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1.
The Bouguer anomaly map of the Kalabsha and Seiyal areas was analysed on the basis of the available data about the depth to the basement from three boreholes. The density contrast between the basement complex and the Nubia formation was estimated from the gravity values and basement depths. Applying the estimated value of the density contrast, a residual map representing the basement effect and a basement relief map were constructed. The basement depth in Kalabsha and Seiyal areas range from 150 to 500 m below mean sea level. Comparing the general characteristics of the Bouguer anomaly of the Kalabsha and Seiyal areas with the clusters of earthquakes in the area since 1982 till present reveals a gravity low coinciding with a deep focal area. The gravity values increase toward a shallow focal area. 相似文献
2.
根据航磁、重力和地震数据以及地质和辅助地球物理资料，对约旦东北部前寒武纪岩石的轮廓和变化及其上覆的沉积岩石的厚度进行了研究．识别出5个具有特定磁性特征的磁场区，每个磁场区都有其特征的样式和突变的边界，每个磁场区的物质组成存在明显差异，其构造边界均与断层相对应．计算表明基底表面有很大起伏，磁化的前寒武纪岩石深度变化范围为-5000m至-10000m，可以识别出由基底下陷相对应的5个盆地或拗陷带，同时可见3个起伏较大的构造隆起．探测结果表明，古生代建造中发育的主要断裂呈N-S与NNE向，而在新生代建造中发育的断裂则呈NE-SW，NW-SE和E-W向．研究区构造发展的第一构造阶段与E-W向张力有关，第二构造阶段的产物明显受到第三构造阶段发生的构造变形的改造，并与阿拉伯板块的逆时针旋转有关．磁场区之间的移位、错断、拖曳和并置被认为剪切断层所造成．剪切形式表明位移是左行的，即北侧的块体向北西方向移动． 相似文献
3.
2018年1月23日,在美国阿拉斯加湾海域发生了一次MW7.9地震.震源机制解表明这次地震以走滑为主,可能发生在近东西向或南北向的陡倾角断层上,早期余震并非线型展布.我们利用视震源时间函数分析确定了此次地震的总体破裂方向,并结合余震的空间展布特征构建了相互交叉的双断层模型,进而通过联合反演远场P波和SH波数据获得了此次地震的时空破裂过程.视震源时间函数分析表明总体破裂方向既非东西也非南北,而且反演结果表明,两个断层上都发生了错动,总体破裂时间~50 s,释放标量地震矩~8.11×1020 Nm.震源时间函数表现出多事件特征,且两个断层破裂的时间过程也不相同.破裂首先在南北向断层的南端开始,很快触发了东西向断层,最后终止于南北向断层的北端.每个断层都具有相当的时空复杂性,位错分布很不均匀.东西向断层具有三个凹凸体,一个位于震源附近,其他两个位于断层两端.南北向断层有两个凹凸体,均位于断层北段,最大滑动量~5.0 m就出现在这里.发生最大位错的南北向断层延伸至阿拉斯加海沟,增加了触发阿拉斯加海沟其他断层发生破裂的可能性. 相似文献
4.
Aswan Lake is the second largest man-made lake in the world. Its filling started 1964 and reached the maximum water level in 1978. An earthquake of magnitude 5.5 took place in 1981 along the most active fault near the lake (Kalabsha fault). This earthquake was follwed by a tremendous number of smaller events that continue till now.Seismicity and the underground water table around the lake are monitored continuously through a radio-telemetered network. A local geodetic network was established around parts of the active faults in the northwestern part of the High Dam Lake, for monitoring vertical and lateral movements. The Kalabsha local geodetic network (the first one) was established around an active part of the Kalabsha fault in 1983. Precise geodetic measurements have benn carried out twice a year since 1984.On the basis of the repeated geodetic measurements, seismicity of the area and geophysical as well as geological data, the present state of the geodynamical properties of the Kalabsha area is studied.Remarkable horizontal movements were detected; they are correlated with the seismicity of the area and are attributed to the differential loading by the lake. The Kalabsha fault is a right-lateral strike-slip motion on an E-W plane. The magnitude of the movements detected along the fault is variable for the different epochs of measurements and is correlated with both seismicity and water loading in the lake. 相似文献
5.
