Natural disasters, including earthquakes, are basically unpredictable because they occur beyond our control. However, that does not mean humans give up. We are still trying to overcome natural disasters by continuing to learn from events that have occurred.
One form of human effort in dealing with natural disasters, especially earthquakes is with earthquake detection devices and tsunami detection devices.
So, talking about earthquake detection and warning tools, Japan is arguably the champion of all countries in the world. Being in an earthquake-prone area, Japan has repeatedly experienced earthquakes. Some of them are even very powerful.
Realizing that technology to alert the public could save hundreds to thousands of lives, researchers at the University of Tokyo's Earthquake Research Institute (ERI) devised a new technique that detects subtle gravitational signals traveling just before an earthquake occurs.
In the study, published in the scientific journal "Earth, Planets and Space", researchers found important information among the large amount of seismic data generated by the 2011 Tohoku earthquake in eastern Japan.
The research was inspired when Professor Shingo Watada read a paper from the Istituto Nazionale di Fisica Nucleare in Italy which suggested gravimeters, sensors that measure the strength of local gravity, could potentially be used to detect earthquakes.
"This made me think, if we have enough seismic and gravity data from the time and place of the occurrence of large earthquakes, we can learn to detect earthquakes with a gravimeter as well as a seismometer. This could be an important tool for research of seismic phenomena in the future," said Professor Watada quoted from Earth.com.
Earthquake detection process
As seismic waves transmit energy through the Earth, the density of the subsurface material through which they travel becomes denser and develops a slightly greater gravitational pull.
Gravity is generated at the speed of light, which means that a sensitive gravimeter can pick up on these changes in density before the seismic waves arrive.
"This is the first time anyone has shown a definite earthquake signal with such a method. Others have investigated the idea, but found no reliable signal," explained one of the ERI graduates, Masaya Kimura.
"Our approach is unique in that it examines a wider range of sensors that were active during the 2011 earthquake. And we use a special processing method to isolate the quiet gravitational signal from the noisy data," he explained.
The researchers used a variety of data collected from seismic instruments located on land and sea, and collected data from a superconducting gravimeter in central Japan.
The signal analysis performed by the team was so reliable that it received a score known as 7-sigma accuracy, meaning there is only a one-in-a-trillion chance that the result will be wrong.
This will be very useful in the calibration of future instruments specially made for detecting earthquakes. Professor Masaki Ando of the Physics Department of the University of Tokyo has invented a new type of gravimeter, namely the torsion bar antenna (TOBA), which aims to be the first tool for such detection purposes.
"SGs and seismometers are not ideal because the sensors inside move in unison with the instruments, which nearly cancels out subtle signals from earthquakes," explains Professor Nobuki Kame from ERI.
"This is known as the Einstein lift, or equivalence principle. However, TOBA will solve this problem. This device senses changes in the gravitational gradient despite motion. It was originally designed to detect gravitational waves from big bangs, such as earthquakes in outer space, but our goal is now more down to earth," he explained.
The researchers then envision a network of TOBA instruments distributed throughout the seismically active region. This early warning system is claimed to be able to warn people 10 seconds before the first seismic wave arrives.
10 seconds may feel tight. However, detection and early warning as soon as possible is very meaningful impact in efforts to save disaster victims.