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1.
Preferred orientation of the dominant phyllosilicate phase (serpentine) in the matrix of the Murchison meteorite (C2) was determined by X-ray pole figure goniometry. The basal plane (001) of the phyllosilicate shows a clear preferred orientation of an axial concentration type. The preferred orientation is very weak in comparison with the orientations of known terrestrial tectonites, and it resembles the weakest case observed in the loosely consolidated clayey sediments from the deep ocean bottom. However, gentle sedimentation of platy phyllosilicate grains on a flat surface under a weak gravity field does not generate a sufficient preferred orientation. It is suggested that the preferred orientation in the matrix of Murchison was generated by uniaxial compaction, and the magnitude of strain to give rise to the observed degree of preferred orientation is evaluated as ?9%. There are two possible explanations of the deformation: dynamic compression caused by impact, and static compaction in a parent body. Though the latter case appears to be appropriate in the present case, it is not straightforward, however, to conclude that the suggested deformation is caused by burial compaction along gravity under lithostatic stress in a small primitive parent body. 相似文献
2.
当外力的合力不通过活动地块的质量中心时，该地块将产生旋扭运动，运动的结果在其周边形成旋卷构造应力场．在该应力场作用下，与主应力作用面方向一致的断裂将由作用面的力学性质决定其活动方式．与主张应力作用面一致的断裂将产生张破裂，长期作用下将形成断陷盆地；与主压应力作用面一致的断裂将产生逆冲或逆掩活动，或形成褶皱．地质资料表明，长期稳定的华北地块在早第三纪初期解体，其中晋冀陕地块发生过逆时针转动，形成其周缘断陷系；上新世时晋冀陕地块解体，地块东边界西移，出现山西地堑系，形成鄂尔多斯地块．晋冀陕地块周缘的一些主要断裂的构造形迹及力学性质可用旋转构造应力场的主应力作用面解释． 相似文献
3.
Discussion on rotational tectonic stress field and the genesis of circum-Ordos landmass fault system 总被引：1，自引：0，他引：1
谢新生 《地震学报(英文版)》2004,17(4):464-472
Introduction Rotation is a universal form of the motion of matter, such as the rotation of cyclones in the air, eddies in streams and spiral nebulas in the universe. Rotational structure is a commonly seen structure in the crust, such as broom-shaped structure, S-shaped or reverse S-shaped structure, lo-tus-like structure, and turbine-like structure. They are the result of non-uniform motion of matter and dissymmetrical force actions in the nature. Turbine-like structure is the most complete … 相似文献
4.
《Physics of the Earth and Planetary Interiors》2006,154(3-4):234-242
We have measured magnetic hysteresis loops, zero-field-cooled (ZFC) and field-cooled (FC) remanence, and low-field AC susceptibility as a function of temperature between 2 and 40 K for a single crystal several mm in size and for two powders of manganese carbonate (mineral rhodochrosite, MnCO3), one ground from a natural precipitate (grainsize ∼100 μm) and another synthesized in the laboratory (grainsize ∼10 μm). For the single crystal, measurements carried out both in the basal (easy magnetization) plane and along the trigonal (hard magnetization) axis yielded, expectedly, grossly different magnetic properties. In the basal plane, hysteresis appears to be mostly controlled by domain wall movement at the two lowest temperatures studied, 5 and 15 K, as indicated by a fairly broad switching field distribution. At 25 K and above, however, magnetization reversal occurs at a single, well defined magnetic field, which we interpret as a characteristic field of the in-plane magnetic anisotropy. Hysteresis in the basal plane is observed up to 36 K which is above the nominal Néel temperature of rhodochrosite (34.3 K). In addition, a sharp coercivity peak occurs at 34.5 K. Rather unexpectedly, hysteresis is also observed for the magnetic field applied along the trigonal axis. It is very small at 5 K but develops gradually with increasing temperature, coercivity reaching maximum of 100 mT at 28 K and remanence peaking at slightly higher temperature (30–31 K). Hysteresis along the trigonal axis is observed up to 37 K. Hysteresis temperature dependence conforms with the AC susceptibility versus temperature curve which shows a maximum at 36.5 K. ZFC/FC remanence curves also closely match the temperature dependence of remanence extracted from hysteresis loops. We suggest that this behavior could be due to the presence of a minor, about 1 at.% amount of Fe2+ substituting for Mn in the crystalline lattice of rhodochrosite. Hysteresis measurements on powders have revealed a significant enhance in coercivity, up to 50 mT for the 100-μm powder and up to 150 mT for the 10-μm one. FC/ZFC ratio amounts to about 2 for the natural powder, while for the synthetic one, which is essentially pure material, it barely exceeds unity. FC/ZFC ratio can thus be viewed as a sensitive indicator of iron incorporation into rhodochrosite. 相似文献
5.
