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The geometry and deformation characteristics of Baiyun Submarine Landslide

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... The SCS is the largest and deepest marginal sea in the western Pacific ( Fig. 1) and it experienced complex tectonic evolution during the Cenozoic (e.g. Lüdmann and Wong, 1999;Yan et al., 2001;Xie et al., 2006;Y.B. Sun et al., 2008a;Z. Sun et al., 2008b;Sibuet et al., 2016). It was formed by seafloor spreading during late Oligocene to early Miocene (Briais et al., 1993;Taylor and Hayes, 1983) and drifted to its present position in the middle Miocene (Briais et al., 1993;Hall, 2002). ...
... A large-scale product of slope failure named as the Baiyun Slide (In this study, we use the nomenclature of "mass transport deposit (MTD)" to represent the product of slope failure) was identified in the slope region of the PRMB (Y.B. Sun et al., 2008a). Limitations of the available datasets meant that the characteristics of the Baiyun Slide were not correctly identified and the coverage of the Baiyun Slide was greatly overestimated (estimated areal extent was~13,000 km 2 on the slope (Y.B. ...
... Sun et al., 2008a). Limitations of the available datasets meant that the characteristics of the Baiyun Slide were not correctly identified and the coverage of the Baiyun Slide was greatly overestimated (estimated areal extent was~13,000 km 2 on the slope (Y.B. Sun et al., 2008a) and the actual area in the slope region is 5500 km 2 documented in this study). Based on seabed morphologies observed from the bathymetric data, development phases and slide areas of the Baiyun Slide were subdivided by Li et al. (2014) and Wang et al. (2014), respectively. ...
... MTDs in the Pearl River Mouth Basin (PRMB) of northern South China Sea (SCS) were first reported by Sun et al. (2008) and they estimated that the MTDs covered an area of~13,000 km 2 , using 2-D seismic data. Afterwards, Li et al. (2014a,b) and Wang et al. (2014) studied the same MTDs, mainly based on 2-D seismic data and multibeam bathymetric data. ...
... The MTDs in the PRMB were investigated by a few previous studies (Sun et al., 2008;Li et al., 2014a,b;Wang et al., 2014). Sun et al. (2008) named a large MTD as the Baiyun Submarine Slide Complex, which covers an area of 13,000 km 2 and is imaged by multibeam bathymetry and 2-D/3-D seismic data (Li et al., 2014b;Wang et al., 2014). ...
... The MTDs in the PRMB were investigated by a few previous studies (Sun et al., 2008;Li et al., 2014a,b;Wang et al., 2014). Sun et al. (2008) named a large MTD as the Baiyun Submarine Slide Complex, which covers an area of 13,000 km 2 and is imaged by multibeam bathymetry and 2-D/3-D seismic data (Li et al., 2014b;Wang et al., 2014). It extends from an irregular headwall at about 1500 m water depth seaward of the steep canyoned slope of the lowstand Pearl River delta (Fig. 1b). ...
Article
Three superimposed Quaternary mass transport deposits (MTD1, MTD2 and MTD3) in the Pearl River Mouth Basin of the northern South China Sea are identified using high-resolution three dimensional seismic data. This study dissects the three stacked MTDs in detail and interprets their distribution based on antecedent bathymetry and their kinematics from identified structures and sedimentological models. Each MTD is characterized by linear grooves at its base, by chaotic seismic reflections and complex internal structures, such as remnant, rafted and faulted blocks. The linear grooves and internal structures of MTDs indicate that the sediments mainly flowed from the NW to SE in the study area. Moreover, internal structures suggest that MTD2 is a spread and MTD3 is a rotational slump, both terminating upslope at a regional linear escarpment. MTD1 is interpreted as the distal part of a larger MTD. The ages of MTD1, MTD2 and MTD3, based on seismic correlation with ODP Site 1146, are 0.54 Ma, 0.79 Ma and 1.59 Ma respectively. High-amplitude seismic reflections observed below the MTDs are interpreted as coarse-grained turbidites. Headscarp locations are controlled by both the underlying structures (such as basement highs and related faults) and the distribution of weak layers that are probably gas-bearing thin turbidite silt beds. This study provides precise ages of stacked MTDs in the northern South China Sea for the first time and at least locally provides clear evidence for the flow directions and controlling factors of the stacked MTDs. Similar lower slope–rise MTDs, of local origin, may be widespread elsewhere, but would be difficult to distinguish without 3-D seismic data.
... Yang et al. (2011) described, in details, the types and features of geological disasters in the deepwater area to south-east Hainan in South China Sea. Sun et al. (2008) described the geometrical shapes and deforming characteristics of Baiyun Landslide, a large submarine landslide discovered in NSCS, by using the multi-beam water depth strategy and 3D seismic data. Sun (2011) had deep research on the forming mechanism of geological disasters in the deepwater continental slope area of NSCS; one of important inclusion is that the submarine landslide in NSCS is relative to hydrocarbon. ...
... Meanwhile, Baiyun Depression is located at Zhujiangkou Basin, an area with relatively mature development of hydrocarbon in China (Jiang 2009); a submarine landslide occurs in this area may cause profound impact and damages. Based on data from many marine geological surveys (Marine Geological Survey Bureau of the Ministry of Geology and Mineral Resources, China 1993;Sun et al. 2008), this paper studies the characteristics of submarine landslides in NSCS, did numerical calculations of possible tsunamis to be generated by the landslides, and analyzed the tsunami hazards that may be caused by submarine landslide. ...
... Through the analysis of data from deepwater area drilling, tracing and interpretation of many seismic reflection profiles at Zhujiangkou Basin where Baiyun Depression is located (Liu 2010), and comparison of adjacent strata it was observedthat eight sets of seismic sequences have been developed in the deepwater area of Zhujiangkou Basin, i.e. the Quaternary System, Wanshan Formation, Yuehai Formation, Hanjiang Formation, Zhujiang Formation, Enping Formation and Wenchang Formation strata from up to down (Sun et al. 2008). In Wenchang Formation and Enping Formation, lacustrine deposit and large lake basin deposit are developed, respectively, mainly comprising source rocks. ...
Article
Full-text available
Background With mature hydrocarbon industry, Northern South China Sea (NSCS) is a hot spot for future economic development. However, the local government and researchers lack of estimations about damages brought by a submarine landslide-generated tsunami. According to oceanographic surveys, eleven landslides in different scale have been discovered in Baiyun Depression of NSCS. Hence, the need to study potential tsunamis generated by submarine landslides in NSCS is urgent and necessary. This research, focused on potential threat linked to local tsunami sources, is in its early stage in China but it is of capital importance for the local people, local government and offshore economics. Finding Taking landslide S4 for example, the formation, spreading and run-up are predicted. As calculated, the greatest height of tsunami generated by Landslide S4 is 17.5 m, occurring near Dongsha Islands, and the greatest run-up formed on the coastal line is 5.3 m, occurring near Shanwei City; the general height of waves attacking the coastal line is no more than 1.5m, but abnormally high waves might occur in 32 regions. Conclusions Prediction of tsunami generated by Landslide S4 suggests that local landslides in NSCS may trigger tsunami hazards. Therefore, more efforts shall be made to investigate potential damages caused by a submarine landslide, particularly the submarine landslides at Baiyun Depression in NSCS.
