SEOUL, South Korea (AP) — South Korea's weather agency said a magnitude 3.2 earthquake was detected in North Korea on Saturday close to where the country recently conducted a nuclear test, but it assessed the quake as natural.
The quake was detected in an area around Kilju, in northeastern North Korea, just 6 kilometers (3.7 miles) northwest of where the North conducted its sixth and most powerful nuclear test on Sept. 3, according to an official from Seoul's Korea Meteorological Administration.
The area isn't where natural earthquakes normally occur. A South Korean expert said the quake could have been caused by geological stress created from the recent nuclear explosion. Other possible causes include landslides or the collapsing of test structures such as tunnels, said Hong Tae-kyung, a professor at the department of Earth System Sciences at Yonsei University.
"It could be a natural earthquake that really was man-made as the nuclear test would have transferred a lot of stress," he said. "The quake is small enough to suspect that it could have been caused by a tunnel collapse, and satellite data shows there have been many landslides in the area since the nuclear test."
China's official Xinhua News Agency said the country's seismic service detected a magnitude 3.4 quake in North Korea and saw the likely cause as an explosion. The news agency issued a fresh report later, saying the seismic service after further study concluded the quake was natural and not the result of a nuclear test.
The South Korean weather agency official said the analysis of seismic waves and the lack of sound waves clearly showed that the quake wasn't caused by an artificial explosion. She spoke on condition of anonymity, citing office rules.
Another Korea Meteorological Administration official, who also didn't want to be named, said the agency saw the possibility of the earthquake being caused by a tunnel collapse as low.
The U.S. Geological Survey said that it detected a magnitude 3.5 quake in the area of previous North Korean nuclear tests, but that it was unable to confirm whether the event was natural.
North Korea's weakest nuclear test, its first one, conducted in 2006, generated a magnitude 4.3 quake. The USGS measured this month's nuclear test at magnitude 6.3. The latest test was followed by a second magnitude 4.1 quake that experts said could have been caused by landslides or a tunnel collapsing after the explosion.
Analysts examining satellite images of North Korea's mountainous test site after the latest nuclear test said they spotted landslides and surface disturbances that were more numerous and widespread than what was seen from any of the five previous tests.
North Korea has been maintaining a torrid pace in nuclear and weapons tests as it accelerates its pursuit of nuclear weapons that could viably target the United States and its allies in Asia.
North Korea said its recent nuclear test was a detonation of a thermonuclear weapon built for its developmental intercontinental ballistic missiles. In two July flight tests, those missiles showed potential capability to reach deep into the U.S. mainland when perfected.