HVSR prospecting in multi-layered environments: An example from the Tyrnavos Basin (Greece) 总被引：1，自引：0，他引：1
The Tyrnavos Basin (Central Greece) is an E-W trending graben bordered by two major antithetic sets of right-stepping dip-slip normal faults that began forming during Middle Pleistocene as a consequence of the N-S extension which affected the whole Aegean Region. This Quaternary structure is superimposed on the Pliocene-Early Pleistocene NW-SE trending Larissa Basin, approximately 700–800 m deep. Seismic activity is instrumentally well documented within and surrounding the investigated area. Based on structural, morphotectonic and palaeoseismological data, several structures previously characterised as active faults have been investigated by applying the HVSR method. This method is commonly used to map the thickness of sedimentary layers in a basin based on the variation of the fundamental 1-D frequency. The polyphased structural evolution and the consequently complex geological setting do not allow for the contouring of a unique continuous surface. We therefore developed a new interpretation technique for statistically significant HVSR peaks, in order to obtain 2-D sections that can be interpreted in a seismic-like fashion. We applied this technique across the major active faults bordering the basin. The results confirm their occurrence at depth and document the important vertical component of displacement. 相似文献
6.
The Kunming basin is a Cenozoic faulted basin controlled by N-S trending active faults. there are totally 8 main active faults in and around the Kunming basin area. Inversion of fault slip data suggests that the stress field of the Kunming basin has experienced two major stages. In the first stage (from the late-Pliocene to mid-Pleistocene), the regional tectonic stress field was characterized by near E-W compression and near N-S extension. In the second stage (from the late-Pleistocene to the present), the tectonic stress field has been mainly characterized by NNW-SSE compression and NEE-SWW extension. Under such a stress field, the near N-S trending faults in the region mainly show a lateral slip. 相似文献
7.
Aswan Lake started impounding in 1964 and reached the highest water level so far in 1978 with a capacity of 133.8 km3, thus forming the second largest man-made lake in the world. An earthquake of magnitude 5.3 (Ms) took place on 14 November 1981 along the most active part of the E-W Kalabsha fault beneath the Kalabsha bay (the largest bay of the lake). This earthquake was followed by a tremendous number of smaller events that continue till now. A radio-telemetry network of 13 seismic short period stations and a piezometer network of six wells were established around the northern part of the lake.Epicenters were found to cluster around active faults near the lake. The space-time distribution and the relation of the seismicity with the lake water level fluctuations were studied. Six years after flooding the eastern segment of the Kalabsha fault, strong seismicity began following the main shock of 14 November 1981. It occurred four days after the reservoir had reached its seasonal max level. The effect of the North African drought (1982 to present) is clearly seen in the reservoir water level. As it decreased and left the most active fault segments uncovered, the activity (Gebel Marawa area) decreased sharply. Also, the shallow activity was found to be more sensitive to rapid discharging than to the filling. This study indicates that geology, topography, lineations in seismicity, offsets in the faults, changes in fault trends and focal mechanisms are closely related. No relation was found between earthquake activity and both-ground water table fluctuations and water temperatures measured in wells located around the Kalabsha area. 相似文献
8.
D. Hatzfeld A.A. Christodoulou E.M. Scordilis D. Panagiotopoulos P.M. Hatzidimitriou 《Earth and Planetary Science Letters》1987,81(4)
During March and April 1984, a temporary network of 29 portable stations was operated in the region of the Mygdonian graben near Thessaloniki (northern Greece), where a destructive earthquake (Ms = 6.5) had occurred in the Summer of 1978. During a period of six weeks we recorded 540 earthquakes with magnitudes ranging from −0.2 to 3.0. From this set of data, 254 events are selected which according to us have a precision in epicenter and depth better than 1.5 km. A total of 54 single-event focal mechanisms have been determined.The seismicity and focal mechanisms show a rather complex pattern. There are no clear individual faults, but the E-W and NW-SE striking zones show N-S extension. Zones striking NNE-SSW show dextral strike-slip motion but NW-SE zones with sinistral strike-slip are also observed.In the center of the graben where the 1978 earthquake was located, we observe several thrust mechanisms distributed in two groups showing either NW-SE or E-W compression; these earthquakes seem to be located 2 km above the earthquakes showing normal mechanisms.The mean direction of the T-axes, found from the focal mechanisms, trends N15° and dips sub-horizontal.We propose a model for the formation and evolution of a complex graben system comprising several stages. In the initial stage the deformation occurs along pre-existing NW-SE or NNE-SSW faults, with normal or strike-slip movements. In the second stage, a new, E-W trending group of normal faults is formed over the ancient fault network. These new faults have a direction perpendicular to the mean T-axis and accommodate better the actual state of stress. At this stage the initial faults adjust to the deformation produced by the E-W trending new faults, and may constitute geometric barriers to the evolution of the new normal faults. 相似文献
9.
