洪积扇顶部活动走滑断裂的断错地貌分析 ——以新疆塔城盆地东缘阿合别斗河冲洪积扇为例

依据山前洪积扇顶部的扇形地形和向下游方向逐渐降低的地形特征,文中首先分析了断层面直立、向河流上游倾斜、向河流下游倾斜3种条件下左旋走滑断层错动在洪积扇顶部形成的断层陡坎的坡向和高度变化.其次,分析了左旋逆走滑断层、左旋正走滑断层在不同断层倾向条件下,断层错动在洪积扇顶部形成的断层陡坎的坡向和高度变化.利用无人机实测地形...     

基于高分辨率地形数据的断层陡坎形态演化与强震活动关系研究

断层陡坎的形态可以保存有关断层带上地震活动等重要信息,陡坎上的坡折就是多次地震发生后陡坎演化留下的微地貌信息。以往研究选取的断层陡坎多为位于标准阶地面上的断层陡坎,而断层沿线地貌现象复杂,因此需要探索一种具有普适性的断层陡坎形态研究方法。本研究将常见的断层陡坎剖面按照形态划分为三种类型,以LiDAR技术获取的0.2m分辨率DEM数据为基础,选择了8个属于不同断层陡坎剖面类型的实验区,每个实验区采集不少于20条剖面,通过窗口检验确定研究区最佳数据获取移动窗口为7个像元并计算每条剖面的坡度值,通过坡度约束限定陡坎范围,进而识别坡折并获取坡折信息。对坡折信息进行概率密度统计,根据概率密度统计图中的峰值个数确定强震事件的次数。结果显示,陡坎形态研究结果与古地震探槽结果表现出较好的一致性,表明本文提出的陡坎形态研究方法可以适用于不同类型断层陡坎来确定强震事件次数。     

基于LiDAR数据开展活动断层填图的实验研究——以新疆独山子背斜-逆冲断裂带为例

机载LiDAR技术为描绘活动构造相关构造地貌和最新的地表形变提供更精确的基础数据。如何将LiDAR新技术、新数据应用于活动构造填图和活动断层地震危险性评价等方面,是今后活动构造研究领域的一个重要的发展方向。文中以新疆天山北麓的独山子背斜-逆冲断裂带为试验区,开展了基于LiDAR数据的活动构造填图实验研究。首先,采用机载LiDAR技术进行数据采集,获得点云密度为6.6个/m2、平均点间距为0.39m的LiDAR原始数据;其次,利用试验区内12个测量精度可达mm级的GPS静态测量点评估LiDAR的相对垂直精度为0.12m、均方差值为0.078m;最后,对密度为6.4个/m2的地面点云数据进行DEM最佳分辨率评估,利用反距离权重算法获得0.5m分辨率的数据高程模型(DEM)。该分辨率的DEM数据足以完成独山子背斜-逆冲断裂带的精细构造地貌特征的确定以及高精度的空间解译。文中仅使用DEM可视化工具从不同虚拟的视角、不同色度或其他处理方式来识别微构造地貌、划分地貌面和确定断层位置等,宏观上获得与前人通过航片解译和野外调查一致的断裂分布特征,微观上较前者具有更高的精细程度。此外,数据采集、数据质量检验、数据处理及数据应用等技术和方法适用于其他能够获得LiDAR地形数据的活动断裂研究工作。     

地形起伏对基于地震波形的浅源地震深度反演影响——以2017年9月3日朝鲜M6.3事件为例

震源深度是核试验以及塌陷等浅源地震研究中的关键参数,可以为事件成因分析提供关键信息.然而朝鲜核试验区域地形起伏较大,地形效应可能对震源深度反演的结果造成影响.本文基于理论地震图进行测试,研究了地形起伏对震源深度反演的影响.发现震源深度小于2km时,不考虑地形影响,反演得到的震源深度会系统偏浅0.2km左右.然后利用MDJ2速度结构模型,我们反演了2017年9月3日朝鲜M6.3事件的震源参数,结果显示震源深度约为0.8km.进一步基于带地形的格林函数重新反演了该事件的震源深度,发现在1km处波形拟合结果较好.不同速度模型测试结果显示该事件的震源深度反演误差约为1km.案例研究表明,基于层状均匀速度模型,利用区域地震波形资料反演的震源深度可以为浅源事件成因分析提供关键约束.     

