Deep-large faults controlling on the distribution of the venting gas hydrate system in the middle of the Qiongdongnan Basin, South China Sea

Many locations with concentrated hydrates at vents have confirmed the presence of abundant thermogenic gas in the middle of the Qiongdongnan Basin(QDNB).However,the impact of deep structures on gasbearing fluids migration and gas hydrates distribution in tectonically inactive regions is still unclear.In this study,the authors apply high-resolution 3D seismic and logging while drilling(LWD)data from the middle of the QDNB to investigate the influence of deep-large faults on gas chimneys and preferred gasescape pipes.The findings reveal the following:(1)Two significant deep-large faults,F1 and F2,developed on the edge of the Songnan Low Uplift,control the dominant migration of thermogenic hydrocarbons and determine the initial locations of gas chimneys.(2)The formation of gas chimneys is likely related to fault activation and reactivation.Gas chimney 1 is primarily arises from convergent fluid migration resulting from the intersection of the two faults,while the gas chimney 2 benefits from a steeper fault plane and shorter migration distance of fault F2.(3)Most gas-escape pipes are situated near the apex of the two faults.Their reactivations facilitate free gas flow into the GHSZ and contribute to the formation of fracture‐filling hydrates.

＂Institutionalization＂ as Weapons of the Weak： ASEAN Countries and the South China Sea Disputes

＂Institutionalization＂ can be understood as a process of norm and law setting to regulate and control individual attitudes. An institutionalized area could be more stable and ordered, then the relationships between the factors can be identified by the predicted signals. Institutions can help to provide a key form of such frameworks, through which all states, but especially the stronger states, can use rules and other normative expectations of conduct in the international relation. Weaker states, in return, gain limits on the action of the leading states and access to the political process, in which they can press their interests. This article analyzes the disputes in the South China Sea~, particularly between China and ASEAN countries to prove the argument. It is argued that ASEAN, in the situation of power asymmetry between dominant （power-holders） and dominated groups, has used ＂institution＂ and ＂institutionalization＂ as a countermeasure to constrain the powerful China in the two ways： （1） trying to lock-in China in a rule-based order, in order to restrict its power, and （2） by institutionalizing the way in which the disputes in the South China Sea should be resolved, ASEAN countries want to create a frameworks for setting rules of games, which are shaped by principles and norms instead of balance-of-power.

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.

A 3D basin modeling study of the factors controlling gas hydrate accumulation in the Shenhu Area of the South China Sea

Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.

The status quo and perfection of maritime law enforcement system in China-from the perspective of law enforcement of rights and security in the South China Sea

China enjoys historic rights over the South China Sea. It has become a controversial sea area due to the loopholes in the modern law of the sea. It is competed by neighboring countries for its interests, which exacerbate the tense situation in China＇s enforcement of maritime rights protection and poses the serious threat to our country＇s sovereignty over the South China Sea. The article takes the South China Sea controversial maritime rights enforcement model as the starting point. It contrasts the status quo of maritime rights enforcement system both at home and abroad, and analyzes the existing laws and regulations of maritime rights protection system in our country, such as the imperfect laws and regulations, the unreasonable establishment of law enforcement agencies and the imperfect law enforcement system. It also puts forward the strategy and idea of perfecting the law enforcement system of maritime rights protection in our country, which is of far-reaching significance to the strategy of safeguarding the maritime rights and interests of China and building a maritime power.

Seismic Imaging and 3D Architecture of Yongle Atoll of the Xisha Archipelago, South China Sea

Yongle atoll in the Xisha(Paracel) Archipelago is an isolated carbonate platform developed on Precambrian metamorphic and Mesozoic volcanic rocks since the early Miocene. To identify the 3D stratigraphic architecture and evolution of this platform, 13 high-resolution seismic profiles and shallow-to-deep water multi-beam data were processed and analyzed to reveal seismic facies, sequence boundary reflectors, seismic units, and platform architecture. Nine types of seismic facies were recognized based on their geometry, which included seismic amplitude, continuity, and termination patterns;additionally, six reflections, i.e., Tg, T60, T50, T40, T30, and T20, were identified in the Cenozoic strata. Five seismic units, SQ1(lower Miocene), SQ2(middle Miocene), SQ3(upper Miocene), SQ4(Pliocene), and SQ5(Quaternary), were identified from bottom to top across the platform. The platform grew rapidly in the middle Miocene and backstepped in the late Miocene–Pliocene. Here, we discuss the developmental characteristics and evolution of the Yongle Atoll, in combination with drilling wells, which can be divided into four stages: the initiation stage in the early Miocene, the flourishing stage in the middle Miocene, the partial-drowning stage in the late Miocene–Pliocene, and modern atoll in the Quaternary.

