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Search Results: 1 - 10 of 44018 matches for " WU Shiguo "
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Sedimentary processes and development of the Zenisu deep-sea channel, Philippine Sea
Shiguo Wu,Sakamoto Izumi
Chinese Science Bulletin , 2003, DOI: 10.1007/BF02900946
Abstract: Zenisu deep-sea channel originated from a volcanic arc region, Izu-Ogasawara Island Arc, and vanished in the Shikoku Basin of the Philippine Sea. According to the swath bathymetry, the deep-sea channel can be divided into three segments. They are Zenisu canyon, E-W fan channel and trough-axis channel. A lot of volcanic detritus were deposited in the Zenisu Trough via the deep-sea channel because it originated from volcanic arc settings. On the basis of the swath bathymetry, submersible and seismic reflection data, the deposits are characterized by turbidite and debrite deposits as those in the other major deep-sea channels. Erosion or few sediments were observed in the Zenisu canyon, whereas a lot of turbidites and debrites occurred in the E-W channel and trough axis channel. Cold seep communities, active fault and fluid flow were discovered along the lower slope of the Zenisu Ridge. Vertical sedimentary sequences in the Zenisu Trough consist of the four post-rift sequence units of the Shikoku Basin, among which Units A and B are two turbidite units. The development of Zenisu canyon is controlled by the N-S shear fault, the E-W fan channel is related to the E-W shear fault, and the trough-axis channel is related to the subsidence of central basin.
Deep-Sea Geohazards in the South China Sea Deep-Sea Geohazards in the South China Sea
WU Shiguo,WANG Dawei,V?LKER David
- , 2018,
Abstract: 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
Geophysical Indicators of Gas Hydrate in the Northern Continental Margin, South China Sea
Xiujuan Wang,Shiguo Wu,Yiqun Guo,Shengxiong Yang,Yuehua Gong
Journal of Geological Research , 2011, DOI: 10.1155/2011/359597
Abstract: Gas hydrate drilling results show that gas hydrate has a close relationship with strong bottom-simulating reflectors (BSRs) identified from seismic data in the Baiyun sag, South China Sea. The BSRs observed on seismic profiles at the crests of submarine canyons indicate the likely existence of gas hydrate. We calculate the acoustic impedance using constrained sparse spike inversion (CSSI), the interval velocity, and the seismic reflection characteristics such as reflection strength, instantaneous frequency, blanking, and enhanced reflection to demonstrate the presence of gas hydrate. Higher acoustic impedance and P-wave velocity were identified above the BSR. A remarkable low impedance, low frequency, and acoustic blanking indicated the presence of gas below gas hydrate stability zone. The occurrence of gas hydrate at the crests of canyons suggests that the abundance of gas hydrate in Baiyun sag may be due to the migrating submarine canyons providing the structural reliefs and the topographic ridges. 1. Introduction Gas hydrates are ice-like crystalline solids and are composed of water molecules and hydrocarbon gas (usually methane). They are distributed worldwide in the continental margin sediments and beneath permafrost [1, 2]. Bottom simulating reflectors (BSRs) identified from seismic reflection profiles are conventionally interpreted as indicators for gas hydrate beneath seafloor [3]. Gas hydrates-associated BSRs have been recognized from the seismic data of other geophysical studies, and their presences have been validated by drilling or coring either in accretionary wedges [4–7] or in the continental margin of the world [8–11]. The Hikurangi Margin, east of New Zealand’s North Island, is a large marine gas hydrate province. The BSRs were identified on the multichannel seismic data and there is a strong correlation between BSR strength and geological features indicating the fluid migration [12, 13]. Geophysical parameters show that gas hydrate-bearing sediments have high elastic impedance, high P-impedance, and high P-wave velocity; and the sediments containing free gas have low elastic impedance, low P-impedance, and low P-wave velocity [14]. The anomalous velocity and the variation in amplitude and polarity of reflectors at the base of gas hydrate-bearing stability zone were used to indicate the presence of gas hydrate [15, 16]. The acoustic impedance inversion of seismic data, log to seismic correlation, and seismic attribute analyses were combined to delineate gas hydrate zone [17]. In China, eight sites were drilled in 2007 in Shenhu area,
