Bead experiment suggests avalanches’ size can be predicted
March 9, 2009 by: Sindh Today
London, March 9 (ANI): An experiment using steel beads has demonstrated that it is possible to know how big or small an avalanche can be, which could also have important consequences for predicting earthquakes.
Phenomena as diverse as earthquakes, stock market collapses and avalanches follow so-called power-law distributions.
It is now known that even a minor perturbation can cause a major event when such systems reach a critical state because of a build-up of stress.
“Similarly, the Bak-Tang-Wiesenfeld model of sandpile avalanches, shows there is no way of knowing whether the next event would be big or small,” said Henrik Jensen of Imperial College London, an expert on complex systems.
Now, according to a report in New Scientist, Osvanny Ramos of the Ecole Normale Superieure in Lyon, France, and colleagues say prediction is possible after all.
They designed an experiment that induced avalanches in a two-dimensional pile of 4-millimetre-diameter steel beads.
They placed a 60-centimetre row of randomly spaced beads between two parallel, vertical glass plates 4.5 millimeters apart, with the beads glued to the bottom to simulate the ground under a natural pile. Then they dropped in one bead at a time, creating piles of up to 55,000 beads.
After each drop, the team photographed the pile and measured the position of each bead to calculate the “space factor” - a measure of the disorder in the system, which was related to the space surrounding each bead.
The greater the disorder round a bead, the more likely an avalanche was. If one or more beads moved when a new bead fell on the pile, that was considered to be an avalanche.
An extra-large avalanche involved between 317 and 1000 beads.
The researchers found that if the space factor before a bead dropped was greater than it had been 50 steps earlier, they could predict an extra-large avalanche with 64 per cent accuracy.
According to Ramos, they can improve the odds by analyzing more information, such as the size of the pile.
The work could also have important consequences for predicting earthquakes.
Ramos has an inkling why forecasting earthquakes is so difficult: seismologist tend to use information about the time and size of events, known as a time series, which doesn’t help predict the next big avalanche.
“When seismologists try to predict earthquakes, they analyze the time series,” he said.
He argues that they would have more success analyzing data analogous to the internal disorder in the pile of beads. (ANI)
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