Ilya Tsvankin 《Geophysical Prospecting》1997,45(3):479-512
The transversely isotropic (TI) model with a tilted axis of symmetry may be typical, for instance, for sediments near the flanks of salt domes. This work is devoted to an analysis of reflection moveout from horizontal and dipping reflectors in the symmetry plane of TI media that contains the symmetry axis. While for vertical and horizontal transverse isotropy zero-offset reflections exist for the full range of dips up to 90°, this is no longer the case for intermediate axis orientations. For typical homogeneous models with a symmetry axis tilted towards the reflector, wavefront distortions make it impossible to generate specular zero-offset reflected rays from steep interfaces. The ‘missing’ dipping planes can be imaged only in vertically inhomogeneous media by using turning waves. These unusual phenomena may have serious implications in salt imaging. In non-elliptical TI media, the tilt of the symmetry axis may have a drastic influence on normal-moveout (NMO) velocity from horizontal reflectors, as well as on the dependence of NMO velocity on the ray parameter p (the ‘dip-moveout (DMO) signature’). The DMO signature retains the same character as for vertical transverse isotropy only for near-vertical and near-horizontal orientation of the symmetry axis. The behaviour of NMO velocity rapidly changes if the symmetry axis is tilted away from the vertical, with a tilt of ±20° being almost sufficient to eliminate the influence of the anisotropy on the DMO signature. For larger tilt angles and typical positive values of the difference between the anisotropic parameters ε and δ, the NMO velocity increases with p more slowly than in homogeneous isotropic media; a dependence usually caused by a vertical velocity gradient. Dip-moveout processing for a wide range of tilt angles requires application of anisotropic DMO algorithms. The strong influence of the tilt angle on P-wave moveout can be used to constrain the tilt using P-wave NMO velocity in the plane that includes the symmetry axis. However, if the azimuth of the axis is unknown, the inversion for the axis orientation cannot be performed without a 3D analysis of reflection traveltimes on lines with different azimuthal directions. 相似文献
6.
Electrical anisotropy, the effect of current density in a medium being a function of the orientation of the electric field,
is being recognized increasingly as an important effect in explaining Earth electromagnetic observations. A consideration
of anisotropy, however, in most cases is an admission of spatial aliasing in earth structure, wherein the averaging volume
of diffusive EM fields may be greater than the characteristic dimensions of a family of oriented structures, thus leading
to a response which is equivalent to a bulk anisotropic medium. Even for two-dimensional geometries, there can be strong non-parallelism
of principal axes of vertical magnetic field relative to the impedance over broad areas, as well as impedance phase variations
which leave normal quadrants, if there are multiple directions of anisotropy or anisotropy strike distinct from bulk geometric
(2D) strike. This paper concentrates on experience with regional field studies in continental settings where bulk anisotropy
is apparent. Upper crustal anisotropy may result from preferred orientations of fracture porosity, or lithologic layering,
or oriented heterogeneity. Lower crustal anisotropy may result from preferred orientations of fluidized/melt-bearing or graphitized
shear zones, but does not necessarily reflect current state of stress per se. In the upper mantle, the prior causes all may act in pertinent domains, but added to these is the possibility of strong
electrical anisotropy due to hydrous defects within shear-aligned olivine crystals (solid-state conduction). Several field
examples from continental MT investigations will be discussed, which roughly fall into active transpressional, active transtensional,
and fossil transpressional regimes. A general challenge in interpreting data with apparent anisotropic effects is to establish
the tradeoff between heterogeneity and anisotropy in the inversion of EM responses. 相似文献
7.
采用Hypo2000和双差定位方法对2013年云南洱源MS5.5和MS5.0地震序列进行了重新定位. 结果显示: 精定位后洱源地震序列分布优势方向集中在160°; 用CAP方法反演了两次5级地震震源机制, 节面Ⅱ的走向158°和157°与余震优势分布方向一致; 现场考察MS5.5和MS5.0地震极震区的长轴方向也是NW向. 上述结果与维西—乔后断裂NNW走向一致, 据此判定该断裂为洱源MS5.5和MS5.0地震的发震构造. 序列震源机制解显示, 洱源地震序列表现出不同的错断性质以及不同方向主压应力, 可能与维西—乔后断裂所处区域复杂构造应力场有关. 相似文献
8.
