Kyeong Ok Kim

Three-dimensional tsunami runup simulation for the port of Koborinai on the Sanriku coast of Japan

ABSTRACT Kim, D.C., Kim, K.O., Pelinovsky, E., Didenkulova, I. and Choi, B.H., 2013. Three-dimensional tsunami runup simulation for the port of Koborinai on the Sanriku coast of Japan. The huge tsunami generated by the earthquake that occurred off the Pacific coast of Japan at 14:46 JST (05:46 UTC) on Friday, 11 March 2011 produced a maximum runup of 40 m on the east coast of Japan. The earthquake triggered extremely destructive tsunami waves up to 37.9 m in height that struck Japan minutes after the quake. Koborinai is a tiny fishery port located north of Miyako City in the Iwate Prefecture. A survey team from the University of Tokyo Earthquake Research Institute (ERI) found high water marks and other evidence of a gigantic wave at the port of Koborinai. The port is on low land sandwiched between two mountains. A joint survey team from ERI-Sungkyunkwan University (SKKU) and Korea Ocean Research & Development Institute (KORDI) visited again and surveyed the site in detail. The 3D Princeton Ocean Model was applied to describe the propagation and runup of the tsunami on the Japanese coast. The numerical simulation results obtained were in satisfactory agreement with observations made in the general area, except those made in many v-shaped valleys along the northern Iwate coast. The extremely high runup of tsunami waves at the port at Koborinai were successfully reproduced by numerical simulation through stepwise refinement of the spatial scale using multi-nesting and consideration of the vertical acceleration of flow along steep slopes using a CFD model to solve the Reynolds-averaged Navier–Stokes (RANS) equations. The velocity field was also computed, and the simulation results show that the water flow that climbed the coast possessed a strong vertical velocity component.

Three-dimensional runup simulation of the 2004 Indian Ocean tsunami at the Lhok Nga twin peaks

ABSTRACT Kim, D.C., Kim, K.O., Choi, B.H., Kim K.H. and Pelinovsky, E., 2013. Three-dimensional runup simulation of the 2004 Indian Ocean tsunami at the Lhok Nga twin peaks. A post-tsunami runup survey for the 2004 Sumatra–Andaman earthquake showed that the highest runup which was recorded at Lhok Nga (West Banda Aceh, Sumatra). A reported maximum tsunami height of 35 m and maximum runup height of up to 51 m occurred near the Lhok Nga Twin Peaks (Labuhan and Ritieng). A numerical simulation was performed to reproduce tsunami characteristics in this area. The tsunami source was computed using fault parameters proposed by Tanioka et al. Tsunami wave propagation from the source to the coast was studied with 3D shallow-water equations. The coastal runup behavior of the tsunami at the Lhok Nga Twin Peaks was studied within a framework of fully nonlinear dispersive Reynolds-averaged Navier–Stokes equations using the FLOW3D code. This approach made it possible to reproduce the extreme characteristics of the tsunami in this coastal area, including observed overflow through a saddleback between the twin peaks. The numerical simulation results compare well with data from field surveys.

Swell Prediction for the Korean Coast

ABSTRACT Yuk, J.-H.; Kim, K.O.; Jung, K.T., and Choi, B.H., 2016. Swell prediction for the Korean coast. The accurate prediction of abnormally high waves occurring in the East Sea during winter is important in terms of the prevention of coastal disasters along the east Korean coast. This study attempts to hindcast the abnormally high swell wave events that occurred in October 2006 and February 2008 using the unstructured grid wave model UnSWAN with high-resolution reanalysis data from the European Centre for Medium-Range Weather Forecasts as meteorological inputs. The model used in this study incorporates an additional weighting factor for the relative wave-number in dissipation source term to improve swell propagation and wave period. Wave heights and periods are well reproduced compared with the observational data. Examination of the meteorological data and model results shows that the abnormally high waves in October 2006 were induced by the overlap of a swell wave and a wind-generated wave with nearly the same heading directions; the wave generated in February 2008 was, however, induced by the swell that propagated over very long distances from the northeastern area of the East (Japan) Sea due to enhanced atmospheric low pressure. Use of the reanalysis meteorological data and a wave model equipped with a weighting factor is found to be useful in identifying the generation mechanisms as well as reasonable estimates of abnormally high wave events.

