Three dimensional shear wave velocity structure of crust and upper mantle in South China Sea and its adjacent regions by surface waveform inversion

We assembled approximately 328 seismic records. The data set was from 4 digitally recording long-period and broadband stations of CDSN. We carried out the inversion based on the partitioned waveform inversion (PWI). It partitions the large-scale optimization problem into a number of independent small-scale problems. We adopted surface waveform inversion with an equal block (2((2() discretization in order to acquire the images of shear velocity structure at different depths (from surface to 430 km) in the crust and upper-mantle. The resolution of all these anomalies has been established with (check-board( resolution tests. These results show significant difference in velocity, lithosphere and asthenosphere structure between South China Sea and its adjacent regions.

Characteristics of Upper Mantle Activity in the South China Sea Region and the Indochina Mantle Plume

Abstract According to computed results of the mantle traction field beneath the lithosphere based on satellite-modelled gravity anomalies of different degrees, it has been revealed that the three types of mantle convection on different scales existing in the South China Sea region is the key factor controlling the geodynamics. The mantle convection models on large and middle scales have been proved by natural seismic S-wave tomographic data and interpreted by using the present mantle plume concept. In consideration of other relevant geological and geophysical data, the authors put emphasis on discussing the expression form, origin and age of the Indochina mantle plume and its important effect on the conversion of organic matter and hydrocarbon accumulation in Cenozoic basins.

Interpretation of the west segment of the coastal fault zone in the coastal region of South China based on the gravity data

By systemic processing, comprehensive analysis, and interpretation of gravity data, we confirmed the existence of the west segment of the coastal fault zone(west of Yangjiang to Beibu Bay) in the coastal region of South China. This showed an apparent high gravity gradient in the NEE direction, and worse linearity and less compactness than that in the Pearl River month. This also revealed a relatively large curvature and a complicated gravity structure. In the finding images processed by the gravity data system, each fault was well reflected and primarily characterized by isolines or thick black stripes with a cutting depth greater than 30 km. Though mutually cut by NW-trending and NE-trending faults, the apparent NEE stripe-shaped structure of the west segment of the coastal fault zone remained unchanged,with good continuity and an activity strength higher than that of NW and NE-trending faults. Moreover,we determined that the west segment of the coastal fault zone is the major seismogenic structure responsible for strong earthquakes in the coastal region in the border area of Guangdong, Guangxi, and Hainan.

From Basin Black Shales to Platform Carbonate Rocks:A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China

In the Upper-Yangtze region, especially in Guizhou Province and its adjacent areas, the Lower Cambrian is well developed and is marked by a succession from black shales of the basin facies to carbonate rocks of the platform facies. The drowning event of the platform occurring at the turn from Sinian to Cambrian resulted in a set of black shales, i.e. the Niutitang Formation, which makes up the bottom part of the Lower Cambrian. With the shoaling of the sedimentary environment, a set of carbonate rocks, i.e. the Qingxudong Formation, was formed in the top part of the Lower Cambrian. Thus, the Lower Cambrian in the study area makes up one second-order sequence that can be further subdivided into five third-order sequences, and forms a regularly cyclic succession of transgression-regression. There is a regularly vertical stacking pattern for the third-order sequences in the second-order sequence. From bottom to top, the succession of the ＂CS （condensed section） ＋HST （high-stand system tract）＂ of the third-order sequences is changed into the succession of the ＂TST （transgressive system tract）＋CS＋HST＂. Correspondingly, the drowning-type sequence boundary is changed into the exposure-type one. Therefore, both the second-order and the third-order sequences have similar sedimentary-facies architectures. A concomitant with these temporal changes, the Lower Cambrian with a thickness of 1000 m that contains five third-order sequences is changed into a condensed succession that cannot identify third-order sequences toward the southeast with the deepening of the sedimentary environment. According to the elementary features of the third-order sequences, i.e. the regularity o sedimentary-facies successions in space and the synchronism of sedimentary-environment changes in time, the detailed division of the third-order sequences at main logged sections in different paleogeographical background becomes the basis to establish the sequence-stratigraphic framework that can demonstrate two types of facies-changing surface and two types of diachronism in the stratigraphic records. This sequence-stratigraphic framework shows a growing process of the carbonate platform from the base of the condensed succession formed by black shales of basin facies. Resulting from the rapid transgression at the turn from Sinian to Cambrian the ecological space became open, which formed the antecedent condition of paleogeographical setting for ＂the Cambrian Biological Explosion＂. Ultimately, the genetic relationship between the depositional events and the biological-diversity events is very complex and there remain lots of problems that need further research in the future.

