喜马拉雅东构造结上地壳各向异性特征

本文利用雅鲁藏布江下游台阵的16个台站2016年度的近震数据,通过横波窗内的横波分裂测量,在各台站总计得到369个有效的横波分裂参数对,分析得出喜马拉雅东构造结上地壳各向异性特征。空间上,各台站的快波偏振优势方向整体上自西向东由近EW向,转为NE向,然后转向近NS或NNE向,最后转向NW向。大部分靠近或位于活动断裂带上的台站的快波偏振优势方向与断裂的走向一致,主要体现在墨竹工卡断裂上的ZOS台,雅鲁藏布江断裂上的WOL,NYG,ZIB和DOJ台站,墨脱断裂上的BEB和DEX台站,以及迫龙—旁辛断裂上的BAX和DAM台站;而距离雅鲁藏布江断裂西段和东段各有一定距离的LAD和YIG台站,以及位于雅鲁藏布江断裂东段与嘉利断裂交会处的TOM台的快波偏振优势方向与断裂走向存在一定角度,但其与喜马拉雅东构造结主压应力场方向NNE向基本一致。上地壳各向异性整体体现了结构控制和应力控制的特征,但各台站的横波分裂参数并未表现出随时间的规律变化特征,这可能与2016年研究区地震活动强度较弱有关。研究区各台站间存在较大的横波分裂参数差异和自身离散度,反映出东构造结复杂的构造特征和剧烈的变形作用。      

GEOLOGICAL EVIDENCES OF LATE QUATERNARY ACTIVITY OF MOTUO FAULT IN EASTERN HIMALAYAN SYNTAXIS

Motuo Fault locates at the east of Namjagbarwa Peak in eastern Himalayan syntaxis.Based on the remote sensing interpretation,the previous work,and with the field investigation,this paper obtains the spatial distribution and movement characteristics of Motuo Fault in China,and geological evidences of late Quaternary activity.Two trenches in Motuo village and Dongdi village located in Yalung Zangbo Grand Canyon reveal that the Motuo Fault dislocates the late Quternary stratum and behaves as a reverse fault in Motuo village and normal fault in Dongdi village.Motuo Fault is dominated by left-lateral strike-slip associated with the faulted landforms,with different characteristics of the tilting movement in different segments.The trench at Didong village reveals the latest stratum dislocated is~2780±30 a BP according to radiocarbon dating,implying that Motuo Fault has ruptured the ground surface since late Holocene.The movement of left-lateral strike-slip of Motuo Fault is related to the northward movement process of Indian pate.     

GEOMORPHOLOGY OF THE GYARING CO FAULT ZONAL DRAINAGE SYSTEM AND ITS STRUCTURAL IMPLICATIONS

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau. The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau. The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone. The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co. From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin. Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics. In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement. In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images (Landsat and GeoEye) and field work. We acquired basic geomorphic parameters of 153 sub-basin (such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve. Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault. Southern drainage basins' relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity. Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east. By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins. Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift. The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.     

