Tag Archives: temblor

Chile earthquake triggered icequakes in Antarctica

JAMEY STUTZ, OHIO STATE UNIVERSITY

Chile is one of the most seismically active countries in the world. In 2010, it was struck by a powerful 8.8 earthquake which produced temblors throughout the entire country, as well as in Peru and Argentina. But a new study concluded that its effects were felt even further, in Antarctica, where several seismic stations recorded “icequakes,” probably due to fracturing of the ice as the planet’s crust shook.

It’s been documented for a while that big earthquakes can affect Antarctica’s ice sheets both directly, and through generated tsunamis. Tsunamis can propagate across very long distances, pushing and shoving big chunks of ice on the frozen continent. But seismic waves can also chip away at Antarctica’s ice sheet, and that mechanism is not yet entirely understood.  Zhigang Peng, a geophysicist at the Georgia Institute of Technology in Atlanta figured it out almost by accident, while he was studying the effects of the Chile earthquake in South America.

His team was searching for the effects of surface waves – Love and Rayleigh waves.

 

Even though they generate very different ground movement, both Love and Rayleigh wave often generate powerful microtemblors as they travel across the surface. So, while Peng was searching for more recordings of the earthquake, he also analyzed data from Antarctica stations, and he started to observe an interesting pattern.

“We started to find tiny seismic signals that we believe are associated with ice cracking.”

It’s the first time that ice cracks have been thoroughly analyzed following a remote earthquake; the first thing which geophysicists noticed was that only Rayleigh waves (ground roll waves) generate ice quakes. After studying seismic data at 42 Antarctic stations from within 6 hours of the Maule temblor, the team found that 12 of the stations registered “clear evidence” of Rayleigh waves generated by the Chile earthquake passing through the crust beneath the ice sheet, in the form of small icequakes. Because both type of waves generate significant ground movement, but only Rayleigh waves generate ice quakes, they suspect that ice quakes are fundamentally different from earthquakes.

The study suggests a “coupling with the ground that seems to be important,” says Jeremy Bassis, a geophysicist at the University of Michigan, Ann Arbor, who was not involved in the work, but was among the first to link tsunamis with ice shelf cracking.

“I think the big picture of this is that we keep on finding out that these relatively small environmental perturbations generated far away—the ice seems to actually feel them,” Bassis says. By the time they get to the ice sheet, the signals are tiny, but they still can cause the ice to break and change a little bit. “Ten years ago, I don’t think anybody would have thought that.”

Peng admits that his results, while interesting, don’t yet paint a clear picture of what is happening in Antarctica. It’s still not clear if this is a common phenomenon, or if the earthquake (among the biggest ones on record) had some very specific circumstances.

“At this point we cannot say definitively that large events play an important role in accelerating or changing ice behaviors there,” he says.

 

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.

Massive Indian Ocean quakes may signal tectonic break-up

The past few years have been marked by numerous seismic events, some of dramatic magnitude; aside from the huge 9.1 temblor in Japan, the world was also shocked by the pair of massive earthquakes that rocked the Indian Ocean on 11 April 2012. However, as geophysicists warn, this may only be the beginning – the birth of a new plate boundary.

A pair of massive earthquakes

Credits: Harvard University

The undersea earthquakes measured magnitudes of 8.6 and 8.2 and triggered tsunamis throughout the Indian Ocean. The damage was somewhat smaller than what you’d expect, but now, researchers claim their effects may be more far-reaching than first believed. Basically, the earthquakes were caused by accumulated geologic stress breaking the Indo-Australian plate apart; when they took place, they released energy across numerous faults and unleashed aftershocks for almost a week afterwards.

Ever since the 1980s, researchers believed the Indo-Australian plate is breaking apart, but until now, there hasn’t really been any conclusive evidence to support those claims. The April 11 earthquakes represents the most spectacular example of the process in action, as Matthias Delescluse, a geophysicist at the Ecole Normale Supérieure in Paris explains: “it’s the clearest example of newly formed plate boundaries,” he says.

Plate tectonics

According to generally accepted theories, the internal stressing and deformation of the Indo-Australian plate began some 10 million years ago; while the plate moved northwards, the Indian part was stopped by the Eurasian plate and dove under the Himalayas, rising them. However, the Australian part forged ahead, creating the tension which is breaking the plate apart today.

Gregory Beroza, a seismologist at Stanford University in Palo Alto, California, is also a believer in this model:

“The 2004 and 2005 earthquakes by themselves would not have caused this other earthquake. There had to be other stresses”, he says.

Earthquakes and strike-slips

Most earthquakes form at the boundary of tectonic plates, as you can see from the second picture above; one plate drifts beneath the other, creating massive earthquakes – this is called subduction. However, this is not the only form of contact between plates: plates or portions of plates can also slip by each other, horizontally, resulting in what is called as ‘strike-slip’ earthquakes. Typically, these earthquakes are smaller and less dangerous (though dangerous as well).

However, the first of the two earthquakes defied all expectations, being the largest strike slip earthquake on record, and one of the biggest to occur away from any plate boundaries.

Another study drew some pretty interesting, but worrying conclusion: the earthquake was created by accumulated stress throughout the plate, and the release of this stress created one of the most complex fault patterns in the world – something you really don’t want to hear if you live in that area. Typically, an earthquake like this shakes along a single fault, or maybe two if it’s a really big one; but this one shook no less than four faults, one of which slipped more than 20 meters. While this pattern has been described partially in previous work, nobody has analyzed slip amounts in so much detail: Beroza says that Lay and his team “do a splendid job of picking apart this very important earthquake” in their paper.

Aftershocks

So not only was this earthquake unique due to its high magnitude and slip, its aftershocks are also special. In yet another study, researchers found that for the six days following the temblor, aftershocks with magnitudes bigger than 5.5 occurred 5 times more often than normal.

“Aftershocks are usually restricted to the immediate vicinity of a main shock,” says lead author Fred Pollitz, a geophysicist at the US Geological Survey in Menlo Park, California.

However, this changes the general belief of how soon and how close aftershocks can occur after earthquakes, raising the importance of this particular earthquake even more.

“Every earthquake is important to study, but this earthquake is rather unique,” says Hiroo Kanamori, a seismologist at the California Institute of Technology in Pasadena.

Scientific sources: 1 2 3

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.