The upper part of the continental slope in the northern South China Sea is prone to submarine landslide disasters,especially in submarine canyons.This work studies borehole sediments,discusses geotechnical properties ...The upper part of the continental slope in the northern South China Sea is prone to submarine landslide disasters,especially in submarine canyons.This work studies borehole sediments,discusses geotechnical properties of sediments,and evaluates sediment stability in the study area.The results show that sediment shear strength increases with increasing depth,with good linear correlation.Variations in shear strength of sediments with burial depth have a significantly greater rate of change in the canyon head and middle part than those in the canyon bottom.For sediments at the same burial depth,shear strength gradually increased and then decreased from the head to the bottom of the canyon,and has no obvious correlation with the slope angle of the sampling site.Under static conditions,the critical equilibrium slope angle of the sediments in the middle part of the canyon is 10°to 12°,and the critical slope angle in the head and the bottom of the canyon is 7°.The results indicate that potential landslide hazard areas are mainly distributed in distinct spots or narrow strips on the canyon walls where there are high slope angles.展开更多
The canyon system,including 17 small slope-confined canyons in the Shenhu area,northern South China Sea,is significantly characterized by mounded or undulating features on the canyon flanks and canyon heads.However,th...The canyon system,including 17 small slope-confined canyons in the Shenhu area,northern South China Sea,is significantly characterized by mounded or undulating features on the canyon flanks and canyon heads.However,the mechanism underlying the formation of these features has yet to be elucidated.In previous studies,most of them were interpreted as sediment deformation on the exploration seismic profiles.In this paper,we collected high-resolution bathymetric data,chirp profiles and geotechnical test data to investigate their detailed morphology,internal structures,and origin.The bathymetric data indicated that most mounded seismic units have smooth seafloors and are separated by grooves or depressions.The distance between two adjacent mounded units is only hundreds of meters.On chirp profiles,mounded seismic units usually exhibit chaotic reflections and wavy reflections,of which the crests migrate upslope.The slope stability analysis results revealed that the critical angle of the soil layers in the study area tends to be 9°,indicating that most mounded seismic units on the canyon flanks and heads are stable at present.The terrain characteristics and seismic configurations combined with the slope stability analysis results indicated that most mounded seismic units are not sediment deformation but depositional structures or mixed systems composed of deformation and depositional structures.展开更多
Before the implementation of offshore oil and gas exploitation,it is essential to understand the various factors that influence the stability of submarine sediments surrounding the project.Considering the factors such...Before the implementation of offshore oil and gas exploitation,it is essential to understand the various factors that influence the stability of submarine sediments surrounding the project.Considering the factors such as cost and operability,it is not feasible to assess the physical-mechanical properties of sediments covering the entire region by borehole sampling.In this study,the correlation between near seafloor seismic amplitude and the mean shear strength of shallow sediments was explored using seismic and core testing data from the northern continental slope area of the South China Sea.Results showed that the mean water content of sediments in the layer up to 12 m below the seafloor(mbsf)gradually increased with increasing water depth,and the mean shear strength tended to decrease rapidly near the 1000 m depth contour.The near seafloor seismic amplitude could reflect the mean shear strength of sediments in the 12 mbsf layer under seismic frequency of 65 Hz and wave velocity of 1600 m/s.When the mean shear strength was greater than 10 kPa or the water depth was less than 1000 m,there was a significant linear positive correlation between mean shear strength and near seafloor seismic amplitude.Otherwise,there was a significant linear negative correlation between mean shear strength and near seafloor seismic amplitude.On the basis of these correlations,the pattern of shear strength was estimated from near seafloor seismic amplitude and mapped.The mean shear strength of sediments above 12 mbsf gradually decreased with increasing water depth in the continental slope area,whereas little change occurred in the continental shelf and the end of the canyon.Within the canyon area,the mean shear strength of sediments was characterized by larger values in both sides of the canyon walls and smaller values in the canyon bottom,which was consistent with the infinite slope stability theory.The study provides a method for using near seafloor seismic amplitude data to guide sediment sampling design,and presents a continuous dataset of sediment strength for the simulation of regional sediment stability.展开更多
基金The National Natural Science Foundation of China under contract No.41706065the National Program on Global Change and Air-Sea Interaction of China under contract No.GASI-GEOGE-05+1 种基金the Special Fund of Chinese Central Government for Basic Scientific Research Operations in Commonweal Research Institutes under contract No.2015G08the NSFC-Shandong Joint Fund for Marine Science Research Centers of China under contract No.U1606401
文摘The upper part of the continental slope in the northern South China Sea is prone to submarine landslide disasters,especially in submarine canyons.This work studies borehole sediments,discusses geotechnical properties of sediments,and evaluates sediment stability in the study area.The results show that sediment shear strength increases with increasing depth,with good linear correlation.Variations in shear strength of sediments with burial depth have a significantly greater rate of change in the canyon head and middle part than those in the canyon bottom.For sediments at the same burial depth,shear strength gradually increased and then decreased from the head to the bottom of the canyon,and has no obvious correlation with the slope angle of the sampling site.Under static conditions,the critical equilibrium slope angle of the sediments in the middle part of the canyon is 10°to 12°,and the critical slope angle in the head and the bottom of the canyon is 7°.The results indicate that potential landslide hazard areas are mainly distributed in distinct spots or narrow strips on the canyon walls where there are high slope angles.
