Quake Shakes Post-Nuke Test Asia

As Asia sorted out another batch of diplomatic back-and-forth and rhetoric from North Korea over Monday's nuclear weapons test, with a U.N. vote on sanctions expected soon - a quake hit in northern Japan early Wednesday and reports spread that North Korea might have done a second nuclear test.

Within a short time, officials in Japan, the U.S. and South Korea all said they had no evidence that a nuclear test had taken place.

A source at the CIA told CBS News national security correspondent David Martin that the agency has found no seismic readings that would indicate a North Korean nuclear blast or other independent information to corroborate the claim. S. Korean monitors reported the same, and Japan's prime minister said he had no confirmation of a second blast — a stance seconded by the White House.

The worldwide alarm underlined the jitters felt after North Korea announced Monday it had tested its first nuclear bomb, leading to a U.S.-backed push to have the U.N. Security Council sanction the reclusive communist state. Some say the regime may conduct more tests amid suspicion the first, relatively small explosion might have partially failed.

Concern was triggered early Wednesday after the Japanese government detected tremors that led it to suspect North Korea had conducted another nuclear test, according to news reports and a Foreign Ministry spokesman.

Shortly afterward, the country's meteorological agency reported a magnitude-6.0 earthquake shook northern Japan. However, agency spokesman Yukuhiro Watanabe said that quake was being considered separately from reports of new tremors in North Korea.

Data from elsewhere suggested all was quiet in North Korea.

"There's no signal from North Korea, even no small event," Chi Heon-cheol, director of the South's Korea Earthquake Research Center, told The Associated Press.

"There has been no activity in the last two hours," U.S. Geological Survey official Rafael Abreu told AP just after 9 a.m. in Korea.

The agency can detect most tremors if they are above 3.5 magnitude, he said.

But the region's anxiety was reflected by Australia's foreign minister saying Wednesday that Australia has "real concerns" that North Korea will conduct a second nuclear test soon.

"We have very real concerns that they may conduct another nuclear test and that they may do so very soon," Foreign Minister Alexander Downer said, without elaborating.

In Washington, White House spokesman Blair Jones said signs pointed to an earthquake, not another underground nuclear detonation.

"We have detected no evidence of additional North Korea testing," Jones said. "Japanese officials are now saying that this occurrence may be related to an earthquake in northern Japan. We will continue to monitor the situation closely and consult with our allies in the region."

Pentagon spokesman, Army Lt. Col. Brian Maka, said: "We have received no credible information to confirm any of that. No seismic activity has been detected on our part."

Japanese Prime Minister Shinzo Abe told a parliamentary meeting early Wednesday that he had no information to confirm a second nuclear test by North Korea.

"I have had not received information about any indications... that a test has take place," said Abe.