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1.
Trenching is a primary technique on paleoseismology to reveal evidence of surface deformation produced by large earthquakes.A good trenching site requires completeness of geologic recording on paleoseismic events and corresponding reliable dating from radiocarbon samples.Based on three-dimension trenching,we show a structure of a small triangular pull-apart basin at the Daqingliangzi section on the Zemuhe fault,then explore interrelation between paleoseismic surface rupturing and evolution of the pull-apart basin,and give a corresponding identification model.Sedimentary boundary of the pull-apart basin is tightly bounded by two branch faults,which produced multiple paleoseismic events with deformation of some large fissures in sequence.Strata are thinner at north of the pull-apart basin,however thicker at south.These above characteristics show that evolution of the pull-apart basin is a continuous sedimentation process accompanying extensional deformation produced by multiple paleoseismic events.Small pull-apart basins are favorable sites for trenching and paleoseismic study on active strike-slip faults.  相似文献   

2.
The Yinchuan basin, located on the western margin of the Ordos block, has the characteristics of an active continental rift. A NW-striking deep seismic reflection profile across the center of Yinchuan basin precisely revealed the fine structure of the crust. The images showed that the crust in the Yinchuan basin was characterized by vertical stratifications along a detachment located at a two-way travel time(TWT) of 8.0 s.The most outstanding feature of this seismic profile was the almost flat Mohorovicˇic′ discontinuity(Moho) and a high-reflection zone in the lower crust. This sub-horizontal Moho conflicts with the general assumption of an uplifted Moho under sedimentary basins and continental rifts, and may indicate the action of different processes at depth during the evolution of sedimentary basins or rifts.We present a possible interpretation of these deep processes and the sub-horizontal Moho. The high-reflection zone, which consists of sheets of high-density, mantlederived materials, may have compensated for crustal thinning in the Yinchuan basin, leading to the formation of a sub-horizontal Moho. These high-density materials may have been emplaced by underplating with mantlesourced magma.  相似文献   

3.
In an extensional basin,the process of hanging wall block rotation above a detachment fault zone is controlled by block geometry,the shape of the main normal faults,and the detachment depth.A formula for calculating the detachment depth of a tilted block is established in geometrical aspect from the tilting angle of the rotational block,dip angle of the main boundary fault,and the sedimentary thickness in the basin.The calculated result shows that the detachment depth of the tilted block,controlled by a rotational planar normal fault in the Linxian basin,on the eastern slope of Taihangshan Mountain,North China,is about 12.5 km,which is consistent with the analytic result of seismic data in the area.The value is similar to the estimated depth of the usual brittle ductile transition in a rift zone.The geometrical model presented in this paper,however,can provide a range of structural patterns of hanging wall and the detachment depth for reference in hydrocarbon exploration and earthquake processes.  相似文献   

4.
Ordos block was squeezed by the Qinghai-Tibetan block and North China block, and the tectonic activity was intense. In the periphery of Ordos block, there was a series of folds zones and compressed faults with complicate structures. This paper used three-phase data of 1980,1990 and 2014 to calculate vertical velocity of Northwestern margin of Ordos and the analytical results indicated that ① the Hetao basin between the rise of Yinshan fault block and Ordos fault block showed relatively subsidence, in which Linhe basin was the most evident and the subsidence rate was about 2-4mm/a. The subsidence rate of Jartai -Yinchuan rift zone on the western margin of Ordos block was about 2mm/a; ② the whole testing zone exhibited the evident inherited movement characterized by mountain rise and basin subsidence; ③the two leveling section through the northern margin fault and Dengkou-Benjing fault showed that the difference between vertical velocities on two sides of the fault was less than 0.5mm/a.  相似文献   

5.
Under the background of global water cycle, theregional water cycle systems of the arid inland regionsof northwest China are characterized by the fact thatthe area is composed of various relatively independentinland river basins, each of which is a system of inter-related climate, hydrology, water resources, ecologyand environment. An inland river basin consists of amountain area and the plain and basin area in front ofthe mountains. The vertical landscape zonality of aninland river basin can …  相似文献   

