Tag Archives: magnitude

Invisibility cloak could help protect cities from earthquakes

French researchers say they are close to developing seismic ‘invisibility cloaks’ which would cancel out potentially hazardous earthquake shockwaves, protecting key buildings or even entire cities.

Destroyed buildings in the aftermath of the Japan 2011 earthquake. The system proposed here could protect key areas like the Fukushima nuclear plant, or even entire cities. Via BBC.

Nuclear power plants especially, and potentially entire cities could be cloaked using this technology – if the researchers’ theories are true (which seems highly likely). They believe that by drilling boreholes in a precise pattern into the ground, they could divert seismic waves and averting any negative results. They’ve already teamed up with geo-engineering company Ménard to build upon their results.

“You can build on this knowledge to create an invisibility cloak which will actually protect a specific site from seismic waves,” says the leader of the team, physicist Sebastien Guenneau, who published the work in Physics Review Letters in late March.

They are currently testing to see if they can protect an area the size of a football field from an earthquake.

Invisibility cloaks and earthquakes

In the early 2000s John Pendry from Imperial College London, shook the world when he proposed an invisibility cloak. Several years later, in 2006, he actually built one, but it wasn’t invisible in visible light, but in microwaves. The big problem when trying to develop invisibility cloaks is the sheer difference in size between light waves and real life objects. However, seismic waves are relatively similar in size to large objects like buildings or even cities. This technology works on the same basic principles as proposed invisibility cloaks – but this approach is incredibly creative, a pure example of out-of-the-box scientific thinking.

Seismic waves are basically acoustic waves – but instead of propagating through air, they propagate through the ground. They therefore share a similar behavior (in some cases) with light waves. Invisibility cloaks work by developing materials with geometric structures smaller than the wavelength of the light they are deflecting. In the case of the earthquakes, the holes are boreholes in the ground. The team calculated that for earthquake wavelengths of around 1.5 meters, the boreholes would need to be 30 cm wide and spaced 1.73 meters apart. How this works is that the holes scatter the incoming waves, and if you place the boreholes just right, the scattering makes the waves to cancel each other out. But there are several issues with this approach.

First of all, you can’t really control the properties of soil – like you can do to a material in the lab. Soils vary laterally, and are dynamic in nature.

“Soil is a different story. Its properties are difficult to characterize, and depend on different things, such as the weather! It makes the mathematical models much more difficult.”

Other researchers have toyed with a different approach for an earthquake invisibility cloak, but when the French scientists first come up with this idea in 2010, they were ridiculed by many. However, they stuck to their idea and convinced Stephane Brûlé, an open-minded geo-engineer to join them. Luckily enough,  Brûlé has a company -Ménard, and he was able to jump start the project.

Practical results

In 2012, they got the first practical results. After looking carefully through the weather prognosis, they chose three days of consistent sunny weather in August, near Grenoble, at the foot of the Alps. They measured the seismic waves naturally hitting the area, and after that, they dug their holes: three rows of five meter deep boreholes. They then stopped an measured again – it worked.

Sebastien Guenneau. Leave him alone ladies, he has work to do!

Just as the model predicted, most of the earthquake’s energy was scattered – only 20% of the earthquake’s energy actually reached the surface in the protected area!

“It’s interesting because these are the first experimental results on this topic,” says physicist Boris Kuhlmey who studies electromagnetic metamaterials at the University of Sydney. But he points out the bore pattern the team used would only reflect seismic waves of a specific frequency. “If your aim is to stop an earthquake you don’t get to choose the frequency,” he says.

That’s the second problem with this approach. While you can study a statistical distribution of earthquake frequencies and make a very educated guess (in some cases more than others), you might still be off in your estimates. But Guenneau developed a mathematical model that might provide a “zero stop band”, which can stop a wide range of earthquake waves.

“That would be really key to get it to work well. Maybe it’s possible, on the scale of a city, to diminish the impact of an earthquake considerably,” says Kuhlmey.

Now, they’re set to try it out for good – they’re going to simulate really big earthquakes (magnitude 6) around their test site, which will be protected by boreholes. The boreholes are arranged in a ring with a diameter of about 200 meters. To say that I’m really looking forward to the results is an understatement.

“It would be a dream for me to see this done for real one day, not just tests,” muses Guenneau. In the meantime he is already turning his skills to other problems, such as tsunami control. “Imagine some columns of wood, 200 m from the sea shore, arranged in a similar fashion to the bore holes in the seismic experiments. The effect will be that you deflect the tsunami to a non-sensitive coastal area.”

 

Major earthquake strikes off the coast of Alaska

An earthquake with a 7.5 – 7.7 magnitude shook the Pacific Ocean, striking just off the coast of Alaska, geophysicists working at USGS announced.