GEOMORPHOLOGICAL CHARACTERISTICS OF DAQINGSHAN DRAINAGE AREA IN THE NORTHERN MARGIN OF HETAO BASIN

The Daqingshan Fault located in the northern margin of the Hetao Basin has experienced intensive activity since late Quaternary, which is of great significance to the molding of the present geomorphology. Since basin geomorphological factors can be used to reflect regional geomorphological type and development characteristics, the use of typical geomorphology characteristics indexes may reveal the main factors that control the formation of topography. In recent years, more successful research experience has been accumulated by using hypsometric integral(HI) values and channel steepness index(k_sn)to quantitatively obtain geomorphic parameters to reveal regional tectonic uplift information. The rate of bedrock uplifting can be reflected by channel steepness index, the region with steep gradient has high rate of bedrock uplifting, while the region with slower slope has low rate of bedrock uplifting. The tectonic uplift can shape the geomorphic characteristics by changing the elevation fluctuation of mountains in study area, and then affect the hypsometric integral values distribution trend, thus, the HI value can be used to reflect the intensity of regional tectonic activity, with obvious indicating effect. Knick point can be formed by fault activity, and the information of knick point and its continuous migration to upstream can be recorded along the longitudinal profile of stream. Therefore, it is possible and feasible to obtain the information of tectonic activity from the geomorphic characteristics of Daqinshan area. The research on the quantitative analysis of regional large-scale tectonic activities in the Daqingshan area of the Yellow River in the Hetao Basin is still deficient so far. Taking this area as an example, based on the method of hypsometric integral(HI) and channel steepness index(k_sn), we use the DEM data with 30m resolution and GIS spatial analysis technology to extract the networks of drainage system and seven sub-basins. Then, we calculate the hypsometric integral(HI) values of each sub-basin and fit its spatial distribution characteristics. Finally, we obtain the values of channel steepness index and its fitting spatial distribution characteristics based on the improved Chi-plot bedrock analysis method. Combining the extraction results of geomorphic parameters with the characteristics of fault activity, we attempt to explore the characteristics of drainage system development and the response of stream profile and geomorphology to tectonic activities in the Daqingshan section of the Yellow River Basin. The results show that the values of the hypsometric integral in the Daqingshan drainage area are medium, between 0.5~0.6, and the Strahler curve of each tributary is S-shaped, suggesting that the geomorphological development of the Daqingshan area is in its prime, and the tectonic activity and erosion is strong. Continuous low HI value is found in the tectonic subsidence area on the hanging wall of the Daqingshan Fault. The distribution characteristics of the HI value reveal that the Daqingshan Fault controls the geomorphic difference between basin and mountain. Longitudinal profiles of the river reveal the existence of many knick points. The steepness index of river distributes in high value along the trend of mountain which lies in the tectonic uplift area on the footwall of the Daqingshan Fault. It reflects that the bedrock uplift rate of Daqingshan area is faster. The distribution characteristics of the channel steepness index show that the uplift amplitude of Daqingshan area is strong and the bedrock is rapidly uplifted, which is significantly different from the subsidence amplitude in the depression basin at the south margin of the fault, indicating that the main power source controlling the basin mountain differential movement comes from Daqingshan Fault. Based on the comparison and analysis on tectonic, lithology and climate, there is no obvious corresponding relationship between the difference of rock erosion resistance and the change of geomorphic parameters, and the precipitation has little effect on the geomorphic transformation of Daqingshan area, and its contribution to the geomorphic development is limited. Thus, we think the lithology and rainfall conditions have limited impact on the hypsometric integral, longitudinal profiles of the river and channel steepness index. Lithology maybe has some influences on the channel knick points, while tectonic activity of piedmont faults is the main controlling factor that causes the unbalanced characteristics of the longitudinal profile of the channel and plays a crucial role in the development of the channel knick points. So, tectonic activity of the Daqingshan Fault is the main factor controlling the uplift and geomorphic evolution of the Daqingshan area.     

阿尔泰山东缘主要活动断裂影像特征分析

文中采用遥感资料,对阿尔泰山东缘的主要活动断裂———科布多(Hovd)断裂与哈尔乌苏湖(Har-Nuur)断裂进行研究,从地貌特征上对断裂进行详细分析,揭示其几何学和运动学特征。初步研究表明阿尔泰山东缘的活动断裂规模、滑动速率和强地震活动并不弱于其西南缘。其中科布多断裂走向NNW,右旋走滑,长约600km,中更新世(Q2p)以来最大水系右旋位错约9.0km,滑动速率可达3.8～12.3mm/a,平均滑动速率约7.8mm/a;哈尔乌苏湖断裂走向NNW,右旋走滑,长约480km,全新世以来活动性明显增强,第四纪洪积扇上发现有最新的断裂迹象。阿尔泰山东缘的新构造运动与强地震活动,除了与印度-欧亚板块碰撞作用有关外,可能还与局部地区的动力学过程有关     