6.
Songpan-Garze massif is located at the turning position of tectonics from the nearly west-east direction to the nearly north-south direction in the northeastern margin of Tibetan Plateau,with Zoigê basin in the centre of the massif.In this paper,we build a crustal structure model of Zoigê basin and its surrounding folded orogenic belts using the deep seismic sounding data in this region.We also discuss structures and properties of the basement in Zoigê basin,tectonic relations between Zoigê upland basin and its surrounding folded orogenic belts,crustal deformation and thickening in the northeastern margin of Tibetan Plateau,and decoupling and relaxing processes in the crust.The results indicate that a special "Mesozoic basement" is formed of Triassic rocks with high density (2.65-2.75 g/cm3) and high velocity (5.6 km/s) in Zoigê basin.Songpan-Garze tectonic massif was transformed into two types of tectonic units with different crustal structures,i.e.,relatively stable Zoigê upland basin and active folded orogenic belts around the basin,in the course of the crustal material of Tibetan Plateau flowing eastward and obstructed by surrounding stable blocks.The thickening of the crust in the northeastern margin of Tibetan Plateau mainly occurred in the mid and lower crust,and the structure characterized by low velocities and multiple reflectors obviously appears in the folded orogenic belts around Zoigê basin.It implies that the mid and lower crust underwent a strong tectonic deformation in the folded orogenic areas.The thickness of the crust is about 50 km in Zoigê basin and the folded orogenic belts at the both southern and northern sides of Zoigê basin.The "Mountain root" cannot be identified.It is inferred that during the later orogenic period the eastwards flowing deep materials moved clockwise along the relatively relaxing southern side around the eastern tectonic knot under the obstructing of surrounding rigid massifs,and it resulted in the strong stretching action of the folded orogenic belts around Zoigê basin.  相似文献   

7.
Reconstruction of uplift history of the Tibetan Plateau is crucial for understanding its environmental impacts. The Oiyug Basin in southern Tibet contains multiple periods of sedimentary sequences and volcanic rocks that span much of the Cenozoic and has great potential for further studying this issue. However, these strata were poorly dated. This paper presents a chronological study of the 145 m thick and horizontally-distributed lacustrine sequence using paleomagnetic method as well as a K-Ar dating of the underlying volcanic rocks. Based on these dating results, a chronostratigraphic framework and the basin-developmental history have been established for the past 15 Ma, during which three tectonic stages are identified. The period of 15-8.1 Ma is characterized by intense volcanic activities involving at least three major eruptions. Subsequently, the basin came into a tectonically quiescent period and a lacustrine sedimentary sequence was developed. Around 2.5 Ma, an N-S fault occurred across the southern margin of the basin, leading to the disappearance of the lake environment and the development of the Oiyug River. The Gyirong basin on northern slope of the Himalayas shows a similar basin developmental history and thus there is a good agreement in tectonic activities between the Himalayan and Gangdise orogenic belts. Therefore, the tectonic evolution stages experienced by the Oiyug Basin during the past 15 Ma could have a regional significance for southern Tibet. The chronological data obtained from this study may provide some constraints for further studies with regard to the tectonic processes and environmental changes in southern Tibetan Plateau.  相似文献   

8.
Threshold of environmental elements in drainage basin sediment yield refers to, under effect of climate, underlying surface and human activity, a turning point of abrupt changes in drainage sediment yield related to environmental element characteristics. Previous studies on threshold of sediment yield of relevant drainage basins were mainly concentrated on impact of natural zones with a few researches on impact of other environmental elements. Particularly studies on compound environmental element threshold in drainage basin sediment yield remain blank today. Studies indicate that sediment yield in drainage basins is affected by compound interactions and complex actions. Based on single element analysis, the present paper gives quantitatively compound threshold of environmental elements affecting sediment yield of the drainage basin between Hekouzhen and Tongguan in the middle Yellow River by the method of multi-variant, polynomial formula regression analysis.  相似文献   

9.
During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition,in the absence of dams or river training works.The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity.Turbidity can be considered as representative synthetic index of the climatic conditions,the lithological features and the land cover of the basin,and the geometric characteristics of the river network.The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italian regions that have very different morphological,geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres.The results can be considered satisfying.  相似文献   