The Turn of the Tide:Explaining China’s Growing Assertiveness in the South China Sea

Before the late 2000s,China employed a diplomatic“next generation”approach to its territorial disputes in the South China Sea(SCS).Beginning in the late 2000s,however,China has assumed threatening attitudes,and taken a strong stand against other disputants.Why has China recently shown its assertiveness when dealing with the South China Sea issue?This study argues that two factors-China’s growing naval capabilities and the growing presence of China’s strategic rivals around the South China Sea-led China to adopt a more assertive policy regarding the South China Sea issue.

3D Velocity Structure and Its Tectonic Implications in the East China Sea and Yellow Sea

3D structure of the crust and upper mantle in the studied area has been analyzed from surface wave tomography. The velocity distribution in the uppermost crust is symmetrical on two sides of the central line of the sea, and coincides with the structure of crystalline basement. The essential difference in tectonics between the East China Sea and the Yellow Sea mainly lies in that the velocity structures of their lower crust and upper mantle are identical to those of South China and North China respectively. In the upper mantle there exists a high-velocity zone with a nearly EW strike from the Hangzhou Bay, China, to the Tokara Channel, Japan, along about the latitude of 30°N. It is found that between the East China Sea and the Yellow Sea there are systematical differences in geomorphology, geology, seismicity, heat flow, quality factor and gravity and aeromagnetic anomalies, which is related to both left-lateral shear dislocation and right-lateral tear of the Benioff zone from the Hangzhou Bay to the Tokara Channel.It is inferred that the East China Sea was formed by Cenozoic back-arc extension. The boundary between the North China and South China crustal blocks stretches along the southern piedmont of Mts. Daba-Dabie-Hangzhou Bay-Tokara Channel, and the subduction zone at the Okinawa trench is the eastern boundary of the South China crustal block. The movements of the Pacific plate, Indian plate and upper mantle rather than the Philippine plate subduction have played a dominant role for the modern tectonic movements in East Asia.

Lateral bearing characteristics of subsea wellhead assembly in the hydrate trial production engineering

Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering,which have the advantages of high operation efficiency and short construction period.In order to drill a horizontal well in the shallow hydrate reservoir in the deep water,the suction anchor wellhead assembly is employed to undertake the main vertical bearing capacity in the second round of hydrate trial production project,so as to reduce the conductor running depth and heighten the kick-off point position.However,the deformation law of the deep-water suction anchor wellhead assembly under the moving load of the riser is not clear,and it is necessary to understand the lateral bearing characteristics to guide the design of its structural scheme.Based on 3D solid finite element method,the solid finite element model of the suction anchor wellhead assembly is established.In the model,the seabed soil is divided into seven layers,the contact between the wellhead assembly and the soil is simulated,and the vertical load and bending moment are applied to the wellhead node to simulate the riser movement when working in the deep water.The lateral bearing stability of conventional wellhead assembly and suction anchor wellhead assembly under the influence of wellhead load is discussed.The analysis results show that the bending moment is the main factor affecting the lateral deformation of the wellhead string;the anti-bending performance from increasing the outer conductor diameter is better than that from increasing the conductor wall thickness;for the subsea wellhead,the suction anchor obviously improves the lateral bearing capacity and reduces the lateral deformation.The conduct of the suction anchor wellhead assembly still needs to be lowered to a certain depth that below the maximum disturbed depth to ensure the lateral bearing stability,Thus,a method for the minimum conductor running depth for the suction anchor wellhead assembly is developed.The field implementations show that compared with the first round of hydrate trial production project,the conductor running depth is increased by 9.42 m,and there is no risk of wellhead overturning during the trial production.The method for determining the minimum conductor running depth in this paper is feasible and will still play an important role in the subsequent hydrate exploration and development.

South China Sea Territorial Disputes and Sino-Philippine Trade

As political factors affect trade activities greatly, this paper considers whether a series of political events have had a negative impact on Sino-Philippine trade relations. Of particular concern is the influence on bilateral relations and the Philippines' domestic economy from political and diplomatic tensions between China and the Philippines caused by territorial disputes in the South China Sea. Political events are divided into two levels, general conflicts and serious conflicts, which are analyzed from the perspectives of both overall level and product level to present their final impact on trade. This research finds that territorial disputes between the two countries deteriorated trade, as the volume of trade usually decreased distinctly after conflicts. The negative impact on trade generated by serious conflicts usually occurred more rapidly and on a larger scale. The effect of trade deterioration caused by political events weakened over time. Furthermore, after serious conflicts, although the volume of trade of certain products decreased temporarily, it rebounded quickly or even increased soon. However, industrial equipment or industrial raw materials trade activities between the two countries were basically independent of the conflicts' impact.

