Seismic waves can trigger aftershocks long after quakes

January 4th, 2008 - 1:47 pm ICT by admin  

Washington, Jan 4 (ANI): Researchers have proven that seismic waves, which are sounds radiated from earthquakes, can bring on aftershocks, often long after a quake has subsided.

The research was carried out using a novel device that simulates earthquakes in a laboratory setting in Los Alamos, New Mexico, US.

This apparatus mimics earthquakes by pressing plates atop a layer of tiny glass beads. When enough energy is applied to the plates, they slip, like tectonic plates above the mantle.

With the help of this device, researchers explained how wave energy can be stored in certain types of granular materialslike the type found along certain fault lines across the globeand how this stored energy can suddenly be released as an earthquake when hit by relatively small seismic waves far beyond the traditional aftershock zone of a main quake.

The earthquake machine revealed that when sound waves were applied for a short period just before the quake, they could induce smaller quakes, or, in some instances, delay the occurrence of the next major one. In fact, the sound waves seemed to affect earthquake behavior for as many as 10 earthquake events after they were applied.

The most surprising fact that the researchers found was that the release of energy can occur minutes, hours, or even days after the sound waves pass; with the cause of the delay remaining an alluring mystery.

More surprising still, the team found that the granular beads in the device could store a memory even after the system had undergone a quake and the beads had rearranged themselves.

The memory part is the most puzzling because during an earthquake, there is so much energy being released and the event is so violent that you have to wonder, why doesnt the system reset itself? said Los Alamos researcher Paul Johnson.

Though the research has helped confirm that earthquakes are periodic events and that sound can disrupt them, catastrophic events in other granular mediasuch as avalanches or the sudden collapse of sand dunescould help provide clues into the physics of earthquakes.

This could also help researchers to unravel the mystery of stored memory in granular systems. (ANI)

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