QUANTITATIVE STUDY OF FAULT ACTIVITY BASED ON HIGH-PRECISION AIRBORNE LiDAR DATA: A CASE OF XIAOHONGSHAN FAULT IN XIANGSHAN-TIANJINGSHAN FAULT ZONE

High-precision and high-resolution topography are the basis of quantitative study of active tectonics. Traditional methods are mainly interpreted from the remote sensing image and can only obtain two-dimensional, medium-resolution DEM(5~10m grid unit)or local three-dimensional surface deformation characteristics. A combination of offset and micro-relief information is essential for understanding the long-term rupture pattern of faults, such as in seismic hazard evaluation. The recently developed high-resolution light detection and ranging(LiDAR)technology can directly carry out high-precision and omni-directional three-dimensional measurement of the landform, and provide fine geomorphologic data for the study of active tectonics, which is helpful to deepen the understanding of surface rupture process and fault activity characteristics. In this study, we take part of the Xiaohongshan Fault, the western segment of Xiangshan-Tianjingshan Fault located in Gansu Province(NE Tibet), as an example of how LiDAR data may be used to improve the study of active faults. Using the airborne LiDAR technology, we obtain the three-dimensional surface deformation characteristics with high accuracy and establish the three-dimensional topographic model of the fault geomorphic. A high-resolution digital elevation model(DEM)of the Jingtai-Xiaohongshan Fault was extracted based on high-precision LiDAR data. Then the faulted geomorphic markers(gullies, ridges and terraces)were measured in detail along the fault, and different offset clusters and long-term sliding vector of different segments of the fault were finally acquired. We obtained the 82 horizontal displacements and 62 vertical displacements of geomorphic markers. According to the offset amounts, we observed peaks in the histogram by using the method of cumulative offset probability density and interpreted that each peak may represent an earthquake that ruptured the Xiaohongshan Fault. The results show that the horizontal and vertical displacements fall into five clusters, and the smallest cluster may indicate the coseismic slip of the most recent earthquake, while the other clusters may represent the slip accumulation of multiple preceding earthquakes. The sliding vectors constrained by the horizontal and vertical displacement of several typical geomorphic markers show obvious differences on different segments of the fault. The results show that the fault segment is divided into three segments from west to east, which indicates that the fault activity is not uniform along the fault.     

