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Japanese scientists develop advanced earthquake detection method

A TOBA with door open to reveal cryogenically cooled sensor platform inside.

Japanese scientists have devised a new way of sensing earthquakes that claim thousands of lives every year. Early warnings can help people move to safer locations and even a few seconds can make a lot of difference. Researchers at the University of Tokyo, commonly known as Utokyo, have demonstrated a new earthquake detection method. Their analysis suggests a subtle gravitational signature that precede an earthquake’s earliest tremors.

This new detection plan might be able to help earthquake warning system sound an alarm before the disaster strikes, providing people the time they need to evacuate buildings and move to safer places.

The use of seismic and gravitational data

Taking inspiration from an Italian research paper that suggested earthquakes could be detected using gravimeters, researchers at the University of Tokyo’s Earthquake Research Institute decided to use seismic and gravitational data from the time and place a big earthquake struck. This would be highly useful in detecting earthquakes using gravimeters and seismometers.  

Shingo Watanda, Associate Professor at Earthquake Research Institute, and his team of fellow researchers were able to locate early earthquake signals from the massive amount of seismic and gravitational data produced during the 2011 Tohoku earthquake in eastern Japan.

According to Masaya Kimura, postgraduate, ERI, said, “This is the first time anyone has shown definitive earthquake signals with such a method. Others have investigated the idea, but haven’t yet found reliable signals.”

Kimura added, “Our approach is unique as we examined a broader range of sensors active during the 2011 earthquake. And we used special processing methods to isolate quiet gravitational signals from the noisy data.”

Japan is a seismic active country with a wide network of seismic instruments not only on land, but on sea as well. The researchers have used seismic data from superconducting gravimeters (SGs) in Kamioka, Gifu Prefecture, Matsushiro and Nagano Prefecture in central Japan.

Superconducting gravimeters

Scientists performed what they called signal analysis. This was an extremely reliable analysis and they call it 7-stigma accuracy. This meant that there would be only one-in-a-trillion chance where the result could be incorrect. This would greatly help not only prove the concept but can also be used for calibration for future experiments that would be tried specifically to detect earthquakes. Associate Professor, Masaki Ando, Department of Physics, has invented a one-of-a-kind gravimeter – the torsion bar antenna (TOBA) – the first of such instruments.

SGs and seismometers are not the ideal instruments as the sensors move with the instrument which cancels even the delicate signals from earthquakes.

According to Nobuki Kame, Associate Professor, ERI, “SGs and seismometers are not ideal as the sensors within them move together with the instrument, which almost cancels subtle signals from earthquakes.”

Kame added, “This is known as an Einstein’s elevator, or the equivalence principle. However, the TOBA will overcome this problem. It senses changes in gravity gradient despite motion. It was originally designed to detect gravitational waves from the big bang, like earthquakes in space, but our purpose is more down-to-earth.”

The team has a vision of building a network of TOBA that would be distributed around regions that are seismically active and also devising an early warning system that would alert people at least 10 seconds before the first tremble arrives from an epicentre 100 kms away.