共查询到20条相似文献，搜索用时 31 毫秒
1.
Marina G. Persova Yuri G. Soloveichik Denis V. Vagin Dmitry S. Kiselev Alexander M. Grif Yulia I. Koshkina Anastasia P. Sivenkova 《Geophysical Prospecting》2020,68(7):2217-2253
We propose the approach to 3D inversion of airborne electromagnetic data, which is intended for discovering subvertical bodies overlapped by essentially inhomogeneous conductive layers. The approach is based on the geometric inversion in which a geoelectrical medium is parameterized with the use of block structures. During the inversion, the coordinates of the borders between the blocks and the rows of the blocks as well as resistivities inside them are determined. In order to solve the forward problem of the airborne electromagnetic survey, we use the non-conforming optimized mesh with the hexahedral cells, which enables us to reduce the number of degrees of freedom and smoothly approximate the curved borders of a geological medium. For a more reliable discovery of subvertical objects, we propose to carry out 3D inversions at several rotations of block structures relative to the flight lines. The workability of this approach is demonstrated using the data which are synthesized for complex geoelectrical models with topography, inhomogeneous overlapping layers and target subvertical bodies oriented differently relative to the flight lines. The results of this investigation show that, in some way or other, the elongated subvertical object is discovered and its orientation (the direction of its long side) is defined at different rotations of block structures used in 3D inversions. However, the most accurate recovery of the subvertical object length is achieved when the direction of its long side almost coincides with the direction of one of the block structures axes. Thus, the block structures rotations allow not only more reliably discovering a target object in complex geoelectrical conditions, but also more exactly defining its orientation and length. 相似文献
2.
本文首先制作了TI地层模型井,对模型井的速度、密度等物理参数进行了测量,通过快速模拟退火算法得到了该介质的五个TI刚性系数,然后采用缩尺的偶极子探头在HTI地层井孔内进行超声测量实验模拟了实际的偶极子声波测井,并结合数值模拟的结果,研究了不同偏振方向的声源在HTI地层井孔中进行偶极子声波测井的响应特征.模拟结果表明,弯曲波的幅度和速度随声源的偏振方向不同而不同.正交分量的波形幅度在声源偏振方向平行或垂直于快横波面方位时最小,在与快横波面方位呈一定夹角时较大;同向分量波形幅度随声源的偏振方向的变化规律同正交分量相反.弯曲波速度在声源的偏振方向与快横波面方位的夹角小于30°或者大于60°时,分别接近于快弯曲波和慢弯曲波的速度,对于夹角的变化不敏感;当夹角在30°和60°之间时,弯曲波的速度对该夹角变化非常敏感,由接近快弯曲波速度快速变化到接近慢弯曲波速度. 相似文献
3.
云南地区上地幔各向异性研究 总被引：12，自引：3，他引：12
对云南23个数字地震台11次地震的SKS记录，采用理论切向分量与实测切向分量拟合的方法，确定了快S波的偏振方向和快、慢波之间的时间延迟．结果表明，除鹤庆台外，在各台都观测到了S波分裂现象；云南地区的快方向总体特征是北北东向，时间延迟变化范围为0.5～2.0ｓ．在地质构造复杂地区断层对分析的影响很大．分析表明，作为青藏高原与华南块体之间的过渡带，云南地区的S波快方向反映了印度板块向欧亚板块俯冲是该地区地球动力学的基本背景，而由于青藏高原隆起造成的康滇菱形块体的南东-南南东向运动是造成复杂构造、应力环境的重要因素．快方向与上地幔运动的方向存在差异，说明在云南地区低速层或者软流层的运动与地壳块体的运动之间存在着复杂的耦合作用，构造驱动力如同向北东方向张开的手掌．从时间延迟出发，推断各向异性层的厚度为60～225ｋｍ．其变化范围与低速层埋深的变化范围（104～260ｋｍ）相当，认为各向异性层顶面可能在地壳底部，也可能在低速层，且在不同地点是不相同的，这与云南及周边地区莫霍面变化剧烈有因果关系．进一步推断出上地幔的各向异性主要存在于岩石圈而不是整个上地幔． 相似文献
4.
