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1.
Submarine landslides occur frequently on most continental margins. They are effective mechanisms of sediment transfer but also a geological hazard to seafloor installations. In this paper, submarine slope stability is evaluated using a 2D limit equilibrium method. Considerations of slope, sediment, and triggering force on the factor of safety (FOS) were calculated in drained and undrained (Φ=0) cases. Results show that submarine slopes are stable when the slope is <16° under static conditions and without a weak interlayer. With a weak interlayer, slopes are stable at <18° in the drained case and at <9° in the undrained case. Earthquake loading can drastically reduce the shear strength of sediment with increased pore water pressure. The slope became unstable at >13° with earthquake peak ground acceleration (PGA) of 0.5 g; whereas with a weak layer, a PGA of 0.2 g could trigger instability at slopes >10°, and >3° for PGA of 0.5 g. The northern slope of the South China Sea is geomorphologically stable under static conditions. However, because of the possibility of high PGA at the eastern margin of the South China Sea, submarine slides are likely on the Taiwan Bank slope and eastern part of the Dongsha slope. Therefore, submarine slides recognized in seismic profiles on the Taiwan Bank slope would be triggered by an earthquake, the most important factor for triggering submarine slides on the northern slope of the South China Sea. Considering the distribution of PGA, we consider the northern slope of the South China Sea to be stable, excluding the Taiwan Bank slope, which is tectonically active.  相似文献   

2.
Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods.These features include submarine landslides,pockmark fields,shallow free gas,gas hydrates,mud diapirs and earthquake tsunami,which are widely distributed in the continental slope and reefal islands of the South China Sea.Although the study and assessment of geohazards in the South China Sea came into operation only recently,advances in various aspects are evolving at full speed to comply with National Marine Strategy and‘the Belt and Road’Policy.The characteristics of geohazards in deep-water seafloor of the South China Sea are summarized based on new scientific advances.This progress is aimed to aid ongoing deep-water drilling activities and decrease geological risks in ocean development.  相似文献   

3.
The Liwan (Lw) gas field located in the northern slope of the South China Sea (SCS) is extremely complex for its sea-floor topograghy, which is a huge challenge for the safety of subsea facilities. It is economically impractical to obtain parameters for risk assessment of slope stability through a large amount of sampling over the whole field. The linkage between soil shear strength and seabed peak amplitude derived from 2D/3D seismic data is helpful for understanding the regional slope-instability risk. In this paper, the relationships among seabed peak, acoustic impedance and shear strength of shallow soil in the study area were discussed based on statistical analysis results. We obtained a similar relationship to that obtained in other deep-water areas. There is a positive correlation between seabed peak amplitude and acoustic impedance and an exponential relationship between acoustic impedance and shear strength of sediment. The acoustic impedance is the key factor linking the seismic amplitude and shear strength. Infinite slope stability analysis results indicate the areas have a high potential of shallow landslide on slopes exceeding 15° when the thickness of loose sediments exceeds 8 m in the Lw gas field. Our prediction shows that they are mainly located in the heads and walls of submarine canyons.  相似文献   

4.
The primary objective of landslide susceptibility mapping is the prediction of potential landslides in landslide-prone areas.The predictive power of a landslide susceptibility mapping model could be tested in an adjacent area of similar geoenvironmental conditions to find out the reliability.Both the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake occurred in the Longmen Mountain seismic zone,with similar topographical and geological conditions.The two earthquakes are both featured by thrust fault and similar seismic mechanism.This paper adopted the susceptibility mapping model of co-seismic landslides triggered by Wenchuan earthquake to predict the spatial distribution of landslides induced by Lushan earthquake.Six influencing parameters were taken into consideration: distance from the seismic fault,slope gradient,lithology,distance from drainage,elevation and Peak Ground Acceleration(PGA).The preliminary results suggested that the zones with high susceptibility of coseismic landslides were mainly distributed in the mountainous areas of Lushan,Baoxing and Tianquan counties.The co-seismic landslide susceptibility map was completed in two days after the quake and sent to the field investigators to provide guidance for rescue and relief work.The predictive power of the susceptibility map was validated by ROC curve analysis method using 2037 co-seismic landslides in the epicenter area.The AUC value of 0.710 indicated that the susceptibility model derived from Wenchuan Earthquake landslides showed good accuracy in predicting the landslides triggered by Lushan earthquake.  相似文献   