ANALYSIS OF EVOLUTION OF THE RIYUESHAN FAULT SINCE LATE PLEISTOCENE USING STRUCTURAL GEOMORPHOLOGY

The northeastern margin of Tibetan plateau is an active block controlled by the eastern Kunlun fault zone, the Qilian Shan-Haiyuan fault zone, and the Altyn Tagh fault zone. It is the frontier and the sensitive area of neotectonic activity since the Cenozoic. There are widespread folds, thrust faults and stike-slip faults in the northeastern Tibetan plateau produced by the intensive tectonic deformation, indicating that this area is suffering the crustal shortening, left-lateral shear and vertical uplift. The Riyueshan Fault is one of the major faults in the dextral strike-slip faults systems, which lies between the two major large-scale left-lateral strike-slip faults, the Qilian-Haiyuan Fault and the eastern Kunlun Fault. In the process of growing and expanding of the entire Tibetan plateau, the dextral strike-slip faults play an important role in regulating the deformation and transformation between the secondary blocks. In the early Quaternary, because of the northeastward expansion of the northeastern Tibetan plateau, tectonic deformations such as NE-direction extrusion shortening, clockwise rotation, and SEE-direction extrusion occurred in the northeastern margin of the Tibetan plateau, which lead to the left-lateral slip movement of the NWW-trending major regional boundary faults. As the result, the NNW-trending faults which lie between these NWW direction faults are developed. The main geomorphic units developed within the research area are controlled by the Riyueshan Fault, formed due to the northeastward motion of the Tibet block. These geomorphic units could be classified as:Qinghai Lake Basin, Haiyan Basin, Datonghe Basin, Dezhou Basin, and the mountains developed between the basins such as the Datongshan and the Riyueshan. Paleo basins, alluvial fans, multiple levels of terraces are developed at mountain fronts. The climate variation caused the formation of the geomorphic units during the expansion period of the lakes within the northeastern Tibetan plateau. There are two levels of alluvial fans and three levels of fluvial terrace developed in the study area, the sediments of the alluvial fans and fluvial terraces formed by different sources are developed in the same period. The Riyueshan Fault connects with the NNW-trending left-lateral strike-slip north marginal Tuoleshan fault in the north, and obliquely connects with the Lajishan thrust fault in the south. The fault extends for about 180km from north to south, passing through Datonghe, Reshui coal mine, Chaka River, Tuole, Ketu and Xicha, and connecting with the Lajishan thrusts near the Kesuer Basin. The Riyueshan Fault consists of five discontinuous right-step en-echelon sub-fault segments, with a spacing of 2~3km, and pull-apart basins are formed in the stepovers. The Riyueshan Fault is a secondary fault located in the Qaidam-Qilian active block which is controlled by the major boundary faults, such as the East Kunlun Fault and the Qilian-Haiyuan Fault. Its activity characteristics provide information of the outward expansion of the northeastern margin of Tibet. Tectonic landforms are developed along the Riyueshan Fault. Focusing on the distinct geomorphic deformation since late Pleistocene, the paper obtains the vertical displacement along the fault strike by RTK measurement method. Based on the fault growth-linkage theory, the evolution of the Riyueshan Fault and the related kinetic background are discussed. The following three conclusions are obtained:1)According to the characteristics of development of the three-stage 200km-long steep fault scarp developed in the landforms of the late Pleistocene alluvial fans and terraces, the Riyueshan Fault is divided into five segments, with the most important segment located in the third stepover(CD-3); 2)The three-stage displacement distribution pattern of the Riyueshan Fault reveals that the fault was formed by the growths and connections of multiple secondary faults and is in the second stage of fault growth and connection. With CD-3 as the boundary, the faults on the NW side continue to grow and connect; the fault activity time on the SE side is shorter, and the activity intensity is weaker; 3)The extreme value of the fault displacement distribution curve indicates the location of strain concentration and stress accumulation. With the stepover CD-3 as the boundary, the stress and strain on NW side are mainly concentrated in the middle and fault stepovers. The long-term accumulation range of stress on the SE side is relatively dispersed. The stress state may be related to the counterclockwise rotation inside the block under the compression of regional tectonic stress.     

Testing geomorphic signal of active normal faulting: The case of the Cittanova Fault (Calabria,southern Italy)

Extracting tectonic signals from the landscape is an important challenge for constraining the style and rate of deformation associated with active faults, especially where their displacement history cannot be independently determined. Based on previous paleoseismological data coupled with new geomorphological field work and ¹⁴C dating of geomorphic markers, we analysed the geomorphic signal of the along‐strike differential throw of the Cittanova Fault in southern Calabria (Italy), the recent activity of which is already well documented and constrained. Through DTM‐derived stream power law parameters (SL and χ), we provide evidence of drainage network disequilibrium and reorganization in response to fault growth and deformation style. Furthermore, a methodological test of the reliability of the χ metric as a proxy for the differential throw along the strike of active normal faults provided good preliminary results, consistent with a strong inverse linear correlation with fault throw. Copyright © 2018 John Wiley & Sons, Ltd.     

罐罐岭断裂带最新活动特征

断层的最新活动时代以及分段特征一直在重大工程安全性评价中具有特别重要的意义。在解决黄河黑山峡地震地质问题时,通过对罐罐岭断裂带的航片解译、野外追踪调查、地形地貌测量和古地震槽探资料研究,从而确定了该断裂带的活动时代以及分段特征。该断裂带发育在青藏块体东北缘,是中卫-同心弧形活动构造带的一部分,总体走向近EW,长约60km,分为5条不连续的次级断层,各段成左阶羽列,晚第四纪以来表现出强烈的左旋走滑兼挤压逆冲活动特征。断层错断了一系列山脊、小冲沟和阶地等,发育醒目的断层陡坎。研究发现,罐罐岭断裂最新一次地震破裂发生在距今700～1200a之间,最大同震位移位于罐罐岭附近,全新世以来水平左旋最大错距达6m     

