Geophysical and Crustal Movement Characteristic of Western Sichuan Basin

Analysis and research of large complex phenomena before and after the devastating earthquake to reduce the threat of natural disasters to human survival environment is of great significance.This paper analyzes the Wenchuan earthquake zone characteristics of gravity anomaly distributions,and then use edge detection and Euler deconvolution method to inverse Longmenshan gravity anomaly before earthquake.Fault distribution features and the general depth about the fault top of Longmenshan and its adjacent area before earthquake has been obtained.Morphology difference and possible earthquake formation have been analyzed through the Euler deconvolution result of gravity anomaly profile before and after the earthquake.

Risk assessment of mountain tourism on the Western Sichuan Plateau,China

As an important site for tourism activities,mountainous areas may generate greater tourism risks than plain areas due to potential natural disasters,social issues,scenic area management,and tourist behavior.Western Sichuan Plateau is mostly mountainous area and tourism is its pillar industry,Therefore,the assessment of the tourism risks on the Western Sichuan Plateau is of academic value and practical significance.In this study,we use statistical and remote sensing data,fishbone diagram,and the entropy weighting method to construct a tourism risk evaluation model and classify risks into different levels,and we also use a geographic information system(GIS)for spatial mapping to quantify and spatialize the results.The objectives are 1)to identify the risk sources in the Western Sichuan Plateau and analyze their causal mechanisms,precisely reveal the distribution of tourism risks in the study area;2)improve the precision of tourism risk evaluation in scenic areas and analyze the causes and spatial distribution patterns of tourism risks and propose targeted management measures.This study found that the evaluation results of the four elements of hazard,exposure,vulnerability,and disaster prevention and mitigation capacity on the Western Sichuan Plateau showed significant spatial variability,depending on the natural conditions and the quantity difference of tourism resources in different regions.In addition,the tourism risk is low in most areas of the Western Sichuan Plateau,and disaster prevention and mitigation capacity is higher in areas with high tourism risk where attractions are densely populated and tourism is concentrated.Our study can provide a reference for future analyses of tourism risks in mountainous tourist areas such as in China and worldwide.

Climate Regionalization for Morchella esculenta Cultivation in the Western Sichuan Plateau Based on GIS

Based on the meteorological data and DEM data in the producing areas of Morchella esculenta in the western Sichuan plateau from 1991 to 2020, the biological characteristics of M. esculenta, as well as the survey of production in the planting area, the correlation between M. esculenta production and the climatic ecological conditions at an altitude of 1 200-3 000 m in the western Sichuan plateau was comprehensively analyzed by using the inverse distance weight method, analytic hierarchy process, climate risk assessment model and geographic information system(GIS), and restrictive or high impact climatic ecological factors were selected as the suitability zoning indicators to carry out the analysis of climatic ecological suitability and planting zoning. The results show that the climatic factors affecting M. esculenta cultivation in the western Sichuan plateau were mainly temperature, temperature difference between day and night, and humidity, and the main meteorological disaster was freezing disaster. Under the influence of vertical changes in temperature, topography and cold damage, the growing areas of M. esculenta in the western Sichuan plateau were mainly distributed in the Minjiang River basin and the river valley along the Dadu River basin at an altitude of 1 200-2 000 m, and were distributed in strips and branches along the rivers. The suitable areas were mainly distributed in Wenchuan, Lixian, Maoxian, Kangding, Jiulong and Luding counties(cities), which were the main producing areas of M. esculenta, but the area was small, accounting for only 3.5% of the study area;the sub-suitable areas were mainly distributed in some towns of Danba, Xiaojin, Wenchuan, Lixian, Maoxian, Heishui and Jiuzhaigou counties, accounting for 36.0% of the total area, and they were the main planting areas of M. esculenta.

A Comparative Study on No-tillage Late DirectSowing Varieties of Brassica napus L. in Western Sichuan Plain

[Objective] There are continuous rainy days in Western Sichuan Plain in autumn. In order to avoid the impact of wet injury in sowing period, new varieties of Brassica napus L. with low erucidic acid and glucosinolate content which are suitable for no-tillage late direct-sowing in Western Sichuan Plain were screened in this study. [Method] Ten major varieties of Brassica napus L. were screened by randomized block design and triplicated plot test with no-tillage late direct-sowing and straw mulching for comparative experiment. [Result] ‘Chuanyou 58＇, ‘Huayouza 10＇and ‘Ningza 11＇ have high yield（per unit area yield above 3 000 kg/hm2）, excellent comprehensive characters, short growth period, high resistance and high quality;‘Huayouza 13＇ and ‘Zheshuang 3＇ have high yield potential（per unit area yield above 2 775 kg/hm2）, high resistance, high quality and moderate growth period; other varieties have extremely significant yield reduction, poor comprehensive characters and low resistance compared with control. [Conclusion] Excellent varieties of Brassica napus L. in the middle and lower reaches of Yangtze River such as ‘Huayouza10＇, ‘Ningza 11＇, ‘Huayouza 13＇ and ‘Zheshuang 3＇ can be successfully introduced and applied for large-area cultivation in Western Sichuan Plain.