Three-dimensional simulation of 2011 East Japan-off Pacific coast earthquake tsunami induced vortex flows in the Oarai port

ABSTRACT Kim, K.O., Choi, B.H., Pelinovsky, E. and Jung, K.T., 2013. Three-dimensional simulation of 2011 East Japan-off Pacific coast earthquake tsunami induced vortex flows in the Oarai port. The huge tsunami was generated by the 11 March 2011 off coast of the Pacific side of East Japan, recording a maximum 40 meter run up in Iwate prefecture. The tsunami wave attacked the Oarai port of Ibaraki prefecture within 30 minutes, and created an enormous vortex flow within the harbor. A similar feature was observed in the Imwon port, in the Eastern Korean coast during the 1983 tsunami event in the East (Japan) Sea. A set of simulations have been performed to investigate the generation of the powerful vortex caused by the 2011 tsunami event at the Oarai Port. The application of numerical models has successfully reproduced the formation of the vortex in the center of the port, which can be clearly identified in a photograph taken during the tsunami. The simulation of tsunami generation and propagation at the outer sea is performed with a hydrostatic model and, for the investigation of a more detailed transient pattern of water flows, the model which uses full Reynolds-averaged Navier–Stokes equations is applied. Examination of the Oarai and Imwon vortexes implies that the generation and strength of a vortex due to tsunami wave is strongly related in the size and the shape of port and breakwater layouts. The present work indicates that time-variation the inflow through the mouth of a harbor controls the transient pattern of the vortex.

Propagation of a tsunami wave generated by an earthquake in the Nankai Trough onto the South Korean coast

ABSTRACT Kim, K.O., Jung, K.T. and Choi, B.H., 2013. Propagation of a tsunami wave generated by an earthquake in the Nankai Trough onto the South Korean coast. The earthquake of magnitude 9.0 that occurred in March 2011 and the ensuing crisis at the Fukushima Daiichi nuclear power plant prompted sweeping reviews of Japans disaster preparedness and criticism over apparent failures to take into account potential risks. Based on studies conducted after the catastrophes, the Japanese government revised its tsunami projections in a report posted on a government website. While the earlier forecast in 2003 put the potential maximum height of a tsunami runup at less than 20 m, a governmental panel of experts in Japan recently reported that the occurrence of a magnitude-9.0 earthquake in the Nankai trough, which runs east of Japans main island of Honshu to the southern island of Kyushu, might generate a tsunami runup with a height of more than 34 m, which would inundate much of Japans Pacific coast. A chronicle of Cheju Island (Tamraji) reports that a tsunami was propagated by the 1707 Hoei earthquake. The tsunami from the 2011 earthquake event was also propagated to the southern shore of Korea. In this study, we conducted a numerical simulation of the propagation of the tsunami from Japans Pacific coast to the southern shore of the Korean Peninsula. Simulation results are presented for 11 scenarios of initial water displacement identified by the Japanese government. The simulation results indicate that after an earthquake in the Nankai Trough, tsunami waves would reach Cheju Island in approximately 3.5 hours and the southern coast of Korea in approximately 4 hours, with a maximum runup height of approximately 1.5 m.

Transoceanic Propagation of 2011 East Japan Earthquake Tsunami

The 2011 Tohoku earthquake triggered extremely destructive tsunami waves which propagated over the Pacific Ocean, Atlantic Ocean through Drake Passage and Indian Ocean respectively. A total of 10 tide-gauge records collected from the UNESCO/IOC site were analyzed through a band-pass digital filtering device to examine the observed tsunami characteristics. The ray tracing method and finite-difference model with GEBCO 30 arc second bathymetry were also applied to compare the travel times of the Tohoku-originated tsunami, particularly at Rodrigues in the Indian Ocean and King Edward Point in the Atlantic Ocean with observation-based estimates. At both locations the finite-difference model produced the shortest arrival times, while the ray method produced the longest arrival times. Values of the travel time difference however appear to be within tolerable ranges, considering the propagation distance of the tsunami waves. The observed tsunami at Rodrigues, Mauritius in the west of the Madagascar was found to take a clockwise travel path around Australia and New Zealand, while the observed tsunami at King Edward Point in the southern Atlantic Ocean was found to traverse the Pacific Ocean and then passed into the Atlantic Ocean through the Drake Strait. The formation of icebergs captured by satellite images in Sulzberger in the Antarctica also supports the long-range propagation of the Tohoku-originated tsunami.

