Esto!... es Divulgación Científica //how do they estimate what time the waves will arrive?

En inglés, pero refleja muy bien lo que hace un verdadero divulgador [científico], y también la forma en que las redes sociales sirven para este propósito. Tumblr se gana un punto por hacerlo posible, y GeologyRocks, se gana mi respeto por hacerlo realidad:

itssabotage asked: how do they estimate what time the waves will arrive?

That is a great question.  The National Oceanic and Atmospheric Administration does a lot in Modeling and Resarch of Tsunamis.  The main goal for them is to develop models for faster and more reliable forecast.  In the scientific community, we understand waves in great detail.  A wave is a disturbance in space and time regarding a transfer of energy.  I won’t get into all the details, but this transfer of energy is the waves motion.  We measure the wave three ways, period (otherwise known as wavelength), height (or amplitude associated with poser of the wave), and period (time for one oscillation).  The amount of oscillations tells the frequency.  See the below picture.

That can describe every type of wave, but with a tsunami it is different.  When a tsunami is triggered, it is much like throwing a stone into a pond, and it is sent in every direction outward from the spot.  Since we are dealing with open oceans, a tsunami may only be a couple of inches or centimeters in the open ocean, but as it approaches the shore, since the depth is shallower, the the unchanging wave height is not visible as a wall of water.  

So three parts that you need to know in order to guess how and when a tsuanmi will land, you need to know the source (like the stone in the pond, in our case a 8.9 magnitude earthquake), how it propagates through open water, and how it approaches a land mass (have to consider the angle of approach, slope of the beach, etc).

The NOAA Center for Tsunami Research uses a model that breaks the tsunami into these three parts, the earthquake, transoceanic propagation, and inundation of dry land.  Therfore, the location and magnitude of the earthquake is put into a ground deformation model to estimate the vertical displacement of the ocean floor to estimate the size of the wave.  The model will then compute a sequence of different simulation scaled from a pre-computed database of model runs prior to an actual event.  As new information about the earthquake and the tsunami itself.

 Next, as the wave propagates through the ocean, data on the wave is collected by what are called DART buoy stations.  With the technology today, we can know the precise location of these buoys with GPS, and the will measure the change in sea level at the station with relation to the depth of the ocean.  Since there are much more than one of the stations, we can also measure the speed which the wave is traveling since we know the distance between the stations and the time that the wave got to them.  This is all happening constantly and being updated frequently to ensure an accurate arival time estimation.  In the deep water, the wavelength is long since the wave’s energy isn’t actually dragging on the ocean floor.

As the wave approaches the shore, the wavelength shortens and the amplitude rises.  In the models are topographic maps of the cast, so the model is now able to calculate the height of the tsunami as it relates to the water depth.

All of this is very technical, and I am sure I am missing some key points as well, but the facts remain the same.  Obviously, the model isn’t much help if you are very close to the source of the earthquake, but the model does give accurate warnings when a tsunami is traveling across the ocean.  We saw this happen this morning.  A couple of decades ago, most of the pacific islands would have received no warning at all of an earthquake, so progress is being made.  If we were able to accurately predict earthquakes before they happened, then we would be much better off, and work is being done to this process.  If you would like to do any more reading into this, here is the site I referenced.

http://nctr.pmel.noaa.gov/model.html

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