华南夏季12—30d持续性强降水的低频特征分析

利用1982—2011年夏季(5—8月)中国气象观测站点逐日降水资料、NCEP/NCAR逐日再分析资料、NOAA逐日向外长波辐射和海表温度资料集,通过选取低频降水事件的方法,分析了华南夏季12—30 d持续性强降水事件的基本特征,然后利用位相合成法对持续性强降水期间伴随的低频大气环流型以及低频信号的来源和传播情况进行研究,同时也分析了低频海-气耦合过程对持续性强降水的影响。结果表明:(1)华南夏季降水具有显著的12—30 d低频振荡特征,持续性强降水事件在6月发生次数最多,低频降水期间的雨带自东南向西北传播。(2)在持续性强降水发生期间,华南及邻近海域低层受强大的低频气旋式环流控制,低频上升运动显著,而中国南海—菲律宾海一带则是强的低频反气旋式环流,其西侧向北的低频水汽输送不断将中国南海的水汽送至华南及邻近海域进行辐合上升。低层的低频信号来源于热带西太平洋和中国南海—菲律宾海一带低频振荡的西北向传播,同时伴随着西太平洋副热带高压明显的西伸东退过程。(3)在高层,华南北侧(22°—45°N,95°—130°E)区域强大的低频气旋式环流和孟加拉湾—中国南海一带的低频反气旋式环流相互配合,使华南高层处于强大的辐散环境中,从而加强了华南低层的辐合与低频上升运动,造成持续性强降水的增强。高层的低频信号来源于低频罗斯贝波列的东南向传播。(4)低频大气环流异常通过云辐射和热通量过程改变低频海表温度异常,而由大气强迫的低频海表温度异常通过影响低层大气的稳定性来对大气施加明显的反馈作用,该海-气耦合过程有利于大气低层低频信号向华南地区传播,从而影响了华南持续性强降水的发生、发展与结束。

利用drifter资料分析南海北部涡旋特征

利用卫星跟踪的drifter表面漂流浮标轨迹资料,对南海北部的涡旋特征进行了时空分布统计分析,特别是卫星高度计资料无法分辨出的次级中尺度涡旋的特征,并初步分析了其动力机理。研究发现南海北部半径小于10km的次级涡旋要占所有涡旋的绝大部分,涡旋平均半径可达11.7km,反气旋涡数量与气旋涡数量之比约为2.6∶1。研究结果可为未来在南海布放drifter浮标提供技术参考。

Relations between sedimentary sequence and paleoclimatic changes during last 200 ka in the southern South China Sea

Core NS-93-5 was taken from the mild slope terrace of the southern South China Sea (SCS), which has preserved the steadiness depositional record of the normal marine environment since late Quaternary. Sedimentary sequence and oxygen isotopic stratigraphy of high resolution in the near 200 ka of the southern SCS has been established. By the comparative analysis with GISP2’s ice core, the depositional record of D/O’s events 1-21 and Heinrich’s events H1-H6 in the southern SCS that reflected the quick climate change in short time scale since the last interglacial stage is revealed, which indicates that in the last 200 ka in the southern SCS and the Arctic area there was tele-connection of paleoclimate and the unstability of the Western Pacific Warm Pool. This note shows that the sedimentary layers order of this sea area classified by color identification and by oxygen isotope stratum has the very good corresponding relation. The color feature of sediment changes along with the climate and the former

Patterns and Dynamics of Rifting on Passive Continental Margin from Shelf to Slope of the Northern South China Sea:Evidence from 3D Analogue Modeling

Affected by thermal perturbation due to mantle uprising, the rheological structure of the lithosphere could be modified, which could lead to different rifting patterns from shelf to slope in a passive continental margin. From the observed deformation style on the northern South China Sea and analogue modeling experiments, we find that the rift zone located on the shelf is characterized by half grabens or simple grabens controlled mainly by long faults with large vertical offset, supposed to be formed with normal lithosphere extension. On the slope, where the lithosphere is very hot due to mantle upweUing and heating, composite grabens composed of symmetric grabens developed. The boundary and inner faults are all short with small vertical offset. Between the zones with very hot and normal lithosphere, composite half grabens composed of half grabens or asymmetric grabens formed, whose boundary faults are long with large vertical offset, while the inner faults are relatively short. Along with the thickness decrease of the brittle upper crust due to high temperature, the deformation becomes more sensitive to the shape of a pre-existing weakness zone and shows orientation variation along strike. When there was a bend in the pre-existing weakness zone, and the basal plate was pulled by a clockwise rotating stress, the strongest deformation always occurs along the middle segment and at the transition area from the middle to the eastern segments, which contributes to a hotter lithosphere in the middle segment, where the Baiyun （白云） sag formed.