... However, recent activity in submarine exploration has produced high-resolution bathymetric and 2-D/3-D seismic data that reveal hundreds of submarine landslides in the continental slopes of the SCS including those observed in the Pearl River Mouth Basin He et al., 2014;W. Li, Wu, Völker, et al., 2014;Sun, Alves, et al., 2018;Sun, Cartwright, et al., 2018;Sun et al., 2017;Sun et al., 2008;Wang et al., 2014;Wu et al., 2011), offshore southwest Taiwan (Su et al., 2012), southeast Hainan (e.g. W. Li, Alves, et al., 2015;Wang et al., 2013), north Borneo (Gee et al., 2007), and west Luzon (Armada, 2016). ...
... The geomorphology, internal structure, and spatial distribution of the Baiyun slide complex as well as the kinematics of slope failure have been studied using high-resolution 2-D/3-D seismic data, multibeam bathymetric data, and sediment cores (W. Li, Wu, Völker, et al., 2014;Sun, Alves, et al., 2018;Sun, Cartwright, et al., 2018;Sun et al., 2017;Sun et al., 2008;Wang et al., 2014;Wang et al., 2017;Wu et al., 2011). These studies provide valuable information of the key landslide features (i.e., initial water depth, slide thickness distribution, volume, etc.), which forms a good basis for more realistic tsunami hazard assessments. ...
... The Baiyun Slide complex is found in the deeper part of the Pearl River Mouth Basin on the northern SCS slope (Figure 1a; W. Li, Wu, Völker, et al., 2014;Sun, Alves, et al., 2018;Sun, Cartwright, et al., 2018;Sun et al., 2017;Sun et al., 2008;Wang et al., 2014;Wu et al., 2011). Recent geophysical data suggest that the Baiyun Slide complex has a spatial coverage of~5,500 km 2 on the slope (Sun, Cartwright, et al., 2018) and a conservative volume of~1,035 km 3 (Sun, Alves, et al., 2018;Sun, Cartwright, et al., 2018). ...
Article
Full-text available
The Baiyun slide complex contains geological evidence for some of the largest landslide ever discovered in the continental slopes of the South China Sea. High‐resolution seismic data suggest that a variety of landslides with varied scales have occurred repeatedly in this area. The largest landslide reconstructed from bathymetric and seismic data has an estimated spatial coverage of ~5,500 km² and a conservative volume of ~1,035 km³. Here, using geomorphological and geotechnical data, we construct a series of probable landslide scenarios and assess their tsunamigenic capacity. By treating the slides as deformable mudflows, we simulate the dynamics of landslide movements. The simulated landslide motions match the geophysical observations interpreted in previous studies. Particularly, we are able to reproduce the spatial distribution of observed runout, including the distance, shape, and deposit thickness, for the most credible slide scenario. We investigate tsunami impacts generated by different slide scenarios and highlight the importance of initial water depth, sliding direction, and nearshore bathymetry. The worst‐case scenario is capable of producing basin‐wide tsunami, with maximum wave amplitudes reaching ~5 m near Hong Kong and Macau, 1–3 m in western Philippines, and at least 1 m along central Vietnam, southeast Hainan, and southern Taiwan. The most noticeable phenomenon we observed is that the southern Chinese coast is the hardest‐hit region in all the simulated scenarios regardless of the diverse slide features. We conclude that the persistence of high tsunami impact is caused by the unique bathymetric feature of the wide continental shelf in front of southern China.
... Sun et al. 2012). Sun et al. (2008) and Wu et al. (2010) reported seismic evidence for the Baiyun slide, estimated to have originated at the shelf break and having an areal coverage of 13,000 km 2 . It is thought to have occurred in the period from the Late Miocene to the Quaternary, and to have been triggered by gas hydrate dissociation and the Dongsha event. ...
... This appears to be inconsistent with earlier findings. In fact, an inferred sliding period lasting from the Late Miocene to the Quaternary was initially suggested by Sun et al. (2008), and later supported by Wu et al. (2010). Thereafter, Li et al. (2014) estimated that the age of the Baiyun slide was 0.6 Ma based on sedimentation rate data and the thickness of the sedimentary drape overlying the slide. ...
... There may be two possible reasons for the discrepancy. Firstly, the term 'Baiyun slide' used by Sun et al. (2008) and Wu et al. (2010) is in conflict with the term 'Baiyun submarine slide complex' used in the present study. In fact, the area covered by the 'Baiyun slide' approximately equals the sum of the areas encompassing the SSSC and the BSSC. ...
Article
The Baiyun submarine slide complex (BSSC) along the Pearl River Canyon of the northern South China Sea has been imaged by multibeam bathymetry and 2D/3D seismic data. By means of maximum likelihood classification with slope aspect and gradient as inputs, the BSSC is subdivided into four domains, denoted as slide area I, II, III and IV. Slide area I is surrounded by cliffs on three sides and has been intensely reshaped by turbidity currents generated by other kinds of mass movement outside the area; slide area II incorporates a shield volcano with a diameter of approximately 10 km and unconfined slides possibly resulting from the toe collapse of inter-canyon ridges; slide area III is dominated by repeated slides that mainly originated from cliffs constituting the eastern boundary of the BSSC; slide area IV is distinguished by a conical seamount with a diameter of 6.5 km and a height of 375 m, and two slides probably having a common source that are separated from each other by a suite of residual strata. The BSSC is interpreted to be composed of numerous slide events, which occurred in the period from 10.5 to 5.5 Ma BP. Six specific factors may have contributed to the development of the BSSC, i.e., gas hydrate dissociation, gas-bearing sediments, submarine volcanic activity, seismicity, sedimentation rate and seafloor geomorphology. A 2D conceptual geological model combining these factors is proposed as a plausible mechanism explaining the formation of the BSSC. However, the BSSC may also have been affected by the Dongsha event (10 Ma BP) as an overriding factor.
