Characteristics of Gas Hydrate Stability Zone and Resource Evaluation in Okinawa Trough

According to the processing and interpretation of multichannel seismic reflection data in the area of Okinawa Trough, the BSR （bottom simulating reflector） was identified in 16 seismic profiles. By means of special processing technologies such as AVO and waveform inversion, the authors, for the first time, directly used the BSR to outline the distribution tendency of thickness of gas hydrate stability zone in the Trough and thought that the largest stability zone thickness was in the south and the smallest in the north. Then through calculation the authors got the thickness of hydrate stability zone and resource of the hydrate. This would be useful to the future hydrate exploration and resource evaluation in the Okinawa Trough.

Wave Height Distribution for Spilling Waves in and outside the Surf Zone

The wave characteristics affecting coastal sediment transport include wave height, wave period and breaking wave direction. Wave height is a critical factor in determining the amount of sediment transport in the coastal area. The force of sediment transport is much more intense under breaking waves than under non-breaking waves. Breaking waves exhibit various patterns, principal- ly depending on the incident wave steepness and the beach slope. Based on the equations of con- servation of mass, momentum and energy, a theoretical model for wave deformation in and outside the surf zone was obtained, which is used to calculate the wave shoaling, wave set-up and set- down and wave height distributions in and outside the surf zone. The analysis and comparison were made about the breaking point location and the wave height decay caused by the wave breaking and the bottom friction. Flume experiments relating to the spilling wave height distribution across the surf zone were conducted to verify the theoretical model. Advanced wave maker, data sampling de- vices and data processing system were utilized in the flume experiments with a slope covered by sands of different diameters to facilitate the observation and research on the wave transformation and breaking. The agreement between the theoretical and experimental results is good.

A flume test on erosion mechanism for an abandoned section of the Huanghe(Yellow)River Delta

The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe （Yellow） River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profllc equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion.