Buried Mangrove Forests Protect Buildings Above From Earthquakes

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What’s the News: To dampen structural vibrations from earthquakes, engineers often place a flexible layer of rubber bearings in between buildings and the soil. Now, scientists are learning that Mother Nature uses a similar technique. A research team has found that a buried layer of mangrove in the Caribbean island of Guadeloupe absorbs earthquake energy, shielding the above ground from soil liquefaction. This discovery could be exploited to help protect new buildings in the Caribbean islands.

How the Heck:

• Using an array of accelerometers at the Belleplaine test site in Guadeloupe, the team, lead by Philippe Gueguen at the University Joseph Fourier in Grenoble, measured the vibrations of 62 tremors in the area. They noticed that the shaking was less pronounced at the site when compared to nearby locations.
• They then drilled bore holes into the ground and discovered an old mangrove swamp.
• By analyzing the swamp and the soil column, the team learned that the mangrove dampened the quake waves and decreased the shaking of the ground soil, according to their paper posted on the non-peer reviewed arXiv.
• Furthermore, the mangrove reduced the frequency variability of seismic motion on the ground, which should make it easier for scientists to determine earthquakes’ resonant frequency.

What’s the Context:

• The Caribbean islands are prone to sometimes devastating earthquakes, as evidenced by the recent catastrophe in Haiti.
• The researchers say that soil structures similar to Guadeloupe’s exist on many of the islands.
• While the mangrove does dampen most of the seismic waves from earthquakes, the buried forests do have a specific resonant frequency that can still prove disastrous. If engineers build houses and structures that resonate at a different frequency than the earthquakes, they should be able to avoid major damage.

The Future Holds: Scientists need to work out the resonant frequency of quakes, and then engineers can try to design new buildings that will be more resistant to damage.

References: Philippe Gueguen, Mickael Langlais, Pierre Foray, Christophe Rousseau, Julie Maury. arXiv:1106.1268v1: A Natural Seismic Isolating System: The Buried Mangrove Effects.

http://blogs.discovermagazine.com/80beats/2011/06/13/buried-mangrove-forests-protect-buildings-above-from-earthquakes/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+80beats+%2880beats%29

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