Recent tremors likely not nuclear tests

Two low-magnitude events were detected near North Korea’s nuclear test site Saturday afternoon, apparently as a result of the Sept. 3 nuclear detonation, said Lassina Zerbo, executive secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization (CNTBTO), a global watchdog group of nuclear activity.

A 2.6 magnitude event was detected at 1:43 p.m. Saturday and a second one with a magnitude of 3.2 was detected at 5:29 p.m. the same day, according to South Korea’s weather authority, the Korea Metrological Administration. Both occurred 2 kilometers (1.2 miles) below ground, the agency said, five to six kilometers from where North Korea carried out its sixth nuclear test in Punggye-ri.

The China Earthquake Administration, which only mentioned the second event, initially said it was artificial but later concluded it was natural. The Chinese agency measured the second event to have a magnitude of 3.4 at zero-depth, while the United States Geological Survey said it had a magnitude of 3.5 at five kilometers below ground. Using CNTBTO’s analysis, local geologists are saying the events were related to Pyongyang’s most recent nuclear test, which created a 6.3-magnitude tremor.

Yun Sung-hyo of Pusan National University’s Earth Science Education Department agreed with Zerbo from the CNTBTO that the events were the result of geological stress, saying more are likely to follow.

“There weren’t any natural earthquakes in Punggye-ri in the past,” said Hong Tae-kyung of Yonsei University’s Earth System Sciences Department, who said the tremors on Saturday were likely the result of geological stress, a massive landslide or the collapse of an underground tunnel used at the nuclear test site.

If the quakes were a result of geological stress, and that goes on to affect Mount Paektu’s magma chamber, it could lead to a volcanic eruption, warned Hong.

Mount Paektu, an active volcano that last erupted in 946, straddles the North Korea-China border and is the highest mountain on the Korean Peninsula at a height of 9,003 feet.

In an earlier report, Yun of Pusan National University predicted that a volcanic eruption could lead to tremors in South Korea so strong that high buildings could have their windows shattered and walls could be left with serious cracks. A worse-case scenario would be if all North Korea’s radioactive material at the Punggye-ri nuclear test site were unleashed, polluting the air and water of nearby countries.

BY LEE CHUL-JAE [lee.sungeun@joongang.co.kr]