time.)

https://tsunami.gov/?page=message_definitions

A warning, the highest level, means “a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring.”

The actual criteria are here:

https://tsunami.gov/operations/opsmanual.pdf (Section 3)

Note that the level of initial alert for an area is influenced by both the magnitude of the quake and the distance/time from quake to the area the alert covers.

> I wonder if the Tsunami situation with all the under water variables is a lot more unknown?

Yeah,I don't think there is anything as clear and with the coverage of radar for tsunamis, and warning when you see one is going to be too late.

i believe they have monitoring deep ocean buoys

How do these detect tsunamis? They must be observing elevation changes, right? Is that GPS based?

i think they monitor pressure waves somehow

here is an interactive map, looks like some of them are picking up something https://www.ndbc.noaa.gov/obs.shtml?lat=13&lon=-173&zoom=2&p...

Triangulation can tell you where a point is between three sources but you need four to determine elevation, because it’s not the radius of a circle but the radius of a sphere.

But at sea there’s not much to obscure satellite signals so I believe resolving buoy position was a solved problem back when gps car navigation still sucked balls because tall buildings make everything harder. You need a lot more satellites to see three or four at the same moment.

Reply on news.ycombinator.com