Estimation of Runup Heights of the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami Based on Numerical Simulations

A strong earthquake (M9.0) occurred at 14 h 46 m (JST) on March 11, 2011 in the Pacific Ocean east of the Tohoku district in the northeast part of Honshu Island, Japan. The earthquake was accompanied by a large tsunami. The main goal of this study is to use numerical modelling to reproduce the observed characteristics of the 2011 tsunami. First, the water elevation records of DART buoys, coastal tidal gauges and GPS wave buoys are compared with the numerical simulation. Then, the observed runup heights that were published by the Joint Survey Group are compared with the results of the numerical simulations in the Pacific coast of the Tohoku district. For tsunami modelling in ocean and coastal zone, numerical computations were performed with the Princeton Ocean Model (POM). The finite fault model of the U.S. Geological Survey is chosen to reproduce the tsunami source. For computing the runup height, the time series of the water height that were determined by the numerical model in the last sea grid points were converted by the 1D analytical nonlinear theory of long-wave runup. The computed runup heights on the shore roughly correlate with the observed runup heights, with the exception of the northern Miyagi Prefecture, which was directly hit by the tsunami.

Migration of radioactivity in multi-fraction sediments

A new 3D radioactivity transport model coupled with multiscale circulation and multi-fractional sediment transport modules is presented. The sediment transport module simulates the transport of a mixture of one cohesive sediment fraction and a number of fractions of non-cohesive sediments of different sizes and densities. The model of radionuclide transport describes the key transport and exchange processes in the system of water-suspended and bottom multi-fraction sediments. Two-step kinetics with two successive reversible fast and slow reactions is used in the model. A noticeable feature of the model is approximation of the sediment and contamination profiles in the bed by multiple well-mixed layers to describe the vertical migration of radioactivity within bottom sediments due to erosion/deposition, molecular diffusion and bioturbation. The model accurately reproduced a laboratory experiment on the uptake of radiocesium by lake sediments. An analytical solution describing mutual adjustment of the concentrations of radioactivity in the pore water and in the multi-fraction sediment showed that activity was redistributed between different fractions of sediments far slower than between water and the total concentration in the sediment. The extended one-layer model of bottom contamination of multi-fraction sediments was derived from a general model and compared with a multi-layer model. It was found, however, that the one-layer approximation was not capable of correctly predicting the inventory due to the fact that one-layer averaged concentration can essentially differ from the near-surface value in the multi-layer model. Radionuclide transport in channel with bottom depression was simulated to estimate the effects of erosion/deposition and the multi-fractionality of sediments on the transport process. It was shown that these factors affect the distribution of sediments by forming local maxima and minima of activity at the beginning and end of the depression, respectively, due to the redistribution of contaminated bottom sediments by flow. The developed model can also be used to simulate the transport of a wide class of toxic substances sorbed on sediments.

Simulation of Typhoon Bolaven using Integrally Coupled Tide-Surge-Wave Models based on locally Enhanced Fine-Mesh Unstructured Grid System

ABSTRACT Kim, K.O.; Yuk, J.-H., and Choi, B.H., 2016. Simulation of Typhoon Bolaven using integrally coupled tide-surge-wave models based on locally enhanced fine-mesh unstructured grid system. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1127 - 1131. Coconut Creek (Florida), ISSN 0749-0208. The integrally coupled wave-tide-surge models based on hydrodynamic and spectral wave models with an unstructured mesh system were tested in the typhoon Bolaven, which hit the Korean Peninsula in 2012 and caused the deaths of 19 victims. The identical and homogeneous mesh allows the physics of wave-circulation interactions to be correctly resolved in both models. The unstructured mesh can be applied to a large domain allowing all energy from deep to shallow waters to be seamlessly followed. The model results were compared with the observations, and the model performance was evaluated. The results show that it is important to incorporate the wave-current interaction effect into coastal areas in the wave-tide-surge coupled model. The model should consider effects of depth-induced wave breaking, wind field, currents and sea surface elevation in the prediction of waves. The resulting modeling system can be used for hindcasting (prediction) and forecasting the wave-tide-surge coupled environments at complex coastlines, shallow water and fine sediment areas, such as around the Korean Peninsula.

Integral Tide-Surge-Wave Model of the Yellow Sea for Understanding Local Sediment Transport

ABSTRACT Choi, B.H.; Yuk, J.-H., and Kim, K.O., 2016. Integral tide-surge-wave model of the Yellow Sea for understanding local sediment transport. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 208–212. Coconut Creek (Florida), ISSN 0749-0208. Numerical simulations of tide and tidal current for the effect of the new port on Saemangeum area were carried out based on finely resolved meshes and integral tide-surge-wave model of the whole Yellow Sea and also for a compact model optimized for the field operation. The resulting modelling system can be used for hindcasting (prediction) the tide-surge-wave coupled environments at complex coastline, shallow water and fine-grained sediment area like areas around Korean Peninsula. We investigated and discussed the changes of tidal residual current, maximum bottom shear stress and tidal energy dissipation due to the new port for Saemangeum area where the construction of new large port is being built.