Seismic Expression of Polygonal Faults and Its Impact on Fluid Flow Migration for Gas Hydrates Formation in Deep Water of the South China Sea
Duanxin Chen,Shiguo Wu,Xiujuan Wang,Fuliang Lv
Journal of Geological Research , 2011, DOI: 10.1155/2011/384785
Abstract: Polygonal faults were identified from three-dimensional (3D) seismic data in the middle-late Miocene marine sequences of the South China Sea. Polygonal faults in the study area are normal faults with fault lengths ranging from 100 to 1500?m, fault spaces ranging from 40 to 800?m, and throws ranging from 10 to 40?m. Gas hydrate was inferred from the seismic polarity, the reflection strength, and the temperature-pressure equilibrium computation results. Gas hydrates located in the sediments above the polygonal faults layer. Polygonal faults can act as pathways for the migration of fluid flow, which can supply hydrocarbons for the formation of gas hydrates. 1. Introduction Polygonal faults are a network of layer-bound, mesoscale (throws from 10 to 100?m) extensional faults arranged in a polygonal structure developing in deep-water sequence [1]. The term “polygonal fault” was named by Cartwright [2] when he analyzed the shale sedimentary throughout the 3D seismic data obtained from North Sea basin. Up to now, more than 50 basins have found the existence of polygonal faults. Some geologists presented different formation mechanisms, including density inversion [3, 4], gravity sliding or collapse [5], episodic hydrofracturing [6], “volumetric contraction” [7], and low coefficients of friction [8]. In the South China Sea (SCS), polygonal faults were for the first time identified in the Qiongdongnan basin (QDNB) in 2009 [9]. Sun et al. [10] mentioned the migration of hydrocarbon through polygonal faults in QDNB. However, there is no document about reservoirs of gas hydrates associated with polygonal faults in SCS. In this paper, we will show the seismic geometry and distribution of polygonal faults and investigate the geophysical characters of gas hydrates in deep water of QDNB and Zhongjiannan basin (ZJNB) (Figure 1). We use high-resolution 2D and 3D seismic data integrated with local sedimentary history to study the function of polygonal faults in acting as conduits of gas hydrate provinces. Figure 1: (a) The schematic map of South China Sea. The map shows the distribution of polygonal faults and prospective gas hydrate zones in QDNB and ZJNB. (b) The 3D seismic survey in deep water of QDNB. The basemap is the time depth of the sequence boundary of the base of upper Miocene. Lines plotted in the map will be discussed below. 2. Geological Backgrounds Sedimentary basins in northern South China Sea margin underwent an early syn-rifting stage in Paleogene and a postrifting thermal subsidence stage in Neogene and Quaternary [11]. The separation for syn-rifting and
Rifting process and formation mechanisms of syn-rift stage prolongation in the deepwater basin, northern South China Sea
DongDong Dong,ShiGuo Wu,GongCheng Zhang,ShengQiang Yuan
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0326-1
Abstract: Based on the latest seismic and geological data, tectonic subsidence of three seismic lines in the deepwater area of Pearl River Mouth Basin (PRMB), the northern South China Sea (SCS), is calculated. The result shows that the rifting process of study area is different from the typical passive continental margin basin. Although the seafloor spreading of SCS initiated at 32 Ma, the tectonic subsidence rate does not decrease but increases instead, and then decreases at about 23 Ma, which indicates that the rifting continued after the onset of seafloor spreading until about 23 Ma. The formation thickness exhibits the same phenomenon, that is the syn-rift stage prolonged and the post-rift thermal subsidence delayed. The formation mechanisms are supposed to be three: (1) the lithospheric rigidity of the northern SCS is weak and its ductility is relatively strong, which delayed the strain relaxation resulting from the seafloor spreading; (2) the differential layered independent extension of the lithosphere may be one reason for the delay of post-rift stage; and (3) the southward transition of SCS spreading ridge during 24 to 21 Ma and the corresponding acceleration of seafloor spreading rate then triggered the initiation of large-scale thermal subsidence in the study area at about 23 Ma.
