GPS satellites orbiting the Earth may be more efficient at detecting tsunamis and much faster than seismic sensors, according to a study.
The method could serve as an effective warning system for countries around the world, said researchers from University College London, UK.
Tsunami waves are low in deep water, but can travel at speeds of up to 800 kilometers per hour in deep sea, and when they enter shallow water, they slow down, increasing in height.
Although the waves are usually a few centimeters high, they still disturb the upper atmosphere, pushing the air and creating an acoustic wave that amplifies as it rises higher.
This acoustic wave can reach a height of 300 km in the ionosphere in about seven minutes, and the decrease in electron density that occurs as a result can be detected by satellite signals in 10 to 15 minutes, the researchers found.
As the density of electrons in the region is reduced, this affects radio signals sent from GPS satellites to GPS receivers on the ground, slowing down or accelerating different parts of the signal or changing the direction of the signal depending on the frequency, the team explained in an article published in Natural Hazards and Earth System Sciences.
While some tsunamis reach shores in less than 10 minutes, researchers say the method could also be used to predict a second or third wave, helping to determine whether a tsunami warning should be lifted or maintained after the first wave.
“Our study demonstrates a new method of tsunami detection that is inexpensive because it relies on existing GPS networks and can be applied worldwide, complementing other ways to detect tsunamis and improving the accuracy of warning systems,” said Professor Serge Gilas from UCL Statistical Science.
For the study, researchers from UCL and universities in Japan looked at GPS data during the devastating earthquake and tsunami in Tohoku-Oki in 2011.
They found that a tsunami alert could be issued with confidence within 15 minutes of the quake – at least 10 minutes before the first tsunami hit Japan’s east coast.
They also found that the warning could only have been issued using data from only 5% of Japan’s 1,200 GPS receivers – meaning the method could be used in countries with a rarer GPS network than Japan. .
The team said the next step in the study would be to investigate further to see if the method could be used to make more accurate estimates of the size and scope of the tsunami.
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