5.
This paper investigates the size distribution of submarine landslides on the middle continental slope of the East China Sea (ECS) using the size of the landslide source regions. Geomorphometric mapping is used to identify 102 mass movements from multibeam bathymetric data and to extract morphological information about the head scarps and side walls. These mass movements have areas ranging between 0.06 km2 and 15.51 km2 and volumes between 0.002 km3 and 2 km3. The area vs volume relationship of these failure scarps is approximately linear, suggesting a fairly uniform failure thickness in each event with scarce deep excavating landslides. The cumulative area distribution of the slope failures can be described by an inverse power law. The submarine landslides on the mid-ECS continental slope could be considered as a large-scale self-organizing system because they have the characteristics of a dissipative system in a critical state.  相似文献   

6.
Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea, such as bottom simulating reflections(BSRs), undersea gas springs, pyrite associated with methane leakage, mud diapirs/mud volcanos, bottom-water methane anomalies and so on. In this study, six key stratigraphic interfaces including T_0(seafloor), T_1(LGM, 23 kyr B.P.), T_2(2.58 Myr), T_3(5.33 Myr), T_4(11.02 Myr) and T_5(16.12 Myr) were identified, and then five third-order sequences of SQIII1 to SQIII5 were divided. However, T5 in southern continental slope is not found, which shows that the middle-northern Okinawa Trough had begun to rift in the early Miocene, earlier than the southern segment. Four system tracts including lowstand systems tract(LST), transgressive systems tract(TST), highstand systems tract(HST) and falling stage systems tract(FSST) are further divided. The marine erosion interface of 11.02 Myr and regressive unconformity interface of 23 kyr B.P. indicate two large-scale sea level drop events in the research area. Seven typical seismic facies identified in the continental slope are continental shelf-edge deltas, littoral fluvial-delta plains, incised channels or submarine canyons, slope fans, submarine fans or coastal sandbars, littoral-neritic finegrained sediments, mud volcanos and some other geological bodies respectively. The minimum water depth for hydrate occurrence in the Okinawa Trough is 630 m, and the thickness of gas hydrate stability zone in continental slope is between 0 and 590 m. The calculated bottom boundary of hydrate stability zone is slightly deeper than BSRs on the seismic sections. The re-depositional turbidite sand bodies, such as canyon channels, slope fans and submarine fans developed in Quaternary strata, are the predominant hydrate reservoirs. According to developing process, the dynamic accumulation of hydrate systems can be divided into three evolutionary stages including canyon erosion and hydrate stability zone migration stage, sediments destabilizing and methane leakage stage, and channel filling and hydrate re-occurrence stage.  相似文献   

7.
Marine geological disasters occurred frequently in the deep-water slope area of the northern South China Sea, especially submarine landslides, which caused serious damage to marine facilities. The cyclic elastoplastic model that can describe the cyclic stress-strain response characteristic for soft clay, is embedded into the coupled Eulerian-Lagrangian(CEL) algorithm of ABAQUS by means of subroutine interface technology. On the basis of CEL technique and undrained cyclic elastoplastic model, a method for analyzing the dynamic instability process of marine slopes under the action of earthquake load is developed. The rationality for cyclic elastoplastic constitutive model is validated by comparing its calculated results with those of von Mises model built in Abaqus. The dynamic instability process of slopes under different conditions are analyzed. The results indicate that the deformation accumulation of soft clay have a significant effect on the dynamic instability process of submarine slopes under earthquake loading. The cumulative deformation is taken into our model and this makes the calculated final deformation of the slope under earthquake load larger than the results of conventional numerical method. When different contact conditions are used for analysis, the smaller the friction coefficient is, the larger the deformation of slopes will be. A numerical analysis method that can both reflect the dynamic properties of soft clay and display the dynamic instability process of submarine landslide is proposed, which could visually predict the topographies of the previous and post failure for submarine slope.  相似文献   

8.
Dongsha Island and the adjacent sea area locate at the northern continental margin of the South China Sea (SCS), and is connected to the east by the Manila Trench. Analyses of seismic stratigraphy and gravity, magnetic and drilling wells data led to the discovery of three post-fault sequences (Ⅴ, Ⅵ, Ⅶ). Extensive tectonic uplift, magma activity and erosion occurred in Dongsha Island and the adjacent area, where most of the faults in the northeastern SCS were still active during Pliocene and Quaternary. Two groups of faults trending NEE and NW were developed during Late Cenozoic. We conclude that three important tectonic movements, especially Dongsha movement(4.4 - 5.2 Ma) and Liuhua movement (1.4 - 1.89 Ma), controlled the structural framework in the Dongsha rise; whose deformation in the east is stronger than that in the west and whose stress field variation suggests that the tectonic uplift in the study area contributed to magmato-tectonic events correlated to the main collision phases between the East China and Taiwan 5 - 3 and 3 - 0 Ma ago.  相似文献   