Quantification and timing of porosity evolution in tight sand gas reservoirs:an example from the Middle Jurassic Shaximiao Formation,western Sichuan,China

The diagenesis and porosity evolution of the Middle Jurassic Shaximiao sandstones were analyzed based on petrographic observations, X-ray diffractometry, scanning electron microscopy observations, carbon and oxygen stable isotope geochemistry, fluid inclusion mi- crothermometry, and thermal and burial history modeling results. The point count data show that secondary pores （av. 5.5 %） are more abundant than primary pores （av. 3.7 %） and are thus the dominant pore type in the Shaximiao sandstones. Analysis of porosity evolution indicates that alteration of sandstones mainly occurred during two paragenetic stages. Mechanical compaction and cementa- tion by early chlorite, calcite, and quartz typically decrease the depositional porosity （40.9 %） by an average of 37.2 %, leaving porosity of 3.7 % after stage I （〈85 ℃, 175-145 Ma）. The original intergranular porosity loss due to compaction is calculated to be 29.3 %, suggesting that mechanical compaction is the most significant diagenetic process in primary porosity destruction. Stage II can be further divided into two sub-stages （Stage IIa and Stage IIb）. Stage IIa （85-120 ℃, 145-125 Ma） is characterized by late dissolution, which enhanced porosity by 8.8 %, and the porosity increased from 3.7 % to 12.5 %. During stage IIb （〉120 ℃, 125-0 Ma）, the precipitation of late chlorite, calcite, quartz, and kaolinite destroyed 3.3 % porosity, leaving porosity of 9.2 % in the rock today.

Genesis of the low-permeability reservoir bed of upper Triassic Xujiahe Formation in Xinchang gas field,western Sichuan Depression

The genesis of a reservoir is a result of the combined action of deposition, diagenesis, tectonic reworking, and interaction of rock and fluid and the evolutionary environment. We discuss the genetic and evolution mechanism of a low-permeability reservoir bed of the Xujiahe Formation in the western Sichuan Depression on the basis of the study of diagenesis, diagenetic reservoir facies and the diagenetic evolution sequence. The research indicated that this reservoir bed can be divided into five types of diagenetic reservoir facies, namely strong dissolution, chlorite-lined intergranular pores, compaction and pressure solution, carbonate cementation and secondary quartz increase. There are, however, just two diagenetic reservoir facies which provide low-permeability reservoir beds, namely strong dissolution and chlorite-lined intergranular pores. We also analyzed their diagenetic evolution sequences and the origin of the low-permeability reservoir bed. Besides, it was also indicated that the composition and structure of sandstones, types of sedimentary microfacies, diagenesis history as well as the tectonic reworking in later periods are the main factors controlling the formation of the low-permeability reservoir bed. The above- mentioned factors establish the foundation for the forecasting the distribution of high quality reservoir beds.

Tectonic Fractures in Tight Gas Sandstones of the Upper Triassic Xujiahe Formation in the Western Sichuan Basin,China

The western Sichuan Basin, which is located at the front of the Longmen Mountains in the west of Sichuan Province, China, is a foreland basin formed in the Late Triassic. The Upper Triassic Xujiahe Formation is a tight gas sandstone reservoir with low porosity and ultra-low permeability, whose gas accumulation and production are controlled by well-developed fracture zones. There are mainly three types of fractures developed in the Upper Triassic tight gas sandstones, namely tectonic fractures, diagenetic fractures and overpressure-related fractures, of which high-angle tectonic fractures are the most important. The tectonic fractures can be classified into four sets, i.e., N-S-, NE-, E-W- and NW-striking fractures. In addition, there are a number of approximately horizontal shear fractures in some of the medium-grained sandstones and grit stones nearby the thrusts or slip layers. Tectonic fractures were mainly formed at the end of the Triassic, the end of the Cretaceous and the end of the Neogene-Early Pleistocene. The development degree of tectonic fractures was controlled by lithology, thickness, structure, stress and fluid pressure. Overpressure makes not only the rock shear strength decrease, but also the stress state change from compression to tension. Thus, tensional fractures can he formed in fold-thrust belts. Tectonic fractures are mainly developed along the NE- and N-S-striking structural belts, and are the important storage space and the principal flow channels in the tight gas sandstone. The porosity of fractures here is 28.4% of the gross reservoir porosity, and the permeability of fractures being two or three grades higher than that of the matrix pores. Four sets of high-angle tectonic fractures and horizontal shear fractures formed a good network system and controlled the distribution and production of gas in the tight sandstones.