... The sedimentation rate related to the Fig. 1 The topographic map of the Pearl River Mouth Basin and the location of Baiyun Sag compact of sediment, and the production of excess pore water pressure is an important factor affecting submarine slope stability (Leynaud et al. 2007). Baiyun submarine landslides are caused by the unbalanced gravity of sediment from the continental shelf and the edge of continental slope of Pliocene and Quaternary, which are formed by the rapid accumulations of sediments (Sun et al. 2008). Based on backstripping results, it has been suggested that the depocenter of Baiyun Sag retreated to the continental shelf and the sedimentation rate in the central sag dropped to 100 m/million years after 10.5 Ma (Xie et al. 2013). ...
... They theorized that thermal warming and increased deposition could cause instability of the hydrates, which can be seen intersecting the landslide scar areas. The high-resolution seismic profile and numerical simulation results have indicated that gas hydrate dissociation has reduced the shear strength in the soil and resulted in submarine slope failure in Baiyun Sag region (Sun et al. 2008;Liu et al. 2010;Wang 2011;Wang et al. 2014). It is difficult to find direct evidence of slope failure and Baiyun submarine landslide due to limitations on seismic data. ...
Article
Full-text available
It is a significant task to evaluate the seafloor stability for the exploitation of marine resources and the construction of marine structures. This paper analyzes the impact factors of submarine slope instability using geological and geophysical data of the Baiyun Sag in the Pearl River Mouth Basin and builds the evaluation index system of submarine slope instability. The weight of each index is calculated by analytic hierarchy process method to weaken subjective effect. Gray clustering method is applied to estimate the risk of submarine slope instability in Baiyun Sag qualitatively and quantitatively. The assessment standard is divided into five grades, and the whitening function of each gray cluster is determined by the assessment scheme. The gray evaluation weight vector of each indicator is calculated by the table-dispatching method. The gray assessment value is estimated by making the gray assessment weight vector single value, and the gray grade is determined according to the maximum principle. The evaluation results show quantitatively that the risk grade of submarine slope instability in the Baiyun Sag is medium, and the gray clustering method is reasonable and feasible.
... Over the last 15 years several submarine explorations have identified a large number of submarine landslides with various volumes in the SCS [e.g., Gee et al. (2007), Wu et al. (2011), Wang et al. (2014), Li W. et al. (2015), Sun et al. (2017), Sun et al. (2018a), Sun et al. (2018b)]. Some of these landslides are among the largest slides in the world with volumes exceeding 1,000 km 3 , such as the Brunei Slide has estimated volume of 1,200 km 3 (Gee et al., 2007) and the Baiyun complex has~1,035 km 3 (Sun et al., 2008;Sun et al., 2017;Sun et al., 2018a;Wang J. et al., 2018). Besides the giant slides observed in the open continental slopes, the majority of submarine landslides in the SCS are relatively small, typically on the order of a few km 3 , especially those developed in the submarine canyons (He et al., 2014;Chen et al., 2016;Zhou et al., 2019), steep continental slope in the west (Fyhn et al., 2009a;Fyhn et al., 2009b;Hong Nguyen et al., 2012) and carbonate islands (Wang W. et al., 2018;Huang et al., 2020). ...
... Besides the giant slides observed in the open continental slopes, the majority of submarine landslides in the SCS are relatively small, typically on the order of a few km 3 , especially those developed in the submarine canyons (He et al., 2014;Chen et al., 2016;Zhou et al., 2019), steep continental slope in the west (Fyhn et al., 2009a;Fyhn et al., 2009b;Hong Nguyen et al., 2012) and carbonate islands (Wang W. et al., 2018;Huang et al., 2020). Previous studies generally focus on interpreting the characteristics of submarine landslides themselves (e.g., morphology, geometric features, evolution processes etc.) through high-resolution bathymetric and 2D/3D seismic data (Gee et al., 2007;Sun et al., 2008;Fyhn et al., 2009a;Huang et al., 2020). Whether those landslides are tsunamigenic and to what extent they can cause hazard are still poorly understood, particularly for submarine landslides with relatively small scales. ...
Article
Full-text available
The 109 meridian fault is located in the west of the South China Sea (SCS) connecting to the offshore Red River Shear Zone. Seismic data from the central Vietnamese shelf indicates that many submarine landslides were developed along the steep continental slope in this offshore region. Here, we analyze the potential for such landslides to trigger damaging tsunamis based on the local geological background and sedimentary environment. We assess their tsunamigenic potential along the coast of Southern Central Vietnam (SCV). We point out that the evolutionary processes of the 109° meridian fault: striking-subsidence of the adjacent basin, combined with the high sediment input from numerous montane rivers of the hinterland generate conditions that likely favor the development of submarine landslides along the well-defined and steep continental slope near SCV. To estimate the impact of tsunami waves on the SCV coastline, we conducted a pilot study using two numerical models: NHWAVE and FUNWAVE-TVD to model 4 representative landslides with volumes ranging between 1.3 and 14 km3 and water depth of 300–1000 m. The submarine landslides were treated as rigid slump and deformable slide corresponding to two different sedimentary environments. Our results show that the tsunami waves generated by rigid slump can reach up to 20 m height in the landslide source area and ∼5 m when arriving at the closest coastline. Tsunami waves could arrive at the central Vietnam coast within 30 min in eight scenarios. Our initial results also suggest that seafloor topography, i.e., waveguide effects of ocean ridges, shelf resonance and the potential bay resonance cause significant variability in potential run-up. We note that ocean ridges located in the deep basin of the SCS focus the tsunami energy propagating towards the northwest coast of Luzon Island, Philippines where tsunami wave heights of ∼2.3 m wave height are modeled. These findings underscore the importance of tsunami hazard assessments that account for both earthquake generated and earthquake triggered tsunamis. Our work also highlights a continued need to examine tsunami sources in the region as mitigation and preparedness for the socio-economically important and heavily populated coastlines of the SCS is reliant on a detailed understanding of the hazard.
... Much of the previous research on the continental shelf and upper continental slope of this area has paid little attention to the hydrate-related geohazards in these areas [29][30][31][32][33][34][35]. Although research has been done on submarine landslides in areas of natural gas hydrate exploration [32][33][34][35][36][37][38], the focus has been mainly on the spatial distribution and geometric characteristics of the landslides. Unfortunately, the relationships between the distribution of gas hydrates and the characteristics of submarine landslides, such as their classification, geomorphic features, distribution, and genesis, have not been investigated systematically [36,[39][40][41][42]. ...
... In our study area, the continental slope itself is an important factor in the development of seabed landslides, but several other factors also contributed to the production of topographical features that provided favorable conditions for seabed landslides, and these include the general tectonic activity in the area, the presence of volcanoes, the puncturing or uplift of the seabed as a result of magma movements, and differential uplift due to Neotectonic movements [34,37]. The geological, geomorphological, and geophysical data reveal 24 landslides in the Shenhu and Dongsha areas of the continental slope, and in Figure 12 we show how the various categories of these 24 landslides are distributed. ...
