Earthquake power laws emerge in bamboo chopsticks (w/ video)

January 29, 2016 by Lisa Zyga

The sounds made when a bamboo chopstick is broken follow the three main power laws that describe earthquakes, yet scientists also show that they can explain this power law behavior using geometry. Credit: Tsai, et al. ©2016 American Physical Society

(Phys.org)—Whereas a dry twig can be broken with a single snap, breaking a bamboo chopstick produces more than 400 crackling sounds. In a new study, researchers have found similarities between the complex acoustic emission of breaking a bamboo chopstick and the three famous power laws that describe earthquake activity. The scientists also propose that the underlying mechanism behind these laws may be simpler than currently thought.

The researchers, Sun-Ting Tsai et al., from National Tsing Hua University, have published their paper on the sounds of breaking a single bamboo chopstick in a recent issue of Physical Review Letters.

Bamboo and earthquakes

Bamboo is made of a bundle of fibers, similar to how a handful of uncooked spaghetti is made of a bundle of noodles. When a chopstick breaks, each fiber cracks at a different time. Further, a single fiber within a bundle breaks only a little bit at a time. This produces a multitude of crackling sounds: about 80 main cracks (roughly corresponding to the number of fibers) and four to eight smaller cracks following each main crack, in analogy with an earthquake's main shock and many smaller aftershocks.

Like many natural phenomena, the breaking of a bamboo chopstick does not happen randomly. The researchers showed that the crackling sounds mimic earthquake activity by closely following the three main seismic power laws.

First, the researchers found that quieter (lower-energy) sounds are much more common than louder (higher-energy) sounds, and the distribution of sounds in terms of their acoustic energy follows a power law similar to the Gutenberg-Richter law. This law describes how much more common smaller-magnitude earthquakes are than larger-magnitude earthquakes.

Second, the rate of bamboo aftershocks decreases quickly after the main shock. This rate is described by a power law that is very similar to Omori's law, which shows that the likelihood that an aftershock will occur decreases more and more each day after the initial quake, also in a power-law fashion.

Third, in the bamboo chopstick, the ratio between the magnitude of the main shock and that of the largest aftershock does not depend on the magnitude of the main shock. This observation follows Båth's law, which says the same thing for earthquakes.

Video available here:

http://phys.org/news/2016-01-earthquake-power-laws-emerge-bamboo.html#jCp