Post-Rifting Magmatism and the Drowned Reefs in the Xisha Archipelago Domain Post-Rifting Magmatism and the Drowned Reefs in the Xisha Archipelago Domain
WANG Hongli,ZHAO Qiang,WU Shiguo,WANG Dawei,WANG Bin
- , 2018,
Abstract: Fourteen isolated drowned reefs have been identified around the Xisha Uplift by multibeam and seismic data. The drowning processes of these reefs can be divided into three different stages, which correspond to three different accelerated tectonic subsidence periods. The drowning of the Xisha reefs is the result of the combined action of tectonic subsidence and sea level fluctuations, and the tectonic subsidence rate had to remain above 0.2 mm yr~(-1 )for a long time. Three abrupt accelerated tectonic subsidence events that occurred in the late Miocene, Pliocene and early Quaternary in the Xisha Uplift were closely related to the thermal subsidence processes after three stages of post-rifting magmatism. The magmatism of the middle Miocene and the following thermal subsidence resulted in the drowning of reefs in the northwestern Xisha uplift(Zone A). During the early Pliocene, massive magmatic intrusions and volcanic eruptions occurred in the Xisha Uplift. Then, the subsequent thermal subsidence started the drowning process of reefs in the northeastern and western regions of the Xisha Uplift(Zone B and C). During the early Quaternary, large-scale magmatism also occurred in the Xisha Uplift. The subsequent thermal subsidence resulted in a new rapid tectonic subsidence, which caused the reefs in the southern and southeastern regions of the Xisha Uplift to drown(Zone D and E)
Relation of Submarine Landslide to Hydrate Occurrences in Baiyun Depression, South China Sea Relation of Submarine Landslide to Hydrate Occurrences in Baiyun Depression, South China Sea
SUN Yunbao,ZHANG Xiaohua,WU Shiguo,WANG Lei,YANG Shengxiong
- , 2018,
Abstract: Submarine landslides have been observed in the Baiyun Depression of the South China Sea. The occurrence of hydrates below these landslides indicates that these slope instabilities may be closely related to the massive release of methane. In this study, we used a simple Monte-Carlo model to determine the first-order deformation pattern of a gravitationally destabilizing slope. The results show that a stress concentration occurs due to hydrate dissociation on the nearby glide surface and on top of a gas chimney structure. Upon the dissolution of the gas hydrate, slope failure occurs due to the excess pore pressure generated by the dissociation of the gas hydrates. When gas hydrates dissociate at shallow depths, the excess pore pressure generated can be greater than the total stress acting at those points, along with the forces that resist sliding. Initially, the failure occurs at the toe of the slope, then extends to the interior. Although our investigation focused only on the contribution of hydrate decomposition to submarine landslide, this process is also affected by both the slope material properties and topography
Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea
ZHANG Xiaohua,SUN Yunbao,WU Shiguo,DONG Dongdong
- , 2018,
Abstract: 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
南海共轭陆缘新生代碳酸盐台地 对海盆构造演化的响应
Response of Cenozoic Carbonate Platform on Tectonic Evolution in the Conjugated Margin of South China Sea

吴时国,张新元,
Wu Shiguo''
, Zhang Xinyuanl

地球科学(中国地质大学学报) , 2015, DOI: 10.3799/dqkx.2015.017
Abstract: 南海新生代碳酸盐台地分布面积广、厚度巨大,但大部分已经淹没,成为淹没碳酸盐台地,它们孕育着南海海盆演变的 重要信息.南海碳酸盐台地伴随着南海陆缘张裂而发育,最初主要发育在两个共轭陆缘伸展地块的构造高地.南海经历了大陆 边缘伸展、岩石圈减薄和地幔剥露等过程,始新世到早渐新世的第二期NE-SW 向扩张,形成了破裂不整合面,随之发生了晚 渐新世至早中新世的海底扩张,形成中央海盆.构造沉降提供了台地生长的可容纳空间,构造掀斜作用、断裂作用和前陆盆地 前沿挤压褶皱的迁移控制了台地各单元厚度、沉积相和地震反射终止特征在横向上的变化,构造控制的相对海平面的变化控 制了不同级序生物礁碳酸盐台地的沉积旋回,而后期加速沉降导致碳酸盐台地淹没.
Cenozoic carbonate platforms of great thickness are widely deve1oped in the South China Sea, most of which have been drowned since the Late Cenozoic and named drown carbonate platform accordingly. The carbonate platforms in the South China Sea are unique and rich in tectonic evolution information. The carbonate platforms were deve1oped by the rifting proces- ses, and were initiated on the faulted b1ock shoulder in the conjugated rifting margin. The South China Sea margin experienced rifting, thinning, and mantle exhumation. The Eocene and Early 01igocene NE-SW direction riftingled to breakup unconformi- ty. Then Centra1 Ocean Basin occurred during Late 01igocene-Early Miocene sea f1oor spreading. Tectonic tilt, faulting and mi- gration of compressive fold in the front of foreland basins contro11ed the distribution, thickness and seismic reflection horizonta1 variation. Tectonic induced relative sealeve1 changes contro11ed the sedimentary cycles of carbonate platforrns. ^nd more, later rapid subsidence in Late Miocene induced the drowning of most carbonate platforms
Image Authentication Based on Neural Networks
Shiguo Lian
Computer Science , 2007,
Abstract: Neural network has been attracting more and more researchers since the past decades. The properties, such as parameter sensitivity, random similarity, learning ability, etc., make it suitable for information protection, such as data encryption, data authentication, intrusion detection, etc. In this paper, by investigating neural networks' properties, the low-cost authentication method based on neural networks is proposed and used to authenticate images or videos. The authentication method can detect whether the images or videos are modified maliciously. Firstly, this chapter introduces neural networks' properties, such as parameter sensitivity, random similarity, diffusion property, confusion property, one-way property, etc. Secondly, the chapter gives an introduction to neural network based protection methods. Thirdly, an image or video authentication scheme based on neural networks is presented, and its performances, including security, robustness and efficiency, are analyzed. Finally, conclusions are drawn, and some open issues in this field are presented.
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