Article
Full-text available
Integrated investigations have revealed abundant resources of gas hydrates on the northern slope of the South China Sea (SCS). Regarding the gas hydrate research of northern SCS, the gas hydrate related environment problem such as seabed landslides were also concentrated on in those areas. Based on 2D seismic data and sub-bottom profiles of the gas hydrate areas, submarine landslides in the areas of Qiongdongnan, Xisha, Shenhu, and Dongsha have been identified, characterized, and interpreted, and the geophysical characteristics of the northern SCS region investigated comprehensively. The results show 6 major landslides in the gas hydrate zone of the northern SCS and 24 landslides in the Shenhu and Dongsha slope areas of the northern SCS. The landslide zones are located mainly at water depths of 200–3000 m, and they occur on the sides of valleys on the slope, on the flanks of volcanoes, and on the uplifted steep slopes above magmatic intrusions. All landslides extend laterally towards the NE or NEE and show a close relationship to the ancient coastline and the steep terrain of the seabed. We speculate that the distribution and development of submarine landslides in this area has a close relationship with the tectonic setting and sedimentary filling characteristics of the slopes where they are located. Seismic activity is the important factor controlling the submarine landslide in Dongsha area, but the important factor controlling the submarine landslides in Shenhu area is the decomposition of natural gas hydrates.
... Many researches have reported that the potential geo- hazards, such as active sand wave/sand hill, pockmark, land- slide, scarp, abrupt slope, submarine canyon, paleo-channel, shallow gas and diaper, are present on the shelf and the slope of the northern South China Sea [11][12][13]. As for the Pearl River Mouth Basin, there are also several kinds of unfavora- ble geological bodies, such as large seafloor landslides in the Baiyun Depression [14], and mud volcano, seafloor landslide and shallow gas in the outer shelf [15]. ...
... The high deposition rates, active tectonics, and gas-rich structures (Ding et al. 2009;Yu et al. 2014) on the continental slope of the Northern South China Sea are very similar to the continental slope of the East China Sea, Norwegian Sea, and Gulf of Mexico, where submarine landslides develop (Lastras et al. 2002;Hu et al. 2004a, b;Wu et al. 2008a, b). Many studies have reported submarine landslides on the continental shelf and slope of the Northern South China Sea (Feng and Shi 1994;Wu and Qin 2009), and have discussed the morphological and structural characteristics and triggering mechanisms of the large landslides (the scope of a large landslide is approximately 13,000 km 2 ), identifying tectonic movement as the controlling factor of the large landslides (Sun and Wu 2008;Chen et al. 2012;Ma 2014). However, little attention has been paid toward the smaller submarine landslides with a mean width less than 2.5 km and an impact scope less than 10 2 km (Tappin et al. 2001;Haflidason et al. 2004;Gales et al. 2014), especially in canyon areas. ...
Article
Full-text available
Although the structural characteristics and triggering mechanisms of submarine landslides have been investigated, little attention has been paid toward the submarine landslides in canyons. In the Baiyun canyon, there are many small submarine landslides that could be an important sediment transport process of the canyons, but few have been studied. This study aims to examine the characteristics and mechanisms of submarine landslides in the Baiyun canyon on the northern continental slope of the South China Sea using multibeam depth data, acoustic sub-bottom profiles, and borehole data. The results suggest that the submarine landslides are mainly distributed in the head and side valley walls of the canyons. The surface morphology of the landslides is broken-stepped, tongued, or round, and the area of the landslides varies between 0.04 and 15.13 km2. Nevertheless, most of the landslides have an area of less than 2 km2. The scarp height of most landslides is between 20 and 40 m. Based on the internal acoustic structures of the landslides, the submarine landslides can be divided into brittle and plastic. The brittle landslides have clear landslide walls or sliding surfaces, whereas the interior of the landslides in the upper slope area of 650–740 m near the source of submarine canyon has the original stratigraphic structure. The interior of the plastic landslides is typically chaotic and has no clear landslide walls or sliding surfaces. The plastic landslides mainly occur in the head and sides of the canyon. We determined the slope stability using the software GeoSlope and concluded that the strength of the soil on the seabed slopes and the slope gradient are the main factors that control the landslides in the study area. Landslides occur when the slope gradient is greater than 9°. In addition, when the horizontal seismic load is not zero, slopes with a gradient of less than 9° are unstable. This study will be helpful in geological risk assessments and understanding of sediment transportation in the northern margin of the Northern South China Sea.
... Feng et al. (1994) inferred there might be a large submarine landslide of about 400 km 2 in the region. Sun et al. (2008) and presumed that the area and adjacent slope regions might be made up of a huge active mass transport complex, covering an area over 10,000 km 2 . In our study, numerous small-scale submarine canyon-associated landslides but not a huge landslide as previously suggested, are identified by a detailed analysis of the newly-acquired high-resolution, highdensity seismic profiles and the high-precision multibeam bathymetry map. ...
Article
High-resolution and high-density 2-D multichannel seismic data, combined with high-precision multibeam bathymetric map, are utilized to investigate the characteristics and distribution of submarine landslides in the middle of the northern continental slope, South China Sea. In the region, a series of 19 downslope-extending submarine canyons are developed. The canyons are kilometers apart, and separated by inter-canyon sedimentary ridges. Numerous submarine landslides, bounded by headscarps and basal glide surfaces, are identified on the seismic profiles by their distorted to chaotic reflections. Listric faults and rotational blocks in head areas and compressional folds and inverse faults at the toes of the landslides are possibly developed. Three types of submarine landslides, i.e., creeps, slumps, and landslide complexes, are recognized. These landslides are mostly distributed in the head areas and on the flanks of the canyons. As the most widespread landslides in the region, creeps are usually composed of multiple laterally-coalesced creep bodies, in which the boundaries of singular component creep bodies are difficult to delineate. In addition, a total of 77 landslides are defined, including 61 singular slumps and 16 landslide complexes that consist of two or more component landslides. Statistics show that most landslides are of a small dimension (0.53–18.09 km² in area) and a short runout distance (less than 3.5 km). Regional and local slope gradients and rheological behavior of the displaced materials might play important roles in the generation and distribution of the submarine landslides. A conceptual model for the co-evolution of the canyons and the associated landslides in the study area is presented. In the model it is assumed that the canyons are initiated from gullies created by landslides on steeper sites of the continental slope. The nascent canyons would then experience successive retrogressive landsliding events to extend upslope; at the same time canyon downcutting or incision would steepen the canyon walls to induce more landslides.
... According to previous investigations of submarine landslides, the length-to-thickness ratios of a series of landslides in the northern South China Sea are 0.9%-1.0% (Sun et al. 2008). Therefore, the stability analysis of submarine slopes using the limit equilibrium method (LEM) of the infinite slope model is very suitable. ...