Tomographic inversion for the three-dimensional seismic velocity structure of the Aswan region,Egypt
The Thurber iterative simultaneous inversion program is used to determine the three-dimensionalP-wave velocity structure in the Aswan seismic region of Egypt. The tomographic inversion presented in this study is based on 1131P-phase observations at 13 stations from 89 local earthquakes, all of which occurred within the Kalabsha fault zone. The assumed initial velocity model is that deduced from local explosion experiments. The results indicate that the Aswan region is characterized by a heterogeneous crust, consisting of a shallow, low-velocity zone and a deeper high-velocity anomaly. Seismic velocity structure within the shallow part demonstrates that the inferred change in velocity exists primarily across the east-west trending Kalabsha fault scarp, whereas the high-velocity zone is located south of this fault. Two well-resolved, low-velocity zones appear within the upper 6 km of the crust. The first coincides with a graben structure located between the Kalabsha and Seiyal faults and the second exists between the N-S Kurkur fault and the main axis of Lake Aswan. Both low-velocity zones occupy an area of approximately 30×40 km, located along the western bank of the lake. The most significant result of this study is that the location of the deeper, high-velocity anomaly coincides with the concentration of seismic activity in the lower crustal layer. 相似文献
10.
Lake Van is located in very intensely deformed tectonic settings in the eastern Turkey. The surrounding area of Lake Van has
major tectonic structures; NE and NW trending active conjugate strike-slip faults, pull-apart basins along these faults, E-W
trending active thrust faults, folds, compressional ramp basins, N-S trending folds, NE-SW aligned continental collision-related
volcanoes and N-S trending tensional cracks functioned as magma conduits. Since the area is tectonically very active, the
earthquake activity within the basin and the surrounding area of Lake Van is very high. In this study, we have analysed the
records of VANB broadband station of Kandilli Observatory and Earthquake Research Institute's network for the seismic events
(2000–2004) that occurred in the basin and in the vicinity of Lake Van. Based on the spectral analysis of earthquake data,
we have mainly observed three types of seismic events; hybrid event, long period event and tremor. We have suggested that
the observed hybrid, long period and tremor type of seismic events that occurred in the study area are related to the upward
moving materials and stress loading in the mid and lower crust based on the geophysical data. 相似文献
11.
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
12.
Late amagmatic extension along the central and eastern segments of the West Philippine Basin fossil spreading axis 总被引：2，自引：0，他引：2
The spreading processes within the West Philippine Basin (WPB) remain partly unknown. This study presents an analysis of the tectono-magmatic processes that happened along its spreading axis during the conclusion of the last spreading phase at 33/30 Ma. We demonstrate that the late episode of N-S opening from an E-W-trending spreading system has been followed by a late tectonic event occurring in the central and eastern parts of the basin. This event was responsible for transtensional strain accommodated along the NW-SE faults cutting through the former E-W rift valley in the central part of the basin. In its eastern part, the same event occurred at a larger extent and led to the creation of a new NW-SE axis, obliquely cutting the older E-W spreading segments and their associated spreading fabrics. At this location, several tens of kilometers of slightly oblique amagmatic extension occurred following a ∼60° direction. We propose that this late event is associated with the onset of E-W opening of the Parece-Vela Basin located along the eastern border of the WPB at 30 Ma. Extensive stresses within this basin were probably transmitted to the hot and easily deformable rift zone of the WPB. The newly-created NW-SE axis most likely propagated from east to west, being responsible for scissors opening within the WPB. NE-SW extension ceased when well-organized spreading started at 26 Ma in Parece-Vela Basin, accommodating entirely the global extensive stress pattern. 相似文献
13.
