Tag: tsunami

Could Underwater Sound Waves Be The Key To Early Tsunami Warnings?

Mathematicians think they have devised a way of calculating the size and force of a tsunami in advance of it hitting land, which can help early detection.

Experts say naturally occurring high-speed acoustic gravity waves are created after “tsunami trigger events”.

Cardiff University scientists hope to make a real-time early warning system.

Alaska was under a tsunami warning earlier this week after a 7.9-magnitude earthquake struck 280km (173 miles) off the coast of the American state.

The deadliest recorded tsunami was the 2004 Boxing Day Indian Ocean tsunami, which killed almost 230,000 people in 11 different countries.




But scientists in Cardiff hope to help give extra warning time for tsunamis by using the fast-moving underwater sound waves.

By taking measurements of acoustic gravity waves, we basically have everything we need to set off a tsunami alarm,” said Dr Usama Kadri, lead author for the study from Cardiff University’s school of mathematics.

Underwater earthquakes are triggered by the movement of tectonic plates on the ocean floor and are the main cause of tsunamis.

Scientists say sound waves can travel over 10 times faster than tsunamis and spread out in all directions, regardless of the trajectory of the tsunami, making them easy to pick up using standard underwater hydrophones.

They say this is an ideal source of information for early warning systems.

In a new study published in the Journal of Fluid Mechanics, Cardiff University scientists show how the key characteristics of an earthquake – such as its location, duration, dimensions, orientation and speed – can be determined when the gravity waves are detected by a single hydrophone in the ocean.

The sound waves move through the deep ocean at the speed of sound and can travel thousands of meters below the surface.

Tsunamis are currently detected by floating buoys that are able to measure pressure changes in the ocean caused by tsunamis.

However, experts say the technology relies on a tsunami physically reaching the buoys.

The current technology also requires the distribution of a huge number of expensive buoys in oceans all around the world.

Though we can currently measure earthquakes using seismic sensors, these do not tell us if tsunamis are likely to follow,” Dr Kadri continued.

Using sound signals in the water, we can identify the characteristics of the earthquake fault, from which we can then calculate the characteristics of a tsunami. Since our solution is analytical, everything can be calculated in near real-time.

Our aim is to be able to set off a tsunami alarm within a few minutes from recording the sound signals in a hydrophone station.

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Pass it on: New Scientist

A Powerful Earthquake In Alaska Didn’t Trigger A Big Tsunami

Last Tuesday night, a magnitude 7.9 earthquake struck southeast of Kodiak Island in the Gulf of Alaska, prompting a tsunami warning that forced people to flee to higher grounds in the middle of the night.

Fortunately, the tsunami waves were less than a foot high, and the advisories were canceled a little after 4AM local time. So why was Alaska so lucky?

Powerful quakes that happen out at sea are known to cause destructive tsunamis. In 2011, a magnitude 9 earthquake in northeastern Japan triggered waves as high as 126 feet, killing nearly 20,000 people.




In 2004, a similarly strong quake off the coast of Indonesia caused a tsunami that killed more than 200,000 people.

Alaska also has a history of strong earthquakes: in 1964, the state experienced the most powerful quake ever recorded in the US, a 9.2 magnitude tremor followed by a tsunami that killed over 100 people.

Earthquakes occur because the Earth’s crust is divided into plates. These plates can move smoothly against each other or become stuck.

When they become stuck, they build up strain over time, until one day, the plates unstick, releasing energy that causes an earthquake.

Just south of Alaska, the Pacific plate is sliding underneath the North American plate, an area called the subduction zone. That’s why the state is highly seismic, Blakeman tells said.

Last Tuesday night’s earthquake generated because of all the strain building up on the subduction zone, but it did not occur exactly on a fault where the Pacific Ocean seafloor is sliding under the North American plate, Blakeman says.

Instead, the quake occurred a little farther out, in a place where the fault is moving horizontally.

This type of quake, called a strike-slip earthquake, is less likely to trigger large tsunamis, and this is probably why Alaska only saw waves of less than a foot, according to Blakeman.

When earthquakes happen on the subduction zone itself, where one plate is pushing down while the other is going up, then high waves form.

To get a tsunami, you have to have substantial vertical movement on the seabed,” Blakeman says. Those types of earthquakes were responsible for the massive tsunamis in Japan and Indonesia.

Aftershocks in Alaska could continue for weeks or months, Blakeman says. If the quakes generate from the same zone as last night, then large tsunamis should not be expected.

But because the state sits by the Pacific-North America plate boundary, it’s normal that new earthquakes will happen in the future. When and where, exactly?

That’s impossible to say. Earthquakes are so complicated that scientists aren’t able to predict them — at least not yet. “Since we can’t predict them, all we can do is be prepared,” Blakeman says.

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Ancient Skull May Be History’s Earliest Known Tsunami Victim

In 1929, an Australian geologist named Paul S. Hossfeld was investigating the northern coast of Papua New Guinea for petroleum.

He found bone fragments embedded in a creek bank about seven miles inland and about 170 feet above sea level.

At first, Dr. Hossfeld believed that the specimen was from the skull of Homo erectus, an extinct relative of modern humans. Later analysis would show it belonged to a modern human who lived about 6,000 years ago.

Now recent research suggests the remains known as the Aitape skull could be something more: the earliest known victim of a tsunami.

