| Submarine landslide is one of the types of geological disasters widely developed in slope area.It is a dominant factor of the shaping submarine topography and geomorphology,and it is also an important way to transport sediments to deep sea basin on the continental slope.There are abundant natural gas hydrate and oil-gas resources in the Northern Slope of the South China Sea,at the same time,landslides and other geological disasters are extremely developed in this area.This paper is based on the North Slope in Baiyun Sag of the South China Sea as the research area, to carry out the research of the landslides’ distribution,the landslides’ characteristics and formation mechanism of the landslides.The results of the research have a strong guiding significance for the safety assessment of deepwater oil,gas drilling and submarine pipeline.In addition to this,there are certain scientific significance in understanding the continental slope sediment transport.The research area is located in the North Slope in Baiyun Sag of the South China Sea, the water depth is approximately 200m~1700m.The depth of the water and landscape types here change greatly.This paper comprehensively uses multi-beam bathymetric data,shallow stratum profile and the side-scan sonar data to carry out the research of the landslides’ distribution,the landslides’ characteristics and formation mechanism of the landslides,gained the conclusions as follows:(1) Based on the multibeam data,identify the submarine landslides using steep slope automatic identification program,and then test and verify the identified landslides by seismic data and side scan sonar data.The results show that the program for rapid identification of submarine landslides is feasible, but the identification result is mainly affected by the accuracy of water depth data.(2) The landslides in the study area are mainly distributed in the valley bottom,where in the head of the canyon and both sides of the canyon is the submarine landslides concentrated distribution area.In the study area,identified 145 submarine landslides, the statistics showed, landslides’ size are between 0.04~15.88km2 range,the landslides’ area which is less than 4km2 occupy 91.7%.There are about 110 submarine landslides(about 76%) distributed in the canyon walls and nearby area.(3) The results for different positions(upper slope, mid slope and lower slope)analysis of internal acoustic structure of typical landslide show the upper slope landslides belong to brittle landslide,which is characterized in that the interior remained the original structure and stratification. The mid slope landslides have a obvious arc sliding surface,the landslides on the canyon wall belong to the plastic slide,which internal structure and bedding are disorderly.The landslides on the ridges between two canyon belong to brittle landslide.The lower slope landslides are mainly plastic landslide,and the slide surface is not very obviously.(4) The seabed falling gradient and the soil strengh are the main control factors of submarine landslides.Based on the Geo Slope numerical analysis software,founded3°、6°、8°、9°、12°and 15° six submarine slope models.The calculation results show that, the earthquake and the slope gradient are both important affecting factors of the submarine slope stability.On the smaller gradient slope,the effect of earthquake to the slope stability is more obviously.With the increase of slope gradient, when the slope gradient is greater than the critical slope gradient,the slope will be in an unstable state, in this case,the effect of earthquake action will become less pronounced.Through the comparison of 8° and 9° slope models, then combined with the seabed falling gradient and landslides distribution characteristics in the study area, knows that the study area slope stability critical gradient is consistent with numerical simulation results were about 9 degrees. |
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