NEW DISCOVERY OF RESHUI-TAOSTUO RIVER FAULT IN DULAN,QINGHAI PROVINCE AND ITS IMPLICATIONS

The 40km-long, NEE trending Reshui-Taostuo River Fault was found in the southern Dulan-Chaka highland by recent field investigation, which is a strike-slip fault with some normal component. DEM data was generated by small unmanned aerial vehicle(UAV)on key geomorphic units with resolution<0.05m. Based on the interpretation and field investigation, we get two conclusions:1)It is the first time to define the Reshui-Taostuo River Fault, and the fault is 40km long with a 6km-long surface rupture; 2)There are left-handed dislocations in the gullies and terraces cut by the fault. On the high-resolution DEM image obtained by UAV, the offsets are(9.3±0.5) m, (17.9±1.5) m, and(36.8±2) m, measured by topographic profile recovery of gullies. The recovery measurements of two terraces present that the horizontal offset of T₁/T₀ is(18.2±1.5) m and the T₂/T₁ is (35.8±2) m, which is consistent with the offsets from gullies. According to the historical earthquake records, a M5 3/4 earthquake on April 10, 1938 and a M_S5.0 earthquake on March 21, 1952 occurred at the eastern end of the surface rupture, which may be related to the activity of the fault. By checking the county records of Dulan and other relevant data, we find that there are no literature records about the two earthquakes, which is possibly due to the far distance to the epicenter at that time, the scarcity of population in Dulan, or that the earthquake occurred too long ago that led to losing its records. The southernmost ends of the Eastern Kunlun Fault and the Elashan Fault converge to form a wedge-shaped extruded fault block toward the northwest. The Dulan Basin, located at the end of the wedge-shaped fault block, is affected by regional NE and SW principal compressive stress and the shear stress of the two boundary faults. The Dulan Basin experienced a complex deformation process of compression accompanying with extension. In the process of extrusion, the specific form of extension is the strike-slip faults at each side of the wedge, and there is indeed a north-east and south-west compression between the two controlling wedge-shaped fault block boundary faults, the Eastern Kunlun and Elashan Faults. The inferred mechanism of triangular wedge extrusion deformation in this area is quite different from the pure rigid extrusion model. Therefore, Dulan Basin is a wedge-shaped block sandwiched between the two large-scale strike-slip faults. Due to the compression of the northeast and southwest directions of the region, the peripheral faults of the Dulan Basin form a series of southeast converging plume thrust faults on the northeast edge of the basin near the Elashan Fault, which are parallel to the Elashan Fault in morphology and may converge with the Elashan Fault in subsurface. The southern marginal fault of the Dulan Basin(Reshui-Taostuo River Fault)near the Eastern Kunlun fault zone is jointly affected by the left-lateral strike-slip Eastern Kunlun Fault and the right-lateral strike-slip Elashan Fault, presenting a left-lateral strike-slip characteristic. Meanwhile, the wedge-shaped fault block extrudes to the northwest, causing local extension at the southeast end, and the fault shows the extensional deformation. These faults absorb or transform the shear stress in the northeastern margin of the Tibet Plateau. Therefore, our discovery of the Dulan Reshui-Taostuo River Fault provides important constraints for better understanding of the internal deformation mode and mechanism of the fault block in the northeastern Tibetan plateau. The strike of Reshui-Taostuo River Fault is different from the southern marginal fault of the Qaidam Basin. The Qaidam south marginal burial fault is the boundary fault between the Qaidam Basin and the East Kunlun structural belt, with a total length of ~500km. The geophysical data show that Qaidam south marginal burial fault forms at the boundary between the positive gravity anomaly of the southern East Kunlun structural belt and the negative gravity anomaly gradient zone of the northern Qaidam Basin, showing as a thrust fault towards the basin. The western segment of the fault was active at late Pleistocene, and the eastern segment near Dulan County was active at early-middle Pleistocene. The Reshui-Taostuo River Fault is characterized by sinistral strike-slip with a normal component. The field evidence indicates that the latest active period of this fault was Holocene, with a total length of only 40km. Neither remote sensing image interpretation nor field investigation indicate the fault extends further westward and intersects with the Qaidam south marginal burial fault. Moreover, it shows that its strike is relatively consistent with the East Kunlun fault zone in spatial distribution and has a certain angle with the burial fault in the southern margin of Qaidam Basin. Therefore, there is no structural connection between the Reshui-Taostuo River Fault and the Qaidam south marginal burial fault.     

