Epic voyage to uncover what causes tsunamis
Emily Verdouw |
It’s not possible to predict when and where the next tsunami will happen.
That’s because it’s also impossible to predict an earthquake.
But Australian scientists are about to join an expedition to try to get closer to uncovering the causes.
They are part of an international team of scientists going to the Tōhoku-oki earthquake fault zone to drill into the very fault line that shifted in 2011, causing a 9.1 magnitude earthquake – the most powerful in Japan’s recorded history and the third most powerful recorded globally.
Less than an hour after tectonic plates shifted, that power generated a tsunami with a wave height around 40m, travelling 700km/h to reach 10km inland, leading to deadly destruction along 2000km of Japan’s east coast.
The earthquake and tsunami would go on to claim almost 20,000 lives, displacing hundreds of thousands of people and triggering the Fukushima nuclear disaster, making it also one of the costliest natural disasters in recorded history.
ANU geophysicist Associate Professor Ron Hackney tells AAP the 2011 event was unusual.
“The earthquake was unusual in that the break on the fault went right to the sea floor. Normally the break and movement on the fault is deeper down. With the break all the way to the sea floor, the sea floor was moved more, the jump to the east, which shoved the water more and produced a tsunami that was bigger than expected for that region.”
Assoc Prof Hackney is on his way to Japan as the director of the Australian and New Zealand International Scientific Drilling Consortium (ANZIC), accompanied by ANU Associate Professor Will Grant.
Assoc Prof Hackney says to go back to the very place it all began, scientists can figure out if that unusual activity was something that could happen again.
“We hadn’t seen that behaviour before, but it means other areas near Japan or elsewhere in the world might be susceptible to that same behaviour,” Assoc Prof Hackney says.
Australia has been playing a small but significant part in an international collaboration that has spanned a decade and is known as the International Ocean Discovery Program.
The Australian team will fly to the city of Sendai in Japan then jump into a helicopter and fly 300km off the coast to their research ship, a journey that’ll take an hour.
“We can’t see any land from out there at all,” Assoc Prof Hackeny says.
The scientists will work seven days a week, 12 hours a day for seven weeks.
Japan is the most seismologically studied country in the world, so it makes sense it’s also home to the most sophisticated equipment, including the ship the team will work from – Chikyu.
“It’s the most advanced ship built for science that’s out there,” Assoc Prof Hackney says.
It comes with a drill string that’s 8km long, but to get it about 1km beneath the seafloor and into the earthquake fault line is a bold and challenging task.
“It’s 7km of water down… setting up equipment like that it needs to stay in position. You imagine a ship that’s 200m long, with wind blowing, the current of the ocean, it’s hard to keep it in place, but there’s special thrusters in the ship to keep it in same place. The technology is incredible,” Assoc Prof Hackney says.
That drill acts a bit like a straw in a cake, allowing scientist to see the quality of the surface below.
Drill samples of rocks come up to labs on the ship where the team measure their quality and density, and how susceptible they are to earthquakes.
“Some samples get quite dense and mud-like, like potting clay … in some other places its dried and hard, Assoc Prof Hackney explains.
“If it’s wet and squishy, it’s kind of like a ball of clay, it’ll make a flat pancake. If it’s dried it could crumble and fall apart, they can break and move suddenly. If it’s a little bit more squishy they’ll slide gently past each other and not fail catastrophically.”
But thankfully for the Sendai region of Japan, what scientists do know is that 2011 won’t repeat any time soon.
“It would take hundreds of years for stress to build up before that would be likely to happen again,” Assoc Prof Hackney says.
But that’s not to say other parts of Japan aren’t in the firing line or other regions in the world, afterall, that 2011 activity was unusual. But unusual only so far as recorded history can tell us – about 100 years out of the billions of years that earth has been evolving, Assoc Prof Hackney cautions.
“For the people of Japan, knowing how this earthquake happened means in other parts of Japan they can be better prepared.
“They’ll know if they need bigger barriers to prevent tsunamis coming onto land, if nuclear power stations need better safety measures to protect from a tsunami. Then that’s translatable to other regions in the world.”
AAP