Article
With the continuous expansion of energy demand, the deep-water continental slope in the northern South China Sea has become one of the significant offshore oil and gas exploration regions. The frequent occurrence of marine geological hazards in this region, especially submarine landslides, can cause serious damage to engineering facilities. However, there have been few studies on the stability of the northern continental slope of the South China Sea; these studies mainly focused on a specific submarine slope or small-range evaluation, resulting in a lack of large-scale and quantitative understanding. Hence, considering the variation in the physical and mechanical properties of marine soils with depth, formulas for calculating the safety factor of submarine slopes by an infinite sliding model are established, and the factors affecting slope stability such as soil properties, slope gradient and horizontal seismic action are systematically investigated. Using GIS techniques, the terrain slope gradients and a historical seismic database of the northern South China Sea are obtained. Combined with soil mechanical parameters, a regional stability evaluation of the northern continental slope is carried out. Furthermore, the distribution of risk zones is given. On the whole, under strong seismic action, large-scale submarine slope instability occurs and must be highly considered when assessing risk. This achievement is of great significance to engineering sites, route selection and engineering risk assessment.
... Based on a comprehensive statistical investigation of 534 submarine slide cases, it was found that submarine slides may occur on a relatively 'flat' seafloor with a gradient of ~ 0.22° and may travel up to a distance of 850 km, covering areas as large as 88000 km 2 (Hance 2003). Examples of submarine slides include: the Storegga Slides in Norway (Kvalstad et al. 2005); the Brunei Slide in the North West Borneo Margin (Gee et al. 2007); the Baiyun Slide in the north margin of South China Sea (Sun et al. 2008); slides on the Sigsbee Escarpment of the Gulf of Mexico (Jeanjean et al. 2005); slides along the Hikurangi Margin in the Southwest Pacific Region (Lamarche et al. 2008); and slides along the Eastern Australian Continental Margin (Clarke et al. 2016). For the safety of offshore pipelines, it is clear that careful assessment of slide-pipeline interaction is necessary. ...
Conference Paper
Historically, there have been many devastating events in which offshore pipelines were displaced over a large distance or fractured under the impact of submarine slide hazards, which has stimulated detailed assessment of the interaction forces between a sliding soil mass and submarine pipelines. In particular, the impact force from the sliding material may be sufficient to compromise the integrity and functionality of any pipeline crossing the path of the slide run-out. Previous studies focused on the interaction forces between a submarine slide and a fixed pipeline, which is either partially embedded or suspended at some depth within the slide flow, and with particular attention to the horizontal forces and axial drag. This paper focuses on the vertical component of force, and considers a realistic scenario where the pipeline is constrained only in the direction parallel to the slide travel and is thus free to move vertically. The vertical responses of the pipeline under impact at different slide velocities are investigated from multiphase (slide material and the ambient seawater) fluid-structure interaction simulations using ANSYS-CFX. The pipeline kinematics in the vertical direction and changes in the slide-pipeline forces are analyzed for the first time, providing new insights for the assessment of submarine slide hazards on pipelines.
... Here, largescale MTDs are grouped together to form the Baiyun Submarine Slide Complex (BSSC), and cover an area of more than 10,000 km 2 . They are imaged on multibeam bathymetry and 2D/3D seismic data on the continental slope off the Pearl River Mouth Basin (Sun et al., 2008;Li et al., 2014;Wang et al., 2014;Sun et al., 2017). The BSSC is composed of, at least, three vertically stacked MTDs, which were respectively emplaced at 0.19 Ma, 0.50 Ma and 1.59 Ma before present (Sun et al., 2017). ...
Article
Free gas is an important trigger of instability on continental slopes, and resulting mass-wasting strata can potentially form competent seals to hydrocarbon accumulations. This work uses two high-quality 3D seismic volumes to investigate fluid accumulations at the base of mass-transport deposits in the Pearl River Mouth Basin, South China Sea. In parallel, IODP/ODP borehole data are used to document the petrophysical character of mass-transport deposits formed in similar continental-slope environments to the South China Sea. The interpreted data show gas accumulations as comprising enhanced seismic reflections that are discordant, or vertically stacked, below mass-transport deposits with chaotic seismic facies. Gas was accumulated in basal shear zones of mass-transport deposits in response to differences in capillary pressure and porosity. Free gas in Zone A covers an area of at least 18 km2. In Zone B, the free gas is sub-circular in plan view and covers an area of 30.58 km2 for a volume of sediment approaching 1.5 km3. This work is important as it shows that vertical migration of gas is not significant in mass-transport deposits from the Pearl River Mouth Basin, but up-dip migration along their basal shear zones is suggested in multiple locations. As a result, free gas can pinch-out laterally to extend 1–2 km beyond these same basal shear zones. As a corollary, we show that free gas accumulations below mass-transport deposits comprise an important geohazard and should be taken into account when drilling continental-slope successions in both the South China Sea and continental margins recording important mass wasting. Strata charged with free gas form weak layers, hinting at a novel trigger of retrogressive slope failures on continental slopes worldwide.
... The northern South China Sea margin is characterized by an interplay between contour-parallel sediment transport processes, evident from sediment drift bodies at around 2000 m water depth (e.g. Shao et al. 2007) and gravitational transport processes, including large-scale mass wasting at several locations (Sun et al. 2010;Wu et al. 2011). The Baiyun Slide Complex is the largest documented submarine landslide in this region, with an affected area of c. 10000 km 2 . ...
Article
A large submarine slope failure, the Baiyun Slide Complex, has been discovered in the northern South China Sea. We describe the slide complex morphology, the seismic character of its structural elements and the slide evolution based on high-quality seismic reflection and multi-beam bathymetry data. The Baiyun Slide Complex has three major slide scars that show differences in headwall and sidewall geometry, the nature of the basal shear surfaces and the internal architecture of the deposits. From these observations, we propose a four-phase emplacement model. An extrapolation of the post-slide drape thickness (60 m) gives a rough age estimate for the mass transport events of 0.3 Ma. Pore pressure models for the unfailed continental slope in the vicinity of the Baiyun Slide are based on porosity measurements at nearby Ocean Drilling Program Site 1146. They show that excess pore pressure in slope sediments is anomalously high at a depth around 93 m, most probably as a consequence of a dramatic increase in sedimentation rates over the past 1.8 Ma. This excess pore pressure is proposed to be the major preconditioning factor for the slide initiation, possibly aided by volcano-tectonic activity and gas hydrate dissociation. The unfailed slope is stable under static conditions. However, a near-field earthquake of Mw 5 would suffice to induce a slope instability at c. 93 m depth.