9.
为了明确南海西南次海盆V型尖端地壳岩石圈发生最终裂解的特征及其演化过程,通过精细的构造解释、断层活动性定量分析、不同构造演化阶段盆地原型分析、沉降速率分析、沉降史模拟等方法综合分析表明,南海西南次海盆V型尖端临界破裂区为远端带和洋陆转换带构成的地壳岩石圈强烈伸展区,依据地壳岩石圈几何形态,该区域可进一步划分为箱型域和楔型域。楔型域内盆地原型可划分为断陷盆地（Tb-SD）、拆离盆地（SD-PD）和拗陷盆地（PD-Bi）;箱型域在古新世-渐新世（Tb-SD）盆地原型为断陷盆地,之后该区域进入被动沉降期。新生代以来,南海西南次海盆V型尖端在构造演化过程中,盆地沉降中心由陆向洋方向逐渐迁移,岩浆作用在断拗转换幕发育最强烈,致使岩石圈地壳最终发生裂解。区域资料对比分析表明,南海西南次海盆V型尖端在不同构造带内,盆地构造-地层格架具有差异性,且南海西南次海盆V型尖端经历"双拆离作用"后地壳发生破裂,岩浆侵入,形成原洋洋壳。该认识对南海西南部深水盆地内油气勘探具有重大指示意义。   相似文献   

10.
As one of the biggest marginal seas in the western Pacific margin, the South China Sea (SCS) experienced continental rifting and seafloor spreading during the Cenozoic. The northern continental margin of the SCS is classified as a passive continental margin. However, its depositional and structural evolution remains controversial, especially in the deep slope area. The lack of data hindered the correlation between continental shelf and oceanic basin, and prevented the establishment of sequence stratigraphic frame of the whole margin. The slope basins in the mid-northern margin of SCS developed in the Cenozoic; the sediments and basin infill recorded the geological history of the continental margin and the SCS spreading. Using multi-channel seismic dataset acquired in three survey cruises during 1987 to 2004, combined with the data of ODP Leg 184 core and industrial wells, we carried out the sequence stratigraphic division and correlation of the Cenozoic in the middle-northern margin of SCS with seismic profiles and sedimentary facies. We interpreted the seismic reflection properties including continuity, amplitude, frequency, reflection terminals, and 15 sequence boundaries of the Cenozoic in the study area, and correlated the well data in geological age. The depositional environment changed from river and lake, shallow bay to open-deep sea, in correspondence to tectonic events of syn-rifting, early drifting, and late drifting stages of basin evolution.  相似文献   

11.
Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.  相似文献   

12.
The Okinawa Trough is a very active tectonic zone at the margin of the Northwest Pacific and is typical of back-arc rifting at the young stage of tectonic evolution. Many scientists from Japan,China, Germany, France, the U. S.A. and Russia have done a lot of geologic and geophysical investigations there. It is well known that the Okinawa Trough is an active back-arc rift with extremely high heat flow, very strong hydrothermal circulation, strong volcanic and magmatic activity, frequent earthquakes,rapid subsidence and rifting, well-developed fault and central graben. But up to now, there are still some important tectonic problems about the Okinawa Trough that require clarification on some aspects such as the type of its crust, its forming time, its tectonic evolution, the distribution of its central grabens, the relationship between its high heat flow and tectonic activity. Based on the data obtained from seismic sur-vey, geomagnetic and gravity measurements, submarine sampling and heat flow measurements in the last 15 years, the author discusses the following tectonic problems about the Okinawa Trough: (1) If the Okinawa Trough develops oceanic crust or not. (2) Is the South Okinawa Trough tectonically more active than the North Okinawa Trough with shallower water and few investigation data on it. (3) The formation time of the Okinawa Trough and its tectonic evolution. The Okinawa Trough has a very thin continental crust. Up to now, there is no evidence of oceanic crust in the Okinawa Trough. The North, Middle and South Okinawa Trough are all very strongly active areas. From 6 Ma B.P. , the Okinawa Trough began to form. Since 2 Ma, the Okinawa Trough has been very active.  相似文献   

