A second earthquake event measuring 4.6 magnitude detected by the China Earthquake Networks Center on Sunday may have been a tunnel collapse, a U.S. earthquake monitoring service said.
The event, which took place at a reported depth of 0km and allegedly occurred eight minutes after the first nuclear test, was confirmed by the USGS Earthquake Hazards Program later as a 4.1 magnitude “collapse”.
“(This was a) seismic event collocated with the larger possible explosion 8 minutes and 32 seconds earlier,” the USGS said of the quake.
“This significantly smaller event is likely a secondary feature (possibly a structural collapse) associated with the larger event.”
Chinese authorities described the second earthquake as being caused by a “cave in,” Agence France Press earlier said.
The second earthquake occurred around one kilometer northwest from the location North Korea appears to have conducted its sixth nuclear test, the USGS data shows.
Depending on the nature of any tunnel collapse, it remains possible that radioactive fallout from the prior nuclear event may have been released into the nearby environment and atmosphere.
While citizens of nearby Yanji in China and Vladivostok in Russia both reported feeling earthquake tremors for several seconds during the first event, the second earthquake was not however felt, two informed sources in Yanji told NK News.
Meanwhile, South Korean and Japanese authorities have not yet stated that a second earthquake event took place.
Sunday’s nuclear weapons test comes following North Korean state media in the morning showcasing a hydrogen bomb that could be loaded on an intercontinental ballistic missile (ICBM).
The test occurred just under a year after North Korea’s fifth nuclear test on September 9.
Main picture: USGS
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