The South Korean weather agency said analysts have detected seismic activity of a 3.2 magnitude about 6 kilometers (more than 3 miles) from the site used for nuclear tests.
But Japan's Kyodo News earlier reported that a 3.4 magnitude natural disaster was detected at a depth of zero kilometres near the North's nuke test site, citing China's quake agency.
Japanese Defense Minister Itsunori Onodera said North Korea might conduct an H-bomb test with a medium-range or intercontinental ballistic missile, given its recent advances in missile and nuclear weapons development.
China has announced that it will limit energy supplies to North Korea and stop buying its textiles under United Nations sanctions imposed over its nuclear and missile development, further reducing support from Pyongyang's last ally. On its website, the USGS said that it "cannot conclusively confirm at this time the nature (natural or human-made) of the event".
North Korea has launched dozens of missiles this year, several flying over Japan, as it accelerates its program aimed at enabling it to target the United States with a nuclear-tipped missile.More news: United States to give $32 million in aid to Rohingya
The exercises were meant to underscore "the seriousness with which we take DPRK's reckless behavior", White said, using an acronym for North Korea.
China's Earthquake Administration said the quake was not a nuclear explosion and had the characteristics of a natural tremor.
Kim on Friday threatened the "highest level of hard-line countermeasure in history" in a tirade against Trump's warning that Washington would "totally destroy" the North if the United States or its allies were threatened.
Pyongyang conducted its sixth and most powerful nuclear test on September 3, claiming it had tested a hydrogen bomb that could be loaded into an intercontinental ballistic missile.
China on Saturday announced that it will implement United Nations sanctions on North Korea, by cutting off oil exports to Pyongyang over its nuclear and missile developments.More news: Banner drop urges Britain to sign nuke ban treaty
North Korean Foreign Minister Ri Yong-ho, in NY for the U.N. General Assembly, said Thursday evening that his country could detonate a hydrogen bomb over the Pacific Ocean, but also told reporters, "We have no idea about what actions could be taken, as it will be ordered by leader Kim Jong Un". Trump tweeted Friday that Kim was "obviously a madman" who would be "tested like never before".
"It would also send a disturbing signal to the USA and the worldwide community that North Korea had now "arrived" as a full-fledged nuclear weapon state".
Mr Trump delivered a combative speech on Tuesday at the UN General Assembly, where he mocked Kim as a "Rocket Man" on a "suicide mission".
He said sanctions would have no effect on Pyongyang's resolve to develop its nuclear weapons, with the ultimate goal being "balance of power with the US".
"We are prepared to use the full range of military capabilities to defend the U.S. homeland and our allies".More news: Egypt's Sisi meets Israeli PM at United Nations for first public talks
President Donald Trump has added economic action to his fiery military threats against North Korea, authorizing stiffer new sanctions in response to the Koreans' nuclear weapons advances.