音频大地电磁法对断层分辨能力的正演模拟及其应用

通过几个模型的正演模拟,在分析不同模型正演响应的TM模式Bostick一维反演断面特征的基础上,探讨了点距、点位、第四系低阻层对AMT法定位断层的影响以及AMT法对断层的位置、倾向、倾角、发育深度等特征的分辨能力。研究表明,在点位和点距布设合理的情况下,AMT法对断层倾向、发育平面位置的推断是可靠的。最后,通过AMT法在太行山区找水的应用实例,验证了正演模拟方法的实用性。     

音频大地电磁测深法对正、逆断层的精细解释

在隧道勘察中,使用音频大地电磁测深法（AMT）寻找断层、破碎带等。从正、逆断层地电模型的二维正演模拟出发,使用合成数据进行一维、二维反演,研究正、逆断层及低阻破碎带在实测数据拟断面和一维反演、二维反演结果上的区别,以确定如何利于现有的技术手段对断层破碎带D的倾向进行有效的定性、定量解释。从所获结果中可以得出,实测数据解释应以TM模式数据分层,TE模式数据判断倾向。     

基于断层模型的AMT数值模拟及其应用

为研究音频大地电磁测深法(AMT)在识别断层模型方面的可行性,结合实际电性特征,建立了不同倾角、不同倾向和不同电性的地质模型,进行了AMT的正演数值模拟;通过ZONDMT2D软件的正演计算,得出关于正演模型的视电阻率和阻抗相位拟断面图,分析了在普通和某种特定地质模型下的AMT正演响应,为之后AMT实测资料的处理和解释提供了参考。数值模拟表明:1在二维介质中,TE模式视电阻率信息对目标体反映良好,但相位资料易产生虚假异常中心;TM模型视电阻率易受静态效应影响,对横向不均匀电性体的差异具有"放大作用",其阻抗相位资料质量好,可信度高。2当断层倾角分别为30°,60°,90°时,TE、TM模式的阻抗相位拟断面图都明显优于视电阻率图。3在TM模型中,对于正断层模型,AMT正演结果会在断层顶部对应地面的投影位置附近产生一个相对"凹陷"的曲线形态;逆断层模型则会在相应位置出现相对"凸起"的曲线形态。最后,通过对西藏扎西康铅锌多金属矿整装勘查区的实测资料的分析,圈定隐伏断层在剖面上的展布,经过实际钻孔的验证,证实该正演模拟结论对于实测资料的处理和解释具有参考价值。     

AMT数据地形畸变影响与带地形反演效果研究

在山区进行音频大地电磁测深(AMT)时,电磁场易受地形起伏影响发生畸变。为研究起伏地形对AMT数据的影响,采用WinGlink软件基于有限差分算法的正演模块,建立二维起伏地形和平地地电模型,并对比分析了两个理论模型的正演响应。结果表明:TE模式的视电阻率曲线在高频段受干扰程度相对较大,在低频段影响减小甚至消失;TM模式的视电阻曲线变化正好相反;二者相位受地形影响则较小。对含异常体的带地形地电模型进行正演计算,在正演响应中加入2.5%的随机误差模拟实测数据,利用WinGlink软件基于非线性共轭梯度(NLCG)算法的反演模块,分别进行带地形和不带地形的TE、TM和TE+TM模式的二维反演。各反演结果的对比表明,带地形的二维反演结果明显优于不带地形的反演结果,能够较好地反映出异常体的位置、形态及电阻率值。依据得到的认识,对青海祁连隧道工程的AMT实测数据进行带地形二维反演,取得了理想的应用效果。     

AMT静态效应和对导电薄层分辨能力的正演模拟

静态效应是AMT法在山区找水中不可回避的问题,第四系地下水勘查中人们有时更多关注隔水层黏土层的空间分布。针对这两个问题,利用二维有限单元数值模拟方法来讨论静态效应对TE、TM极化方式视电阻率曲线的影响以及对导电薄层的垂向分辨能力。研究表明：TM模式视电阻率受静态影响严重,TE模式视电阻率对深部地质体的反映优于TM模式;TM极化模式放大了横向上不同电性体的电性差别,在山区找水中对断层反映敏感;AMT对导电薄层的垂向分辨力与围岩的电阻率比值有关,加密点距,并不能提高垂向分辨率。     