... The significance of submarine landsliding for tsunamigenesis is a legitimate concern across the Asia-Pacific region (Tappin et al. 2008;Goff 2011;Paris et al. 2014;Terry et al. 2017), because volcanic island flanks, carbonate platforms and atolls, and thick sediment wedges on offshore continental slopes, all offer potential for large-scale failure (Fig. 1). This is evidenced by arcuate landslide scars (scalloping) along affected coastlines (Goff and Terry 2016) and the discovery of giant submarine failure deposits offshore (Gee et al. 2007;Sun et al. 2008). A historical tsunami in Taiwan in 1781/2 that killed some 40,000 people has also been linked to submarine slope failure (Li et al. 2015). ...
Article
Two recent tsunamis in Indonesia highlight the importance of submarine landslides. Although both events had different origins (volcanic, seismic), submarine landsliding was probably the key component in tsunamigenesis. While a few recent submarine landslide-generated tsunamis have been discussed in the literature, these types of events have not been seriously scrutinised by geoscientists or hazard modellers. This is most likely because of both a lack of awareness and also the common perception that such events are too remote a possibility to be of major concern. However, by catching us off-guard, these two Indonesian events have brought slope-failure tsunamigenesis into sharper focus. It is hoped that this will stimulate greater scholarship on the issue of slope-failure tsunamigenesis worldwide, with an aim to better understanding event characteristics, probabilities, and ultimately better inform existing risk reduction strategies.
... With the continuous advancement of marine exploration technology, the study of MTDs along the northern South China Sea (SCS) margin, including the Pearl River Mouth Basin (PRMB) (Sun et al., 2008(Sun et al., , 2017a(Sun et al., , 2017b(Sun et al., , 2018a(Sun et al., , 2018bZhao et al., 2015a;Zhou et al., 2015;Guan et al., 2016;Wang et al., 2017) and the Qiongdongnan Basin (QDNB) (Wang et al., 2011(Wang et al., , 2014a(Wang et al., , 2014bHe et al., 2013aHe et al., , 2013bLi et al., 2013Li et al., , 2015Gong et al., 2014), has attracted significant attention in the geological community. Based on a study of the physical property characteristics of MTDs in the southern QDNB, Wang et al. (2011) found that MTDs could act as hydrocarbon seals and facilitate the accumulation of gas hydrates because of their dense interior and low permeability. ...
Article
Mass transport deposits can cause marine geohazards and transport sediments to deep-water areas and act as hydrocarbon reservoirs and seals, which have been extensively examined throughout the last decade in the northern South China Sea. Based on 2D and newly acquired high-resolution 3D seismic data, as well as logging-while-drilling (LWD) data, we document the characteristics, distributions, sources, and triggering mechanisms of the Quaternary MTDs in the Qiongdongnan Basin (QDNB). Moreover, their impacts on deep-water channels, gas hydrate accumulation and marine geohazards are discussed. The results show that there are ten phases of Quaternary MTDs development in the study area. Among them, MTD3 covers the largest area, ~627 km², while the smallest is MTD10 at ~89 km². These MTDs are characterized by chaotic and translucent/transparent seismic facies and negative-phased seismic reflections on their seismic profiles. The transport directions of these MTDs mainly occur from the northwest to southeast, northeast to southwest, and southwest to northeast, with sources in the Northern Slope Area and Western Slope Area or Guangle Uplift Area. Based on an analysis of the tectono-sedimentary evolution of the QDNB, these Quaternary MTDs may have been triggered by an anomalously high sedimentation rate, increased slope gradient, fault reactivation, earthquakes, and sea level fluctuation. Among these processes, earthquakes and rapid sea level fluctuation could be the most critical triggering mechanisms. Furthermore, the MTDs primarily act as hydrocarbon seals in the study area, facilitating the accumulation in the shallow gas reservoirs and gas hydrates within the Quaternary strata. MTDs and related tsunamis are also major marine geohazards, which need in-depth integrated researches by multidisciplinary scientists.
... Many researches have reported that the potential geohazards, such as active sand wave/sand hill, pockmark, landslide, scarp, abrupt slope, submarine canyon, paleo-channel, shallow gas and diaper, are present on the shelf and the slope of the northern South China Sea [11][12][13]. As for the Pearl River Mouth Basin, there are also several kinds of unfavorable geological bodies, such as large seafloor landslides in the Baiyun Depression [14], and mud volcano, seafloor landslide and shallow gas in the outer shelf [15]. ...
Article
Full-text available
Geographical Information Systems is a useful tool for marine geohazard mapping. This paper describes an integrated and systematic map-based approach for identification and characterization of submarine landslide with multidis-ciplinary data such as multibeam bathymetric data, multichannel seismic data, sidescan sonar and so on. Taking Liwan 3-1 gas field in northern continental slope of Southern China Sea as a case study, a regional database is established to provide convenient services to manage search and extract the target data for geohazard mapping and identification. Bathymetric map and seismo-geomorphologic map are calculated and produced with GIS to establish an elementary understanding of geomorphologic features. With this integrated approach, dozens of landslides are identified in the study area and they are featured as small and multiple superimposed failure scars. Fundamental information of landslides can also be provided for further detail interpretation, quantification and assessment of their mechanism and potential risks.
... Research has shown that there were a great number of submarine landslides with different scales in the Liwan area, especially in the submarine canyon section of the submarine pipeline routing area (Fig. 1). There still is much chance that the submarine landslide would happen again (Feng et al., 1994;Chen and Yang, 1996;Sun et al., 2008;Yang et al., 2014), and the following mass movement would present a great risk to the submarine pipeline. So the mass movement of the potential submarine landslide in this area must be considered for the pipeline design and construction. ...
Article
Full-text available
A large number of submarine landslides with different scales have been identified in the canyon area of the submarine pipeline route of Liwan 3-1 gas field. There is still much chance that submarine slope failures would happen, and the following mass movement would present great risk to the submarine pipeline. In view of this, a numerical prediction method based on Eulerian-Eulerian two-phase flow model is introduced to simulate the mass movement of potential submarine landslides. The sliding soil and ambient water are respectively simulated by Herschel-Bulkley rheology model and Newtonian fluid model. The turbulence is simulated using the k-ε model. Compared with both the experiment data and Bing result, the two-phase flow model shows a good accuracy, and its result is more close to the actual situation; the dynamic coupling between soil and ambient water can be effectively simulated and the phenomena of hydroplaning and head detachment can be obtained. Finally, the soil movement of a potential submarine landslide is simulated as an example, according to the seismic profile in the canyon area. The result shows that the hydroplaning occurs during the movement process. The runout distance calculated by the two-phase flow model is 877 m, which is 27.1% larger than the Bing result. However, the peak front velocity of soil is relative small, with a maximum value of 8.32 m/s. The Bing program with a simple and rapid process can be used for a preliminary evaluation, while the two-phase flow model is more appropriate for an accurate assessment.