Adrian E. Scheidegger 《Surveys in Geophysics》1981,4(3):233-253
The neotectonic stress field in the Alpine-Mediterranean region is investigated. It is shown that information on this field can be obtained from insitu measurements, from earthquake fault plane solutions, from the orientation of joints and even from valley trends. The available data are collected and collated. It is shown that there is a general correspondence in any one area between these types of data. Maps showing the orientations of the principal stress directions are given. 相似文献
9.
The principal stress axes and eigenvalue ratios of the stress tensors from two active seismic regions in Alaska (eastern Aleutian Arc and eastern Gulf of Alaska) are computed. These results are obtained using focal mechanisms of earthquakes with magnitudes ranging from 5.5 to 8.2 and show for both regions slightly different compressional states with an orientation of the pressure axis of N26°W for the eastern Gulf of Alaska and N27°W for the east Aleutian Arc. The eigenvalue ratios for the eastern Gulf of Alaska and east Aleutian Arc are 0.84 and 0.99, respectively. The algorithm used in computations allows us to detect some focal mechanisms which are incoherent with respect to the obtained stress tensors. These incoherences are explained in terms of some tectonic features of the region. The orientations of possible pre-existing fractures which would need an unrealistically high maximum shear stress to start a slip on their fault planes are also investigated. These critical orientations depend on a constitutive frictional law as well as on eigenvalue ratios and eigenvectors of the stress tensors. The orientation, which is given in our case by the angle between the normal vector to a fracture and the regional tensional axis, is approximately 59° for the eastern Aleutian Arc. This angle ranges from 49° to 59° for the eastern Gulf of Alaska. It must be pointed out that fractures which need unrealistically high shear stress to start slip on their fault planes are defined by a very narrow band of possible angles between tensional direction and the normal vector to fault plane. 相似文献
10.
月球深部断裂是研究月球早期应力场演化和动力机制的一类重要构造.本文基于GRAIL月球重力数据计算了全月布格重力梯度,在此基础上对月球深部断裂进行了全球绘制,共识别月球深部断裂226条.计算了断裂的长度和走向等基本参数,断裂总长度达到37137 km,平均长度为164 km.统计月球深部断裂在不同范围内的分布情况,发现多数断裂分布在月球的中低纬度地区,且北半球的断裂多于南半球.此外,大型月海集中区所在的纬向带断裂分布最多,断裂经向分布最多的区域为风暴洋的西侧.从全球尺度和不同经纬度带绘制断裂走向玫瑰花图,总体上月球全球尺度上的深部断裂表现出NE-SW和NW-SE的优势走向,不同经度带断裂的优势走向变化不明显,但在纬度带上有显著的变化.南北半球的中纬度带和高纬度带具有相同的优势走向,分别为NE-SW和NW-SE、E-W,在低纬度带的优势走向有所差异,分别是南半球的NE-SW和NW-SE以及北半球的N-S. 相似文献
11.
S. L. Shalimov 《Izvestiya Physics of the Solid Earth》2017,53(3):488-491
It is shown that magnetostrophic waves which are generated in the equatorial plane of the Earth’s core due to the instability of the equatorial jet and which propagate almost transversely to the rotational axis off the tangent cylinder, have a negative helicity in the northern hemisphere and positive helicity in the southern hemisphere. When the wave trains propagate through the regions with a constant azimuthal magnetic field caused by the Ω-effect, this helicity distribution induces an electromotive force (emf) (due to the α-effect), which may lead to the maintenance of the initial dipole field by the scenario of the α-Ω dynamo. 相似文献
12.
多极化冰雷达所揭示的DOME A区域冰盖内部冰晶组构特征 总被引：3，自引：0，他引：3
The ice exceeding one million years old has significant meaning for verifying and interpreting the middle Pleistocene transition （MPT） and the relationship between greenhouse gas and climate change. The region near Dome A in Antarctica satisfies the conditions for obtaining million-years-old ice since it has low temperatures and low accumulation rates. We analyze the corresponding relation between radar wave features and the crystal orientation fabric （COF） types based on the results of multi-polarization plane radio echo sounding （RES）. The results show that, even in the summit of the ice sheet, the COF type is not perfect, but is an elongated single-pole COF. Principal-axis-orientation differences of the COF among the different periods exist and reveal that the ice flow orientations are not constant but deviate clockwise with the increasing depth. This may be related to the adjacent basal valley or both height and position changes of the summit during the glacial-interglacial periods. 相似文献
13.
14.