Reflection moveout inversion in azimuthally anisotropic media: accuracy, limitations and acquisition 总被引：1，自引：0，他引：1
AbdulFattah Al-Dajani Tariq Alkhalifah & Frank Dale Morgan 《Geophysical Prospecting》1999,47(5):735-756
Parameter estimation from the elliptical variations in the normal-moveout (NMO) velocity in azimuthally anisotropic media is sensitive to the angular separation between the survey lines in 2D, or equivalently, the source-to-receiver azimuth in 3D, and to the set of azimuths used in the inversion procedure. The accuracy in estimating the orientation of an NMO ellipse, in particular the parameter α, is also sensitive to the magnitude of anisotropy. On the other hand, the accuracy in estimating the semi-axes of the NMO-velocity ellipse is about the same for any magnitude of anisotropy. To invert for the NMO ellipse parameters at least three NMO-velocity measurements along distinct azimuth directions are needed. In order to maximize the accuracy and stability in parameter estimation, it is best to have the azimuths for the three source-to-receiver directions 60° apart. Having more than three distinct source-to-receiver azimuths (e.g. full azimuthal coverage) provides a useful data redundancy that enhances the quality of the estimates. In order to maximize quality in the inversion process, it is recommended to design the seismic data acquisition such that it contains small sectors (≤10°) with adequate fold and offset distribution. Using three NMO-velocity measurements, 60° apart, an azimuthally anisotropic layer overlain by an azimuthally isotropic overburden (as might occur for fractured reservoirs) should have a relative thickness (in time) with respect to the total thickness at least equal to the ratio of the error in the NMO (stacking) velocity to the interval anisotropy of the fractured layer. Coverage along more than three azimuths, however, improves this limitation, which is imposed by Dix differentiation, by at most 50%, depending on the number of observations (NMO velocities) that enter the inversion procedure. 相似文献
5.
6.
The receiver function (RF) technique is a well-established method to investigate the crustal and upper mantle structures based on three-component seismograms of teleseismic events. In the present study, we propose a modified automatic procedure to determine the back azimuth and polarization angles of a teleseismic event based on the RF technique. The method is tested for the recording of 3 permanent and 3 temporary broadband seismic stations located in the vicinity of Poland. Additionally, the analysis of Rayleigh wave polarization is conducted to show that the new procedure is not sensitive to incorrect seismometer orientation. The synthetic modelling of RF by a modified ray-tracing method for 2.5D models beneath each seismic station down to a depth of 60 km is performed to show the effectiveness of the proposed method in the calculation of RF for a complex structure with dipping layers. 相似文献
7.
The Apollo 17 astronauts removed four rocks samples to represent each of the lithologies they recognized in the boulder at station 7: sample 77215 from an off-white meter-sized block; sample 77075 from one of the thin dikes that cross the off-white block; 77115 from the blue-gray rock adjacent to the off-white block and apparently continuous with thin dikes that cross the block; sample 77135 of the tan-gray or green-gray vesicular rock adjacent to the blue-gray (77115) rock. A consortium of investigators has been organized, under the leadership of E.C.T. Chao, to study the samples. Each sample shows a number of lithologic types in terms of clasts (or xenoliths) and matrices. A table shows how subsamples have been allocated for consortium study. Maps and photographs show the relations between subsample locations and lithologies for the two more dissected samples, 77115 and 77135. 相似文献
8.
腔隙性脑梗塞的CT诊断及临床特点 总被引：1，自引：1，他引：0
本文回顾性分析了１２０例脑腔隙性梗塞的ＣＴ诊断及临床特点,认为梗塞病灶可被清晰、准确的发现。有助于临床的定性分析,为治疗提供了依据。ＣＴ是目前诊断脑腔隙性梗塞的最有效的检查手段。 相似文献
9.
利用土工静力-动力液压三轴-扭转多功能剪切仪,针对相对密度Dr=30％的福建标准砂,进行了不排水条件下的单调剪切试验。在剪切过程中,控制平均固结应力和中主应力系数保持不变,而总主应力方向不固定。与剪切过程中总主应力方向固定不变条件下的单调剪切试验进行了对比分析。试验研究表明,当饱和砂土试样具有水平沉积面时,初始固结主应力方向与剪切方向的不同组合,导致单调剪切过程中总的主应力方向的不断变化,从而显著地影响着饱和砂土不排水单调剪切特性。总的主应力方向是影响饱和砂土不排水单调剪切特性的最根本原因。 相似文献
10.
地质找矿改革发展大讨论是地质工作准确定位,统一部署,解决体制机制障碍,实现地质找矿重大突破的一项重要工作。笔者从国家地质工作的性质与定位,中国地质调查局和大区中心的定位与职责问题和统筹规划地质工作三方面探讨了制约地质找矿实现突破的主要问题。从找矿思路、找矿方向、找矿工作的部署及资金的投入,地质工作的部署和组织实施以及矿业权的设置和配置等方面,分析了制约地质找矿重大突破的关键因素。并从加强基础地质工作,拓展地质服务领域,做好统一部署整合勘查工作和矿业权配置政策研究方面,提出了初步的建议与思考。 相似文献
11.