10.
We presented a boundary element method using the approximate analytical Green's function given by Sánchez-Sesma et al.Coordinate transform is introduced to extend the method to deal with the model with constant-gradient velocity along oblique direction.The method is validated by comparing the numerical results with other independent methods.This method provides a useful tool for analyzing local site effects.We computed seismic response for two series of models.The results in both frequency and time domains are analyzed and show complex amplification patterns.The fundamental mode of resonance is dependent not only on the velocity at the free surface but also on the velocity distribution of the whole basin.For the higher modes of vibration the heterogeneous basin also has its own characteristic.  相似文献   

11.
A case study on the responses of streamflow to climate change in the Toutun River basin was carried out based on data analysis of streamflow, precipitation, and temperatures during the past 50 years.Temporal series of the streamflow change in the Toutun River basin was analyzed and tested using the Mann-Kendall nonparametric test. Results revealed that the annual runoff of the Toutun River had been in a monotonic decreasing trend for the past 50 years. Compared with the 1950s and 1960s, the annual runoff in the 1990s decreased by 4.0×105 m3 and 7.2×105 m3. The precipitation did not show monotonic trend during the past 50 years, but the annual temperature increased by 1.12℃ since the 1950s. Further data analysis indicated that the monthly runoff of the Toutun River decreased significantly from August to October, with precipitation displaying the similar pattern of seasonal change. Analysis suggests that the reduction of streamflow in the Toutun River basin is possibly caused by the seasonal change of precipitation, especially the precipitation reduction in summer, and temperature increases.  相似文献   

12.
The Nenjiang Formation in the Songliao Basin is a symmetrical sequence of progradation-retrogradation,and is formed in the transgression cycle and regression cycle(T-R cycles)of the base level of deposition.We analyzed the drilling,well logging,core data,and seismic profiles of basin level,and by using the sequence stratigraphy,identified one secondary sequence boundary,two third-order sequence boundaries,and eight fourth-order sequence boundaries in the Nenjiang Formation.These eleven sequence boundaries can be divided into structural unconformity,depositional unconformity,flooding surface,and forced regression surface.Therefore the Nenjiang Formation can be subdivided into one secondary sequence,three third-order sequences,and ten fourth-order sequences.We have restored the sedimentary filling evolution within the stratigraphic framework of fourth-order sequences in the Nenjiang Formation.The sedimentary period of the first member of the Nenjiang Formation was corresponded to the global transgression period,which is also the development period of transgression cycle(T cycle),when the lake basin had the largest scope and deepest sedimentary water,the SB07(the maximum flooding surface)was formed on the top of strata during this period;covering above the SB07,there developed a set of condensation layer-oil shale,which is distributed in the whole basin and is the important source bed and regional cover.Therefore,a retrogradation sequence was formed in the T cycle of the first member of the Nenjiang Formation,characterized by the retrograding delta at a low angle.The delta has a giant front,a small plain,and many underwater distributary channels.Meanwhile,large gravity flow channels and sublacustrine fans are developed in the front of the delta.During the depositional period of the second member of the Nenjiang Formation,the R cycle began to develop due to the compression of the pacific tectonic domain;the source direction rotated 90°along with the eastern uplifting of the basin,and formed a series of east-west prograded and forced retrogradations.The prograding delta at high angel was developed in the interior of the sequence;the delta had a small front,a giant plain,and fewer underwater distributary channels,with the collapse at the foreslope,forming a series of slump fans.The slump fans can be divided into three types:discrete type,superimposed type,and fluid type.We built a whole"triad model"of the slump fan.Pointed out that the sequence of forced retrogradation formed by R cycle is a good structural mark of basin optimization,and rejected the viewpoint of"transgression"in the Nenjiang Formation of the Songliao Basin.  相似文献   

13.
The analyzing data on stratigraphic temperature measurement , thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93℃/100 m, and the average heat flow value is 61.78 mW/m2, which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.  相似文献   

14.
The microstructures of fault rocks from the Wasatch fault zone in Utah (USA) have been studied using a polarizing microscope,a scanning electron microscope (SEM) and an ultrahigh-voltage electron microscope (HVHM).This fault zone may be recognized as one a with long history of seismic activity according to the microstructural characteristics such as type, deformation characteristics,melting structure and surface textures of the fault rocks.However,the main fault now present seems not to have been noticeably active since the late Pleistocene (Q_3),as shown by the eroded-surface texture on the quartz fragments in the fault gouge.Meanwhile,those faults supposed to be strongly active in modern times are branching faults much closer to the basin side and are covered by the Holocene sediments in the basin.  相似文献   

