"The event has earthquake-like characteristics, however, we can not conclusively confirm at this time the nature (natural or human-made) of the event", the USGS said in a brief statement.
It was the latest in a string of aftershocks following North Korea's sixth nuclear test on September 3, which caused a 6.3 magnitude natural disaster, according to the USGS.
The KMA said that it was a naturally-occurring quake with a depth of three kilometers, expecting no damage from the tremor.
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The forensic tests should be completed by Friday morning, and police and SES are continuing to search for the missing woman. State Emergency Service area controller Sean McGuinness said the search is proving to be hard .
"The depth is poorly constrained and has been held to 5 km by the seismologist". In September, it detonated a hydrogen bomb which caused a 6.3 magnitude quake in the northeast of the country where the Punggye-ri test site is located.
Previous tests had caused stronger quakes, with all of them stronger than 4.3 magnitude.
Later, the Chinese Academy of Sciences and UC Santa Cruz released a joint report that concluded that tunnels in the test site collapsed after the quake.
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"It was the mountain collapsing into the cavity created by the explosion ... hundreds of meters below the surface, " Thorne Lay, a professor at UC Santa Cruz told the US news outlet.
It came three weeks after a 3.5-magnitude natural disaster struck near the same area, with seismic experts and a United Nations nuclear test ban watchdog calling that tremor on September 23 a likely aftershock of the North's sixth and largest nuclear test.
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