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Sunday, March 4, 2018

How To Know A Tsunami's Strength

Who knew math could be so helpful? Okay, all of you can put your hand down, no one can see you.

Measuring the size and destructive force of a tsunami wave has been a difficult thing to do.

Take for example the hyper destructive tsunami that hit the northeastern coast of Japan back on March 11, 2011... regardless of what height measurement you can find for it on the Internet, there is NOT a definitive measurement of it.

Tsunami are detected (currently) by dart buoys.

These are floating devices that measure pressure changes in the ocean caused by tsunami.

The problem, however, is that the technology relies on a tsunami physically reaching the dart buoys, which could be problematic if the buoys are close to the shoreline. Ergo... not enough time to provide adequate warnings.

Still... after an earthquake, possible tsunami warning are issued for coastal areas almost immediately. The problem is that one is never sure about the tsunami's ferocity.

However, mathematicians from the University of Cardiff have created a way to calculate the size of a tsunami and its destructive force well before it hits the coast by measuring the underwater sound waves.

Because the sound waves are moving faster than the wave itself, it is possible that such a calculation could lead to a real-time early warning tsunami system.

What we call sound waves actually have the fancier more scientific moniker of acoustic gravity waves (AGWs). These AGWs are generated deep in the ocean after an underwater earthquake, which is how tsunami are triggered. By earthquakes, that is.

The reason why being able to measure the AGW is key is because those suckers travel through the water at 10 times  (or more) the speed of the actual tsunami.

And, less one think you have to be directly in front of the AGW and tsunami in order to measure the sound wave, what's interesting about the AGW is the fact that it doesn't JUST travel in one direction.

After the initial event, AGWs are generated in all directions (think about you merely dropping a small pebble into a still surface... and you see how the water ripples out in every direction of a fairly concentric circle).

As such, because of the fact they move in every direction under water—once it starts in one direction, it continues in that same direction—the AGWs are easily picked up by underwater hydrophones, and can thus be used to predict tsunami strength.

The mathematics of it all was recently published by scientists from Cardiff University in the Journal of Fluid Mechanics.

Within it. they say that via an earthquake's location, duration, dimensions, orientation, and speed can all be calculated by an AGW via a single hydrophone in the water.

The study says that after an earthquake fault's characteristics are determined, it is easy to calculate the amplitude and potential destructive force of a tsunami.

And apparently it is easy-peasy.

Andrew Joseph

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