The andesitic stratovolcano Volcán de Colima is one of the most active volcanoes in Mexico. The recent eruption of Volcán de Colima began in November 1998 and was preceded by a 12-month period of seismic activity that included five earthquake swarms. About 600 events with magnitudes from -0.5 to 2.7 were located within a 50-km2 area extending northward from the crater of Volcán de Colima to the Pleistocene volcano Nevado de Colima. The majority of hypocenters within this area did not exceed 5 km depth below sea level. We investigated earthquake focal mechanisms and seismotectonic deformations of the volcanic edifice. Focal mechanisms during four earthquake swarms indicated normal faulting associated with extensional processes, which is in agreement with the general stress regime near the volcano revealed by field measurements of fault slips. Earthquakes in the fifth swarm had focal mechanisms associated with inverse faulting, showing a significant change in the stress situation just before the beginning of the eruption. The calculated deformations varied from 1.3᎒-11 to 2.7᎒-9. The first swarm of November-December 1997 resulted in a N-S horizontal elongation that was two times greater than the E-W horizontal shortening. The volume was also subject to vertical shortening. The second and third swarms, observed in March and May 1998, showed uniform horizontal N-S and E-W elongations accompanied by a vertical elongation of the volume. In June-July 1998, the situation of November-December 1997 was repeated, with N-S horizontal elongation greater than the E-W horizontal shortening of the volume accompanied by intensive vertical shortening. During the last swarm of October-November 1998, slight E-W elongation of the seismic volume was accompanied by strong N-S shortening and very slight vertical shortening. We assume that the seismic activity prior to the 1998 eruption of Volcán de Colima developed along two intersecting tectonic structures, the N-S-trending Colima rift, and the E-W-trending system of faults associated with Tamazula fault. During the first stage (November 1997-July 1998) the passageway for magma was developed along the Tamazula fault system under horizontal extension without any surface manifestation. In October-November 1998, the seismic events began to cluster along the Colima rift structures under predominantly compressional stresses; this condition culminated with the extrusion of andesitic block lava from the summit crater. 相似文献
14.
J. Mrlina A. H. Radwan R. M. Hassan S. M. Mahmoud A. A. Tealeb E. A. Issawy 《Journal of Geodynamics》2003,35(4-5):499-509
The Kalabsha region at the northwest side of Lake Aswan has been a subject of seismological and geodetic investigations since 1981, after the 5.5 M earthquake on 14 November. The subsequent seismic activity was related to the effect of water-level oscillations in the Lake. Geodetic measurements provided indications of regional stress and of the local character of vertical movements. As crustal dynamics represents a potential hazard with respect to the size of the lake, other techniques have been applied to the monitoring system. Repeated gravity test measurements were already made in the late 1980s and in 1994, but only in 1997 was a new epoch of long-term investigation initiated. The measured data showed sufficient accuracy of approx. 5 μGal. Already the first difference of the two campaigns of the years 1997 and 2000 showed a few important features. First of all, the temporal non-tidal changes of gravity exceed the level of confidence significantly. The changes were compared with older available geodetic data, and it was concluded, that the gravity changes were not related directly to the vertical movements of the surface. On the contrary, a water loading effect may be expected on the eastern side of the network, especially in the Kalabsha local net. The development of the stress field is considered to be the main source of observed gravity changes. In both the Kalabsha and Seiyal nets the changes differ according to the relative positions of the particular measuring points with respect to the faults. 相似文献
15.