The Late Triassic Sequence-Stratigraphic Framework of the Upper Yangtze Region,South China

In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China：（1） the formation and uplift of the Qinling-Dabie orogenic belt along the northern margin of the South China Plate, due to its collision with the North China Plate; and 2） the development of a 1300-km-wide intra-continental orogen in the southeastern part of the South China Plate, which led to a northwestward movement of the foreland thrust-fold zone. These tectonic events resulted in the ending of the Yangtze Platform, and were a stable paleogeographic factor from the Eidacaran to the end of the Middle Triassic. This platform was characterized by the widespread development of shallow-water carbonates. After the end of the Yangtze Platform, the upper Yangtze foreland basin（or Sichuan foreland basin） was formed during the Late Triassic and became a accumulation site of fluvial deposits that are composed of related strata of the Xujiahe Formation. In western Sichuan Province, the Xujiahe Formation overlies the Maantang Formation shallow-water carbonate rocks of the Xiaotangzi Formation siliciclastic rocks（from shelf shales to littoral facies）. The sequence-stratigraphic framework of the Upper Triassic in the upper Yangtze foreland basin indicates a particular alluvial architecture, characterized by sequences composed of（1） successions of low-energy fluvial deposits of high-accommodation phases, including coal seams, and（2） high-energy fluvial deposits of low-accommodation phases, including amalgamated river-channel sandstones. The spatial distribution of these fluvial deposits belonging to the Xujiahe Formation and its relative strata is characterized by gradual thinning-out, overlapping, and pinching-out toward both the east and south. This sedimentary record therefore expresses a particular sequence-stratigraphic succession of fluvial deposits within the filling succession of the foreland basin. The sequence-stratigraphic framework for the Upper Triassic in the Upper Yangtze region provides a record of the end of the Yangtze Platform and the formation of the upper Yangtze foreland basin.

Controlling Factors of Organic Nanopore Development: A Case Study on Marine Shale in the Middle and Upper Yangtze Region, South China

The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.

Characteristics of seismic reflections in central region of the South China Sea and their geological significance

More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted. Five seismic interfaces have been distinguished, named T1, T2, T4, T6 and Tg respectively Meanwhile, five seismic sequences numbered I - V have been divided with the ages of Quaternary and Pliocene, Later Mocene, Earlier and Middle Miocene, Oligocene and Pre- Oligocene separately. Sequences I-II overlie all parts of the area. In the continental slope and island slope, Sequences III-V are mainly found in the grabens. Sequence III is found at moot profiles of the deep-sea basin, and Sequnce IV is seen not only at the margins of the east subbasin but also at the margins of the southwest subbasin. Strong reflection from Moho is found at most profiles of the deep-sea basin. The depth of Moho varies between 10 and 12 km, with a thickness of 6- 8 km for the crust. Calculated by age-basement depth correlation formula, the age of basaltic basement in the southwest subbasin is 51-39 Ma. It is indicated that the evolution of the southwest subbasin is simultaneous with or earlier than that of the east subbasin.

Tracing the Provenance of the Huguangyan Maar Lake Sediments in Coastal Regions of South China

The Huguangyan Maar Lake（HML）（21°9＇N,110°17＇E）,situated on the Leizhou Peninsula in the southernmost of China's Mainland,is the deepest recent crater lake among the identified volcanic structures in the Leiqiong Volcanic Field.The bi-lobate lake.

Land degradation in the subtropical hilly andmountain regions of South China

Land degradation, caused by water erosion. closely related to inherent vulnerabilities of itseco-environment in South China. Spatial variation of land degradation from top to foot of a slope wasmainly induced by differentiation of surface materials and their erodibility, nutrient and moisture dueto downslope variation of land erosion. It was showed by comparing maps of land degradationbetween the 1950s and the 1980s that changes of land degradation varied from one area to anotherbecause of differences of human activities, including land reclamation and vegetation depletion.

THE REGIONAL AIR-SEA COUPLED OSCILLATION IN THE SOUTH CHINA SEA

This study examined the regional air sea coupled interaction in the South China Sea (SCS), based on the 1979-1995 NCEP/NCAR reanalysis data of sea surface temperature (SST) and meridional wind (V component). Singular value decomposition (SVD) and single field principal component analysis (PCA) were employed to analyse the SST and V anomalies and compare the results with each other. It was found that the leading mode of SVD explained a predominant amount of squared covariance between the SST and meridional wind V, and that the time series expansion coefficients of the first mode between SST and V from PCA and SVD resembled very much each other. This infers that the meridional wind, as an indicator of Asian monsoon, is closely related with the SST through the air sea interaction in the SCS. The spatial patterns of the first mode of SST and V exhibit ellipse shaped variance in the SCS center and a NE SW oriented main axis, which are much similar to those in winter season. These results show that the most active center for both V and SST is in the SCS, which suggests that a regional air sea coupled oscillation possibly exists there for the whole year and is noticeable especially during the winter season. So the SCS is a very important region for the forming of the Asian Monsoon and the climate of the west Pacific.

