Tokyo, Oct. 9 (AP): A successful nuclear test by North Korea would decisively shift Asia’s diplomatic and military alignment, hardening China and South Korea’s approach towards their reclusive neighbour, strengthening Japan’s security stance and cementing the US presence in the region.

Such a test, which North Korea claimed today, represented Pyongyang’s first demonstration of a nuclear weapon and had a powerful psychological effect in a region that is still emerging from the divisions of World War II and the Cold War.

The suspected blast also raised fears of a wider arms race in Asia. Should non-atomic Japan, for instance, increase defence spending or even consider developing its own nuclear deterrent, that could prompt Seoul — which nurses suspicions about Japanese intentions — and others like Taiwan to follow suit.

“The test inevitably alters the balance of power,” Mark Fitzpatrick, a senior fellow at London’s International Institute for Strategic Studies and a former US deputy assistant secretary of state for non-proliferation, wrote in response to emailed questions. “Now, North Korea has demonstrated it has the ultimate weapon.”

Japanese shoppers read about North Korea’s nuclear test in Tokyo on Monday. (AP)

The diplomatic effects of the possible test were clear in the hours after Pyongyang announced a successful test and meteorological agencies in the region registered a moderate earthquake, a possible sign of an underground blast.

For China and South Korea, the test — which followed calls by both Seoul and Beijing for Pyongyang to stand down — was expected to make it harder for the two to pursue their policies of working with the regime.

In Seoul — a US ally divided from the North by the Cold War’s last frontier — the shock was acute: a war provoked by Pyongyang’s reckless nuclear brinkmanship would devastate South Korea that has put troops on high alert.

“Under this situation, it’s difficult for South Korea to maintain engagement policy,” South Korean President Roh Moo-hyun said.

China, too, while not considering itself a target of the North’s weapons, was expected to come under pressure to distance itself from the regime, a long-time ally whom it supplies with vital energy shipments.

The prospect of a nuclear armed North Korea deeply rattled Japan, Korea’s former colonial ruler and top US ally in the region, making Tokyo the regime’s first target in the region.

The development was certain to allow Japan’s new Prime Minister, nationalist Shinzo Abe, to accelerate his plans of bolstering security cooperation with the US by building a missile defence shield with Washington.

North Korea’s announcement pushed the dollar to an eight-month high against the yen and helped shove oil above $60 a barrel.

Q&A

How are underground tests conducted?

The most common method is to place a test device at the bottom of a vertically drilled hole. Another technique is to place a test device in a horizontal tunnel that leads to a location that is deep enough to contain the blast.

A diagnostic canister is placed in the shaft above the device, it contains instruments to collect data from the blast.

The shaft above the canister is plugged with sand, tar, gravel and epoxy to prevent radioactive materials from escaping.

The different components are lowered into the shaft through an assembly tower that sits at the top.

How deep are the shafts?

Between 600 and 2,500 feet.

Why are the tests carried out under ground?

Atmospheric tests were banned by the 1963 Partial Test Ban Treaty. Concern over large amounts of the cancer-causing radioactive isotope Strontium-90 being produced during atmospheric nuclear weapons tests in the 1950s and 1960s and dispersed worldwide helped drive the change.

The US carried out its last atmospheric test in 1963. France and China moved their tests underground by 1975-1976.

What prohibitions cover nuclear tests?

1963: The Partial Test Ban Treaty (PTBT) that bans nuclear tests in the atmosphere, underwater and in space. The Soviet Union, the US and the UK sign the pact in 1963, the year after the Cuban missile crisis. India, China and France are notable non-signatories.
1974: The Threshold Ban Treaty prohibits underground tests with a yield above 150 kilotons.
1996: The Comprehensive Test Ban Treaty (CTBT) bans all nuclear explosions in all environments, and replaces the PTBT.

France and the UK ratify the CTBT in 1998, but other signatories, the US, China, and Israel have not. India, Pakistan, and North Korea have not signed.

The treaty will not take force until all 44 countries with nuclear power plants sign