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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Pass it on: Popular Science