Article
This paper analyzed the factors of instability of submarine slope, and discussed the pore pressure change of submarine sediments in the northern South China Sea due to gas hydrate dissociation. We select the Shenhu area of the northern South China Sea as the study case, made a quantitative assessment of the stability of submarine infinite slope by utilizing limiting equilibrium theory, and acquired the safety factors of different landslide planes assumed beforehand, numerically simulated the effect of gas hydrate dissociation on stability of submarine slope. The results of the study showed that 15% gas hydrate dissociation will lead to submarine slope failure under the condition of water depth 1200 m, sediments depth 200 m, and slope angle 5°. Under the same condition of water depth and sediments depth, more percentage of gas hydrate dissociation is needed for submarine slope failure for smaller slope angle. For bigger slope angle such as 20°, only 5% gas hydrate dissociation will lead to submarine slope failure.
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A large-scale submarine landslide (Baiyun Slide) covering an area of 10,000 km2 was identified from the multibeam bathymetric data, high-resolution 2D and 3D seismic data acquired in the Baiyun Sag, Pearl River Mouth Basin, northern South China Sea (SCS). Numerous polygonal faults are also found below the translational domain of the Baiyun Slide. Enhanced reflections, bright spots and pull-down reflection have been illustrated from the 2D and 3D seismic data, indicating the presence of gas. The headwall scarps of the slide are located stratigraphically above the sediments where the amplitude anomalies are identified. The focused fluid flow maybe leak from the gas reservoir and migrate upward into the base of the Baiyun Slide. Though the triggering mechanism of the Baiyun Slide is still poorly known, the fluid trapped below the slide will reduce the strength of the sediments and trigger the slope failure. We propose a conceptual model of the relationship between fluid migration and slope stability.
Article
Free gas is an important trigger of instability on continental slopes, and resulting mass-wasting strata can potentially form competent seals to hydrocarbon accumulations. This work uses two high-quality 3D seismic volumes to investigate fluid accumulations at the base of mass-transport deposits in the Pearl River Mouth Basin, South China Sea. In parallel, IODP/ODP borehole data are used to document the petrophysical character of mass-transport deposits formed in similar continental-slope environments to the South China Sea. The interpreted data show gas accumulations as comprising enhanced seismic reflections that are discordant, or vertically stacked, below mass-transport deposits with chaotic seismic facies. Gas was accumulated in basal shear zones of mass-transport deposits in response to differences in capillary pressure and porosity. Free gas in Zone A covers an area of at least 18 km2. In Zone B, the free gas is sub-circular in plan view and covers an area of 30.58 km2 for a volume of sediment approaching 1.5 km3. This work is important as it shows that vertical migration of gas is not significant in mass-transport deposits from the Pearl River Mouth Basin, but up-dip migration along their basal shear zones is suggested in multiple locations. As a result, free gas can pinch-out laterally to extend 1–2 km beyond these same basal shear zones. As a corollary, we show that free gas accumulations below mass-transport deposits comprise an important geohazard and should be taken into account when drilling continental-slope successions in both the South China Sea and continental margins recording important mass wasting. Strata charged with free gas form weak layers, hinting at a novel trigger of retrogressive slope failures on continental slopes worldwide.
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Since Shenhu continental slope in the northern South China Sea is rich in oil and gas resources as well as natural gas hydrate, and its seabed stability is important for oil and gas exploitation and engineering projects. But special study on seabed stability here is far from being enough now. Based on interpretation of 2D seismic data, shallow profiles and multi-beam echo sounder data, this paper focuses on the whole geological environment of this area and identifies 20 different kinds of hazardous geological factors. According to the dynamic source, five hazard types are concluded as follows: tectonic stress-related, gravity-related, hydrodynamics-related, gas effusion-related and soil-related hazards. Each type includes multi-hazardous factors. According to the plan-view distribution of the hazardous geological factors, this area can be divided into the following six hazard regions: intensive areas of buried delta, submarine landslides, volcanism, weak layers, shallow fracture zone and shallow bedrock. Major hazardous factors and their seismic reflection characteristics are presented to provide scientific reference for development of future engineering projects in the study area.
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Based on the geophysical identification characteristics, by the high resolution deep water 2D and 3D seismic data, the mass transport deposits (MTDs) were found in the deep-water formations of the South China Sea, which includes Qiongdongnan Basin, Baiyun Sag and Brunei. The sediment model of MTDs was built, and its significance for deep-water oil and gas exploration was discussed. The results show that MTDs are characterized by low amplitude, chaotic and translucent seismic reflection. And they are easy to form many sedimentary structures such as normal fault, thrust fault, pressure ridge and fold. The typical MTDs can be divided into three sections such as tensional head, compressive body and toe. MTDs are mainly mud-rich sediments and can usually be as excellent cover, and form deep-water trap cooperation with turbidity system. A little fraction of sand-prone MTDs can be a potential reservoir.
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Based on high-resolution 2D and 3D seismic data in Qiongdongnan basin, in northern South China Sea, the characteristics of mass turbidity depositions (MTDs) in different parts of the basin, from the slope system to abyssal plain, have been studied. The result shows that the characteristics of MTDs are different from the eastern to western part in Qiongdongnan basin. In eastern part, the head of MTDs is characterized by the slides, with little or no deformation, and the MTDs are of small scale. While in the western part, chaotic seismic facies and intense erosion are the main features of the head of MTDs, and the MTDs are of large scale, meanwhile, there is a series of parallel or sub-parallel thrusts in the strongly deformed strata in the toe of MTDs. There are mainly two reasons for the differences. Firstly, comparing to the eastern part, the western part of the basin has steeper slope gradient, which is favourable for the development of MTDs. The second lies in the morphology of the basin. The southern high stops the MTDs transporting along the slope. According to the relationship between the head of MTDs and the faults along the shelf margin, the earthquake related to reactivity of the faults is one of the triggers for the development of MTDs.
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Submarine landslides has been gradually attracted attentions because of exploration and exploitation of submarine gashydrate in the past decade. Submarine landslides in the Qiongdongnan basin, Northern South China Sea generally occur in continental slope where gashydrate usually accumulates. They play an important role to their development and exploration. We analyze the detailed geometric characteristics of submarine landslides in the Qiongdongnan basin based on the preexisting 2D seismic profiles to identify three major slide planes which are caused by three landslide events. Each landslide event can be divided into several secondary landslide stages. Typical landslide topography such as slide scarps, slide plane, slide terraces, slide valleys are widely developed in the study area. Based on preliminarily estimated, the Qiongdongnan submarine landslides cover an area of about 2500 km2. The submarine landslides are controlled by continental slope, active faults, sea-level drops, gravity of sediments, seabottom flows, gas hydrate dissociation and other factors. Combined with chronostratigraphic framework, the active period of the landslides in the Qiongdongnan basin can be identified between Late Pliocene and Quaternary.