Alaska

As I am writing this, the earthquake took place just a few minutes ago, so there’s not much info on it; what we do know is that it hit at a depth of about 10km at 0858 GMT, with the epicenter being located 102km west of Craig, Alaska and 110 km from Klawock, according to the USGS. So far, there are no immediate reports of casualties or damage. Also, the Pacific Tsunami Warning Center explained there is no widespread threat of a tsunami at this time, but they did however issue a regional warning in the vicinity of the epicenter.

We will of course keep you posted with any significant developments, should they occur.

Strong quake hits Japan, creates danger of tsunami

A strong earthquake with an epicenter off the northeastern coast of Japan shook buildings all the way to Tokyo, leading to a tsunami warning for coastal areas of the northeast.

The first estimate of the magnitude was 7.4, but was then lowered to 7.3. The United States Geological Survey (USGS) explained there is no risk of a widespread tsunami for other areas in the Pacific, but a warning for a one-meter tsunami was issued for the coast of Miyagi Prefecture in northeastern Japan – the same area which was most hit by the 9.1 earthquake and consequent tsunami in March 2011. However, unlike that massive earthquake, this one poses no threat to the Fukushima power plant – no irregularities were reported at the site.

The 2011 earthquake caused a huge tsunami, much more than the Fukushima power plant was prepared to handle, causing radiation leakage, contamination of food and water and mass evacuations; the Japanese authorities handled the situation absolutely admirable, and a bigger crisis was averted.

As it seems, the geological situation in the area is still extremely volatile; many more such “smaller” temblors are expected, but an earthquake of that magnitude is very unlikely to happen again in the near future.

Earthquake strikes southern Maine – no injuries or immediate damage [shorties]

The earthquake that struck southern Maine was felt in New England as well as Connecticut, but as far as reports tell us, there’s no significant damage, and not even a single injury.

According to USGS, the earthquake had a meager magnitude of 4.0, despite initial estimates of 4.0, but this doesn’t necessarily mean it couldn’t be dangerous. The earthquake seems interesting especially considering how earthquakes are pretty rare in that area, and there’s no major fault system that crosses the zone.

The strongest earthquake recorded in Maine had a magnitude of approximately 5.7, and took place in 1904. Just so you can make an idea, the magnitude is a measure of the earthquakes energy in the hypocenter, and it is a logarithmic measure – so a magnitude 5 is 10 times stronger than a magnitude 4. The earthquake in Japan that took place last year had 100.000 times more energy.

Massive 8.6 quake strikes Indonesia – but didn’t create a monster tsunami

An 8.6-magnitude earthquake and powerful aftershocks struck the coast of Indonesia today, resurrecting fears of a big tsunami like the one responsible for one of the biggest modern disasters ever. However, this earthquake, which struck at 2:38 p.m. local time (4:38 a.m. ET), about 270 miles (435 kilometers) off the coast of the Indonesian island was drastically different than the 9.1 earthquake that hit Indonesia in 2004.

Strike slip, subduction, and the earthquake in Indonesia

Earthquakes come in different sizes and “flavors”. The can occur as a result of subduction zones, when one tectonic plate is moving beneath another one, causing a massive amount of friction and stress, they can be strike-slip earthquakes – when plates are moving laterally one in respect to the other, or they can occur even due to mineral phase changes in the depths of the Earth. While the one in 2004 was a subduction, this one was a strike-slip earthquake, and typically, these kind of events aren’t associated with big tsunami risks.

Diagram of a subduction zone; the earthquake in 2004 was a result of such a subduction zone

“With a strike-slip event you don’t have the same potential hazard for a tsunami as you do with a subduction event because the plates are moving adjacent to each other,” said Julie Dutton, a geophysicist with the U.S. Geological Survey (USGS).

The 8.6 earthquake

The epicenter was pretty much in the same place as the 9.1 one in 2004, which created a tsunami that killed over 220.000 people. However, even though the magnitudes may seem similar, the difference is quite big: the magnitude is measured in a logarithmic scale, which means that in this case, a magnitude of 9 is 10 times bigger than than a magnitude of 8. In the same way, an 8.6 one is over 3 times less powerful than a 9.1 one, so the magnitude difference is quite significant.

The earthquake was followed by an 8.2-magnitude aftershock hit at 6:43 a.m. ET, the USGS said, raising the tsunami alerts, but as I already said, it’s usually subduction earthquakes that are associated with major tsunamis. This happens because when one tectonic plate is diving beneath another, a huge portion of the seafloor is shoved beneath, and that displacement of sea floor also displaces ocean water. Basically, the more seafloor you shove beneath the other plate, the bigger tsunami you get. At a strike slip earthquake, faults in the crust essentially moved from side to side instead of up and down, and as a result, the largest tsunami recorded was smaller than 2 meters, so all alerts have been lowered.

An estimation of the damage caused by the earthquake is still not available, but we’ll keep you posted on the developments as they occur.

