hankyoreh

Hankyoreh reporters speak with the base’s PR staff on August 16. (by Lee Jeong-ah

By Kang Tae-ho, senior staff writer

In September 2010, the Multilateral Civilian-Military Joint Investigation Group (MCMJIG) into the sinking of the ROKS Cheonan corvette released a final report ruling out the possibility of the sinking being caused by a mine. Two years later, it has emerged that at least three or four natural explosions occurred with land control mines modeled after USFK Mark-6 depth charges - both at the time of their 1979 placement and in the years afterward.

An individual who participated in the placement of the mines corroborated the claims. Further supporting evidence came from the Hankyoreh’s phone interview with a Baengnyeong Island resident who described discovering signs of explosions while harvesting sea cucumbers. The resident not only reported seeing mines, but made it clear that they were still present.

Accounts immediately after the March 2010 sinking indicated there might be more than 100 mines in the area. But this is the first time people have testified to seeing mine explosions and actual mines on the seabed.

The first individual, an electrical engineering specialist who spoke on condition of anonymity, was previously involved in the development of military weapons, including detonators using magnetic sensors. In a recent interview with the Hankyoreh, the specialist reported a detonation shortly after the mines’ September 1979 placement in the waters off Yeonhwa village, near the site of the Cheonan sinking off Baengnyeong Island. A subsequent investigation failed to determine the cause.

“It was big enough that the ground was shaking in the nearby village of Jincheon,” the specialist reported. “Soldiers who were there said they saw a water column about 50 meters high.”

The same specialist added that at least two or three detonations occurred at a later date, prompting technicians from the initial installation effort to visit the scene.

But the MCMJIG ruled out the possibility of a mine detonation in its report, saying, “There is no possibility of a natural detonation because more than 30 years have passed since the mines’ placement. There also was not sufficient electricity to trigger the detonator.”

But the specialist said detonation was still a possibility.

“These land control mines were designed with waterproof casings and fiber-reinforcement polymers to resist corrosion by seawater, and in the testing prior to the fitting of the electrical detonator (a USFK Mark 6), they were sensitive enough to be triggered when the gauge was used to measure their current,” the specialist explained.

The Baengnyeong Island resident, who has been diving for seafood for more than 20 years, said a number of the other divers there reported seeing mines.

“I’ve seen them, too,” the resident added. “At a depth of maybe about 7 to 15 meters.”

The same resident reported seeing scarring on rocks under the water. That definitely came from an explosion of some kind,“ the resident said. ”It wasn’t natural.“

The resident reported diving for sea cucumbers and other marine life around the villages of Yeonhwa No. 3 and Gaeul, as well as Sahangpo to the north, since the area to the northwest around Yeonhwa No. 1 (home to the Indangsu waters where the folklore character Shimchung is said to have drowned) has strong currents and mud flats that make it difficult to see.

"I reported it as soon as I saw it," the resident said. "Not only is it dangerous, but the corroded wires are all tangled, which causes problems harvesting sea cucumbers.

“The military unit in Baengnyeong Island didn’t take any action because the conditions were bad, so as far as I know they’re still there.”

The resident also reported a mine removal effort some time around 2008.

“But they couldn’t get all of them, so there’s been a lingering fear since then,” the resident explained. “Not long before the Cheonan sinking, we asked them to clear away the mines, but they wouldn’t do it. The fishermen are still at risk.”

These contentions - that mines are present in the waters where the sinking took place, and that they still pose a detonation threat - conflict with the MCMJIG’s conclusions.

Korea Seismological Institute director Kim So-gu also published a paper in the prominent international journal “Pure and Applied Geophysics” that supports claims that the sinking could have resulted from a mine, based on an analysis of seismic waves from an underwater explosion.

A Russian investigation team that investigated the site of the sinking in June 2010 likewise acknowledged the possibility of a mine explosion being responsible, publishing a report suggesting the Cheonan could have traveled into shallow water and dragged a mine up from the sea floor. Its argument was based on the presence of netting tangled in the ship’s screw axle.

The eyewitness accounts, papers, and reports on the presence of mines raise serious questions about how rigorous the MCMJIG’s investigation and testing were prior to the report’s publication. Scientific analysis and testing, as well as new eyewitness testimony, are indicating that its determination was ill founded.

staff reporter)

Different depths on the spot of sinking 　　

The first issue is the depth of the water. The MCMJIG maintained that the Cheonan was sunk at 47m and at this depth the hull could not have split as it did. At a July 9 public hearing, Captain Park Yeon-soo, operation officer on duty the day of the incident, testified that at the time of the explosion, the ship’s equipment showed they were 20m deep.