山体隆升历史与地貌演化过程的数值模拟约束——以青藏高原东北缘河西走廊中段的周边年轻上升山地为例

地貌演化数值模型是分析构造-气候相互作用,再现地表形态演化过程的重要工具.本文利用地貌演化数值模型模拟了青藏高原东北缘河西走廊中段周边山体的演化过程.河西走廊气候干旱,外动力过程相似,但走廊中段南北两侧各山体间的形态特征存在明显差异(北侧山地:金塔南山东段、金塔南山西段、合黎山;南侧山地:榆木山).首先,各山体内选取典型区域分析了真实地形的特征指标(准周期性谷间距、地形高差与出水口数量);其次利用Landlab平台构建了典型区域的地貌演化数值模型,并通过数值实验正演了各山体地形的演化过程;最后将真实地形与不同时间节点的模拟地形进行比对,以准周期性谷间距等地形特征指标为判识标准,推断了河西走廊中段山体开始强烈隆升的年代和抬升速率.模拟结果与区域已发表的地质地貌证据在年轻上升山地(未达到稳定状态的幼年期地形)地区呈现较好的一致性,表明地貌演化数值模型结合地形特征指标是约束年轻上升山地强烈隆升年代和速率的可靠工具.本文提出的全新研究思路与方法有望在年轻上升山地推广并成为构造地貌学研究的常用手段.     

岩性和侵蚀基准面对构造活跃区河流地貌演化的影响——以青藏高原东北缘老虎山和哈思山地区为例

在构造活跃地区,前人研究着重考虑了构造活动对河流地貌演化的影响,而岩性和局部侵蚀基准面的作用较少被关注.本文以青藏高原东北部海原断裂的影响地区为例,通过对水系形态及地貌特征指数(陡峭指数、河谷宽高比、x等)的计算等,分析了裂点发育和水系重组等不同空间尺度下的河流地貌演化过程.结果 显示,以老虎山和哈思山为中心,分别发育...     

2种基于Matlab平台的断层位移测量软件对比分析——以阿尔金断裂东段为例

测量地表的断层位移对于恢复同震位移和长期累积位移分布非常重要。近年来,编程软件的不断更新和高精度地形数据(例如激光雷达探测与测量和无人机航空摄影测量)的积累为测量密集的断层位移数据提供了前所未有的机会。文中主要对2款比较常用的断层位移测量软件——La Di Caoz和3D_Fault_Offsets进行介绍。首先,基于阿尔金断层东段石包城铁矿附近的1个位移测量实例分别说明这2款软件的工作原理;然后,分别对比和总结了其在目标地貌标志、界面、输入文件类型、自动化程度、适应性、可重复性和输出文件类型等方面的差异和优劣;最后,基于2种软件在阿尔金断裂东段获得的2组断层位移数据的相关性研究,探讨2种软件的结果是否相互验证,以及线性地貌标志的弯曲程度对测量结果的影响。通过对2种软件所得测量结果与野外地质测量结果的对比,以及对软件测量结果的可靠性和地质意义的讨论,我们认为目前这2款软件都存在自动化程度较低和人为因素影响较大等不足之处,高度自动化和人工智能的引入可能是断层位移测量方法的发展方向。     

基于高精度LiDAR数据的断裂活动习性精细定量——以香山-天景山断裂景泰小红山段为例

高精度、高分辨率的地形地貌数据是活动构造定量研究的重要基础数据。传统研究方法中,通过航卫片或遥感影像解译只能获取二维平面特征,中等分辨率DEM(5～10m网格单元)只适用于大尺度三维地貌特征的提取。激光雷达测量(Light Detection and Ranging,Li DAR)技术可直接对地貌进行高精度、全方位的三维地表形态测量,为活动构造研究提供了精细的地貌形态数据,有助于深化对断裂带地表破裂过程和断裂活动特性的理解。文中选取青藏高原东北缘香山-天景山断裂带西段的景泰小红山断裂中一段断错地貌明显的断裂段作为研究对象,基于高精度Li DAR数据生成了景泰小红山断裂0. 3m高分辨率的数字高程模型(DEM),沿断裂带详细识别并测量了地貌标志(冲沟、山脊和阶地)的断错位移,获得了地貌标志的82个水平位移和62个垂直位移,并分析了不同方向上的位移丛集特征。结果显示,沿断裂的水平与垂直位移均可识别出5个丛集,其中最小丛集可能指示最新一次地震的同震位移,而其它位移丛集则反映了断裂带多次地震活动累积的结果。通过对多个断错标志的水平和垂直位移合成的滑动矢量进行分析,可以看出该断层段的运动习性具有...     

