Prof.  So Gu  Kim
Korea Seismological Institute,  Republic of Korea

Title: Characteristics of Underwater Explosions Analyzed through Seismic, Hydroacoustic, Infrasound, and Boundary Element Method (BEM) in Relation to the ROKS Cheonan Sinking

Abstract:

In the case of very shallow underwater explosions, spectral analysis is more effective than cepstral analysis for identifying the characteristics of bubble pulses and reverberation effects. Time-domain analyses reveal both a bubble pulse and a bubble jet, including positive polarities of the first P-wave arrivals on the vertical component. Spectral analyses further clarify the physical parameters associated with these phenomena and the reverberation effects. The sinking of the ROKS Cheonan, attributed to an underwater explosion, generated a bubble jet with a characteristic force of 291 g, causing the ship to split into two pieces, immediately followed by a bubble pulse. This study highlights important findings related to the bubble jet, the bubble pulse, and the toroidal bubble deformation. Additional validation of these research results is provided through ray-tracing and the boundary element method.

The ROKS Cheonan sank off Baengnyeong Island in the Yellow Sea, at a depth of about 8 meters, within a total sea depth of 44 meters, following an explosion equivalent to 136 kg of TNT on March 26, 2010. This quantity of TNT is comparable to one of the abandoned land control mines (LCMs) that were deployed near the Northern Limit Lines (NLL) in the Yellow Sea by the South Korean Navy in the late 1970s. Consequently, the probability that the sinking of the ROKS Cheonan was caused by an LCM is estimated to be 99.9999%.

Biography:

So Gu Kim, the Director of the Korea Seismological Institute and has been a Professor of Physics and Geophysics at Hanyang University in South Korea for about 30 years. He has served as an Invited Professor at the Institute of Seismology and Volcanology at Hokkaido University in Japan and at the Graduate School of Earth and Planetary Sciences at Peking University in China. Additionally, he has been an Invited Scientist at the GFZ in Potsdam, Germany, a Visiting Professor at Hamburg University, and an Invited Professor at the University of New England in Australia. Throughout his career, he has conducted numerous research projects in geophysics, including seismology, exploration geophysics, geophysical oceanography (specifically underwater acoustics and ocean exploration), and petroleum exploration.