黄土覆盖的阶地陡坎附近渭河断裂活断层探测

陕西咸阳渭河北岸窑店、石何杨、杜家堡渭河断裂活断层探测结果表明,对于有黄土覆盖的、与阶地陡坎重合的活断层探测,要综合采用地形地貌分析、浅层人工地震、钻探和探槽等方法进行。特别是对于钻孔探测,要深、中、浅孔结合。首先用中、深孔确定断层在深部的位置,再用浅孔确定断层在近地表的位置和活动性。由于河流侵蚀,阶地陡坎区的河流相沉积地层是倾斜的,风成的古土壤层披盖在已有的倾斜地层上亦呈倾斜状态,因此,用以上地层判断断层的位置和活动量时,钻孔孔距一定要小,以2～3m为宜,孔距太大,会把侵蚀形成的已有陡坎高度加入断层的错距中,严重放大断层的错动量。探测结果表明,渭河断裂在窑店、石何杨、杜家堡等处与Ⅲ级阶地陡坎重合。该断裂在阶地陡坎上的活动量很小,错断晚更新世第1古土壤层1～2m,远小于2个阶地面的高差。可见,以前认为S1错距4.8m、17.94m是不准确的。     

钻探揭示的黄河断裂北段活动性和滑动速率

黄河断裂是银川盆地内展布最长、切割最深的一条深大断裂,也是银川盆地的东边界。由于其北段呈隐伏状,因此,该段的活动性和滑动速率长期未知,影响了对盆地演化和地震危险性的认识。文中选择具有石油地震勘探基础的陶乐镇为研究场点,以人工浅层地震勘探结果为依据,在黄河断裂北段布设了一排钻孔联合剖面,并对标志层进行年代测试,获得了断裂的活动时代和滑动速率。结果表明,黄河断裂北段在晚更新世末期或全新世有过活动,在（28.16±0.12）ka BP 以来的累积位移为0.96m,晚第四纪以来的平均滑动速率为0.04mm/a,该值明显低于南段灵武断层（0.24mm/a）;尽管向下切割了莫霍面,黄河断裂晚第四纪活动强度和发震能力均要低于切割相对浅的贺兰山东麓断裂;黄河断裂可能在新生代之前已经强烈活动并深切莫霍面,新生代以来,银川盆地的构造活动迁移分解到以贺兰山东麓断裂为主的多条断裂之上,地壳双层伸展模型可解释银川盆地现今深浅部构造活动间的联系。     

龙门山南段前缘地区活褶皱-逆断层运动学机制——以芦山地震为例

2013年4月20日发生在龙门山南段的芦山MS7.0地震是继发生在龙门山中北段的汶川MS8.0地震之后的又一次强震。本文通过震后地表变形特征、余震分布、震源机制解、石油地震勘探剖面、历史地震数据等资料,结合前人对龙门山南段主干断裂、褶皱构造特征的研究以及野外实地考察,应用活动褶皱及"褶皱地震"的相关理论,初步分析芦山地震的发震构造模式。认为芦山地震为典型的褶皱地震,发震断裂为前山或山前带一隐伏断裂。构造挤压产生的地壳缩短大部分被褶皱构造吸收。认为龙门山南段前缘地区具有活褶皱-逆断层的运动学特征,表明龙门山逆冲作用正向四川盆地内部扩展。     