Hazard maps are considered essential tools in the communication of volcanic risk between scientists, the local authorities
and the public. This study investigates the efficacy of such maps for the volcanic island of Montserrat in the West Indies
using both quantitative and qualitative research techniques. Normal plan view maps, which have been used on the island over
the last 10 years of the crisis, are evaluated against specially produced three-dimensional (3D) maps and perspective photographs.
Thirty-two demographically representative respondents of mixed backgrounds, sex, education and location were interviewed and
asked to complete a range of tasks and identification on the maps and photographs. The overall results show that ordinary
people have problems interpreting their environment as a mapped representation. We found respondents’ ability to locate and
orientate themselves as well as convey information relating to volcanic hazards was improved when using aerial photographs
rather than traditional plan view contour maps. There was a slight improvement in the use of the 3D maps, especially in terms
of topographic recognition. However, the most striking increase in effectiveness was found with the perspective photographs,
which enabled people to identify features and their orientation much more readily. For Montserrat it appears that well labelled
aerial and perspective photographs are the most effective geo-spatial method of communicating volcanic risks.
相似文献
| Katharine HaynesEmail: |
12.
Dan McKenzie 《Earth and Planetary Science Letters》1976,29(1):189-193
Satellite photographs of Eastern Turkey show a large strike slip fault about 550 km long extending from the Gulf of Iskenderun to the North Anatolian Fault with a strike of 60°E. This fault takes up most of the motion between the Turkish and Arabian plates. 相似文献
13.
The steady‐forced and earthquake responses of SDF systems with a non‐linear fluid viscous damper (FVD) are investigated. The energy dissipation capacity of the FVD is characterized by the supplemental damping ratio ζsd and its non‐linearity by a parameter designated α. It is found that the structural response is most effectively investigated in terms of ζsd and α because (1) these two parameters are dimensionless and independent, and (2) the structural response varies linearly with the excitation intensity. Damper non‐linearity has essentially no influence on the peak response of systems in the velocity‐sensitive spectral region, but differences up to 14% were observed in the other spectral regions. The structural deformation is reduced by up to 25% when ζsd= 5%; and by up to 60% when ζsd= 30%. Non‐linear FVDs are advantageous because they achieve essentially the same reduction in system responses but with a significantly reduced damper force. For practical applications, a procedure is presented to estimate the design values of structural deformation and forces for a system with non‐linear FVD directly from the design spectrum. It is demonstrated that the earthquake‐induced force in a non‐linear FVD can be estimated from the damper force in a corresponding system with linear FVD, its peak deformation, and peak relative velocity; however, the relative velocity should not be approximated by the pseudo‐velocity as this approximation introduces a large error in the damper force. Finally, a procedure is presented to determine the non‐linear damper properties necessary to limit the structural deformation to some design value or the structural capacity for a given design spectrum. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
14.
利用格点尝试法首先分区对鄂尔多斯地块周边的 30 0 0多个小震震源机制解进行了处理。结果显示 ,在震源机制解覆盖的时段内 ,地块周边地区的平均构造应力场有以下特征 :地块周边主要以水平构造作用力为主 ,且其主压应力轴走向以地块西南侧为中心 ,从北至东呈扇形展布。在分区基础上 ,对各区的平均主应力轴分布进行了扫描 ,得到了其随时间的变化过程。其中渭河、六盘山和银川区的构造应力场相对稳定 ,临汾和同心区的构造应力场变化复杂 ,临河、包头、呼和、大同和太原区的构造应力场变化与该区的几次中强地震有密切关系。另外 ,地块周边除个别区外大多数区域在 1992年和 1996年前后 ,主压应力轴走向有趋近于N75°E的现象 相似文献
15.
Introduction The study of the upper mantle anisotropy in Yunnan area benefits the research of deep structure of Sichuan-Yunnan active block and the characteristics of deformation field, the analysis of the coupling relations among different layers of the earth and the promotion of understanding the relation between anisotropy and stress-strain field and geological construction processes. The research results would be of important significance for the interpretation of movement of plates, the … 相似文献
16.
