Tuesday, July 15, 2014

Big earthquakes double in 2014

If you think there have been more earthquakes than usual this year, you're right. A new study finds there were more than twice as many big earthquakes in the first quarter of 2014 as compared with the average since 1979.

"We have recently experienced a period that has had one of the highest rates of great earthquakes ever recorded," said lead study author Tom Parsons, a research geophysicist with the U.S. Geological Survey (USGS) in Menlo Park, California.

                                                  Earthquakes larger than magnitude-7 since 2000.

But even though the global earthquake rate is on the rise,the number of quakes can still be explained by random chance, said Parsons and co-author Eric Geist, also a USGS researcher. Their findings were published online June 21 in the journal Geophysical Research Letters. [Image Gallery: This Millennium's Destructive Earthquakes]

With so many earthquakes rattling the planet in 2014, Parsons actually hoped he might find the opposite -- that the increase in big earthquakes comes from one large quake setting off another huge shaker. Earlier research has shown that seismic waves from one earthquake can travel around the world and trigger tiny temblors elsewhere.

"As our group has been interested in the ability of an earthquake to affect others at a global scale, we wondered if we were seeing it happening. I really expected we would see evidence of something we couldn't explain by randomness," Parsons told Live Science's Our Amazing Planet in an email interview.

The new study isn't the first time researchers have tried and failed to link one earthquake to another in time and across distance. Earlier studies found that the biggest earthquakes on the planet -- the magnitude-8 and magnitude-9 quakes -- typically trigger much smaller jolts, tiny magnitude-2 and magnitude-3 rumblers. Yet, no one has ever proven that large quakes unleash other large quakes. Finding a statistical connection between big earthquakes is a step toward proving such connections takes place.

But despite the recent earthquake storm, the world's great earthquakes still seem to strike at random, the new study found.

                                                                     Japan 2011

The average rate of big earthquakes -- those larger than magnitude 7 -- has been 10 per year since 1979, the study reports. That rate rose to 12.5 per year starting in 1992, and then jumped to 16.7 per year starting in 2010 -- a 65 percent increase compared to the rate since 1979. This increase accelerated in the first three months of 2014 to more than double the average since 1979, the researchers report.

The rise in earthquakes  is statistically similar to the results of flipping a coin, Parsons said: Sometimes heads or tails will repeat several times in a row, even though the process is random.

"Basically, we can't prove that what we saw during the first part of 2014, as well as since 2010, isn't simply a similar thing to getting six tails in a row," he said.

But Parsons said the statistical findings don't rule out the possibility that the largest earthquakes may trigger one another across great distances. Researchers may simply lack the data to understand such global "communication," he said.

"It's possible that global-level communications happen so infrequently that we haven't seen enough to find it among the larger, rarer events," Parsons said.

However, earthquakes smaller than magnitude-5.6 do cluster on a global scale, the researchers found. This suggests these less-powerful quakes are more likely to be influenced by others -- a finding borne out by previous research.

For example, the number of magnitude-5 earthquakes surged after the catastrophic magnitude-9 earthquakes in Japan and Sumatra, even at distances greater than 620 miles (1,000 kilometers), earlier studies found.

                                                                             Sumatra 2004

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Monday, June 30, 2014

Physicists freeze motion of light for a minute

Physicists in Darmstadt have been able to stop something that has the greatest possible speed and that never really stops: light. About a decade ago, physicists stopped it very for just a moment. In recent years, this extended towards stop times of a few seconds for simple light pulses in extremely cold gases and special crystals. But now the researchers at Darmstadt extended the possible duration and applications for freezing the motion of light considerably.

The physicists, headed by Thomas Halfmann at the Institute of Applied Physics of the Technische Universität Darmstadt, stopped light for about one minute. They were also able to save images that were transferred by the light pulse into the crystal for a minute -- a million times longer than previously possible.

                         Light experiment: Success by combining known methods.  Credit: Katrin Binner

The researchers achieved the record by cleverly combining various known methods of their field. The result will have practical significance in future data processing systems that operate using light.

To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions -- electrically charged atoms -- of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped. The first light beam, called the "control beam," changes the optical properties of the crystal: the ions then change the speed of light to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.

More precisely, the light turns into a kind of wave trapped in the crystal lattice. This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement -- mediated by magnetic forces -- propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin," a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave. In this way, the Darmstadt researchers were able to store images, such as a striped pattern, made of laser light within the crystal. The information can be read out again by turning the control laser beam on again.

                                                  Schematic representation of the German "catcher" lights

The fact that only very short storage times were possible until now is because perturbing environments interfered with the spin wave, similar to how moving ships mix up waves in a lake. The information about the stored light wave is thus gradually lost. The perturbations can be alleviated by applying magnetic fields and high-frequency pulses. In our example, these fields reduce the number of boats on the lake, as it were.

How well this works depends strongly on the parameters of the driving optical fields, magnetic fields and the high-frequency pulses. There are very many variations, and the optimal setting can hardly be calculated because of the complexity. Therefore, the Darmstadt researchers used computer algorithms that quickly and entirely automatically find the best solutions during the experiment. One of the algorithms is based on natural evolution, which produces organisms that are adapted as well as possible to the environment. Using the algorithms, the researchers were able to optimize the laser beams, the magnetic field and the high-frequency pulses in such a manner that the spin waves survived nearly as long as is possible in the crystal.

Based on this success, Halfmann's team now intends to explore techniques that can store light significantly longer -- perhaps for a week -- and to achieve a higher bandwidth and data transfer rate for efficient information storage by stopped light.

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