海原断裂带中东段地貌差异及其成因探讨

以定量化地形因子为切入点的构造地貌学方法已成为活动构造研究的有效手段,被广泛用于定性或半定量解析地貌对新构造运动的响应及其演化过程。针对海原断裂带中东段现今地貌差异,以SRTM 90m分辨率DEM为基础,利用ArcGIS软件和Matlab程序脚本,提取了海原断裂带中东段高程、坡度、地形起伏、地形侵蚀以及河流陡峭系数等地形因子。从空间分布上看,上述各项地形因子沿断裂走向均呈现 “西高东低”的整体分布特征。西段海拔高、坡度陡、起伏大、侵蚀强、抬升快,中段和东段海拔低、坡度缓、起伏小、侵蚀弱、抬升慢,此外,在断裂带的东南尾端呈略微增加趋势,达到小范围内的峰值。在此基础上,通过对比分析地形因子与年降水量、基岩岩性,初步探讨了构造与降水、岩性等因素对地形地貌的控制作用,认为不同降水条件对地貌后期改造起显著作用,基岩岩性与现今地貌之间并无显著关系,该区域地貌类型主要受构造抬升差异所控制。沿断裂带走向上的现今地貌差异表明,西段处于相对快速的构造隆升和强挤压造山构造背景,中段由于受到黄河下切及河流冲积作用影响,地貌参数记录的抬升特征并不显著,而东段则反映出大型断裂带尾端挤压调整效应。     

南迦巴瓦构造结西侧里龙断裂晚第四纪活动特征

本文通过卫星影像解译、地质地貌调查、地质探槽开挖、断错地貌测量和样品年代学测试,对南迦巴瓦构造结西侧的里龙断裂晚第四纪活动特征进行了分析和研究,结果表明:里龙断裂是一条以右旋走滑活动为主、兼有挤压逆冲的北北西向断裂,其最新活动时代为全新世;该断裂晚第四纪以来的平均水平滑动速率为3-4mm/a,平均垂直滑动速率为0.10-0.15mm/a。研究还表明,南迦巴瓦构造结晚第四纪以来的向北俯冲运动已经停止,喜马拉雅东构造结地区的构造变形主要受阿萨姆构造结的俯冲影响。     

LIMITATION OF CURRENT TECTONIC DEFORMATION MODES IN THE WESTERN MARGIN OF ORDOS BASED ON SEISMIC ACTIVITY CHARACTERISTICS

Due to the interaction between the Tibetan plateau, the Alxa block and the Ordos block, the western margin of Ordos(33.5°~39°N, 104°~108°E)has complex tectonic features and deformation patterns with strong tectonic activities and active faults. Active faults with different strikes and characteristics have been developed, including the Haiyuan Fault, the Xiangshan-Tianjingshan Fault, the Liupanshan Fault, the Yunwushan Fault, the Yantongshan Fault, the eastern Luoshan Fault, the Sanguankou-Niushoushan Fault, the Yellow River Fault, the west Qinling Fault, and the Xiaoguanshan Fault. In this study, 7 845 earthquakes(M≥1.0)from January 1st, 1990 to June 30th, 2018 were relocated using the double-difference location algorithm, and finally, we got valid locations for 4 417 earthquakes. Meanwhile, we determined focal mechanism solutions for 54 earthquakes(M≥3.5)from February 28th, 2009 to September 2nd, 2017 by the Cut and Paste(CAP)method and collected 15 focal mechanism solutions from previous studies. The spatial distribution law of the earthquake, the main active fault geometry and the regional tectonic stress field characteristics are studied comprehensively. We found that the earthquakes are more spatially concentrated after the relocation, and the epicenters of larger earthquakes(M≥3.5) are located at the edge of main active faults. The average hypocenter depth is about 8km and the seismogenic layer ranges from 0 to 20km. The spatial distributions and geometry structures of the faults and the regional deformation feature are clearly mapped with the relocated earthquakes and vertical profiles. The complex focal mechanism solutions indicate that the arc-shaped tectonic belt consisting of Haiyuan Fault, Xiangshan-Tianjingshan Fault and Yantongshan Fault is dominated by compression and torsion; the Yellow River Fault is mainly by stretching; the west Qinling Fault is characterized by shear and compression. The structural properties of the fault structure are dominated by strike-slip and thrust, with a larger strike-slip component. The near-north-south Yellow River Fault is characterized by high angle NW dipping and normal fault motion. Based on small earthquake relocation and focal mechanism solution results, and in combination with published active structures and geophysical data in the study area, it is confirmed that the western margin of Ordos is affected by the three blocks of the Tibetan plateau, the Alax and the Ordos, presenting different tectonic deformation modes, and there are also obvious differences in motion among the secondary blocks between the active faults. The area south of the Xiangshan-Tianjingshan Fault has moved southeastward since the early Quaternary; the Yinchuan Basin and the block in the eastern margin of the Yellow River Fault move toward the SE direction.     

