Japan’s rising analysis stars: Tatsuya Kubota

That is the third in a Nature Index sequence of profiles about rising early-careers researchers in Japan.

It was the Tohoku earthquake and tsunami in March 2011 that cemented Tatsuya Kubota’s resolve to develop into a seismologist. Then a final-year geology undergraduate at Tohoku College in Sendai, Japan, Kubota was doing benchwork when the bottom began to shake violently, and books started to crash from their cabinets.

He fled the constructing and spent the following few weeks sheltering at dwelling. Sendai, situated some 130 kilometres from the epicentre, was principally spared the large-scale bodily harm of Ishinomaki and different coastal cities within the area. However its residents needed to endure weeks with out water and electrical energy in unforgiving temperatures.

Nature Index 2023 Japan

The 9.0-magnitude earthquake and ensuing tsunami, which additionally brought on the nuclear catastrophe at Fukushima, claimed practically 20,000 lives. Scientists have but to “attain a decisive conclusion” as to why the earthquake — one of the crucial highly effective ever recorded — occurred, says Kubota, now a analysis fellow at Japan’s Nationwide Analysis Institute for Earth Science and Catastrophe Resilience in Tsukuba.

When tectonic plates slide below one another, they generally develop into caught, inflicting an immense build-up of vitality, which when launched leads to an earthquake. Such ‘stick-slips’, as they’re known as, normally happen deep underground the place the strain is greater and plates are likely to lock most strongly collectively, says Kubota. However within the case of the Tohoku earthquake, the Pacific plate and North American plate grew to become caught at each deep and shallow parts (lower than 10 kilometres from the ocean ground). “So far as I do know, no different earthquake has had such a particularly massive slip within the shallow portion like this,” he says.

For years, scientists have deliberated over this anomaly. Underwater sensors close to the epicentre solely went as deep as 3 kilometres, and the closest onshore information have been recorded greater than 200 kilometres away from the rupture, so information have been laborious to come back by. However Kubota knew fixing the thriller was essential: shallow ruptures, not like earthquakes that originate deep underground, lead to bigger vertical actions of the ocean ground and thus greater tsunamis. “Understanding the mechanism of shallow earthquake slips is essential for higher predicting potential tsunami dangers,” he explains.

Kubota and his collaborators first mixed current information (which measure sea-floor location earlier than and after an earthquake) with tsunami information recorded by strain gauges on the ocean ground straight above the fault zone (that provide details about adjustments to the ocean floor). They invented a modelling methodology to analyse the info.

In 2022, the researchers reported their findings¹: within the case of the Tohoku earthquake, the Pacific plate was pinned beneath the Okhotsk tectonic plate so strongly that the 2 moved collectively as one, till the stress merely grew too nice. “This deep mechanical locking was then launched, which brought on the earthquake and provoked slips in each the deep and shallow components of the plate boundary,” explains Kubota. “Our analyses supplied us with a brand new mechanical perspective during which shallow slips can happen with out the vitality accumulation within the shallow portion.”

Kubota — among the many high 5 most prolific early-career researchers in Japan for Nature Index publications within the Earth and environmental sciences since 2015 — was additionally was the lead writer of a Science paper² revealed final yr that examined how the highly effective Hunga Tonga–Hunga Ha‘apai volcanic eruption in January 2022 triggered damaging tsunamis tons of of kilometres away in Australia, New Zealand and Japan,

“The stunning function was that the primary waves arrived two hours sooner than what is predicted for standard tsunamis,” says Kubota. The waves additionally lasted for for much longer than would normally be the case. Utilizing laptop simulations, he and his co-authors revealed that the Tonga tsunamis have been shaped as a result of the eruption was so sturdy — as much as 500 instances extra highly effective than the atomic bomb dropped on Hiroshima within the Second World Warfare — that it brought on the entire ambiance to vibrate. These vibrations, within the type of one thing often known as Lamb waves, raced throughout the globe on the velocity of sound and drove the preliminary tsunamis. The researchers are actually learning the later Tonga tsunamis. As Kubota explains: “The mechanism of the secondary waves isn’t well-clarified, however the waves [generated] are bigger.”

He says {that a} better understanding of such pure phenomena is essential to mitigating future disasters. “I hope my research shall be helpful to danger analysis of future tsunamis and earthquakes.”

This text is a part of Nature Index 2023 Japan, an editorially impartial complement. Advertisers don’t have any affect over the content material.