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.

Moisture Transport and Associated Background Circulation for the Regional Extreme Precipitation Events over South China in Recent 40 Years

Based on the hourly precipitation data at 176 observational stations over south China and the hourly ERA5reanalysis data during the 40-yr period of 1981-2020, we analyzed the universal characteristics of moisture transport and their associated background circulations for four types of regional extreme precipitation events(REPEs) over south China. Main findings are shown as follow.(i) The wind that transported moisture for the REPEs over south China featured a notable diurnal variation, which was consistent with the variations of the precipitation.(ii) Four types of REPEs could be determined, among which the southwest type(SWT) and the southeast type(SET) accounted for ~92%and ~5.7%, respectively, ranking the first and second, respectively.(iii) Trajectory analyses showed that the air particles of the SWT-REPEs had the largest specific humidity and experienced the most intense ascending motion, and therefore their precipitation was the strongest among the four types.(iv) South China was dominated by notable moisture flux convergence for the four types of REPEs, but their moisture transport was controlled by different flow paths.(v)Composite analyses indicated that the background circulation of the four types of REPEs showed different features,particularly for the intensity, location and coverage of a western Pacific subtropical high. For the SWT-REPEs, their moisture transport was mainly driven by a lower-tropospheric strong southwesterly wind band in the low-latitude regions. Air particles for this type of REPEs mainly passed over the Indochina Peninsula and South China Sea. For the SET-REPEs, their moisture transport was mainly steered by a strong low-tropospheric southeasterly wind northeast of a transversal trough. Air particles mainly passed over the South China Sea for this type of REPEs.

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.

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.

ON THE DIFFERENTIATION OF THE ECONOMIC DEVELOPMENT OF CHINA’S NORTH,CENTRAL & SOUTH COASTAL REGIONS

Ⅰ. An analysis of the development trend of the economy in the north,middle aud south coastal regions or China since China began to implementreform and open

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.

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.

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.

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 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.

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.

Physical characteristics of high concentrated gas hydrate reservoir in the Shenhu production test area,South China Sea

High concentrated and heterogeneous distribution of gas hydrates have been identified in the gas hydrate production test region in the Shenhu area,South China Sea.The gas hydrate-bearing sediments with high saturation locate at two ridges of submarine canyon with different thickness and saturations just above the bottom simulating reflection.The crossplots of gamma ray,acoustic impedance(P-impedance)and porosity at four sites show that the sediments can be divided into the upper and lower layers at different depths,indicating different geotechnical reservoir properties.Therefore,the depositional environments and physical properties at two ridges are analyzed and compared to show the different characteristics of hydrate reservoir.High porosity,high P-wave velocity,and coarse grain size indicate better reservoir quality and higher energy depositional environment for gas hydrate at Sites W18 and W19 than those at Sites W11 and W17.Our interpretation is that the base of canyon deposits at Sites W18 and W19 characterized by upward-coarsening units may be turbidity sand layers,thus significantly improving the reservoir quality with increasing gas hydrate saturation.The shelf and slope sliding deposits compose of the fine-grained sediments at Sites W11 and W17.The gas hydrate production test sites were conducted at the ridge of W11 and W17,mainly because of the thicker and larger area of gas hydrate-bearing reservoirs than those at Sites W18 and W19.All the results provide useful insights for assessing reservoir quality in the Shenhu area.

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.

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.

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.

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

Evaluationof eco-environmental competitiveness in south China 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.

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~x 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.