The Relationship between Fractures and Tectonic Stress Field in the Extra Low-Permeability Sandstone Reservoir at the South of Western Sichuan Depression

The formation and distribution of fractures are controlled by paleotectonic stress field, and their preservative status and effects on development are dominated by the modern stress field. Since Triassic, it has experienced four tectonic movements and developed four sets of tectonic fractures in the extra low-permeability sandstone reservoir at the south of western Sichuan depression. The strikes of fractures are in the S-N, NE-SW, E-W, and NW-SE directions respectively. At the end of Triassic, under the horizontal compression tectonic stress field, for which the maximum principal stress direction was NW.SE, the fractures were well developed near the S-N faults and at the end of NE-SW faults, because of their stress concentration. At the end of Cretaceous, in the horizontal compression stress fields of the NE-SW direction, the stress was obviously lower near the NE-SW faults, thus, fractures mainly developed near the S-N faults. At the end of Neogene-Early Pleistocene, under the horizontal compression tectonic stress fields of E-W direction, stress concentrated near the NE-SW faults and fractures developed at these places, especially at the end of the NE-SE faults, the cross positions of NE-SW, and S-N faults. Therefore, fractures developed mostly near S-N faults and NE-SW faults. At the cross positions of the above two sets of faults, the degree of development of the fractures was the highest. Under the modern stress field of the NW-SE direction, the NW-SE fractures were mainly the seepage ones with tensional state, the best connectivity, the widest aperture, the highest permeability, and the minimum opening pressure.

Geochemical characteristics of noble gases in natural gas and their application in tracing natural gas migration in the middle part of the western Sichuan Depression, China

Noble gases in natural gas, from Xiaoquan, Xinchang, Hexingchang and Fenggu gas reservoirs in the middle part of the western Sichuan Depression, China, were analysed. Results show that the volume content of crustal noble gases accounts for 97.9% to 99.7% of the total noble gas content, indicating that the noble gases in the study area are very largely derived from the crust. Moreover, the 40Ar time-accumulating effect of source rocks is used to determine the complex relationship between gases and source rocks in this area, and the results agree well with that from analysis of source rock light hydrocarbons. Due to the short migration distance, the separation of 4He and 40Ar is not significant in Xujiahe natural gas and Lower and Middle Jurassic natural gas, so it is difficult to trace natural gas migration. However, this separation characteristic of 4He and 40Ar in Middle and Upper Jurassic natural gas is significant, which indicates that natural gas migration was from the Middle Jurassic to Upper Jurassic formations. In addition, the variation trends of 3He/4He ratio and δ13C1 value indicates that natural gas migration is from the Xujiahe formation to the Jurassic layer in the study area.

Petrophysical and capillary pressure properties of the upper Triassic Xujiahe Formation tight gas sandstones in western Sichuan,China

The tight sandstones of the Upper Triassic Xujiahe Formation（T_3x） constitute important gas reservoirs in western Sichuan.The Xujiahe sandstones are characterized by low to very low porosity （av.5.22%and 3.62%） for the T_3x^4 and T_3x^2 sandstones,respectively）,extremely low permeability（av. 0.060 mD and 0.058 mD for the T_3x^4 and T_3x^2 sandstones,respectively）,strong heterogeneity,micronano pore throat,and poor pore throat sorting.As a result of complex pore structure and the occurrence of fractures,weak correlations exist between petrophysical properties and pore throat size,demonstrating that porosity or pore throat size alone does not serve as a good permeability predictor.Much improved correlations can be obtained between permeability and porosity when pore throat radii are incorporated. Correlations between porosity,permeability,and pore throat radii corresponding to different saturations of mercury were established,showing that the pore throat radius at 20%mercury saturation（R_（20）） is the best permeability predictor.Multivariate regression analysis and artificial neural network（ANN） methods were used to establish permeability prediction models and the unique characteristics of neural networks enable them to be more successful in predicting permeability than the multivariate regression model.In addition, four petrophysical rock types can be identified based on the distributions of R_（20）,each exhibiting distinct petrophysical properties and corresponding to different flow units.