EXTRACTING FEATURES OF ALLUVIAL FAN AND DISCUSSING LANDFORMS EVOLUTION BASED ON HIGH-RESOLUTION TOPOGRAPHY DATA: TAKING ALLUVIAL FAN OF LAOHUSHAN ALONG HAIYUAN FAULT ZONE AS AN INSTANCE

Range-front alluvial fan deposition in arid and semiarid environments records vast amounts of climatic and tectonic information. Differentiating and characterizing alluvial fan morphology is an important part in Quaternary alluvial fan research. Traditional method such as field observations is a most important part of deciphering and mapping the alluvial fan. Large-scale automatically mapping of alluvial fan stratigraphy before traditional field observations could provide guidance for mapping alluvial fan morphology, thus improving subsequent field work efficiency. In this research, high-resolution topographic data were used to quantify relief and roughness of alluvial fan within the Laohushan. These data suggest that mean surface roughness plotted against the size of the moving window is characterized by an initial increase in surface roughness with increased window size, but it shows no longer increase as a function of windows size. These data also suggest that alluvial fans in this study site smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces which suggests the evolution process of alluvial fan. Researchers usually differentiate alluvial morphology by mapping characteristics of fan surface in the field by describing surface clast size, rock varnish accumulation, and desert pavement development and analysis of aerial photographs or satellite imagery. Recently, the emergence of high-resolution topographic data has renewed interest in the quantitative characterization of alluvial and colluvium landforms. Surface morphology that fan surface initially tends to become smoother with increasing age due to the formation of desert pavement and the degradation of bar-and-swale topography and subsequently, landforms become more dissected due to tectonics and climatic change induced increased erosion and channelization of the surface with time is widely used to distinguish alluvial fan types. Those characteristics would reflect various kinds of morphology metrics extracted from high-resolution topographic data. In the arid and semiarid regions of northwestern China, plenty of alluvial fans are preserved completely for lack of artificial reforming, and there exists sparse surface vegetation. In the meantime, range-front alluvial fan displaced by a number of active faults formed a series of dislocated landforms with different offsets which is a major reference mark in fault activity research. In this research, six map units(Qf₆-Qf₁), youngest to oldest, were observed in the study area by mapping performed by identifying geomorphic features in the field that are spatially discernible using hill-shade and digital orthophoto map. Alluvial fan relief and roughness were computed across multiple observation scales(2m×2m to 100m×100m)based on the topographic parameters of altitude difference and standard deviation of slope, curvature and aspect. In this research, mean relief keeps increasing with increased window size while mean surface roughness is characterized by a rapid increase over wavelengths of 6~15m, representing the typical length scale of bar-and-swale topography. At longer wavelengths, surface roughness values increase by only minor amounts, suggesting the topographic saturation length is 6~15m for those fan surfaces in which saturation length of standard deviation of curvature is less than 8m. Box and whisker plot of surface roughness averaged over 8m² for each alluvial fan unit in the study area suggests that the pattern of surfaces smoothing out with age and then starting to become rougher again as age increases further beyond Qf₄ or Qf₃ unit. The younger alluvial fan is characterized by prominent bar-and-swale while the older alluvial fan is characterized by tributaries headward incision. Cumulative frequency distributions of relief and surface roughness in Figure 8 are determined in an 8m by 8m moving window for the comparison of six alluvial fan units in the northeast piedmont of Laohushan. From these distributions we know that Qf₆ and Qf₁ reflect the prominent relief which is related to bar-and-swale and tributaries headward incision respectively, while Qf₄ and Qf₃ reflect the moderate relief which is related to subdued topography. Surface roughness, in addition to facilitating the characterization of individual fan units, lends insight to alluvial landform development. We summarize an alluvial landform evolutionary scheme which evolves four stages depending on characteristics of alluvial fan morphology development and features of relief and roughness. The initial stage in this study site is defined as the active alluvial fan channels with bars of coarse cobbles and boulders and swales consisting of finer-grained pebbles and sand which could be reflected by high mean relief and mean roughness values. As time goes, bar-and-swale topography is still present, but an immature pavement, composed of finer grained clasts, has started to form. In the third stage, the bar-and-swale topography on the fan surface is subdued, yet still observable, with clasts ranging from pebbles to cobbles in size and there exists obvious headward tributary incision. Eventually, tributary channels form from erosion by surface runoff. Headward incision of these tributaries wears down the steep walls of channels that are incised through the stable, planar surface, transforming the oldest alluvial landforms into convex hillslopes, leaving only small remnants of the planar surface intact. Those evolutionary character suggests that alluvial fans in this area smooth out with time, however, relief or roughness would be translated to increase at greater wavelength with age until a threshold is crossed. This research suggests that relief and roughness calculated from high-resolution topographic data of this study site could reflect alluvial fan morphology development and provide constraint data to differentiate alluvial fan unit.     