Han-Shou Liu 《Physics of the Earth and Planetary Interiors》1985,40(1):43-60
This paper uses plate tectonics and satellite-derived gravity data to further discussion of crustal deformation under the Tibetan Plateau. The first of our three contributions is a spherical harmonic analysis of the global plate boundary system. A distribution of 470 Dirac delta functions is applied to describe the generating forces according to the rates of crustal creation and destruction on the plate boundaries. Analysis of the extensional and compressional forces in the spreading and subducting zones shows that the present global plate motion causes compressional stresses in the N-S direction under the Tibetan Plateau. The second contribution is the calculation of the crustal stresses in Tibet as inferred from satellite gravity data. By applying solutions to the problem of the spherical shells, the satellite-determined stresses indicate that the up-welling mantle material under Tibet induce N-S and E-W extension. Finally, a superimposed stress system is constructed. This stress system shows that the present crustal deformation in Tibet does not produce N-S shortening but generates E-W extension.The results of this paper have provided geodynamical explanations for geological field observations in Tibet and fault plane solutions of earthquakes in the Tibetan side of the India-Eurasia collision. The stress patterns reveal that the cold downwelling mantle convection flow beneath southern Tibet pulls the Indian plate down but applies a bending moment on the end of the plate to uplift and support the mass of the Himalayas. 相似文献
16.
通过对鲁西隆起区重磁资料的分析和反演计算,研究了沂沭断裂带、齐河—广饶断裂带、聊城—兰考断裂带、丰沛断裂带以及地块内部断裂的重磁异常、莫霍面和居里面深度特征,并讨论了鲁西隆起的地质构造特征和构造活动性.结果显示:鲁西隆起基底广泛出露,沉积层主要分布在由断裂下降盘控制的凹陷内,区内断裂深度达20 km以上,其中蒙山断裂深入至上地幔,控制了蒙山金伯利岩型金刚石矿的产出;鲁西隆起区莫霍面深度为30—35 km,整体呈向西开口的箕形,地块中部地壳厚度较厚,除西侧地壳呈阶梯状增厚外隆起地块四周地壳逐渐减薄;居里面深度介于20—33 km之间,中部地区较深,为整体稳定的地块,断裂带分布位置对应于居里面梯度带;地震活动主要集中于断裂带与莫霍面梯度带交会区以及断裂带上的居里面突变区. 相似文献
17.
The feasibility of using temperature measurements at a depth of about 2 m for locating and delineating salt domes and faults has been investigated both theoretically and in experimental field surveys. It is shown that measurable temperature anomalies in the soil are to be expected over shallow salt domes. In a field survey over a salt-dome area bordering the Groningen gas field, a large number of temperature measurements were made in small holes (2 m deep, 3 cm in diameter) within a relatively short time (some weeks). The results clearly indicate several temperature anomalies with differential temperatures of about 1°C. Comparison of our thermal contour map with interpretations of available seismic or gravity data, or with direct evidence from wells, showed an excellent correlation. Seismic data even support the shape of the thermal contours. Results in similar agreement with gravity or well data were obtained over salt ridges in a tropical area. Experiments showed that the technique worked as well in lakes and marshes as on dry land. In addition, some experimental evidence collected so far over shallow and surface faults is presented. In several cases, strong thermal anomalies coincided with known surface faults. A thermal model for a surface-fault zone is suggested which accounts satisfactorily for the observed thermal data. It suggests some diagnostic value for the fault's geometry. For shallow faults, however, lack of knowledge of subsurface detail prevented any unambiguous correlation with observed thermal anomalies. Accordingly any geological use of thermal analysis over shallow faults remains debatable. The field technique is simple, needs little correction and can, where useful, easily be included in routine gravity work to provide additional local information. 相似文献
18.
The Moho depth, crustal thickness and fault systems of the East Vietnam Sea (EVS) are determined by 3D interpretation of satellite gravity. The Moho depth is calculated by 3D Parker inversion from residual gravity anomaly that is obtained by removing the gravity effects of seafloor and Pre-Cenozoic sediment basement topographies from the free air anomaly. The 3D inversion solution is constrained by power density spectrum of gravity anomaly and seismic data. The calculated Moho depths in the EVS vary from 30–31 km near the coast to 9 km in the Central Basin. A map of the lithosphere extension factor in the Cenozoic is constructed from Moho and Pre-Cenozoic sediment basement depths. The fault systems constructed by the maximum horizontal gradient approach include NE-SW, NW-SE, and N-S oriented faults. Based on the interpretation results, the EVS is sub-divided into five structural zones which demonstrated the different characteristics of the crustal structure. 相似文献
19.