Alba Zappone 《Surveys in Geophysics》1994,15(5):619-642
In order to determine the seismic properties of rocks representing the continental crust/upper mantle transition, a structural and petrographical study of peridotites of the Ivrea-Verbano zone (N. Italy) has been undertaken. The seismic behaviour (Vp, Vs, birefringence, orientation of the fast shear-wave polarisation plane) has been calculated from the modal composition of rock samples, together with the crystallographic preferred orientation and the single crystal elastic constants, using the methods of Mainprice (1990). It is shown that the intrinsic anisotropy of peridotites is mainly due to the lattice preferred orientation (LPO) of olivine and to the competing effects due to the LPO of orthopyroxene. If present, well-oriented hydrous phases such as phlogopite, leads to both P- and S-waves velocities becoming drastically reduced, but the anisotropy and the S-wave splitting (mainly on the foliation plane) is increased. An attempt has been made to apply this petrologic and microstructural approach to understand the seismic properties of ultramafic rocks with the aid of a mobile seismic network set up in the Ivrea-Verbano zone. Five recording units with 3-component geophones were installed on the most representative lithologies of the Ivrea-Verbano zone: kinzigites, gabbros, stronalites, and on metapelites of the adjacent outcrop of the Serie dei Laghi. During five months the seismic network recorded 49 events that were mainly regional earthquakes. The preliminary analysis of the first arrival revealed a high-velocity anomaly near the Finero ultramafic massif. Rough calculations indicated that this anomaly could be due to a shallow-depth, peridotitic body about six kilometres thick. S-wave polarisation analysis was carried out on the horizontal components of the seismograms of four regional earthquakes that showed a first arrival propagating almost vertically at the recording sites. Four earthquakes were chosen in order to reconstruct the orientation of the polarisation plane of the shear phases. The preliminary results of this analysis have shown a qualitatively good agreement between the orientation of the polarisation plane of the fast shear-wave and the strike of the foliation at the station near Finero, located on kinzigites of the Ivrea-Verbano zone, although the relationships between the local structural setting and the polarisation orientations at the other recording sites is not yet so clear. 相似文献
15.
Summary The high field torque curves of hematite bearing rocks are not caused by directional differences in the energy of magnetization to saturation, but rather by the couple between the ferromagnetic moment and the applied field. An expression, derived for the high field torque curve of a single crystal of hematite, whose basal plane makes an arbitrary angle with the plane of rotation of the applied field, is found to be in excellent agreement with experiment. Furthermore it is shown that the Fourier spectrum of hematite bearing rocks should in general contain significant higher harmonics and that therefore the high field method is not particularly suitable for determining the preferred crystalline alignment of hematite bearing rocks. 相似文献
16.
基于国家测震台网数据中心提供的波形资料, 采用gCAP方法反演2020年5月18日云南巧家M5.0地震及研究区域51次地震震源机制解, 并收集研究区域震源机制解50个。 采用网格搜索法反演区域构造应力场, 并对研究区域采用不同划分进行应力场反演。 获得以下结论: ① 主震震源机制解节面Ⅰ的走向、 倾角和滑动角分别为175°、 67°和-19°, 节面Ⅱ的走向、 倾角和滑动角分别为273°、 73°和-156°, 矩震级为4.97, 矩心深度为8.8 km。 表明主震属于兼具逆冲分量的走滑型地震; ② 震后区域应力场主压应力轴方位为NWW, 倾角接近水平, 主张应力轴方位为NNE, 倾角接近水平, 属于走滑型应力状态, 与周边地质构造运动状态相吻合; ③ 对研究区域采用不同划分所得应力场结果相差不大, 表明该区域应力场比较稳定, 受深大断裂带和震源机制解类型影响较小。 相似文献
17.
18.