Dynamic Controls on the Formation of Mantle Plume Beneath the South China Sea Region

The South China Sea(SCS)has attracted intensive structural and geophysical research over the past decades,with a focus on its extensional history and relevant dynamic tectonic models.Seismic tomographic images obtained

Economic stability analysis of blue carbon cooperation in the South China sea region using evolutionary game model with Weber's law

The political environment of the South China Sea Region(SCSR)has gradually stabilized,such that regional cooperation in the preservation of marine resources seems realistic.Blue carbon international cooperation is an important solution to the problem of global warming,which has a large number of economic and political attributes.As a region that has incredibly abundant blue carbon resources,further cooperation among SCSR governments would present the opportunity to establish meaningful economic and environmental protections that would promote peaceful blue carbon development of this region.To examine the feasibility of such an undertaking,we leverage the imitator's dynamic game as a research method and introduce Weber's law to examine the subjective psychological factors(i.e.,biases)of participants in qualifying the economic stability of blue carbon cooperation in the SCSR.The results suggest that the economic stability of blue carbon cooperation correlates to Weber's coefficient and the income produced by the different strategies.Based on these findings,we discussed policy recommendations to promote the sustainable economic development of SCSR.

Effects of collapsing gully erosion on soil qualities of farm fields in the hilly granitic region of South China

Collapsing gully erosion is a specific form of soil erosion types in the hilly granitic region of tropical and subtropical South China, and can result in extremely rapid water and soil loss. Knowledge of the soil physical and chemical properties of farmland influenced by collapsing gully erosion is important in understanding the development of soil quality. This study was conducted at the Wuli Watershed of the Tongcheng County, south of Hubei Province, China. The aim is to investigate soil physical and chemical properties of three soil layers （0-20, 20-40 and 40-60 cm） for two farmland types （paddy field and upland field） in three regions influenced by collapsing gully erosion. The three regions are described as follows： strongly influenced region （SIR）, weakly influenced region （WIR） and non-influenced region （NIR）. The results show that collapsing gully erosion significantly increased the soil gravel and sand content in paddy and upland fields, especially the surface soil in the SIR and WIR. In the 0-20 cm layer of the paddy field, the highest gravel content （250.94 g kg-1） was in the SIR and the lowest （78.67 g kg-1） was in the NIR, but in the upland filed, the surface soil （0-20 cm） of the SIR and the 40-60 cm soil layer for the NIR had the highest （177.13 g kg-1） and the lowest （59.96 g kg-1） values of gravel content, respectively. The distribution of gravel and sand decreased with depth in the three influenced regions, but silt and clay showed the inverse change. In the paddy field, the average of sand content decreased from 58.6 （in the SIR） to 49.0% （in the NIR）, but the silt content was in a reverse order, increasing from 27.9 to 36.9%, and the average of the clay content of three regions showed no significant variation （P〈0.05）. But in the upland filed, the sand, silt and clay fluctuated in the NIR and the WIR. Soils in the paddy and upland field were highly acidic （pH〈5.2） in the SIR and WIR; moreover lower nutrient contents （soil organic matter （SOM）, total N and available N, P, K） existed in the SIR. In the 0-20 cm soil layer of the paddy field, compared with the NIR and the WIR, collapsing gully erosion caused a very sharp decrease in the SOM and total N of the SIR （5.23 and 0.56 g kg-1, respectively）. But in the surface soil （0-20 cm） of the upland field, the highest SOM, total N, available N, available P and available K occurred in the NIR, and the lowest ones were in the SIR. Compared with the NIR, the cation exchange capacity （CEC） in the SIR and WIR was found to be relatively lower. These results suggest that collapsing gully erosion seriously affect the soil physical and chemical properties of farmland, lead to coarse particles accumulation in the field and decrease pH and nutrient levels.

Evaluation of reanalysis surface wind products with quality-assured buoy wind measurements along the north coast of the South China Sea

