Japan’s Meteorological Agency says it is investigating after it issued an alert for a very strong earthquake that turned out to be only a mild shake.

Loud alarms rang from cellphones and TVs just before 5 p.m. Japan time on Thursday, warning of an earthquake of magnitude 7.8, which could cause severe damage. It said residents throughout Japan should be prepared for a jolt.

A few minutes later the Meteorological Agency reported a magnitude 2.3 quake cantered in Wakayama prefecture, in western Japan. Under the Japanese system for measuring quakes, it barely registered.

Broadcaster NHK said the agency blamed electronic noise for triggering the apparently false alarm.

Japan beefed up its warning systems following a magnitude 9 earthquake and tsunami in March 2011 that killed more than 18,000 people.

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