A team of scientists at University College London, the Alan Turing Institute, the University of Shizuoka, and Tokai University have come up with a novel way to provide early warning for tsunamis — using existing global navigation satellite system (GNSS) constellations, including GPS.
"Current tsunami warning systems are not as effective as they should be as they often cannot accurately predict the height of a tsunami wave," explains Serge Guillas, UCL professor and senior author of the paper, of the problem the team seeks to solve. "In 2011, Japan’s warning system underestimated the wave’s height. A better warning may have saved lives and reduced the widespread destruction that occurred, allowing people to get to higher ground and further away from the sea.
"Our study, a joint effort by statisticians and space scientists, demonstrates a new method of detecting tsunamis that is low-cost, as it relies on existing GPS networks, and could be implemented worldwide, complementing other ways of detecting tsunamis and improving the accuracy of warning systems."
The proposed approach works without modification to the GNSS satellites currently in orbit, and without the need to replace any hardware; instead, it simply monitors the radio signals sent from the GNSS satellites to the ground for interference from the Earth's ionosphere — itself affected when a tsunami pushes air upwards and creates an acoustic wave, which increases in volume as it progresses, despite the ionosphere being 300km above sea level.
Using GPS data captured at the time of the Tohoku-Oki earthquake and tsunami in 2011, the team found that their approach could have provided a tsunami warning within 15 minutes of the earthquake — providing a clear ten minutes before the first tsunami hit Japan's east coast, and using just five per cent of Japan's GPS Earth Observation Network System receivers.
"Our calculations suggest the size and shape of the wave could be inferred from the disturbance in the ionosphere and so the next step in the research will be to investigate this further to see if the method could be used for more precise predictions of tsunami size and range," adds lead author Ryuichi Kanai.
"From my experience of working for the Japanese government in the past and seeing the damage caused by the tsunami, I believe that if this research comes to fruition, it will surely contribute to saving lives."
The team's work has been published in the journal Natural Hazards and Earth System Sciences under open-access terms.