Three archived reanalysis wind vectors at 10 m height in the wind speed range of 2-15 m/s,namely,the second version of the National Centres for Environmental Prediction(NCEP)Climate Forecast System Reanalysis(CFSv2),European Centre for Medium-Range Weather Forecasting Interim Reanalysis(ERA-I)and NCEPDepartment of Energy(DOE)Reanalysis 2(NCEP-2)products,are evaluated by a comparison with the winds measured by moored buoys in coastal regions of the South China Sea(SCS).The buoy data are first quality controlled by extensive techniques that help eliminate degraded measurements.The evaluation results reveal that the CFSv2 wind vectors are most consistent with the buoy winds(with average biases of 0.01 m/s and 1.76°).The ERA-I winds significantly underestimate the buoy wind speed(with an average bias of-1.57 m/s),while the statistical errors in the NCEP-2 wind direction have the largest magnitude.The diagnosis of the reanalysis wind errors shows the residuals of all three reanalysis wind speeds(reanalysis-buoy)decrease with increasing buoy wind speed,suggesting a narrower wind speed range than that of the observations.Moreover,wind direction errors are examined to depend on the magnitude of the wind speed and the wind speed biases.In general,the evaluation of three reanalysis wind products demonstrates that CFSv2 wind vectors are the closest to the winds along the north coast of the SCS and are sufficiently accurate to be used in numerical models.

Construction of evaluation model of eco-environmental competitiveness in southern hilly region

South China is located in the subtropical zone,with excellent hydrothermal conditions and abundant species.Compared with other regions in China,the environment and natural resources have obvious innate advantages.The crisscross of hills and small plains are the most typical topographic and geomorphic features in South China.Its evaluation of eco-environmental competitiveness is different from other regions in China in terms of index selection and evaluation process.Based on the literature results,combining with the particularity of the southern hilly region and according to certain principles,we construct an evaluation model of ecological environment in southern hilly region,which includes five first-level indicators of ecological resources,environmental status,enconomic society,management response and environmental potential and fifteen second-level index sperated from the first-level,such as forest coverage rate and ambient air quality composite index and so on.Taking Hunan Province,a tipical region of southern hills,as an empirical example to analyse,the conclusion has been verified by other scholars and the new model is more operable than the existing models and methods,which indicates that the model constructed is practical and feasible.

Analysis of a Regional Rainstorm Process in South Shaanxi during July 17-18,2010

Based on conventional high-altitude aerial and ground data, regional intensive rainfall data, Doppler weather radar and satellite cloud data, the occurrence and development process of a regional rainstorm in South Shaanxi during July 17 -18, 2010 was discussed deeply. The results showed that the occurrence and development of the mesoscale weather system resulted in the heavy storm directly besides favorable large-scale background, and the the occurrence and development of the system had strong local and sudden characters. In addition, heavily concentrated wa- ter vapor in the troposphere at low and middle altitudes as well as existence of unstable conditions of convection might be favorable to the develop- ment of the system, while dynamic action of terrain, ground weak cold front and disturbance of the low-level jet stream might trigger the occurrence and development of the system.

Factors influencing the climatological mixed layer depth in the South China Sea:numerical simulations

The mixed layer depth(MLD) in the upper ocean is an important physical parameter for describing the upper ocean mixed layer.We analyzed several major factors influencing the climatological mixed layer depth(CMLD),and established a numerical simulation in the South China Sea(SCS) using the Regional Ocean Model System(ROMS) with a high-resolution(1/12°×1/12°) grid nesting method and 50 vertical layers.Several ideal numerical experiments were tested by modifying the existing sea surface boundary conditions.Especially,we analyzed the sensitivity of the results simulated for the CMLD with factors of sea surface wind stress(SSWS),sea surface net heat flux(SSNHF),and the difference between evaporation and precipitation(DEP).The result shows that of the three factors that change the depth of the CMLD,SSWS is in the first place,when ignoring the impact of SSWS,CMLD will change by 26% on average,and its effect is always to deepen the CMLD;the next comes SSNHF(13%) for deepening the CMLD in October to January and shallowing the CMLD in February to September;and the DEP comes in the third(only 2%).Moreover,we analyzed the temporal and spatial characteristics of CMLD and compared the simulation result with the ARGO observational data.The results indicate that ROMS is applicable for studying CMLD in the SCS area.

“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。

中美博弈:近昔和当今及对中国战略的意涵

过去15年里,中美关系的首要特征是博弈而非协调。两国博弈先在战略阵线开启,继而在战略、经贸、高技术和意识形态四条主要阵线展开。就中美博弈总体而言,美国处于“防守型”战略态势,美国认为它长时期拥有的重大优势地位一个又一个地丧失或被侵蚀,首要动能在中国一边。中共十八大以来,中国逐渐成为一个急剧腾升的强国。大为增强的国力,使中国更加坚定了自信和抱负。中国内外发力,争取在世界政治经济和全球治理的某些问题领域参与引领甚或单独引领,实现在亚洲大陆以及发展中世界的经济和外交优势,大致取得在西太平洋的对美战略和军事优势,进一步地,对第一至第二岛链之间的战略空间的控扼能力愈益被视为必要。回顾奥巴马、特朗普和拜登三届美国政府的对华态势和政策,对未来中美关系应做好准备应对可能的疾风暴雨。