Hydrocarbon Generation and Expulsion of the Upper Triassic T3x5Source Rocks in the Western Sichuan Depression: Assessment for Unconventional Natural Gas

Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation （T3xs） in the Western Sichuan Basin （WSD） are currently regarded as the most prolific emerging unconventional gas plays in China. This study conducted a conventional evaluation of T3x5 source rocks in the WSD, and investigated their hydrocarbon generation and expulsion characteristics, including intensity, efficiency and amount. The results show that, the T3x5 source rocks are thick （generally 〉200 m）, and have a high total organic content （TOC）, ranging from 2.5 to 4.5 wt%. It is thus indivative of a great hydrocarbon generation potential when they underwent high thermal evolution （Ro〉1.2%） in the area. In addition, an improved method of hydrocarbon generation potential is applied, indicating that the source rocks reached a hydrocarbon expulsion threshold with vitrinite reflectance （Ro） reaching 1.06%. and that the comprehensive hydrocarbon expulsion efficiency is about 60%. The amount of hydrocarbon generation and expulsion from Tax5 source rocks is 3.14x10^10 t and 1.86x10^10 t, respectively, with a residual amount of 1.28x10^10t within them. Continuous-type tight-sand gas is predicted to have developed in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration; the Jurassic sandstone reservoirs are tight, and the gas expelled from the T3xs source rocks migrates for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3x10s t. Geological resources of shale gas are up to 1.05x10TM t. Small differences between the amounts calculated by the volumetric method and those obtained by hydrocarbon generation potential method may be due to other gas accumulations present within interbedded sands associated with gas shales.

Scattered Rural Settlements and Development of Mountainous Regions in Western Sichuan,China

Making rural settlements of Mountainous Regions in Western Sichuan as the study objects and using symbolic statistical methods, then combining the case study of Daofu County, the paper analyzes the negative impact of the scattered rural settlements on infrastructure construction, farmers＇ income increase and mountain ecological reconstruction in mountainous regions of western Sichuan. The results indicate that economic density is positively related to both rural settlements density （R^2=0.73） and rural population density （R^2=0.77）, and it is the same for relationship between towns density and rural settlements density （R^2=0.88） and between towns density and economic density （R^2=0.71）, and the scattered distribution pattern of the rural settlements and shortage of economic centers is a major factor to the lagged socioeconomic development. On the eco-economic zoning to Daofu County, the paper indicates the spatial distribution model and the industrial development model of the rural settlements need to be changed, and rural population should be concentrated in larger rural settlements with development of off-farm industries while infrastructure construction is to reinforced.

Gravity variation associated with Wenchuan earthquake in western Sichuan

Based on the data of mobile gravity observation from 1998 to 2008 in western Sichuan, spatial dynamic variation results of regional gravity field are obtained. The relationship between the gravity variation features and Wenchuan Ms8.0 earthquake is systematically analyzed. The results show： 1 ） Gravity variation is closely related to active fault tectonics, and gravity measurement can better reflect material migration following crustal tectonic activity near active fault. 2）The gravity field appeared a wider range regional gravity variation during Wenchuan earthquake occurrence. The dynamic patterns of gravity field demonstrates the evolution process of gravity field ： quasi - homogeneous state non - homogeneous state-earthquake occurrence.

RESERVOIR CHARACTERISTICS OF JURASSIC SHAXIMIAO FORMATION, WESTERN SICHUAN BASIN

研究表明，川西地区沙溪庙组储层主要储集岩为长石砂岩、岩屑长石砂岩，其次为岩屑砂岩、长石岩屑砂岩及岩屑石英砂岩。储集空间分为孔、缝，其中主要储集空间为粒间溶孔，其次为残余粒间孔和粒内溶孔。喉道类型以管状和粒间裂隙为主，属细一微喉型。储层孔隙结构差，具有孔隙小、喉道窄、有效连通孔隙体积小和中一高排驱压力的特征，总体属于低一中孔、低一中渗，局部存在高孔高渗的常规储层，非均质性强。在此基础上通过对储层发育控制因素、储集砂体展布及有利储集区带的研究，为川西沙溪庙组的油气藏勘探开发提供了重要支撑。