— We addressed effects of in situ stress on the formation of flow pathways in fractured rocks in geothermal reservoirs, especially for HDR projects. Here we focused on fractures which are critically-stressed, causing shear slip in a current stress field. The sliding is likely to break sealing in the fractures and, as a result, to increase their permeability. Such a mechanism is possibly significant under high-temperature conditions at geothermal fields because of temperature enhancement on chemical reactions for the sealing. We present a procedure to estimate the orientation of the critically-stressed fractures relative to axes of in situ principal stress with the aid of the Mohr diagram. The procedure allows us to evaluate intuitively how the orientation changes with factors such as magnitude of in situ principal stresses and pore pressure. We applied the procedure to estimate possible orientations of the critically-stressed fractures in major HDR test sites. Results show that overall alignments of microseismicity during hydraulic stimulation are within predicted ranges for possible orientations of the critically-stressed fractures. Furthermore, it was found that if the state of in situ stress is not favorable to cause sliding of natural fractures, it tends to lead a high wellhead pressure at hydraulic stimulation and a high recovery rate at circulation. On the other hand, if the state of in situ stress is favorable for sliding, it tends vice versa to lead a low wellhead pressure at hydraulic stimulation and a low recovery rate at circulation. 相似文献
17.
From August 1976 to June 1979, more than 220 seismic events were recorded by a 7-station network operating over an active gas field in France. 120 earthquakes with magnitudes greater than 1.0 were selected for a detailed study in order to understand the seismic response to a decrease in the gas reservoir pressure of 50 MPa. Composite focal mechanisms were determined for these events. We found that where preexisting fractures were known from well-logs, faults with the most favorable orientation were reactivated. In the part of the gas field where no preexisting faults were known, orientation of the fracture planes was close to the orientations of stratigraphic interfaces.Our kinematic model, constrained by the distribution of the earthquakes and their focal mechanisms, consists of the downward dropping of a block located close to the top of the gas field. The main faults, as defined by the spatial density of the seismic activity, define the limits of this block. The displacements observed along these faults can be either normal or reverse mechanism, dependent on the preexisting orientation of each fault. Another important result is the evidence that the depletion of the gas reservoir exerts the major influence on local seismic displacements, obscuring the effect of regional setting. 相似文献
18.
本文使用中国地震局地壳应力研究所2010—2011年期间在云南地区布设21个宽频带野外流动地震台记录到的波形资料,经时间域迭代反褶积求取远震接收函数,并挑选高质量Pms （莫霍面转换）震相,利用切向能量最小化方法获得283对高信噪比的径向和切向对应的Pms分裂参数,从而得到云南地区各台下方地壳各向异性. 结果显示,研究区内慢波时间延迟量在0.125 s和0.40 s之间变化,平均为0.25 s,且各向异性强弱与构造分布有一定相关性. 在扬子地台和保山地块表现为相对较强的各向异性,而思茅地块相对弱些,说明这些块体受下地壳流的影响作用各不相同. 从各向异性快波方向分布来看,在扬子地台和思茅地块除红河断裂带和澜沧江断裂带走向变化明显地区（如YNL04和YNL12台）外,各向异性方向均与断裂带走向近似平行,说明研究区内大型断裂带控制着下地壳流的构造变形. 腾冲地区的各向异性与其他三个块体均不相同,在该块体内部各向异性快波方向近似呈现出以火山为中心发散状分布,可能说明腾冲火山下方地幔热物质上涌到达下地壳后受上地壳的阻挡作用向四周发散的原因. 相似文献
19.
The sliding block theory was proposed by Newmark for determining the permanent displacement of embankments and dams under earthquake loading. This paper highlights recent applications of sliding block theory to different geotechnical structures. The equations to determine seismic factor of safety, yield acceleration and permanent displacement are given for rock block, soil slope, landfill cover, geosynthetic-reinforced soil retaining wall, and composite breakwater. The presented equations for seismic stability degenerate to that of static stability in the absence of earthquake. The permanent displacement for various structures can be obtained from that of a horizontal sliding block through a correction factor. A simplified procedure is included for the permanent displacement under vertical acceleration. The sliding block approach is rational for design under high seismic load. 相似文献
20.
塔里木周缘的新元古代地层中均记录了涉及Rodinia聚合和裂解的构造热事件,但塔里木在Rodinia超大陆中位置尚存争议.本文综合地层对比以及古地磁的研究方法,将塔里木陆块在Rodinia超大陆中置于澳洲板块的西北缘,并且塔里木的西南缘(现今位置)和澳洲的西北缘(现今位置)相连.基于塔里木周缘的构造热事件和塔里木、澳洲运动学特征分析,认为塔里木陆块周缘在约800~700 Ma中发生了强烈的裂谷事件,导致塔里木从Rodinia超大陆中裂解,但塔里木并没有完全从澳洲裂离,而是随澳洲一起,加入冈瓦纳大陆.在约450 Ma左右,塔里木与澳洲发生分离,其原因为古特提斯洋的扩张. 相似文献