The massive waves called tsunamis can arrive with little notice, making evacuation challenging. A team of earth scientists now report that the devastating walls of water can be predicted by their magnetic fields, which signal the wave’s arrival sooner than anything else. The team’s results were published in the American Geophysical Union’s Journal of Geophysical Research: Solid Earth.
Tsunamis are caused by undersea activities like earthquakes or volcanic eruptions that send powerful shockwaves in every direction. A typical warning sign of a tsunami is the rapid recession of the ocean from the shore. But the phenomenon demonstrated by the recent team illustrates that magnetic fields arrive before the sea level changes, making it the most immediate indicator of a tsunami. This idea had previously been proposed but never actually measured.
“It is very exciting because in previous studies we didn’t have the observation [of] sea level change,” said Zhiheng Lin, a geophysicist at Kyoto University and a co-author of the paper, in an AGU release. “We have observations [of] sea level change and we find that the observation agrees with our magnetic data as well as theoretical simulation.”
To collect their results, the team looked at data from two tsunamis, one that occurred in Samoa in 2009 and another that hit Chile in 2010, to model how the magnetic field of a wave would behave. The two events are some of the earliest times simultaneous data on sea level change and magnetic fields were made for tsunamis.
“We’ve needed a study that compared the magnetic field data with the sea level change from the pressure data and I’m pretty sure they’re the first to really compare how well the sea level from magnetic field matches the sea level from pressure,” said Neesha Schnepf, an earth scientist specializing in geomagnetism at the University of Colorado at Boulder who was unaffiliated with the study, in the same release.
The models had an easier time in deep water situations, as in coastal waters there’s more environmental noise that makes it harder to detect the tsunami’s magnetic field. The behaviour of the magnetic field — the important thing here being its arrival time — varies based on the water’s depth, but if the tsunami originated in water a few miles deep, its magnetic field would arrive on shore a full minute before the water begins to recede, a potentially lifesaving amount of time when every second counts.
“I think the practical goal would be if your ability to model tsunamis is so improved, … you could come up with much better predictions of what areas might need to be warned [and] how badly it might hit certain places,” Schnepf said.