• Ocean and Polar Research
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• v.29 no.1
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• pp.9-31
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• 2007

Most seismic sea waves in the East Sea originate from earthquakes occurring near the Japanese west coast. While the waves propagate in the East Sea, they are deformed by refraction, diffraction and scattering. Though the Boussinesq equation is most applicable for such wave phenomena, it was not used in numerical modelling of seismic sea waves in the East Sea. To examine characteristics of seismic sea waves in the East Sea, numerical models based on the Boussinesq equation are established and used to simulate recent tsunamis. By considering Ursell parameter and Kajiura parameter, it is proved that Boussinesq equation is a proper equation for seismic sea waves in the East Sea. Two models based on the Boussinesq equation and linear wave equation are executed with the same initial conditions and grid size ($1min{\times}1min$), and the results are compared in various respects. The Boussinesq equation model produced better results than the linear model in respect to wave propagation and concentration of wave energy. It is also certified that the Boussinesq equation model can be used for operational purpose if it is optimized. Another Boussinesq equation model whose grid size is $40sec{\times}30sec$ is set up to simulate the 1983 and 1993 tsunamis. As the result of simulation, new propagation charts of 2 seismic sea waves focused on the Korean east coast are proposed. Even though the 1983 and 1993 tsunamis started at different areas, the propagation paths near the Korean east coast are similar and they can be distinguished into 4 paths. Among these, total energy and propagating time of the waves passing over North Korea Plateau(NKP) and South Korea Plateau(SKP) determine wave height at the Korean east coast. In case of the 1993 tsunami, the wave passing over NKP has more energy than the wave over SKP. In case of the 1983 tsunami, the huge energy of the wave passing over SKP brought about great maximum wave heights at Mukho and Imwon. The Boussinesq equation model established in this study is more useful for simulation of seismic sea waves near the Korean east coast than it is the Japanese coast. To improve understanding of seismic sea waves in shallow water, a coastal area model based on the Boussinesq equation is also required.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.156-157
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• 2005

Gas hydrate is ice-like crystalline lattice, formed at appropriate temperature and pressure, in which gas molecules are trapped. It is worldwide popular interesting subject as a potential energy. In korea, a seismic survey for gas hydrate have performed over the East sea by the KIGAM since 1997. In this paper, we had conducted numerical and physical modeling experiments for seismic properties on gas hydrate with field data which had been acquired over the East sea in 1998. We used a finite difference seismic method with staggered grid for 2-D elastic wave equation to generate synthetic seismograms from multi-channel surface seismic survey, OBC(Ocean Bottom Cable) and VSP(Vertical Seismic Profiling). We developed the seismic physical modeling system which is simulated in the deep sea conditions and acquired the physical model data to the various source-receiver geometry. We carried out seismic complex analysis with the obtained data. In numerical and physical modeling data, we observed the phase reversal phenomenon of reflection wave at interface between the gas hydrate and free gas. In seismic physical modeling, seismic properties of the modeling material agree with the seismic velocity estimated from the travel time of reflection events. We could easily find out AVO(Amplitude Versus Offset) in the reflection strength profile through seismic complex analysis.

• Journal of the Korean earth science society
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• v.43 no.4
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• pp.520-531
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• 2022

The Yellow Sea experienced glacio-eustasy sea-level fluctuations during the Quaternary period. In the middle part of the Yellow Sea, the Quaternary successions were accumulated by alternating terrestrial, paralic, and shallow marine deposits that reflected the fluctuating sea levels. A long core of 69.2 m was acquired at the YMGR-102 site (33°50.1782'N and 123°48.3019'E) at a depth of 72.5 m in the middle of the Yellow Sea. A four-layered geoacoustic model was reconstructed for the sedimentary succession. It was based on seismic characteristics from 3.5 kHz SBP and air-gun seismic profiles and 96 grain-size properties in the core sample from YMGR-102. For the underwater simulation and experiments, the in-situ P-wave speeds were calculated using the sound speed ratio of the Hamilton method. The geoacoustic model of YMGR-102 can contribute to the reconstruction of geoacoustic models, reflecting the vertical and lateral variability of the acoustic properties in the continental shelf of the middle Yellow Sea.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.289-298
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• 2009

Optimal data processing parameters were designed to attenuate multiples in seismic data acquired in the south-eastern area of the East Sea, in 2008. Bunch of multiples caused by shallow sea water depth were perceived periodically up to two way travel time of 1,750 ms at every 250 ms over seismic traces. We abbreviated sea bottom multiple as SBM, Peg-leg multiple as PLM, and free-surface multiple as FSM. To attenuate these multiples, seismic data processing flow was constructed including NMO, stack, minimum phase predictive deconvolution filter and wave equation multiple rejections (WEMR). Prevalent multiples were suppressed by predictive deconvolution and remaining multiples were attenuated by WEMR. We concluded that combining deconvolution with WEMR was effective to a seismic data of study area. Derived parameter can be applied to the seismic data processing on adjacent survey area.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.353-362
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• 2022