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Submarine slope failures are considered as a serious geo-hazard because they can rupture undersea pipelines, and seafloor engineering facilities can be subverted by destroying the seabed stability. Submarine slope failures are widely developed in deep-water areas of the northern continental margin of the South China Sea, yet the mechanisms involved in their generation remain poorly known. Observations have proposed that slope instability can be due either to decomposition of gas hydrate or to magma emplacement. Here, we present new high-resolution 2D seismic data from the deep-water areas of the northern continental margin of the South China Sea to reveal an extensive and intimate relationship between magma emplacement and slope failures. This paper shows four landslides on the Dongsha, Shenhu, Xisha and Qiongdongnan slopes that occurred at different locations of the northern continental slope of the South China Sea. There are seismic evidences that magmatic rocks commonly developed and migrated upwards to the overlying layers and they caused these layers to uplift as a dome and possibly decreased their strength and predisposition to failure. The data reveal in detail how magma emplacement influenced slope stability and the seismic reflection features of this type of submarine landslides. The findings illustrate the importance of magma emplacement resulting in slope instability. This paper proposes that magma emplacement is a basic and critical trigger leading to slope failures in the deep-water areas of the northern continental margin of the South China Sea and establishes genetic models for this important trigger.
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Crustal instability to induce the geohazards often results from both the internal tectonic dynamics and external sediment processes. Thus, the detailed geodynamics and kinematics of geohazards are important for understanding the tectonic evolutionary process and evaluating potential geohazards. This paper focuses on the active faults, submarine landslides, earthquakes as well as submarine canyons geomorphology description and kinetics explanation in the northern South China Sea (SCS) continental margin. Firstly, we have estimated the spatial extent, fault-plane geometry and faulting behaviors of the submarine active faults, such as the Littoral Fault Zone, based on cumulative deformation recorded by geophysical seismic reflections and geomorphic markers. We also analyzed the reactivation of preexisting structures, as well as the spatial and temporal distribution and migration of the submarine landslides and canyons. Then, several conceptual models and a comprehensive study of some of the different factors that contributed to the geohazard chain are conducted based on pre-existing theory and available literature. This review study indicates: (i) geohazards of different phases and geohazard chain are generally triggered by both early-phase tectonics-dominated and later-phase sedimentation-dominated processes; (ii) the fault geometric and stress segmentation may have played an important role in controlling on the uneven and asymmetric distribution of earthquakes and submarine canyons of the northern SCS, Especially, the ENE-striking preexisting Littoral Fault Zone is the major seismogenic structure along the Southchina coastline; (iii) the tectono-sedimentary coupling induced landslide and slope failure that has help to shape the modern coastal and slope geomorphology.
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Extending across some 3.5 million square km and with coastlines populated by in excess of 80 million people, the South China Sea (SCS) is bordered by seven independent states. Understanding the risk of tsunamis in the SCS is therefore an imperative, especially given the new priorities for the science community following the endorsement by the UN General Assembly of the Sendai Framework for Disaster Risk Reduction 2015–2030. Our review presents a synthesis of existing literature on the current state of knowledge concerning known tsunamigenic threats, but also highlights a number of other potential sources that have so far received less attention or gone largely un- or under-recognised.
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Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons, gullies, and mass movements. Modern canyons and gullies are roughly elongated NNW–SSW with U-shaped cross sections at water depths of 400–1000 m. Mass movements include slide complexes, slide scars, and debris/turbidity flows. Slide complexes and slide scars are oriented in the NE–SW direction and cover an area of about 1790 and 926 km², respectively. The debris/turbidity flows developed along the lower slope. A detailed facies analysis suggests that four seismic facies exist, and the late Cenozoic stratigraphy above the acoustic basement can be roughly subdivided into three sequences separated by regional unconformities in the study area. The occurrence of gas hydrates is marked by seismic velocity anomalies, bottom-simulating reflectors, gas chimneys, and pockmarks in the study area. Seismic observations suggest that modern canyons and mass movements formed around the transition between the last glacial period and the current interglacial period. The possible existence and dissociation of gas hydrates and the regional tectonic setting may trigger instability and mass movements on the seafloor. Canyons may be the final result of gas hydrate dissociation. Our study aims to contribute new information that is applicable to engineering construction required for deep-water petroleum exploration and gas hydrate surveys along any marginal sea.
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In this paper, we take DLW3101 core obtained at the top of the canyon (no landslide area) and DLW3102 core obtained at the bottom of the canyon (landslide area) on the northern continental slope of the South China Sea as research objects. The chronostratigraphic framework of the DLW3101 core and elemental strata of the DLW3101 core and the DLW3102 core since MIS5 are established by analyzing oxygen isotope, calcium carbonate content, and X-Ray Fluorescence (XRF) scanning elements. On the basis of the information obtained by analyzing the sedimentary structure and chemical elements in the landslide deposition, we found that the DLW3102 core shows four layers of submarine landslides, and each landslide layer is characterized by high Si, K, Ti, and Fe contents, thereby indicating terrigenous clastic sources. L1 (2.15–2.44 m) occurred in MIS2, which is a slump sedimentary layer with a small sliding distance and scale. L2 (15.48–16.00 m) occurred in MIS5 and is a debris flow-deposited layer with a scale and sliding distance that are greater than those of L1. L3 (19.00–20.90 m) occurred in MIS5; its upper part (19.00–20.00 m) is a debris flow-deposited layer, and its lower part (20.00–20.90 m) is a sliding deposition layer. The landslide scale of L3 is large. L4 (22.93–24.27 m) occurred in MIS5; its upper part (22.93–23.50 m) is a turbid sedimentary layer, and its lower part (23.50–24.27 m) is a slump sedimentary layer. The landslide scale of L4 is large.
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The enhanced dispersion of gold on TiO2 was achieved by dispersing TiO2 onto a high-surface-area SiO2 powder support. High temperature reduction, at 773–873 K, in hydrogen leads to very active gold nanoparticles on the support surfaces for CO oxidation at room temperature. The surface sol–gel method results better dispersion for both TiO2 and Au, and higher activity for CO oxidation than that by the conventional impregnation method. Metallic gold with slightly negative charge was evidenced by X-ray photoelectron spectroscopy (XPS) and in situ transmission infrared spectroscopy (FTIR) using CO as a probe. The obtained Au/TiO2/SiO2 catalysts show better stability and higher activities for CO oxidation than that for Au/TiO2. The promotion effects may origin from the formation of thin layer and small crystalline particles of TiO2 anchored on SiO2, leading to a better dispersion of small Au nanoparticles and sinter resisting.
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