| Submarine landslide that widely occurs on the continental slope is one of the major forces which affect the morphology of continental margin, and one of the major mechanisms of sediment transport from the shallow water to the deep basin. Sudden large-scale submarine landslide may trigger tsunami, causing huge losses in property and human life of coastal residents. Therefore, it is important to investigate the distribution, source, mechanisms and evolution model of submarine landslides.East China Sea is a passive continental margin, characterized by rifted, rotated fault blocks and steeper continental slope. Thus, the geological condition is suitable for the development of submarine landslide. However, in the past years, due to lack of high resolution multi-beam bathymetric data, submarine landslides alone the continental slope of the East China Sea have not yet been synthetically studied on its characteristics and mechanism.Typical geomorphologic features of submarine landslide consist of an arcuate headscarp, two sub-parallel sidewalls and sometimes with slumped material appear at the base of the landslide scar. This study is based on seafloor morphology derived from the multi-beam bathymetric data. The discreet multi-beam data are incorporated in the CARIS Hydrographic Information Processing (HIPS) software packages and gridded. Then high resolution digital terrain models are constructed, slope maps and artificial hill-shade images created are used to identify the location of submarine landslides. After the Identification of submarine landslide, various aspects of the failures/fractures, including landslide area, run-out distance, the head-scarp height and slope, and adjacent local un-failed slope gradient, are measured and the relationships statistically analyzed. morphometric statistics give us useful insight into submarine landslides.Based on our investigation, the total number of submarine landslides identified is 102, and the area of the identified landslides ranges from 0.06km2 to 15.51km2, and the volume of the landslide is between 0.001km3 and 1.942km3, and averages 0.165km3. The largest landslide is approximately connected with the reported mud volcanoes.Most landslides occur on the local slopes less than 20°, with the depth of 200m?1200m. There is a high correlation between slope gradient and area. And the thickness of sliding layer is approximately 26m for each landslide. According to previous research experience, submarine landslides could be categorized by the H/L value. The statistic data show that most frequently observed submarine landslide belong to slump, rotational slide and translational slide and that there is a lack of flow slide in the study area. Most slumps and rotational slides are present on the submarine canyon system, and most translational slides are observed on the open continental slope.Three centrifuge modelling experiments of unsaturated soils show that the formation of mud volcano near the submarine landslides is facilitated by the process that the pore gas and water escape under the pressure difference while submarine slope is under instability. The gas in the soil could have effect on the soil strength by affecting its density, and have no significant effect on the rate of the water pore pressure change with the increase of the gravity acceleration.By using Slope/W software, the result of slope stability analysis shows that the sediments deposited in the study area after the last glacial period are under instability in the seismic intensity of 7 degrees, or in the seismic intensity 6 degrees with slope more than 3.1°.but the slope is stable under the self gravityThe main innovations in this dissertation include:(1) Submarine landslides in the continental slope area between 27°N and 30°N are identified, statistically analyzed and preliminarily categorized, based on seafloor morphology derived from multi-beam bathymetric data. (2) Considering the gas content in the soil, the slope stability is analyzed and simulated in the centrifuge model test of submarine unsaturated soil slope with soil samples preparation under the anaerobic condition. |
PDF Full Text Request