基金The National Natural Science Foundation of China under contract No.41876061the National Key Research and Development Program under contract No.2016YFC0301403。
文摘The canyon system,including 17 small slope-confined canyons in the Shenhu area,northern South China Sea,is significantly characterized by mounded or undulating features on the canyon flanks and canyon heads.However,the mechanism underlying the formation of these features has yet to be elucidated.In previous studies,most of them were interpreted as sediment deformation on the exploration seismic profiles.In this paper,we collected high-resolution bathymetric data,chirp profiles and geotechnical test data to investigate their detailed morphology,internal structures,and origin.The bathymetric data indicated that most mounded seismic units have smooth seafloors and are separated by grooves or depressions.The distance between two adjacent mounded units is only hundreds of meters.On chirp profiles,mounded seismic units usually exhibit chaotic reflections and wavy reflections,of which the crests migrate upslope.The slope stability analysis results revealed that the critical angle of the soil layers in the study area tends to be 9°,indicating that most mounded seismic units on the canyon flanks and heads are stable at present.The terrain characteristics and seismic configurations combined with the slope stability analysis results indicated that most mounded seismic units are not sediment deformation but depositional structures or mixed systems composed of deformation and depositional structures.
基金The National Natural Science Foundation of China under contract No.41706065the Basic Scientific Fund for National Public Research Institutes of China under contract No.2015G08+1 种基金the NSFC-Shandong Joint Fund for Marine Science Research Centers of China under contract No.U1606401the National Program on Global Change and Air-sea Interaction of China under contract No.GASI-GEOGE-05.
文摘Before the implementation of offshore oil and gas exploitation,it is essential to understand the various factors that influence the stability of submarine sediments surrounding the project.Considering the factors such as cost and operability,it is not feasible to assess the physical-mechanical properties of sediments covering the entire region by borehole sampling.In this study,the correlation between near seafloor seismic amplitude and the mean shear strength of shallow sediments was explored using seismic and core testing data from the northern continental slope area of the South China Sea.Results showed that the mean water content of sediments in the layer up to 12 m below the seafloor(mbsf)gradually increased with increasing water depth,and the mean shear strength tended to decrease rapidly near the 1000 m depth contour.The near seafloor seismic amplitude could reflect the mean shear strength of sediments in the 12 mbsf layer under seismic frequency of 65 Hz and wave velocity of 1600 m/s.When the mean shear strength was greater than 10 kPa or the water depth was less than 1000 m,there was a significant linear positive correlation between mean shear strength and near seafloor seismic amplitude.Otherwise,there was a significant linear negative correlation between mean shear strength and near seafloor seismic amplitude.On the basis of these correlations,the pattern of shear strength was estimated from near seafloor seismic amplitude and mapped.The mean shear strength of sediments above 12 mbsf gradually decreased with increasing water depth in the continental slope area,whereas little change occurred in the continental shelf and the end of the canyon.Within the canyon area,the mean shear strength of sediments was characterized by larger values in both sides of the canyon walls and smaller values in the canyon bottom,which was consistent with the infinite slope stability theory.The study provides a method for using near seafloor seismic amplitude data to guide sediment sampling design,and presents a continuous dataset of sediment strength for the simulation of regional sediment stability.
