Japan triggered widespread alarm on Friday after its earthquake early warning system "announced" a magnitude-9.9 earthquake alert, prompting emergency phone alerts, public loudspeaker warnings and television broadcasts urging people to take shelter, before the warning was withdrawn eight minutes later.
asserted
warning → trigger → shelter
However, no major shaking followed the alert, which the Japan Meteorological Agency (JMA) later attributed to errors in its earthquake magnitude estimation and location calculations.
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Agency → follow → estimation
The agency is investigating the cause of the malfunction, reportd Japan Times.
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Times → investigate → malfunction
The alert was issued at 12.40 pm (local time), two minutes after a magnitude-6.9 earthquake struck off Russia's Kamchatka Peninsula.
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earthquake → issue → Peninsula
The warning incorrectly placed the epicentre near the Kuril Islands and predicted seismic intensity of up to shindo 7, the highest level on Japan's seven-point seismic intensity scale, across areas stretching from Hokkaido to the Tokai region.
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warning → place → region
In Japan, however, the recorded shaking reached only shindo 1, a level at which vibrations may be barely noticeable.
uncertain
vibrations → record → which
, the JMA issued a cancellation notice, marking the first time an emergency earthquake warning had been formally withdrawn, according to the agency.
uncertain
warning → issue → agency
The predicted magnitude of 9.9 also drew attention because it exceeded the magnitude of any earthquake recorded in history.
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it → predict → history
The 1960 earthquake off Chile's Biobio region, the strongest on record, measured magnitude 9.5.
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earthquake → measure → magnitude
The JMA said 9.9 was the highest magnitude its system could communicate externally.
uncertain
system → say → ?
Ayataka Ebita, head of the JMA's earthquake and tsunami observation division, said the system had mistakenly estimated the earthquake's epicentre and overstated its magnitude.
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system → say → magnitude
The agency ruled out a cyberattack and said it was examining how the error occurred.
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error → rule → cyberattack
At a subsequent briefing, the JMA said the system had applied a magnitude formula designed for earthquakes within Japan to a quake occurring far away.
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system → say → quake
It had also used different estimated locations to calculate the magnitude and forecast shaking, although both calculations should have been based on the same location.
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calculations → use → location
The investigation is continuing.
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investigation → continue → ?
Ebita said lightning was not believed to have caused the error, adding that the processing of seismic sensor data could have contributed to the malfunction.
uncertain
processing → say → malfunction
In Tokyo on Friday, pedestrians paused to check their phones as warnings circulated, while users of the NERV Disaster Prevention app received a magnitude-9.9 alert accompanied by a countdown to shaking that never materialised.
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that → pause → shaking
Lola Milroy-Tompkins, a 20-year-old British student at Waseda University in Tokyo, said she was eating lunch in a campus cafeteria when the alarm sounded.
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alarm → say → cafeteria
“I have never experienced an earthquake before and I expected the grand style shaking and everything to start falling around me,” she said.
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she → experience → me
She recalled students worrying and talking among themselves as they tried to understand what was happening, but the anticipated earthquake never arrived.
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earthquake → recall → themselves
The JMA's early warning system automatically combines readings from seismometers at observation stations to estimate an earthquake's location, magnitude and expected intensity.
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system → combine → location
Ebita said the reliability of such estimates depends on the number of observation stations and the quality of their readings, which can deteriorate when an earthquake occurs far from monitoring equipment.
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earthquake → say → equipment
The incident also disrupted public transport.
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incident → disrupt → transport
The Tokaido Shinkansen line was halted for 15 minutes after an automated safety system was triggered, Central Japan Railway said.
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Railway → halt → minutes
Government officials reported no damage related to the Kamchatka earthquake.
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officials → report → earthquake
Chief cabinet secretary Minoru Kihara said the government took seriously the anxiety caused by the warning and the burden on people who evacuated or took precautionary measures, as well as those whose travel and business activities were disrupted.
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travel → say → measures
False alarms have occurred previously.
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alarms → occur → ?
In July 2020, the JMA issued a warning covering 15 prefectures, including Tokyo, after incorrectly estimating an earthquake's location and magnitude.
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JMA → issue → location
In August 2013, noise from a seabed seismometer was mistakenly combined with readings from a small earthquake, triggering widespread warnings across the Kinki region.
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noise → combine → region
Neither incident produced shaking of shindo 1 or higher, according to the JMA.
uncertain
incident → produce → JMA
The agency's website noted that false alarms can result from sensor noise caused by accidents, lightning or equipment failures.
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alarms → note → accidents
The Aporia
