First of its kind cosmic ray sensor successfully observes tsunami waves

Highly energetic particles called muons are always present in the atmosphere and pass through large objects very easily. Sensitive detectors installed along the Tokyo Bay Tunnel measure muons passing through the ocean above them. This allows changes in the amount of water over the tunnel to be calculated. For the first time, this method was used to accurately detect a mild tsunami after a thunderstorm in 2021.

By the time it takes you to read this sentence, about 100,000 muon particles will have passed through your body. But don’t worry, muons pass through normal matter harmlessly, and they can be extremely useful. Hiroyuki Tanaka, professor of muographics at the University of Tokyo, has made a career out of exploring applications for muons. He has used them to look inside volcanoes and even to locate evidence of ancient earthquakes. Recently, Tanaka and his international team of researchers have turned their attention to meteorological phenomena, particularly tsunamis.

In September 2021, a hurricane from the south approached Japan. As it approached land, it brought with it ocean waves, a tsunami. These were mild on occasion, but throughout history, tsunamis have caused great damage to many coastal areas around Japan. As the vast swell moved into Tokyo Bay, something almost imperceptible happened on a microscopic level. Atmospheric muon particles, generated by cosmic rays from deep space, were scattered by excess amounts of water that they would not have otherwise. This means that the amount of muon passing through Tokyo Bay varies as the ocean rises.

“The Tokyo-Bay Seafloor Hyper Kilometric Submarine Deep Detector (TS-HKMSDD) is the world’s first underwater muon observatory, and it has detected individual muon activity during a tsunami,” Tanaka said. “This variation corresponds to ocean waves that were measured with other methods. Combining these readings means we can more accurately model sea level changes, bypassing other methods that come with drawbacks.” for mugraphic data.

Other methods of measuring sea level changes are physical systems such as tide gauges, satellites, buoys, or sensors at sea level itself. But the TS-HKMSDD and future devices based on it, which are installed in tunnels under the sea, may be cheaper to build and operate, easier to use, and they do not suffer from physical wear and tear because They have no moving parts. Crucially however, TS-HKMSDD’s data is both real-time and highly accurate, two key criteria that can make it suitable for a reliable early warning system.

“Thanks to the success we have had with these early trials, similar systems are already being tested in the UK and Finland,” Tanaka said. “Obviously, such an undertaking comes with challenges and it can be difficult to install delicate equipment in a busy tunnel. But we are grateful for the cooperation of the agencies responsible for the Tokyo Bay Tunnel. To the best of my knowledge The tunnel is now the first active national road in the world to be defined as a laboratory.”

current study. is published in scientific report, Tanaka and his team have several other methods for using muons, including a possible way to accurately synchronize time around the world and, related to this, a spatial positioning system far more accurate than current GPS. .