At a National Assembly Defense Committee meeting on March 27, 2010, Rear Admiral Lee Ki-shik, who headed the Intelligence Operations Bureau in the Joint Chief of Staffs, reported, “The depth of the site was 24m.” The same depth is specified in the daily report that was issued by the Defense Ministry on March 29, and a report by the Korea Coast Guard also has the water depth at 25m.

The water depth in the area of the sinking is widely known to be uneven. Despite this, the MCMJIG refused to make public the Cheonan’s route and continued to insist on a water depth of 47m. Considering that the draft of the Cheonan was 3m and fluctuated, it is possible that the Cheonan pulled a mine.

The MCMJIG also discussed the weight of a mine, which is secured by a tripod inside the water and with this, weighs a total of 200kg. The MCMJIG claimed that even if the ship encountered a mine, it could not have moved it all the way to where the explosion happened. Dr. Lee Pan-mook of the Marine System Security Research Center under the Korea Ocean Research and Development Institute said at the time, “Mines can become loosened by currents and are known to float around.” The current in this area is known to be very strong. In addition, buoyancy would reduce the mine’s weight by half.

The MCMJIG claimed that the firing wire connected to the mine was 6kg per 10m and that is why it would have been impossible to become tangled in the screw. However, mine laying specialists or divers familiar with the waters there have repeatedly said that firing wires, ropes and fishing nets are all tangled up down there. When the mines were first constructed, to specify their position buoys were installed with them; these were connected with ropes. Due to the strong current, the ropes may have been at least 60m long.

Amount of explosives in question 　　

The second issue in question is the amount of explosives. The final MCMJIG report said, “according to the British investigation team, for the ship to break, that required at least twenty times the explosive force of a land control mine.” This is ten times the explosive force the MCMJIG specified in its simulation finding. The JIG had said that the TNT yield was 250kg.

But above all, what makes the MCMJIG findings questionable is the recent study published in “Pure and Applied Geophysics,” by director Kim So-gu and Dr. Yefim Gitterman of the Geophysical Institute of Israel. The study argues that it was indeed a mine that caused the underwater explosion that sank the Cheonan. The two scholars calculated the bubble pulse period - a value needed to determine explosive force and explosion depth - to be 0.990 seconds and the seismic magnitude of the explosion was 2.04. From a comparative study using various methods of simulation, underwater explosion formula and boundary element method (BEM), they found that this bubble pulse period is found in an explosion with TNT yield of 136 kg at 8m depth.

On August 29, the South Korean Ministry of Defense released a statement refuting and criticizing the study, saying that it was wrong. The Ministry claimed that Drs. Kim and Gitterman used the Willis formula to calculate the bubble pulse period, but this formula is used in deep oceans, not shallow waters. But this turned out to be a foot-in-mouth statement since it was the MCMJIG that first came up with the report that discussed the use of the Willis formula “to calculate the bubble pulse period of 1.1 which corresponds to TNT yield of 250kg at 9m.” In fact, Dr. Kim uses the Willis method only partially in his entire study, and he commented on the Defense Ministry criticizing, “I wonder if they even read my study”

Cause of detonation 　

Lastly, the MCMJIG “assessment” said that “there is no possibility of a natural detonation because more than 30 years have passed since the mines’ placement…” However, as said by the specialist who has worked on mine placement, mines have detonated spontaneously and because they are built to be waterproof remain live even after 50 years.

The MCMJIG claimed “nor could there have been sufficient electricity to trigger the detonator.” But this also turned out to be wrong. According to the expert, mines can explode with the amount of electrical current that the MCMJIG claimed was insufficient.

Dr. Kim, who is also an expert in big vessel and ship structures, provided another possibility. Dr. Kim said that electrical charges abound in a vessel, pointing out as example the ICCP unit, which is used to prevent the outer part of the ship from corroding. The current that flows through there, Dr. Kim contends, is enough to detonate the mine

The problem is simple. There are still a number of mines in the sea surrounding the Baegnyeong Island. The divers and residents of the Island have asked the authorities to have them removed due to the danger they pose. This demand must not go unresponded. The solution is to have them removed and use these to carry out the experiment and simulations needed to know the truth of what happened to the ROKS Cheonan.

Please direct questions or comments to [english@hani.co.kr]