13.
mODUCnONGravityflowsedimentationonthenorthwsterncontinentalsl0PeoftheSOuthChinaSea(SCS)are0fgreatinterestfromthescientificandengineeringP0intofview-Th0roughknOWedgofcontinentalsloPepmeessesanddepositionfeatUresispreregUisiteforhydID-carbenexploraion0fdeepwaerandforprotectionofoffhoredrineeopneeringstrUcbes(PlaifonnsandpiPelines)againstnaedhed.ManykindsofmassmovmentPIDCess-eswerefoUndtobeactiveonthen0rthernSCS(Damuth,l979;l98O).High-freqUency(3.5ffo)echo-chaIaCterInaPPingisawell…  相似文献   

14.
Seafloor elongated depressions are indicators of gas seepage or slope instability. Here we report a sequence of slopeparallel elongated depressions that link to headwalls of sediment slides on upper slope. The depressions of about 250 m in width and several kilometers in length are areas of focused gas discharge indicated by bubble-release into the water column and methane enriched pore waters. Sparker seismic profiles running perpendicular and parallel to the coast, show gas migration pathways and trapped gas underneath these depressions with bright spots and seismic blanking. The data indicate that upward gas migration is the initial reason for fracturing sedimentary layers. In the top sediment where two young stages of landslides can be detected, the slopeparallel sediment weakening lengthens and deepens the surficial fractures, creating the elongated depressions in the seafloor supported by sediment erosion due to slope-parallel water currents.  相似文献   

15.
The "4.20" Lushan earthquake in Sichuan province, China has induced a large amount of geological hazards and produced abundant loose materials which are prone to post-earthquake rainfalltriggered landslides. A detailed landslide inventory was acquired through post-earthquake emergent field investigation and high resolution remote sensing interpretation. The rainfall analysis was conducted using historical rainfall records during the period from 1951 to 2010. Results indicate that the average annual rainfall distribution is heterogeneous and the largest average annual rainfall occurs in Yucheng district. The Stability Index MAPping(SINMAP)model was adopted to assess and analyze the postearthquake slope stability under different rainfall scenarios(light rainfall, moderate rainfall, heavy rainfall, and rainstorm). The model parameters were calibrated to reflect the significant influence of strong earthquakes on geological settings. The slope stability maps triggered by different rainfall scenarios wereproduced at a regional scale. The effect of different rainfall conditions on the slope stability is discussed.The expanding trend of the unstable area was quantitatively assessed with the different critical rainfall intensity. They provide a new insight into the spatial distribution and characteristics of postearthquake rainfall-triggered landslides in the Lushan seismic area. An increase of rainfall intensity results in a significant increase of unstable area. The heterogeneous distribution of slope instability is strongly correlated with the distribution of earthquake intensity in spite of different rainfall conditions. The results suggest that the both seismic intensity and rainfall are two crucial factors for postearthquake slope stability. This study provides important references for landslide prevention and mitigation in the Lushan area after earthquake.  相似文献   

16.
Seafloor pockmarks are important indicators of submarine methane seepages and slope instabilities.In order to promote the understanding of submarine pockmarks and their relationship with sediment instabilities and climate changes,here we summarize the research results of pockmarks in the spatio-temporal distributions and shaping factors.Most of pockmarks occur along active or passive continental margins during the last 25 kyr B.P..Circular and ellipse are the most common forms of pockmarks,whereas pockmarks in a special crescent or elongated shape are indicators of slope instabilities,and ring-shape pockmarks are endemic to the gas hydrate zones.Further researches should be focused on the trigger mechanism of climate changes based on the pockmarks in the high latitudes formed during the deglaciation periods,and the role of gas hydrates in the seafloor evolution should be elucidated.In addition,the feature of pockmarks at their early stage(e.g.,developing gas chimneys and gas driving sedimentary doming)and the relations between pockmarks and mass movements,mud diapirs could be further studied to clarify the influences of rapid methane release from submarine sediments on the atmospheric carbon contents.  相似文献   