《Physics of the Earth and Planetary Interiors》2006,154(3-4):337-349
An idealised stable uniaxial single-domain (SD) particle permits only two possible stable positions in which the magnetic moment can lie, either closely parallel or anti-parallel to the particle long (easy) axis. In real acicular SD particles, which have generally been regarded as uniaxial, this implicit two state feature has never been challenged, whilst there has been considerable debate concerning the mechanism of moment reversal between the two states. We present experimental results suggesting that acicular SD particles may actually have a range of several quantifiable stable (or metastable) orientations of the net magnetic moment. In order to help explain our experimental observations we present a new simple model of acicular SD particles, which gives quantitative predictions verified by further experiments. The model also appears to be relevant to other SD particle morphologies and crystal structures (such as hematite). A possible physical basis for our model in acicular particles may lie in non-uniform SD structures (such as the flower or vortex states). Small variations in the non-uniform SD structures available to a particle might allow a range of stable positions of the net moment.The results have several implications for rock magnetism and palaeomagnetism. Firstly, the new model can quantitatively account for several previously unexplained diverse phenomena exhibited by real acicular SD particles. These include the acquisition of gyroremanences and field-impressed anisotropy in dilute dispersions of such particles, as well as observations of transverse components of remanence in individual acicular SD particles. All these phenomena are theoretically impossible in idealised uniaxial SD particles. Interestingly, it appears that these phenomena could now be used to quantify the deviation of real acicular SD particles from ideal uniaxial behaviour and also, therefore, the deviation from a uniform SD structure. In hematite, observations of large field-impressed anisotropy appear to be quantitatively explained by the available positions of the moment in the basal plane.Secondly, computations of the ancient field vector and palaeointensity from remanence anisotropy techniques would not only be controlled by the shape and distribution of the particles, but also by the range of possible stable orientations of the net moment within each SD particle. Laboratory analogue remanences (and, we suspect, natural remanences) would be influenced by the range of possible stable moment positions. Quantifying the range of these stable moment positions, upon acquisition of laboratory or natural remanences, should lead to improved methods of computing the ancient field direction and palaeointensity in anisotropic rocks. 相似文献
19.
北京时间2020年7月23日04时07分,西藏自治区那曲市尼玛县发生MS6.6地震,震源深度10 km,震中位置为（33.19°N,86.81°E）。主震发生当日18时50分,发生一次MS4.8强余震,震源深度为10 km。本文基于西藏、青海、新疆区域波形资料,采用ISOLA近震全波形方法对这两次地震进行震源机制反演。结果显示,尼玛MS6.6主震的最佳断层面解为:节面Ⅰ走向8°/倾角46°/滑动角?93°,节面Ⅱ走向191°/倾角44°/滑动角?87°;矩震级MW6.4,最佳矩心深度7 km。震源区应力主轴的空间取向为:主压力轴P的方位角220°、倾伏角88°,主张力轴T方位角99°、倾伏角1°。MS4.8强余震的最佳断层面解为:节面Ⅰ走向12°/倾角47°/滑动角?106°,节面Ⅱ走向214°/倾角45°/滑动角?74°;矩震级MW5.0,最佳矩心深度6 km。震源区应力主轴的空间取向为:主压力轴P的方位角207°、倾伏角78°,主张力轴T方位角113°、倾伏角1°。震源机制反演结果表明,这两次地震均为以正断型为主的地震事件,与震源区附近先前地震的震源机制有较好的一致性。结合周边地质构造和余震分布,我们认为尼玛MS6.6地震可能是由位于日干配错断裂和依布茶卡盆地西缘断裂之间的一条正断层活动所引发的。 相似文献
20.
Andreas Klügel Thomas R. Walter Stefanie Schwarz Jörg Geldmacher 《Bulletin of Volcanology》2005,68(1):37-46
Many volcanic rift zones show dikes that are oriented oblique rather than parallel to the morphological ridge axis. We have evidence that gravitational spreading of volcanoes may adjust the orientation of ascending dikes within the crust and segment them into en-echelon arrays. This is exemplified by the Desertas Islands which are the surface expression of a 60 km long submarine ridge in southeastern Madeira Archipelago. The azimuth of the main dike swarm (average = 145°) deviates significantly from that of the morphological ridge (163°) defining an en-echelon type arrangement. We propose that this deviation results from the gravitational stress field of the overlapping volcanic edifices, reinforced by volcano spreading on weak substratum. We tested our thesis experimentally by mounting analogue sand piles onto a sand and viscous PDMS substratum. Gravitational spreading of this setup produced en-echelon fractures that clearly mimic the dike orientations observed, with a deviation of 10°–32° between the model’s ridge axis and that of the main fracture swarm. Using simple numerical models of segmented dike intrusion we found systematic changes of displacement vectors with depth and also with distance to the rift zone resulting in a complex displacement field. We propose that at depth beneath the Desertas Islands, magmas ascended along the ridge to produce the overall present-day morphology. Above the oceanic basement, gravitational stress and volcano spreading adjusted the principal stress axes’ orientations causing counterclockwise dike rotation of up to 40°. This effect limits the possible extent of lateral dike propagation at shallow levels and may have strong control on rift evolution and flank stability. The results highlight the importance of gravitational stress as a major, if not dominant factor in the evolution of volcanic rift zones.Editorial responsibility: M Carroll 相似文献