INTERPRETATION AND ANALYSIS OF THE FINE FAULT GEO-METRY BASED ON HIGH-RESOLUTION DEM DATA DERIVED FROM UAV PHOTOGRAMMETRIC TECHNIQUE: A CASE STUDY OF TANGJIAPO SITE ON THE HAIYUAN FAULT

Fault-related tectonic geomorphologic features are integrated expressions of multiple strong seismological events and long-term surface processes, including crucial information about strong earthquake behavior of a fault. It's of great significance to identify the strong seismic activity information from faulted landscapes, which include the date and sequence of the seismic activities, displacements, active fault features, for studying the seismic rupture process, predicting the future seismic recurrence behavior and evaluating the seismic hazard of the fault. However, due to the restriction of measuring techniques and the subsequent poor quality of the acquired data, it has been difficult to accurately extract such information from complex tectonic landforms to study active faults for a long time. Recently, "small Unmanned Aerial Vehicle(sUAV)" photogrammetric technique based on "Structure from Motion(SfM)" provides a cost-efficient and convenient access to high-resolution and high-accuracy "digital elevation models(DEMs)" of tectonic landforms. This paper selects the Tangjiapo area at the Haiyuan Fault to conduct data collection, in which the structural and geomorphic features are well preserved. Using a small quadrotor unmanned aerial vehicle(Inpire 2), we collect 1598 aerial photographs with a coverage area of 0.72km². For calibrating the accuracy of the aerial data, we set 10 ground control points and use differential-GPS to obtain the spatial coordinates of these control points. We use model software Agisoft PhotoScan to process these digital pictures, obtaining high-resolution and high-accuracy DEM data with the geographic information, in which data resolution is 2.6cm/pix and the average density of point cloud is 89.3 point/m². The data with these accuracy and resolution can fully show the real geomorphic features of the landform and meet the requirements for extracting specific structural geomorphic information on the surface. Through the detailed interpretation of the tectonic landforms, we identify a series of structures associated with the strike-slip fault and divide the alluvial fan into four stages, named s₁, s₂, s₃, and s₄, respectively.Wherein, the s₁ is the latest phase of the alluvial fan, which is in the extension direction of the Haiyuan Fault and there isn't any surface fracture, indicating that the s₁ was formed after the M8.5 Haiyuan earthquake in 1920. The rupture zone on the s₂ fan is composed of varied kinds of faulting geomorphologic landforms, such as a series of en echelon tension-shear fractures trending 270°~285°, fault scarps and seismic ridges caused by the left-lateral motion of the seismic fault. In addition, a number of field ridges on the s₂ fan were faulted by the 1920 Haiyuan M8.5 earthquake, recording the co-seismic displacements of the latest earthquake event. Relatively speaking, the surface rupture structure of the s₃ fan is simple, mainly manifested as linear fault scarp with a trend of 270°~285°, which may indicate that multiple earthquakes have connected the different secondary fractures. And a small part of s₄ fan is distributed in the southwest of the study area without fault crossing. Furthermore, we measured the horizontal displacements of river channels and vertical offsets of fault scarps. The faulted ridge on the s₂ fan and faulted gully on the s₃ fan provide good linear markers for obtaining the fault left-lateral dislocation. We used the graphical dislocation measurement software LaDiCaoz developed based on Matlab to restore the gully position before the earthquake by comparing the gully morphology on both sides of the fault, and then determined the horizontal offset of s₂, which is(4.3±0.4)m and that of s₃ is(8.6±0.6)m. In addition, based on the DEM data, we extracted the fault scarp densely along the fault strike, and obtained the vertical offset of s₂, which is(4.3±0.4)m and that of s₃ is(1.79±0.16)m. Moreover, we detect slope breaks in the fault scarp morphology. For compound fault scarps generated by multiple surface rupture earthquakes, there are multiple inflection points on the slope of the topographic section, and each inflection point represents a surface rupture event. Therefore, the slope break point on the scarp becomes an important symbol of multiple rupture of the fault. The statistical result shows that the slope breaks number of s₂ is 1 and that of s₃ is 2. Based on the analysis of horizontal displacements of river channels and vertical offsets of fault scarps as well as its slope breaks, two surface rupturing events can be confirmed along the Tangjiapo area of the Haiyuan Fault. Among them, the horizontal and vertical displacements of the older event are(4.3±0.95)m and(0.85±0.22)m, respectively, while that of the latest event are(4.3±0.4)m and(0.95±0.14)m, which are the coseismic horizontal and vertical offsets of the 1920 Haiyuan earthquake. These recognitions have improved our cognitive level of the fine structure of seismic surface rupture and ability to recognize paleoearthquake events. Therefore, the high-resolution topographic data obtained from the SfM photogrammetry method can be used for interpretation of fine structure and quantitative analysis of microgeomorphology. With the development of research on tectonic geomorphology and active tectonics toward refinement and quantification, this method will be of higher use value and practical significance.