The seismic failure-prone region in Istanbul has been examined in terms of the segmented pipelines. Although some researchers have suggested that this territory should be left as a green land, many people continue to live in this area. This region is about 9-10 km away from the North Anatolian Fault Line. This fault zone is an active right-lateral strike-slip fault line in Turkey and an earthquake with a magnitude of 7.0-7.5 is expected in the Marmara Sea. Therefore, superstructures and infrastructures are under both land sliding risks and seismic risks in this area. Because there are not any pipeline-fault line intersection points in the region, in this study, it has been focused on the behaviors of the segmented (sewage or stormwater) pipelines subject to earthquake-induced permanent ground deformation and seismic wave propagation. Based on the elastic beam theory some necessary analyses have been carried out and obtained results of this approximation have been examined.

• Journal of the Korean earth science society
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• v.44 no.4
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• pp.264-274
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• 2023

The Korea Strait comprises a continental shelf in a shallow sea that experienced glacio-eustastic sea-level changes during the Quaternary period. A long core of 76.6 m in length was acquired at the South Sea Drilling Project site (SSDP-101; 34°19.666'E and 128°16.335'N) with a 60 m water deep. The uppermost massive sand beds were interpreted as sandy sediments of the nearshore marine sand ridge in the shallow sea during the transgression of sea level, whereas the lower parts of alternating sandy and muddy beds were interpreted as deposits in marsh, estuary, and tidal flat environments. A three-layered geoacoustic model was reconstructed for the sedimentary succession in the high-resolution seismic profile based on a 140-grain size and sediment type of core SSDP-101. For the actual underwater simulation and experiments, the in-situ P-wave speeds were calculated using the sound speed ratio of the Hamilton method.

• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.116-131
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• 2019

In order to obtain high-quality high-resolution marine seismic data, the survey needs to be carried out at very low-sea condition. However, the survey is often performed with a slight wave, which degrades the quality of data. In this case, it is possible to improve the quality of seismic data by detecting the exact location of the sea bottom signal and eliminating the influence of waves or swells automatically during data processing. However, if noise is included or the sea bottom signal is weakened due to sea waves, sea bottom detection errors are likely to occur. In this study, we applied a method reducing such errors by estimating the sea bottom location, setting a narrow detection range and detecting the sea bottom location within this range. The expected location of the sea bottom was calculated using previously detected sea bottom locations for each channel of multi-channel data. The expected location calculated in each channel is also compared and verified with expected locations of other channels in a shot gather. As a result of applying this method to the noisy 8-channel high-resolution air-gun seismic data acquired off Yeosu, the errors in selecting the strong noise before sea bottom or the strong subsurface reflected signal after the sea bottom signal are remarkably reduced and it is possible to produce the high-quality seismic section with the correction of ~ 2.5 m swell effect.

• Journal of Ocean Engineering and Technology
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• v.31 no.4
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• pp.308-314
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• 2017

The purpose of this study was to investigate the sea floor using a seismic profiler in the northern part of Chagwi-do of Jeju Island in order to select the optimal location for the 60-m-class berth of a sea test bed for wave energy converters and provide basic environmental data for designing a suction anchor. The echo types of the seismic profiles were classified based on the study of Kim et al. (2016a), and the location for installing the suction anchor was selected based on a sediment thickness of more than 10 m. The physical properties of the surface sediments were determined by analyzing the sediment samples obtained from 16 grab sample points. Based on the investigation and analysis, we proposed a survey area in the North-Eastern sea as an optimum location for the 60-m-class berth where the suction anchor could be installed.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2006.09a
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• pp.37-40
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• 2006

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.220-227
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• 2016

Marine seismic data have not only primary signals from subsurface but also ghost signals reflected from the sea surface. The ghost decreases temporal resolution of seismic data because it attenuates specific frequency components. For eliminating the ghost signals effectively, the exact ghost delaytimes and reflection coefficients are required. Because of undulation of the sea surface and vertical movements of airguns and streamers, the ghost delaytime varies spatially and randomly while acquiring seismic data. The reflection coefficient is a function of frequency, incidence angle of plane-wave and the sea state. In order to estimate the proper ghost delaytimes considering these characteristics, we compared the ghost delaytimes estimated with L-1 norm, L-2 norm and kurtosis of the deghosted trace and its autocorrelation on synthetic data. L-1 norm of autocorrelation showed a minimal error and the reflection coefficient was calculated using Kirchhoff approximation equation which can handle the effect of wave height. We applied the estimated ghost delaytimes and the calculated reflection coefficients to remove the source and receiver ghost effects. By removing ghost signals, we reconstructed the frequency components attenuated near the notch frequency and produced the migrated stack section with enhanced temporal resolution.