17.
琼东南盆地南部梅山组具有独特的丘状反射特征,关于其成因机制引起了广泛关注和讨论。以琼东南盆地大量二维地震资料和高分辨率三维地震资料解释为基础,在深水钻井标定下,从地震相特征、沉积物物源、沉积搬运通道、古地貌特征以及海平面变化和构造活动6个方面,阐明了梅山组丘状体的沉积特征,并讨论了其成因机制。研究结果表明,中中新统梅山组沉积时期,受强制性海退影响,琼东南盆地范围内海平面下降至低水位,南部隆起局部暴露剥蚀,提供了大量沉积物源;上中新统黄流组沉积时期,盆地局部构造活动使得南部隆起物源发生重力失稳,通过深水水道向盆地中央以重力流方式搬运沉积物。琼东南盆地梅山组地层的丘状反射特征是黄流组沉积时期以南部隆起沉积物为物源的浊流侵蚀下伏梅山组地层所致。对该丘状体成因机制的深入研究,不但有助于丰富对丘状地震反射现象的认识,而且揭示了其沉积构成为粗碎屑沉积物而非生物礁滩沉积,对深水油气勘探储层特征及评价具有重要意义。   相似文献   

18.
Wudu County in northwestern China frequently experiences large-scale landslide events.High-magnitude earthquakes and heavy rainfall events are the major triggering factors in the region.The aim of this research is to compare and combine landslide susceptibility assessments of rainfalltriggered and earthquake-triggered landslide events in the study area using Geographical Information System(GIS) and a logistic regression model.Two separate susceptibility maps were produced using inventories reflecting single landslide-triggering events,i.e.,earthquakes and heavy rain storms.Two groups of landslides were utilized: one group containing all landslides triggered by extreme rainfall events between 1995 and 2003 and the other group containing slope failures caused by the 2008 Wenchuan earthquake.Subsequently,the individual maps were combined to illustrate the locations of maximum landslide probability.The use of the resulting three landslide susceptibility maps for landslide forecasting,spatial planning and for developing emergency response actions are discussed.The combined susceptibility map illustrates the total landslide susceptibility in the study area.  相似文献   

19.
为了深入了解油气分布规律，利用流体包裹体显微荧光光谱和显微测温以及一维盆地模拟的埋藏热历史，结合地震构造属性和沉积相分析，对泌阳凹陷北部缓坡带核桃园组油气运聚成藏过程进行了研究。结果显示北部缓坡带核桃园组第三段储层检测到橙黄色、黄绿色和蓝绿色3种颜色荧光油包裹体，反映了3幕不同成熟度的原油捕获。油包裹体的丰度和伴生盐水包裹体均一温度和埋藏史曲线表明，北部储层共存在两期三幕充注事件:第一期规模小，发生于断陷末期的相对低成熟度发橙黄色荧光油，第二期发生在中新世构造抬升期的相对高成熟度的黄绿色和蓝绿色荧光油。流体包裹体古压力模拟显示第二期油气充注时储层是超压状态，推测与当时的构造挤压有关。超压持续作用以及北部地层抬升造成与深凹带源岩增加的流体势差为第二期油气提供了强有力的动力；频繁的断层活动，特别是走滑断裂使得单一的砂体顺层输导转变为砂体顺层输导+断裂垂直输导的复合立体运移输导体系，使得原油以高效率运移到凹陷北部缓坡带。这对精细理解构造抬升控制油气大规模运聚具有重要的意义。   相似文献   

20.
A good understanding of giant landslide-prone areas could greatly enhance the understanding of the formation and failure mechanisms of giant landslides.In this study,a classic giant landslide-prone area named the Diexi area located along the upstream stretch of the Minjiang River on the eastern Tibetan Plateau is adopted to analyze the failure mechanism and evolution process by detailed field investigations,Unmanned Aerial Vehicle(UAV)images and a digital surface model(DSM).The results show that among the 37 giant landslides located in the Diexi area,18 landslides are transverse landslides(wedge failure),and the others are consequent landslides(buckling failure).All landslides blocked rivers,and some barrier lakes still remain.The Diexi area features special geological structural conditions related to the hinge section of the Jiaochang arc tectonic belt,the intersection of two active fault zones(the Songpinggou and Minjiang fault zones)and high levels of geostress.The numerous radial fissures induced by the Jiaochang arcuate belt provided lateral sliding boundaries for buckling deformation(consequent landslides)and head scarps for wedge failure(transverse landslides).The rapid incision(1.88 mm/yr)since the middle Pleistocene formed a deep gorge with steep slopes and strong lateral unloading.Frequent earthquakes and rainfall further reduced the rock mass integrity,and strong earthquakes or other factors triggered the landslides.  相似文献   

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