15.
The Tarim Basin is the largest, oil-bearing, superimposed basin in the northwest of China. The evolution and tectonic properties of the initial Tarim Basin have been hotly disputed and remain enigmatic. The Neoproterozoic basin is covered by a vast desert and a huge-thickness of sedimentary strata, has experienced multiple tectonic movements, had a low signal to noise ratios(SNRs) of deep seismic reflection data, all of which have posed critical obstacles to research. We analysed four field outcrops, 18 wells distributed throughout the basin, 27 reprocessed seismic reflection profiles with higher SNRs across the basin and many ancillary local 2D and 3D profiles and aeromagnetic data. We found about 20 normal fault-controlled rifting depressions of the Cryogenian and Ediacaran scattered throughout the basin, which developed on the Precambrian metamorphic and crystalline basement. The structural framework is clearly different from that of the overlying Phanerozoic. The rifting depressions consist of mainly half grabens, symmetrical troughs and horst-grabens. From the northeast to southwest of the basin,they are divided into three rifting depression groups with the WNW, ENE, and NW-trends that are mainly controlled by normal faults. The maximum thicknesses of the strata are up to 4100 m. From the Cryogenian to Ediacaran, most of the main inherited faults to active and eventually ceased at the end of the Ediacaran or Early Cambrian, while subsidence centres appeared and migrated eastward along the faults. They revealed that the different parts of the Tarim continental block were in NNE-SSWoriented and NNW-SSE-oriented extensional paleo-stress fields(relative to the present) during the Neoproterozoic, and were accompanied by clockwise shearing. According to the analysis of the activities of syn-sedimentary faults, filling sediments,magmatic events, and coordination with aeromagnetic anomalies, the tectonic properties of the fault depressions are different and are primarily continental rifts or intra-continental fault-controlled basins. The rifting phases mainly occurred from 0.8–0.61 Ga.The formation of the rifting depression was associated with the initial opening of the South Altun-West Kunlun Ocean and the South Tianshan Ocean, which were located at the northern and southern margins of the Tarim Block, respectively, in response to the break-up of the Supercontinent Rodinia and the initial opening of the Proto-Tethys Ocean.  相似文献   

16.
Kunming basin is a Cenozoic faulted basin under the control of mainly SN-trending active faults. In and around the basin, there are a total of eight major active faults. Seismo-geological survey and fault slip observation show that the SN- and NE-trending active faults are mostly sinistral strike-slip faults, while the NW-trending faults are mostly dextral strike-slip faults. Using stress tensor inversion method with 706 active fault striation data at 22 measurement sites, we determined tectonic stress field of the study area. The result shows that modern tectonic stress field in and around Kunming basin is characterized by NNW-SSE compression, ENE-WSW extension, and strike-slip stress regimes. The maximum principal compressional stress (σ1) is oriented 335o~2o, with an average dip angle of 21°; the minimum (σ3) is oriented 44o~93o, with an average dip angle of 14°, and the intermediate (σ2) has a high, or nearly vertical, dip angle. The inversion result from fault slip data is consistent with the result from focal mechanism solutions.  相似文献   

17.
1 INTRODUCTION Considerable amount of sediment discharge enters in a canal at the head works. This sediment discharge is carried safely as the slopes of the canal in the head reaches are large. Subsequently, for economy, the slopes of canal are reduced in the downstream reaches. This makes the sediment concentration far excess of its carrying capacity. This excess sediment has to be removed by suitable design of a sedimentation basin. Also, one of the requirements for successful function…  相似文献   