Tectonic characteristics and structural styles of a continental rifted basin:Revelation from deep seismic reflection profiles

The Fushan Depression is a half-graben rifted sub-basin located in the southeast of the Beibuwan Basin, South China Sea. The Paleogene Liushagang sequence is the main hydrocarbon-bearing stratigraphic unit in the sub-basin. Using three-dimensional（3-D）seismic data and logging data over the sub-basin, we analyzed structural styles and sedimentary characteristics of the Liushagang sequence. Five types of structural styles were defined： ancient horst, traditional slope, flexure slope-break, faulted slope-break and multiple-stage faults slope, and interpretations for positions, background and development formations of each structural style were discussed. Structural framework across the sub-basin reveals that the most remarkable tectonic setting is represented by the central transfer zone（CTZ） which divides the sub-basin into two independent depressions, and two kinds of sequence architectures are summarized：（i） the western multi-stage faults slope;（ii） the eastern flexure slope break belt. Combined with regional stress field of the Fushan Depression, we got plane combinations of the faults, and finally built up plan distribution maps of structural system for main sequence. Also, we discussed the controlling factors mainly focused on subsidence history and background tectonic activities such as volcanic activity and earthquakes. The analysis of structural styles and tectonic evolution provides strong theoretical support for future prospecting in the Fushan subbasin and other similar rifted basins of the Beibuwan Basin in South China Sea.

“印太战略”框架下澳越关系的发展及影响

在“印太战略”框架下,近年来澳越两国关系不断升级,双方合作全面推进,两国尤其强化了在防务安全领域的合作和南海问题上的战略协调。澳大利亚希望借助与越南关系的升级提升地区影响力和彰显中等强国地位;越南则希望在南海问题上获得澳大利亚的支持。澳越关系的深化对南海局势及亚太地区秩序的稳定都将产生一定的影响。在推进两国合作制衡中国的战略盘算和应对所谓“中国威胁”的共识下,澳越两国关系将会继续深化,尤其是海洋安全领域的合作将会是两国关系的主要内容。为了维护南海局势和地区秩序的稳定,中国和东盟国家要相向而行,尽力排除域外国家介入南海争端,构建中国和东盟国家共同主导的南海地区秩序。

日本强化东盟国家海上安保能力的政策及影响分析

利用东盟国家在南海问题上发难,是日本牵制中国、呼应美国的重要政策手段。基于这一地缘政治考虑,日本主要从海域态势感知、海上执法与海上防卫等三个方面为东盟强化海上安保能力提供支持。为了评估这一政策的具体落实及其对南海局势的实际影响,本文从地缘政治视角出发,对日本支持东盟强化海上安保能力进行了系统评估,并以南海争端中两个主要争议方越南、菲律宾为重点,分析了日本政策的演进及其特点。总体上看,日本的支持提高了相关东盟国家海上安保能力现代化的水平,增强了相关东盟国家对抗中国的信心,增加了南海冲突发生的机率,从而成为恶化南海局势的重要外部诱因。与此同时,日本政策及其影响受到东盟大国平衡立场以及不同成员国认知的限制。展望未来,日本在美国的鼓励与要求下还会进一步强化其对东南亚局势的介入,部分东盟国家特别是菲律宾与日本的互动可能进一步强化,中国维护南海的和平与稳定的努力也将面临更大的挑战。

越南建构的南海历史地名叙事及其存在的逻辑问题

在中越之间关于南海的争议中,越南方面找到诸多历史资料来支撑其主张。这些史料中的地名繁杂而混乱,但却被罗织成相互关联的地名关系。这种历史叙述看似系统而完整,但其各个节点却缺乏充分的证据和合理的逻辑。以越南发行的白皮书为线索,可以找到越南建构南海历史叙述的主要依据。详细考察这些越南和西方文献中相关地名之间的关系,即可进一步发现越南南海主张中的历史地名叙事逻辑及其问题所在。

边界争端、威胁认知与印越在南海的战略互动态势

面对实力强于自身的国家,选择与他国合作以制衡强国,是行为体的潜在反应之一。在边界争端形势较为严峻的背景下,印度和越南不断强化在南海战略互动和合作,加剧了南海争端的复杂态势。在影响印越南海战略合作的诸多因素中,边界争端和威胁认知是关键变量。边界争端框定两国南海合作政策变化的整体方向,威胁认知左右两国行动意愿强度。当中印和中越边界争端形势均较为严峻时,支撑印越南海靠近的条件较为充分,两国在该区域的战略互动就极易发生;当任意一国和中国边界争端局势有所缓和时,支撑两国南海频繁互动的条件会相应弱化,其在南海的战略合作强度就会有所减弱。通过对中越“中建南事件”和中印“洞朗事件”进行案例比较以及个案内的过程追踪分析,该论点得到了验证。尽管边界争端和共同对华威胁感知是驱使印越强化南海互动的动力源之一,但两国战略重点的不同和高度异质的威胁感知,会增强两国南海战略互动过程的复杂性及效果的不确定性。