Preliminary seismic anisotropy in the upper crust of the south segment of Xiaojiang faults and its tectonic implications

The Xiaojiang faults,striking north-to-south(NS),and the Honghe faults,striking north-to-west(NW),are first-order block boundaries that intersect to form a concentrated stress zone at an acute angle in the southern part of the Sichuan-Yunnan rhombic block(SYB).It is also a crucial zone for material escaping from the Tibetan Plateau(TP)due to the collision between the Indian Plate and the Eurasian Plate.In December 2017,the Institute of Earthquake Forecasting of the China Earthquake Administration(CEA)deployed a linear temporary seismic broadband array,the Honghe-Xiaojiang temporary Seismic Array(HX Array),across first-order block boundaries in the southern SYB.By using the waveform data of small earthquakes recorded by stations in the HX Array across Xiaojiang faults from 2017 to 2019,and by permanent seismic stations of the China National Earthquake Networks from 2012 to 2019,this paper adopts the systematic analysis method of shear-wave splitting(SWS),SAM method,to obtain preliminary results for seismic anisotropy in the upper crust.The study area can be divided into two subzones according to the spatial distribution of the directions of polarization of the fast shear-wave(PFS)at the stations:the northern zone(zone A,where the HX Array is located)and the southern zone(zone B,to the south of the HX Array).The results show that the directions of the PFS at stations in zone A were highly consistent,dominant in the NE direction,correlated with the in-situ principal compressive stress,and were seemingly unaffected by the Xiaojiang faults.The directions of the PFS as recorded at stations in zone B were more complicated,and were dominant in the NS direction parallel to that of the regional principal compressive stress.This suggests the joint influence of complex tectonics and regional stress in this narrow wedge area.By referring to the azimuthal anisotropy derived from seismic ambient noise in the southeast margin of the TP,the NS direction of the PFS in the middle and lower crust,and its EW direction in the upper mantle,this paper concludes that azimuthal anisotropy in the upper crust differed from that in the lower crust in the south segment of Xiaojiang faults,at least beneath the observation area,and azimuthal anisotropy in the crust was different from that in the upper mantle.The results support the pattern of deformation of ductile flow in the lower crust,and the decoupling between the upper and lower crusts as well as that between the crust and the mantle in the study area.The crustal directions of the PFS appeared to be independent of the Xiaojiang faults,suggesting that the influence of the South China block on the SYB passed through the Xiaojiang faults to the Yimen region.The results of this study indicate that anisotropic studies based on data on the dense temporary seismic array can yield clearer tectonic information,and reveal the complex spatial distribution of stress and deformation in the upper crust of the south segment of Xiaojiang faults.     

DNQ3型能见度仪故障分析及校准方法研究

为有效提高国家地面气象观测站能见度仪观测数据准确性和设备运行稳定性,对能见度仪开展日常维护、核查校准、数据质控和故障修复等工作显得尤为重要。该文通过对DNQ3型前向散射能见度仪硬件结构和基本工作原理的介绍,以及对一些典型故障进行分析,总结出能见度仪的检测维修流程,归纳了对应的故障解决措施,凝练出该型能见度仪的核查校准和疑误数据质控方法,为一线业务人员开展能见度仪常规维护、故障排查、运行监控等提供借鉴。     

珠江口盆地阳江东凹裂陷期沉积环境及其构造控制

珠江口盆地阳江东凹形成于古近纪裂陷期,广泛发育烃源岩的富存层段——文昌组、恩平组,具有陆相断陷盆地沉积以及构造控制下多幕演化的特征.沉积环境演变以及构造?沉积的耦合作用是陆相断陷盆地的重要研究方向,认识其动态过程可为烃源岩识别和油气评价建立基础.本文从三维地震资料、钻井资料入手,通过地震反射特征和井震联合分析,划分了研...     

Extensional fault and fold growth: Impact on accommodation evolution and sedimentary infill

Extensional faults and folds exert a fundamental control on the location, thickness and partitioning of sedimentary deposits on rift basins. The connection between the mode of extensional fault reactivation, resulting fault shape and extensional fold growth is well‐established. The impact of folding on accommodation evolution and growth package architecture, however, has received little attention; particularly the role‐played by fault‐perpendicular (transverse) folding. We study a multiphase rift basin with km‐scale fault displacements using a large high‐quality 3D seismic data set from the Fingerdjupet Subbasin in the southwestern Barents Sea. We link growth package architecture to timing and mode of fault reactivation. Dip linkage of deep and shallow fault segments resulted in ramp‐flat‐ramp fault geometry, above which fault‐parallel fault‐bend folds developed. The folds limited the accommodation near their causal faults, leading to deposition within a fault‐bend synclinal growth basin further into the hangingwall. Continued fold growth led to truncation of strata near the crest of the fault‐bend anticline before shortcut faulting bypassed the ramp‐flat‐ramp structure and ended folding. Accommodation along the fault‐parallel axis is controlled by the transverse folds, the location and size of which depends on the degree of linkage in the fault network and the accumulated displacement on causal faults. We construct transverse fold trajectories by tracing transverse fold hinges through space and time to highlight the positions of maximum and minimum accommodation and potential sediment entry points to hangingwall growth basins. The length and shape of the constructed trajectories relate to the displacement on their parent faults, duration of fault activity, timing of transverse basin infill, fault linkage and strain localization. We emphasize that the considerable wavelength, amplitudes and potential periclinal geometry of extensional folds make them viable targets for CO₂ storage or hydrocarbon exploration in rift basins.     

