But South Korea's Meteorological Administration says the quake was natural.
According to 38 North, a Washington-based project which monitors North Korea, numerous landslides throughout the nuclear test site have been detected via satellite images after the sixth test.
China's trade with North Korea fell sharply in September as sanctions finally began to bite, data released by the Chinese government on Friday (Oct 13) showed.
With China's support, the United Nations has agreed on two rounds of sanctions since the beginning of August including bans on North Korean exports of iron, coal, lead, seafood, textiles, and oil import restrictions.
Fox News reported that the absence of two key officials in North Korea's nuclear programme during public events this week, which may suggest that another test was imminent. But China has balked at imposing a complete trade embargo on North Korea, and continues to send the regime the crude oil it needs to keep its military and economy alive.
Customs spokesman Huang Songping did not provide the trade values for September, but said imports of coal, iron ore and apparel from North Korea all declined in the month, and there were no imports of seafood. Still, Beijing is reluctant to trigger an economic collapse and chaos over its shared 1,350-kilometre border.
China-US ties have been strained by President Donald Trump's criticism of China's trade practices and by demands that Beijing do more to put pressure on North Korea. Earlier this month he admonished of Secretary of State Rex Tillerson for "wasting his time" in seeking negotiations, a goal that the sanctions are created to help achieve. In 2006, North Korea's first detonation triggered a 4.1-magnitude quake.
According to South Korea's weather agency, a small quake was detected, on Friday (10/13/2017), near North's nuclear test site, but unlike a nuclear-related quakes, the quake did not appeared to be a man-made one.