Japan briefly warns of quake larger than any ever recorded, magnitude 9.9 alert came from a Kamchatka tremor that produced no shaking in Japan, cancelled after 12 minutes as agency opens investigation

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Japan's Meteorological Agency issued an earthquake early warning on Friday estimating a magnitude 9.9 quake — larger than any ever recorded — and cancelled it twelve minutes later. The actual earthquake, measured by the USGS at magnitude 6.9, struck near Russia's Kamchatka Peninsula and produced no shaking in Japan.

The alert went out at about 12:36 p.m. Friday, late Thursday in the United States, and was cancelled at 12:48, according to NHK. It warned of strong shaking across northern and central Japan, including the Tokyo region. A magnitude 9.9 event would have exceeded the 9.5 quake that struck Chile in 1960, the largest ever recorded. No tsunami warnings were issued.

Japan's early-warning network is built to buy seconds: alerts go out on the first automated estimates of a quake's size, before the shaking arrives, because those first estimates are what the public acts on. On Friday, the location and depth on the agency's display were roughly right — the Kuril Islands region, 140 kilometres down, against a USGS reading of 143. The magnitude was the failure. The scale is logarithmic, and the two steps between an estimated 9.9 and a measured 6.9 multiply out to roughly 32,000 times the energy — the difference between the largest earthquake ever recorded and a deep tremor, 76 kilometres northeast of Ozernovskiy in Russia, that nobody in Japan felt.

The agency said it will investigate the error. The largest earthquake actually recorded remains Chile's magnitude 9.5, from 1960. Japan's warning system announced a bigger one on Friday — and took it back at 12:48 p.m.