August 29, 2013
Acoustic Waves May Warn Of Impending Tsunami
[ Watch the Video: What is a Tsunami? ]
Peter Suciu for redOrbit.com – Your Universe Online
While the waves from a tsunami can be extremely destructive, acoustic waves could help warn of the impending danger. Not much can be done to actually stop these natural disasters, but the earlier a warning goes out that a tsunami could strike the coast, the better the chances of effectively evacuating the area.
Early warning systems play a critical role in ensuring that people reach safety, but most rely on seismic signals. These are problematic in that they are confirmed or cleared by measuring sea level height. This seismic signal approach stems from the fact that shallow earthquakes exceeding a given magnitude are the most likely causes of tsunamis.
The EU has funded a project called NEAREST that could eventually offer a better way of identifying tsunami threats at early stages. This includes the use of a device called the “tsunameter” that is connected with a surface buoy and consists of a set of instruments that collect several types of data. This device can accumulate local data about acceleration and pressure of water, seismic waves and, in particular, the acoustic waves generated by tsunamis.
From the information gathered it seems possible that actual tsunamis can be distinguished from the background noise, “using a specific mathematical algorithm” to interpret the data. Under this new project, the tsunameter had been in a testing phase for a year off the Gulf of Cadiz in Spain at a depth of 3,200 meters.
“We developed a new device we called tsunameter that we put as close as possible to those places where we know that is very likely a tsunami is generated”, says Francesco Chierici, project coordinator and researcher at the Radio Astronomy Institute (IRA), in Bologna, Italy.
“This tsunameter can be placed close to the geological faults that are responsible for the earthquake and, accordingly, for tsunamis. Detecting a tsunami near its source is crucial especially in peculiar environments such as the Mediterranean where the tsunami are generated very close to the coasts.”
Since March 2010 the tsunameters have been utilized in tests in a new research program called Multidisciplinary Oceanic Information SysTem (MOIST), which is run by the Italian National Institute of Geophysics and Vulcanology (INGV) in Rome.
Researchers agree that the use of acoustic waves can be quite effective. “Their speed of propagation is slower than that of seismic waves, but still quicker than that of the tsunami,” added Stefano Tinti, professor of geology at the University of Bologna, Italy, and an expert in tsunamis.
However, there is still the issue that the technology, as Tinti puts it, “still in an experimental stage. ... It’s not so easy to separate the hydroacoustic signal from the others when the detector is so close to the source.”
There is also the cost of installation and maintenance, and these are factors that the researchers admit need to be addressed.
“Off-shore detection systems are more expensive than coastal ones,” admitted Tinti, who believes it could be more effective to use the many islands spread around the Mediterranean. “The detection could be of no use in terms of warning system for the very point where the detection takes place,” he contends, “but it is still very useful for other areas of the coast.”
Other experts have also concluded that earthquake sounds could be used to develop an early warning system for tsunamis. In a recent report published in The Bulletin of the Seismological Society of America, two Stanford University researchers have identified key acoustic characteristics of the 2011 Japan earthquake that could be used to significantly improve tsunami warning systems.
In addition, other research has found that the use of global positioning systems (GPS) to measure ground deformation caused by a large underwater earthquake could also provide accurate warning of the resulting tsunami just minutes after the onset of an earthquake.
Still, significant considerations remain in providing a timely warning to the population. “Measurements would need to be far enough from the land to be affected to give enough time to raise the alarm,” says Philippe Blondel, acoustic remote sensing expert at the department of physics of the University of Bath.
“For example, if the Vesuvius erupts and a flank collapses into the sea, this would affect the millions of people in and around Naples, in Italy. Even with the best organisation, there are only so many roads available for people to get away in a hurry.”