三维地质体对AMT二维反演的影响研究

为探究三维地质体对二维反演结果地影响以及二维反演中极化模式的选择问题,设计了一系列二维、三维地电模型进行正演计算,并对正演结果进行二维反演计算。研究结果表明:相位受到三维畸变的影响较小,视电阻率较大;当三维异常体模型走向延伸较小时,TE模式的反演结果误差较大,TM模式的反演结果相对较好,但是反演得到了虚假的下覆构造,TE+TM联合反演结合了TE和TM模式反演的优点,可以较好地反映异常体的赋存位置及电阻率值;当三维异常体模型走向延伸长度增大时,三维数据的二维反演结果是可靠的,用TM和TE+TM模式反演都比较合理。     

音频大地电磁法对深部隐伏构造的识别与应用:以贵州省松桃县李家湾锰矿为例

面对国家级整装勘查区——贵州铜仁松桃锰矿整装勘查区深部找矿难度加大的现状,特别是隐伏构造的识别对于第二空间(500~2 000m深度)找矿至关重要的问题,鉴于当前锰矿床后期保存条件的研究需要,利用音频大地电磁法对深部隐伏构造的识别很有必要。以区内岩石物性特征为基础,结合"大塘坡式"锰矿地质模型,建立了初步的正演模型,比较了正演TE、TM两支理论正演曲线,TM模式视电阻率响应较TE模式纵向分辨率强;对比了两支曲线在断层上下盘的响应特征。贵州省松桃县李家湾锰矿实测数据的不同反演结果表明:以一维Occam-TE反演作为初始模型的二维NLCG-TE反演能较好地反映真实的电断面结构。通过剖面电性结构特征分析,为查明"大塘坡式"锰矿深部构造格架及其对含锰岩系的破坏程度提供了地球物理依据,为进一步"攻深找盲"工程部署提供参考。     

音频大地电磁在长大深埋隧道勘探中的研究与应用

以成昆线民太隧道岩石物性特征为基础,结合实际地质背景,针对隧道勘察中断层、含水破碎带、岩溶等地质目标体的埋深、规模等问题,建立相应的地质模型,开展正反演模拟计算,进行对比分析,探讨音频大地电磁法对隧道勘探目标的有效性及可行性,旨在提供合理的模型依据和反演参数。分析对比两种极化模式正演数据,TE模式视电阻率资料反映的结果更接近真实情况,TE与TM相位资料具有一定的参考价值。选择不同初始模型的多反演参数对模型进行反演计算,最终确立了以一维Occam-TE反演作为初始模型对成昆线民太隧道实测数据进行二维NLCG-TE+TM反演,结果证明了模型的合理性和反演参数选择的有效性。     

龙首山芨岭岩体南部牛角沟断裂深部发育特征

通过对龙首山成矿带牛角沟地段7条音频大地电磁测深(以下简称AMT)资料反演处理,并结合区内地质资料及部分钻探资料的综合分析,大致查明了牛角沟断裂的深部发育特征。分析表明:该断裂发育于变质岩与岩体的接触带,走向NW,倾向NE,倾角75°～80°,切割深度超过850m,为一条高角度的压扭性逆断层,控制了区内铀异常、点、带的分布。     

印模法在AMT数据处理中的改进与应用

在AMT数据处理中,反演模型的构建决定了最终的反演结果,不合理的反演模型直接导致反演结果的偏差。利用前人提出的印模法思想,对该方法进行了一些改进:以一维TM模式平均电阻率为均匀半空间模型电阻率进行二维反演,并以此反演结果作为元模型,全区一维平均电阻率为辅模型,理论探测深度为印模深度,构建新的反演模型。通过实例对比,认为采用该方法建立的模型能够较好地反映相应的地电结构,达到全区的平衡和统一,具有较好的应用效果。     

Modelling cover deformation and decoupling during inversion,using the Mid-Polish Trough as a case study

Seismic sections across the NW part of the Polish Basin show that thrust faults developed in the sedimentary units above the Zechstein evaporite layer during basin inversion. These cover thrust faults have formed above the basement footwall. Based on the evolution of the basin, a series of scaled analogue models was carried out to study interaction between a basement fault and cover sediments during basin extension and inversion. During model extension, a set of normal faults originated in the sand cover above the basement fault area. The distribution and geometry of these faults were dependent on the thickness of a ductile layer and pre-extension sand layer, synkinematic deposition, the amount of model extension, as well as on the presence of a ductile layer between the cover and basement. Footwall cover was faulted away from the basement only in cases where a large amount of model extension and hanging-wall subsidence were not balanced by synkinematic deposition. Model inversion reactivated major cover faults located above the basement fault tip as reverse faults, whereas other extensional faults were either rotated or activated only in their upper segments, evolving into sub-horizontal thrusts. New normal or reverse faults originated in the footwall cover in models which contained a very thin pre-extension sand layer above the ductile layer. This was also the case in the highly extended and shortened model in which synkinematic hanging-wall subsidence was not balanced by sand deposition during model extension. Model results show that inversion along the basement fault results in shortening of the cover units and formation of thrust faults. This scenario happens only when the cover units are decoupled from the basement by a ductile layer. Given this, we argue that the thrusts in the sedimentary infill of the Polish Basin, which are decoupled from the basement tectonics by Zechstein evaporites, developed due to the inversion of the basement faults during the Late Cretaceous-Early Tertiary.     