日喀则城市活断层地球物理勘探方法和成果

日喀则地质资料匮乏,地球物理勘探资料更加稀缺,该地区在此之前没有开展过地震勘探的工作.本文针对日喀则地区活动断裂,采用夯源为人工震源的浅层地震勘探方法,结合小折射调查低速层,详细讨论工作中的关键性技术问题;提出在该地区地质条件下实施隐伏断裂勘探时的地震仪器选择、方案设计、参数选取、数据处理、断层识别的基本方法;查明拉堆—乃东断裂、抓各落断裂、毕定—甲舍拉断裂、甲岗—谢通门断裂的走向、产状、上断点埋深及其在地表的垂直投影位置等主要参数.为日喀则地区的深浅构造关系等研究提供基础资料,填补该地区地球物理勘探资料的空白.     

Digital elevation models derived from airborne laser scanning point clouds: appropriate spatial resolutions for multi‐temporal characterization and quantification of geomorphological processes

Digital terrain models (DTMs) are a standard data source for a variety of applications. DTM differencing is also widely used for detection and quantification of topographic changes. While several investigations have been made on the accuracy of DTMs, calculated from different kinds of input data, little has been published on the error of DTM differencing, specifically for the quantification of geomorphological processes. In this study, an extensive, multi‐temporal set of airborne laser scanning (ALS) data is used to investigate the accuracy of topographic change calculations in a high alpine environment, caused by different geomorphic processes. Differences from DTMs with cell sizes ranging from 0.25 m to 10 m were calculated and compared to very accurate point‐to‐point calculations for a variety of processes and in nearby stable areas which show no significant surface changes. The representativeness of the DTM differences is then compared to the terrain slope and surface roughness of the investigated areas to show the influence of these parameters on the errors in the differences. Those errors are then taken into account for analyses of the applicability of different cell sizes for the investigation of geomorphic processes with different magnitudes and over different time periods. The analyses show that the error of DTM differences increases with lower point densities and higher roughness and slope values. The higher the error, the greater the differences between two elevation datasets have to be in order to quantify certain morphodynamic processes. Lower point densities and higher roughness and slope values require greater process rates or longer time intervals in order to obtain valid results. Copyright © 2013 John Wiley & Sons, Ltd.     

依兰—伊通断裂北段断层氢气的地球化学特征分析

2017—2018年在依兰—伊通断裂黑龙江段开展断层氢气调查工作,沿断裂选取8个剖面进行跨目标断层观测及土壤氢气采样。结果表明：①断层氢气浓度常存在异常变化;②不同类型的断层,氢气浓度异常变化幅度没有明显差异;③走滑断层异常特征一般为断层两侧低、中间高,呈现“低—高—低”的特点;倾滑断层异常特征一般为断层的上盘略高、下盘略低;④断层氢气排放不仅受微观局部断层的影响,更受宏观的地震活动性大环境的影响。