太行山南端浅层速度结构成像和隐伏断裂探测

利用太行山南端的深地震反射剖面数据,运用初至波层析成像方法反演得到该区域的浅层P波速度结构和基底面展布形态,发现剖面浅部的P波速度变化与沉积盖层厚度和断裂分布有着较好的对应关系。利用跨断裂完成的浅层地震反射剖面,对区域内2条第四纪隐伏活动断裂进行高分辨率成像。结果表明,汤西断裂为东倾的正断层,控制汤阴地堑的西边界,活动年代为中更新世;汤东断裂为西倾的正断层,是汤阴地堑的主控边界断裂,活动年代为晚更新世。     

两郧断裂郧县盆地段地质与地球物理特征研究

通过野外地质调查,结合地球物理探测手段,研究两郧断裂郧县盆地段地质与地球物理特征;参照两郧断裂带多个位置采集断层物质的SEM、TL测试成果,并结合本次对断层上断点沉积物OSL测年数据,对两郧断裂该段第四纪活动性进行分析。研究结果表明,两郧断裂在郧县盆地段埋深相对较深;断裂特征主要为逆断层,部分分支断裂显示为正断性质;断裂带最新活动时代为中更新世晚期-晚更新世早期。     

准噶尔盆地中部永进地区走滑断裂发育特征及成因物理模拟

永进地区位于准噶尔盆地中部,最近发现了多个与走滑断层相关的含油气构造,但关于走滑断层的发育特征及成因机制研究程度不够深入。本文通过三维地震资料精细解释,在研究区三叠系—侏罗系内识别出近东西向、北西西向以及北东东向的三组走滑断裂体系,平面上呈“网格状”展布,剖面上具有不同深度几何学形态差异展布特征。在此基础上基于相似性原理设计四组砂箱模拟对比实验,重现研究区构造演化过程。模拟结果表明,这类走滑断裂的形成与基底先存断层的发育位置有关,是受先存构造和地层属性双重控制的广布式走滑断裂系统,从而建立了研究区的断裂系统成因模式。研究成果对具有相似地质背景地区的走滑断裂成因解释具有借鉴意义。     

南海西缘断裂带右行走滑的地球动力学机制

南海西缘断裂带,北端始于17°30'N附近的海南岛南部,往南延伸止于北西走向的卢帕尔断裂,南北延伸长度约达1 600 km,十分壮观(见图1)。该断裂带除了其名称和延伸长度在不同研究者的文章中各有所不同[1—4]之外,其名称和作用至少在20世纪80年代初已得到广泛的应用,早已成习惯,如在《亚洲地质》[5]一书和杨树康等[1]、陈国达[4]等许多著名科学家的论著中不断地得到了应用。该断裂带的构造地位和作用得到地学界的普遍重视,到目前为止地学界基本上认为它就是印支亚板块与南海亚板块之间的区域性边界断裂。     

珠江口盆地珠三坳陷层序地层样式分析

珠江口盆地珠三坳陷是一个典型的箕状断陷盆地,其层序地层格架受到主干断裂特别是珠三南断裂的强烈控制。由于珠三南断裂活动的差异性,盆地东部、中部和西部表现为不同的格架样式。并据此划分出坳陷内的3种典型层序样式,分别是缓坡型、断控陡坡型和断阶型层序样式。文昌A凹陷与阳江低凸起过渡的斜坡区和文昌B凹陷与琼海低凸起过渡区为具有坡折的缓坡背景,发育缓坡坡折型层序样式,发育斜坡扇、盆底扇、低位楔。珠三南断裂等主干断裂下降盘发育断控陡坡带层序样式,在珠三南断裂中部地区,发育断阶型层序样式。     

南海南部断裂的分形研究

分形几何作为定量描述自然界中复杂非线性现象的强有力工具,将其应用于南海南部断裂体系的研究中,通过数盒子法计算了断裂分布的分维值。研究结果表明这种方法是可行的,断裂分布的分维值能有效地描述断裂的空间分布特征。南海南部断裂体系在标度区间25～250km内具有很好的统计自相似性,全部断裂的分维值为1．6601,北东向断裂的为1．3875,北西向断裂的为1．2693。根据断裂分维等值线,沿西南海盆扩张轴,两侧断裂呈对称展布;北东向的与北西向的在空间上有一定的互补性,这反映了两组断裂在发育过程中的相互制约性。结合南海的构造演化及南海南部油气盆地的分布,初步探讨了断裂分形特征与南海的构造演化及断裂分形特征与油气盆地分布之间的关系。