18.
The buried-hill trend is a typical style of the petroliferous structure in the faulted basin of eastern China. The Xinglongtai structure trend in the Liaohe subbasin,Bohai Bay Basin is a buried faulted-hill trend resulting from the periodic faulting of the Tai’an-Dawa faults. The structure was cut by various faults,which are interlinked and constitute the conduits for petroleum migration. Petroleum accumulated in the Tertiary sandstones and pre-Tertiary basement of metamorphosed rocks through the migration pathways of the fault system. Petroleum in the structure was derived from different hydrocarbon kitchens to form a hybrid field complex. Petroleum charged the structure from different directions and accumulated in various reservoirs through different pathways in different times. The accumulations in the buried hill trend of Xingongtai are composed of two types of traps in the two stratigraphic systems: traps in the Tertiary sandstones were formed by the fault blocks and by the pinchout of the sandstone,and traps in the pre-Tertiary basement of metamorphosed rocks were formed by fissures in the inner part of the buried hills and by the unconformity near the surface of the buried hills.  相似文献   

19.
1 Introduction The Mid-Hunan Basin is located in the south mar- gin of the Ancient Island Arc of Dong’an-Xuefeng and the north part of the interarc basin of Hercynian- Indosinian in Hunan-Guangxi. The basement rock of the basin, which is mainly distributed along the mar- ginal area of the basin and some interior sub-uplifts, is composed of pre-Devonian epimetamorphic-clastic rocks in great thickness, and the cap rock of the basin are dominated by carbonate rock and clastic rocks of Paleo…  相似文献   

20.
Runoffs in the Yellow River and Yangtze River basins,China,have been changing constantly during the last half century.In this paper,data from eight river gauging stations and 529 meteorological stations,inside and adjacent to the study basins,were analyzed and compared to quantify the hydrological processes involved,and to evaluate the role of human activities in changing river discharges.The Inverse Distance Weighted(IDW)interpolation method was used to obtain climatic data coverage from station observations.According to the runoff coefficient equation,the effect of human activities and climate can be expressed by changes in runoff coefficients and changes in precipitation,respectively.Annual runoff coefficients were calculated for the period 1950-2008,according to the correlation between respective hydrological series and regional precipitation.Annual precipitation showed no obvious trend in the upper reaches of the Yellow River but a marked downward trend in the middle and downstream reaches,with declines of 8.8 and 9.8 mm/10 a,respectively.All annual runoff series for the Yellow River basin showed a significant downward trend.Runoff declined by about 7.8 mm/10 a at Sanmenxia and 10.8 mm/10 a at Lijin.The series results indicated that an abrupt change occurred in the late 1980s to early 1990s.The trend of correlations between annual runoff and precipitation decreased significantly at the Yellow River stations,with rates ranging from 0.013/10 a to 0.019/10 a.For the hydrologic series,all precipitation series showed a downward trend in the Yangtze River basin with declines ranging from about 24.7 mm/10 a at Cuntan to 18.2 mm/10 a at Datong.Annual runoff series for the upper reaches of the Yangtze River decreased significantly,at rates ranging from 9.9 to 7.2 mm/10 a.In the middle and lower reaches,the runoff series showed no significant trend,with rates of change ranging from 2.1 to 2.9 mm/10 a.Human activities had the greatest influence on changes in the hydrological series of runoff,regardless of whether the effect was negative or positive.During 1970-2008,human activities contributed to 83% of the reduction in runoff in the Yellow River basin,and to 71% of the increase in runoff in the Yangtze River basin.Moreover,the impacts of human activities across the entire basin increased over time.In the 2000s,the impact of human activities exceeded that of climate change and was responsible for 84% of the decrease and 73% of the increase in runoff in the Yellow River and Yangtze River basins,respectively.The average annual runoff from 1980 to 2008 fell by about 97%,83%,83%,and 91%,compared with 1951-1969,at the Yellow River stations Lanzhou,Sanmenxia,Huayuankou and Lijin,respectively.Most of the reduction in runoff was caused by human activities.Changes in precipitation also caused reductions in runoff of about 3%,17%,17%,and 9% at these four stations,respectively.Falling precipitation rates were the main explanation for runoff changes at the Yangtze River stations Cuntan,Yichang,Hankou,and Datong,causing reductions in runoff of 89%,74%,43%,and 35%,respectively.Underlying surface changes caused decreases in runoff in the Yellow River basin and increases in runoff in the Yangtze River basin.Runoff decreased in arid areas as a result of increased water usage,but increased in humid and sub-humid areas as a result of land reclamation and mass urbanization leading to decreases in evaporation and infiltration.  相似文献   

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