The findings, published Wednesday in the journal PLoS One, may offer useful historical context for how ancient humans living along the Pacific Ocean’s coasts faced fierce natural hazards.

Here we start to see human interaction with some nasty earthquakes and tsunamis,” said James Goff, a retired geologist at the University of New South Wales Sydney and author of the study.




Papua New Guinea occupies the eastern half of a large, bountiful island just north of Australia (the western side is part of Indonesia).

In 1998, after decades of relative geological quiet, a devastating tsunami rocked the country, killing more than 2,000 people.

This huge volume of water struck the coast and swept away everything,” said John Terrell, an anthropologist at the Field Museum in Chicago who has completed research in the country and is a co-author on the paper.

The villages I knew and loved were sheared off.

After struggling for almost two decades to get funding for the project, he returned to the island in 2014 to explore the rain forests and crystal clear creek where Dr. Hossfeld had discovered the skull 85 years earlier.

Dr. Hossfeld had left detailed notes about where he had found the skull, which helped guide Dr. Goff and his team as they collected samples from the same sediment layer at a nearby river-cut cliff.

Back at the lab, they performed geochemical analysis to determine whether the sediment level had been deposited by a tsunami 6,000 years ago.

Because they had previously analyzed geochemical signals from sediment on the island following the 1998 tsunami, the team knew which clues to look for, like grain size and composition.

They found that the sediment collected from the skull site contained fossilized deep sea diatoms. These microscopic organisms were a telltale sign that ocean water had drowned the area at some point.

The researchers also found geochemical signals that matched the signatures they collected in 1998, offering additional evidence that a tsunami had struck around 6,000 years ago.

Bang! Right where the diatoms were looking very sexy and you’re getting excited, you have a signal that says, ‘Hi, I’m seawater,’” said Dr. Goff.

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Plastic Junk Brought Invasive Species to U.S. After Japan’s 2011 Tsunami

In 2011, a massive earthquake shook Japan and reshaped the seafloor. The quake shoved an area the size of Connecticut up by 30 feet.

The tsunami that followed killed roughly 18,000 people. As water swamped the Fukushima Daiichi nuclear power plant, three reactors melted down. Japan’s wounds are still healing.

The tsunami swept 5 million tons of debris into the ocean. Much of the junk did not degrade. Fiberglass boats, far-flung buoys and plastic shards swirled through the Pacific.

Some of the objects came to rest half a world away, like the 60-foot-long polystyrene and concrete dock that landed in Oregon in the summer of 2012.

The dock completed its 4,000-mile journey by beaching itself close to Oregon State University’s Marine Science Center.




A university biologist who specialized in marine invasive species was one of the first people to approach it. Researchers later discovered that the dock harbored close to 100 Japanese species.

That was the neon light,” said marine biologist James Carlton, a Williams College professor based in Mystic, Conn. “That was the harbinger of things to come.”

Carlton and a team of fellow scientists realized the Pacific Northwest faced a flood — not of water but borne by it, of unsinkable junk caked with marine life.

No one could stop the flood, but the researchers could at least document it. The scientists created a network of volunteers in Hawaii and Alaska, down the Pacific Northwest to the middle of California.

State and local officials, park rangers and legions of citizen scientists reported or bagged up what became known, in the biologists’ lingo, as JTMDs: Japanese tsunami marine debris.

If a boat landed on the beach in San Francisco,” Carlton said, “I’d get a call in my lab within a couple of hours.

The JTMDs ferried a lot of animals, as the scientists described in a paper published Thursday in the journal Science.

During six years of study, from June 2012 to February, Carlton and his colleagues counted more than 280 species of Japanese hitchhikers on 600 pieces of debris.

Most were spineless marine critters: sea stars, sea slugs, oysters, barnacles, mussels, amphipods, bryozoa and isopods. Only a few alien arrivals, two species of Japanese fish, had backbones.

This was unlike anything Carlton had witnessed in his 50 years of studying marine invasions, he said. “As time went on, the eyebrows keep going higher and higher. The jaw keeps dropping lower and lower.”

Although the scale of the event was unprecedented, the concept — that rafts carry animals across oceans — was not.

Transoceanic crossings have happened for millions of years.

A recent genetic study of trapdoor spiders found that they must have crossed on a raft from Africa to Australia a few million years ago.

The spider relatives on each continent were too closely related to have last shared an ancestor when Africa and Australia were still geologically connected, some 100 million years back.

Humans have witnessed these arrivals, too. In one well-documented case, 15 iguanas floated atop a cluster of uprooted trees to the Caribbean island of Anguilla in 1995.

The lizards have since established a breeding population on the island.

Of the Japanese species that arrived on the tsunami debris, about a third were already present on the American Pacific coast.

But the foreign animals colonized the wreckage long before the debris came close to shore, Carlton said. The authors of the recent study tracked how currents propelled the debris.

The JTMDs spent the bulk of their journey at sea. “It comes to shore within a few days, acquired by the coastal current — and then, bam! Onto the beach.

The debris at sea becomes like “traveling villages,” Fraser said. “Many rafting organisms brood their young — so their kids grow up on the same raft.” A raft doesn’t have to be artificial.

Fraser and her colleagues tracked marine life that moved hundreds of miles while attached to floating kelp.

Tsunami debris continues to wash up along the Pacific Northwest, most frequently following spring currents. Carlton said he expects the objects and their living cargo to arrive for the next 10 springs to come.

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Pass it on: Popular Science