Powerful 7.2 earthquake shakes Turkey, kills over 60 people

Another powerful seismic event has taken place, this time in Turkey; the 7.2 earthquake in case struck eastern Turkey on Sunday, killing at least 60 people and turning most buildings into big chunks of concrete and metal.

However, Turkish scientists grimly predict that the victim count could easily go above 1000, as housing conditions are especially low in eastern Turkey. The city of Ercis, a city of 75,000 in the mountainous province of Van close to the Iranian border was hit the hardest, and there is still no official report about the state of the city. The city lies on the Ercis fault, one of Turkey’s most seismic prone areas.

“There are so many dead. Several buildings have collapsed. There is too much destruction,” Ercis mayor Zulfikar Arapoglu told NTV television. “We need urgent aid. We need medics.”

Turkey lies in one of the world’s most active seismic regions, with numerous faults that cause massive earthquakes of over 7 (just so you can get an idea, a 7 degree earthquake is 10 times more powerful than one with the magnitude of 6). US scientists reported no less than eight replicas of the temblor, one of which was 5.6.

Massive earthquake hits Japan… again

The seismological events near Japan are far from reaching an equilibrium; a 7.4 or 7.5 earthquake on the Richter scale struck apan’s Miyagi Prefecture and its vicinity in northeastern Japan at 23:32 p.m. (1432 GMT) local Time Thursday, the Japan Meteorological Agency (JMA) said.

The area is not so far away from the major 9.0, which hints at related seismic activity, but more thorough research is conducted in order to find out more about this; the tsunami alert that was originally issued was retreated, and nuclear power plants are under no additional threat.

At the crippled and troubled Fukushima power plant, radiation levels remain high, but there hasn’t been an additional elevation caused by this recent earthquake. It’s still uncertain if this kind of earthquakes will continue to appear in the near future, but it’s definitely something worth considering.

Despite the fact that it hasn’t caused significant damage, blackouts have been reported throughout the whole region, and people are agitated and wondering when the situation will calm down. It’s still unclear if this was an isolated event or part of the “legacy” left by the big temblor, but as the days pass questions are going to be answered. All in all, it’s great to see that there wasn’t any serious damage done, and people are handling this extremely well.

Large earthquakes don’t trigger others far away

Simplified map of seismic hazards in the US

 

Ever since the 9.0 earthquake in Japan, there has been a growing mainstream interest for earthquakes, which will probably fade away as time passes, only to be revived when the next big temblor strikes. However, the good news is that, even for a brief period of time, seismologic studies are given the attention they very much deserve. Such is the case with a study conducted by the Royal Geographic Survey and the University of Texas which concluded that while major earthquakes do, of course, set off strong aftershocks in the nearby vecinity of the epicenter, they won’t have any effect for distances of over 600 miles.

Previous research seemed to indicate that a major earthquake could trigger smaller aftershocks throughout the whole planet, so the team set out to study if this is actually true, by studying seismic data from the past 30 years; they found 205 big earthquakes (with a magnitude of over 7), and no less than 25.222 moderate earthquakes (magnitudes of 5 to 7).

The team checked to see if there was a surge in smaller earthquakes after big ones, and they found out that while moderate earthquakes increase in number after bigger ones, they all take place at less than 400 miles from the major temblor, and in less than 24 hours.

“The regional hazard of larger earthquakes is increased after a mainshock, but the global hazard is not,” the team concludes.

While this is not big news for the seismological community, who would have most definitely noticed a thing like this, the study should go a long way to calming people down after the recent seismic events.

Massive 7.9 magnitude earthquake hits Japan, creates tsunami

It’s been a busy tectonic month, and things aren’t about to chill down. A massive 7.9 magnitude Earthquake has just hit the Northern coast of Japan, triggering a more than four meter tall tsunami that wiped down cars and other property along the coastline, but it’s still unclear how many people were injured or killed. What is also unclear, and shocking to me, is that in the rush of events, some sources reported the earthquake as having a magnitude of 8.9, which would make the earthquake 10 times more powerful.

The national broadcaster, NHK, showed footage of dozens of cars and ferries being washed up on the beach, but additional details are still unavailable. The Japanese Meteorological Agency issued a tsunami warning for the entire Pacific Japanese coast, and residents in the coastal areas have been urged to evacuate and more deeper inland, to higher grounds.

The earthquake, which took place in the Earth’s crust, struck about 125 km off the northern coast, at an estimated depth of 10 km, and is expected to generate further tsunamis with waves of 6-7 meters, especially in the Miyagi Prefecture, in northeastern Japan, where the earthquake’s intensity was 7.

Earthquake’s magnitude and intensity should not be confused, as the magnitude measures the amount of energy released by the earthquake, so it’s the same for everybody in the world, while intensity refers to the felt intensity and damage caused by an earthquake, so this varies from area to area for the same event.