EH-4连续电导率仪与V8多功能电法仪试验效果分析

在龙首山成矿带小白芨芨沟-小青羊地段采用EH-4连续电导率仪与V8多功能电法仪进行不同点距AMT试验结果表明,两套仪器对马路沟及其次级断裂的探测结果均反映明显,其电性特征表现为反演电阻率等值线密集带、舌状低阻带。从不同点距试验结果来看,10、20 m点距探测精度高,反映效果明显好于50m点距;从不同仪器试验结果来看,EH-4连续电导率仪与V8多功能电法仪的测量结果均能客观地反映地下地质体的电阻率分布规律,与地质剖面具有较好的对应关系,均可投入该地区的生产应用。但EH-4连续电导率仪轻便、单点生产效率高,测量结果对断裂构造的分辨能力更好,特别是中浅层的分辨效果。     

The 20 May 2016 Petermann Ranges earthquake: centroid location,magnitude and focal mechanism from full waveform modelling

Ground velocity records of the 20 May 2016 Petermann Ranges earthquake are used to calculate its centroid-moment-tensor in the 3?D heterogeneous Earth model AuSREM. The global-centroid-moment-tensor reported a depth of 12?km, which is the shallowest allowed depth in the algorithm. Solutions from other global and local agencies indicate that the event occurred within the top 12?km of the crust, but the locations vary laterally by up to 100?km. We perform a centroid-moment-tensor inversion through a spatiotemporal grid search in 3?D allowing for time shifts around the origin time. Our 3?D grid encompasses the locations of all proposed global solutions. The inversion produces an ensemble of solutions that constrain the depth, lateral location of the centroid, and strike, dip and rake of the fault. The centroid location stands out with a clear peak in the correlation between real and synthetic data for a depth of 1?km at longitude 129.8° and latitude –25.6°. A collection of acceptable solutions at this centroid location, produced by different time shifts, constrain the fault strike to be 304?±?4° or 138?±?1°. The two nodal planes have dip angles of 64?±?5° and 26?±?4° and rake angles of 96?±?2° and 77?±?5°, respectively. The southwest-dipping nodal plane with the dip angle of 64° could be seen as part of a near vertical splay fault system at the end of the Woodroffe Thrust. The other nodal plane could be interpreted as a conjugate fault rupturing perpendicular to the splay structure. We speculate that the latter is more likely, since the hypocentres reported by several agencies, including the Geoscience Australia, as well as the majority of aftershocks are all located to the northeast of our preferred centroid location. Our best estimate for the moment magnitude of this event is 5.9. The optimum centroid is located on the 20?km surface rupture caused by the earthquake. Given the estimated magnitude, the long surface rupture requires only ～4?km of rupture down dip, which is in agreement with the shallow centroid depth we obtained.     

Mapping folds and fractures in basement and cover rocks using UAV photogrammetry,Cape Liptrap and Cape Paterson,Victoria, Australia

Brittle and ductile deformation of alternating layers of Devonian sandstone and mudstone at Cape Liptrap, Victoria, Australia, resulted in upright folds with associated fold accommodation faults and multiple fracture sets. Structures were mapped at the Fold Stack locality at Cape Liptrap using high-resolution aerial photographs acquired by a digital camera mounted on an unmanned aerial vehicle (UAV). Subsequent photogrammetric modelling resulted in georeferenced spatial datasets (point cloud, digital elevation model and orthophotograph) with sub-cm resolution and cm accuracy, which were used to extract brittle and ductile structure orientation data. An extensive dataset of bedding measurements derived from the dense point cloud was used to compute a 3D implicit structural trend model to visualise along-strike changes of Devonian (Tabberabberan) folds at the Fold Stack locality and to estimate bulk shortening strain. This model and newly collected data indicate that first generation shallowly south-southwest plunging upright folds were gently refolded about a steeply plunging/subvertical fold axis during a Devonian low-strain north–south shortening event. This also led to the local tightening of first generation folds and possibly strike-slip movement along regional scale faults. In order to distinguish fractures associated with Devonian compression from those that formed during Cretaceous extension and later inversion, we compared the five fracture sets defined at Cape Liptrap to previously mapped joints and faults within the overlying sedimentary cover rocks of the Cretaceous Strzelecki Group (Gippsland Basin), which crop out nearby. An east-southeast trending fracture set that is not evident in the Strzelecki Group can be linked to the formation of Devonian folds. Additionally, hinge line traces extracted from the Fold Stack dataset are aligned parallel to a dominant fracture set within the overlying cover sediments. This suggests that basement structures (folds and coeval parallel faults) have an important influence on fault and joint orientations within Cretaceous cover rocks.     