The Chisone Valley is located in the internal NW Alps, in the Pinerolese District, an area characterized by present low to medium seismicity. Fine-grained sediments (sand, silt and clay with interbedded gravel) crop out in the lower Chisone Valley: they were first interpreted as glaciolacustrine deposits, and then as a lacustrine infilling of the valley floor probably due to differential uplifting of the valley mouth. Review of this data, together with new field and palynological observations, lead us to refer the lacustrine deposits to approximately the Lower Pleistocene (Villafranchian). In many outcrops, the lacustrine deposits show strong soft-sediment deformation such as convolute laminations, water-escape structures and disrupted beds, some of them associated with folds and faults (cm to dm in size); only two sites show metric to decametric folds and faults trending E-W and N-S. Detailed structural analysis conducted along a recently exposed section (Rio Gran Dubbione site) shows several soft-sediment deformation features on the limbs of mesoscale folds. Because of their intimate structural association, the origin of these minor structures seems to be connected to synsedimentary activity on reverse and normal faults (m to dm in size) affecting the lacustrine deposits in the same locality. Soft-sediment deformation features can be interpreted as possible paleoseismites. If so, the present seismicity of the Pinerolese District, which is the major area of such activity in NW Italy, cannot be considered an isolated episode in the geological evolution of the region; even if there is no supporting evidence for continuous seismicity, the deformations in the lacustrine sediments of the Chisone Valley testify to Early Pleistocene seismic activity, probably related to the recent tectonic evolution of the internal side of the NW Alps. 相似文献
20.
《Journal of Geodynamics》2003,35(1-2):5-32
The earthquake distribution pattern of Central Europe differs systematically from the neighbouring areas of NW and southern Europe regarding the fault plane kinematics. Within a belt between the French Massif Central and the northern part of the Bohemian Massif (1000 km) sinistral faulting along N-S zones dominates on the contrary to the Alps and their foreland with common bookshelf shears. One of the prominent N-S structures is the Regensburg-Leipzig-Rostock Zone (A) with several epicentral areas, where the main seismic center occurs in the northern Cheb Basin (NW Bohemia). The study demonstrates new structural results for the swarm-quake region in NW-Bohemia, especially for the Nový Kostel area in the Cheb Basin. There the N-S-trending newly found Počatky-Plesná zone (PPZ) is identical with the main earthquake line. The PPZ is connected with a mofette line between Hartušov and Bublák with evidence for CO2 degassing from the subcrustal mantle. The morphologically more prominent Mariánské Lázně fault (MLF) intersects the PPZ obliquely under an acuate angle. In the past the MLF was supposed to be the tectonic structure connected with the epicentral area of Nový Kostel. But evidence from the relocated hypocentres along the PPZ (at 7–12 kms depth) indicate that the MLF is seismically non-active. Asymmetric drainage patterns of the Cheb Basin are caused by fault related movement along Palaeozoic basement faults which initiate a deformation of the cover (Upper Pliocene to Holocene basin filling). The PPZ forms an escarpment in Pliocene and Pleistocene soft rock and is supposingly acting as an earthquake zone since late Pleistocene time. The uppermost Pleistocene of 0.12–0.01 Ma deposited only in front of the fault scarp dates the fault activity. The crossing faults envelope crustal wedges under different local stress conditions. Their intersection line forms a zone beginning at the surface near Nový Kostel, dipping south with increasing depth, probably down to about 12 km. The intersection zone represents a crustal anomaly. There fault movements can be blocked up and peculiar stress condition influence the behaviour of the adjacent crust. An ENE-WNW striking dextral wrench fault was detected which is to expect as kinematic counterpart to the ca. N-S striking sinistral shear zones. Nearly E-W striking fracture segments were formerly only known as remote sensing lineaments or as joint density zones. The ENE shear zone is characterized by a set of compressional m-scale folds and dm-scale faults scattered within a 20 m wide wrench zone. It is built up of different sets of cleavage-like clay plate pattern of microscopical scale. The associated shear planes fit into a Riedel shear system. One characteristic feature are tiny channels of micrometer scale. They have originated after shear plane bending and are the sites of CO2 mantle degassing. 相似文献