Wet Canopy Evaporation Rate of Three Stands in Western Sichuan, China

The wet canopy evaporation rate (Er) wascalculated by Penman-Monteith combination model based on three assumptions and with meteorological variables 2 m above the canopy inthree stands, dominated by spruce (SF), fir (FF) and birch (BF) trees, respectively[(,)( )]in the subalpineforests in western Sichuan, China over a growingseason. The total amount of the E was 44.5 mm forSF, 88.5 mm for FF and 57.8 mm for BF, accounting for 9.2%, 16.6% and 10.2% of the gross rainfall,respectively, in the measuring period. There was the highest average monthly Er and percentage of E togross rainfall for FF compared with SF and BF.Mean Er was 0.097 mm h-1 (ranging from 0.028 to0.487 mm h-1), 0.242 mm h-1 (from 0.068 to 0.711 mm h-1) and 0.149 mm h-1 (from 0.060 to 0.576 mm h-1for SF, FF and BF, respectively. The highest average monthly Er occurred in June was 0.120 mm h-1 forSF, 0.317 mm h-1 for FF and 0.169 mm h-1 for BF, and the lowest value in October was 0.083 mm h-1 for SF, 0.187 mm h-1 for FF and 0.101 mm h-1 for BF,respectively. The averages of Er from 8:00 to 16:00were significantly higher than those from 0:00 to8:00 and from 16:00 to 0:00 for the three stands. The marked daily and monthly differences of Er were contributable to the variations of solar radiation, air temperature and relative humidity above thecanopy.

A Study on Forest Species Diversity and Its Ecological Service Function in the Plateau Area of Western Sichuan

This paper presents a study on species diversity and its ecological service function in the plateau area in western Sichuan. The results show that species diversity in the plantations on the cutover land has a tendency to increase and that its ecological service function is to be improved with stand age growing. The species diversity in forest communities is also gradually increased on different succession stage till reaching a climax level. But the species diversity in the climax community is slightly decreased before it reaches a relatively constant status. Ecological service function of diversity is gradually strengthened with the progress of succession. In addition, species diversity in a stand in a similar site and at a same age differs among forest types. Species diversity index within a coniferous and broad-leaved mixed forest is larger than that within a coniferous forest. Meanwhile, species diversity enriches as the tree density increases.

Neoproteroic Magmatism Related to Lithospheric Delamination: Implications from Three Episodes of Mafic Dykes and Associated Granitoids in the Pengguan Complex, Western Sichuan Province, Yangtze Block

The research on dyke swarms is very important,for it can not only shed light on within-plate geological processes of some regions but also contribute to our understanding on evolution of a specific orogenic belt.The Yangtze Block,

Establishment and Maintenance of Grass Skiing Resort Turf Based on Climatic Characteristics of Western Sichuan

In recent years, a new type of leisure sport—grass skiing, has been introduced from abroad. However, there is no standard design system for this type of turf. This paper, based on climatic characteristics of western Sichuan, introduced the requirements of the construction of grass skiing resort turf in western Sichuan as well as its maintenance management mode, and tried to explore the standard system of turf establishment and maintenance management of grass skiing resort in western Sichuan.

Concerning about the threat of the excessive hydropower exploitation on the Western Sichuan eco-environment

The concept that the economic development and supremacy hydropower energy are superior to any others leads to the excessive hydropower exploitation of the west Sichuan, deeply threatening the fragile eco-environment in this area and that of the whole Yangtze River and even of the whole country simultaneously. The present paper put forward that hydropower should be developed with ecological, social, and economical concern. The primary, extensive, circling-developing development model should be altered immediately, and that based on caring about eco-environment, being harmonious to the regional eco-environment should be highlighted, and sustainability of hydropower should be paid attention to.

Survey of Ecotourism Landscape Resources and Shrub Landscape Resources in Western Sichuan Mountains

As a high-end tourism activity advocating back to nature and protecting the nature,ecotourism has won increasing attention in recent years home and abroad.Being endowed with outstanding topographical and natural landscape resources,Sichuan has been a major ecotourism province in China.Particularly,western Sichuan mountains is more scarcely populated area with great topographical fluctuations,thus it is more suitable for developing ecotourism activities than eastern Sichuan.Based on previous researches and statistical analysis,this paper reviewed the overall situation of ecotourism landscape resources in western Sichuan mountains,including its geomorphological landforms,hydrographic landscapes,biological landscapes,meteorological and climatic landscapes.More importantly,in view of the blank area found in the statistical analysis,the paper analyzed the shrub landscapes on the basis of fi eld investigation,to support further research on the development and utilization of local ecotourism resources.