探地雷达在探测玉树走滑断裂带活动性中的初步应用

探地雷达具有快速、检测范围广、探测深度深、分辨率高及对地表环境无破坏等特点,在活动断层探测应用中具有很大的优势。在简要介绍玉树走滑断裂带活动性的基础上,选择高分辨率的探地雷达对隆宝、昔日达和盘琼沟处断裂带附近的活动断层进行探测。采用时间域有限差分法建立活动断层的数值模型对其雷达波响应特征进行模拟,分析断层在探地雷达剖面上的反射波特征。根据断层的反射波特征解译探地雷达图像,判断断层的位置、走向及空间展布。结合探槽开挖对比,探地雷达图像的解译结果与探槽开挖后的断裂带剖面展示的断层活动性质基本一致。根据隆宝、昔日达和盘琼沟处的探地雷达图像与探槽剖面上断层反射波特征的对比研究,解译了玉树地震震中位置探地雷达剖面上的断层展布。研究表明,探地雷达是一种快速探测活动断层的有效方法,尤其是在地表破裂不明显的区域,不仅可以准确地判断断层的位置、走向及空间展布,还可以将断裂带附近地下岩层的层位信息及探槽断面之外的地表下图像清晰地呈现出来,为以后运用探地雷达探测活动断层提供参考。     

Reverse drag revisited: Why footwall deformation may be the key to inferring listric fault geometry

Although reverse drag, the down warping of hanging wall strata toward a normal fault, is widely accepted as an indicator of listric fault geometry, previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry. In this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near-surface deformation by directly comparing patterns of displacement, stress, and strain around planar and listric faults, as predicted by elastic boundary element models. In agreement with previous work, we find that models with finite planar, planar-detached, and listric-detached faults all develop hanging wall reverse-drag folds. All of these model geometries also predict a region of tension and elevated maximum Coulomb stress in the hanging wall suggesting that the distribution and orientation of near-surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry. The most notable difference between the three models, however, is the magnitude of footwall uplift. Footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape. A parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth. Application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry.     

渤海海峡跨海通道工程区断裂活动性及地震分布特征

利用近年来采集的高分辨率地震剖面资料,编制了渤海海峡跨海通道工程区主要活动断裂分布图,并对其中各断裂的垂直活动速率进行计算,发现渤海海峡跨海通道工程区内NE—NNE向断裂晚更新世以来的平均垂直活动速率为0103 mm/a,NW向断裂的平均垂直活动速率为0080 mm/a,其中NE—NNE向断裂和NW向断裂的活动速率呈由南到北逐渐增强的趋势,NW向断裂还表现出明显的自西向东活动速率逐渐增强的特点。另外,通过与现代小震资料和历史地震资料进行对比,发现研究区内地震分布具有不均匀性,地震活动性随着与断裂之间距离的增加而减弱,且在断裂交点和端点处活动性较强。研究区内地震的这些分布特征能够用弹性回跳学说解释。此外,研究区内地震活动性与断裂的水平位移速率关系可能更为密切,其与断裂垂直活动速率的关系还需要进一步研究。     

川滇地区重力场特征与地壳变形研究

对川滇地区重力场特征进行了研究,获得了研究区内地壳厚度分布及变形特征。总体上,研究区内地壳厚度从西北向东南逐渐减小。川滇菱形块体中内部出现了广泛的地壳增厚现象,并可能一直延伸至菱形块体的最南端。丽江-小金河断裂带在重力场特征上表现为龙门山断裂带向西南的延伸,其东侧主体构造走向等特征与扬子地块一致,推测丽江-小金河断裂带与龙门山断裂、红河断裂带一起构成了扬子地块的西边界。滇西地区布格重力一阶导数与现今地壳变形格局总体一致,主体构造方向为北北西-近南北向,代表了“新”构造主体构造线的方向;上延至45km后,主体构造上转变为以近东西向为主。