排序方式： 共有69条查询结果，搜索用时 265 毫秒
51.
F. Purtscheller T. Pirchl G. Sieder V. Stingl T. Tessadri P. Brunner O. Ennemoser P. Schneider 《Environmental Geology》1995,26(1):32-38
The identification of extremely high indoor radon concentrations in the village Umhausen (Tyrol, Austria) initiated a scientific program to get information about the source and distribution of this noble gas. The high concentrations can not be related to U anomalies or large-scale fault zones. The nearby giant landslide of Koefels, with its highly fractured and crushed orthogneisses, are the only possible source of radon, despite the fact that the U and Ra content of the rocks is by no means exceptional. The reasons for the high emanation rates from the landslide are discussed and compared to results gained from a similar examination of the giant landslide of Langtang Himal (Nepal). The exceptional geologic situation in both cases, as well as the spatial distribution of different concentration levels, indicate that both landslides must be considered as the production sites of radon. Independent of the U and Ra contents of the rocks, the most important factors producing high emanation rates are the production of a high active surface area and circulation pathways for Rn-enriched soil air by brittle deformation due to the impact of the landslidemass. 相似文献
52.
基于所建立的反映岩石冲击压缩、拉伸损伤理论模型以及深孔微差爆破数值模拟结果,研究了爆炸载荷作用下岩石损伤演化和破碎规律,分析了岩石的动态力学特性;通过对水平边界条件下爆破破岩物理、力学过程的研究,探讨了深孔微差爆破的作用机制和爆破设计原则。 相似文献
53.
查明大地震物理机制对地震预测和防震减灾具有重要意义.本文评述了当前主流地震机制假说,指出用于描述浅源地震机制的弹性回跳说和粘滑说存在诸多缺陷;前人提出的脱水致裂、相变失稳、剪切熔融和反裂隙断层作用等中-深源地震机制假说,均存在与观测事实不符的情况.本文简要介绍了近些年我们发展的孕震断层多锁固段脆性破裂理论,指出断层运动导致锁固段累进性破裂发生地震,称锁固段在体积膨胀点和峰值强度点发生的显著地震为标志性地震事件.震例分析表明,浅源、中源、深源及其混合型地震区标志性地震事件的孕育规律均遵循该理论.进一步的讨论指出,弹性回跳说和粘滑说均隐含着断层面上存在锁固段的假设;深源地震震源体具有发生脆性破裂的环境条件;该理论能合理解释地震应力降远小于室内岩石破裂应力降、热流佯谬和自组织临界性这些难点问题.这充分说明,大地震物理机制均可统一解释为锁固段脆性破裂. 相似文献
54.
This paper deals with the tectonic control on the hydrothermal system that gave rise to Sb–Hg ore deposits in the Monte Amiata area that was one of the most relevant mining district for the exploitation of mercury in Italy. The study area (Selvena mining district) is located in southern Tuscany (inner Northern Apennines) one of the most important mineralized area in the western Mediterranean region. Southern Tuscany was severely affected by Middle–Late Miocene low-angle normal faults, later dissected by Pliocene–Pleistocene faults, coeval magmatism (Late Miocene–Pleistocene) and hydrothermal activity (Pliocene–Present). The Selvena mining district is located south of Middle Pleistocene Monte Amiata volcanic complex. Our structural and kinematic study is based on the integration among fieldwork, borehole and mine data. The results highlight two Pleistocene–Holocene left-lateral transtensional shear zones linked by normal faults, defining a coeval pull-apart structure. Here, the Sb–Hg mineralization, transported by meteoric hydrothermal fluids mainly, is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults. Furthermore, a widespread mineralization also occurs in the cataclasites of Miocene low-angle normal faults. Mine evidence suggests that ore-bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis. Geological structures and ore deposit distribution are related to a single hydrothermal circuit, with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones; then, hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike-slip faults. Thus, hydrothermal fluids permeated also the Middle–Late Miocene cataclasites. This study shed light on the relationships between geological structures and mineralization in southern Tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path. 相似文献
55.
Eric Barrier Samir Bouaziz Jacques Angelier Gilles Creuzot Jamel Ouali Pierre Tricart 《Geodinamica Acta》2013,26(1):39-57
AbstractA detailed analysis of brittle deformations in the Saharian platform of southern Tunisia is based on studies of fault-slip data sets and joint sets. It allows reconstruction of the Mesozoic paleostress evolution. During the Permo-Triassic, N-S extensions occurred with high late Permian subsidence rates. During the Norian, strike-slip movements reactivated former normal faults. During the Jurassic and the Cretaceous a succession of extensional events was characterized by : (1) a N-S extension which dominated from late Triassic to early Aptian. We relate this extension to the Africa-Eurasia divergence; (2) a ENE-WSW extension during the Cenomanian. We relate this extension to the opening of «he African basins ; (3) a NE-SW Senonian extension that continued during the Cenozoic in the Jeffara and in the Gabes Gulf, during the further evolution of the northern African margin. The various compressional trends recorded in the platform are attributed to Cenozoic events. 相似文献
56.
We performed a quantitative comparison of brittle thrust wedge experiments to evaluate the variability among analogue models and to appraise the reproducibility and limits of model interpretation. Fifteen analogue modeling laboratories participated in this benchmark initiative. Each laboratory received a shipment of the same type of quartz and corundum sand and all laboratories adhered to a stringent model building protocol and used the same type of foil to cover base and sidewalls of the sandbox. Sieve structure, sifting height, filling rate, and details on off-scraping of excess sand followed prescribed procedures.Our analogue benchmark shows that even for simple plane-strain experiments with prescribed stringent model construction techniques, quantitative model results show variability, most notably for surface slope, thrust spacing and number of forward and backthrusts. One of the sources of the variability in model results is related to slight variations in how sand is deposited in the sandbox. Small changes in sifting height, sifting rate, and scraping will result in slightly heterogeneous material bulk densities, which will affect the mechanical properties of the sand, and will result in lateral and vertical differences in peak and boundary friction angles, as well as cohesion values once the model is constructed. Initial variations in basal friction are inferred to play the most important role in causing model variability.Our comparison shows that the human factor plays a decisive role, and even when one modeler repeats the same experiment, quantitative model results still show variability. Our observations highlight the limits of up-scaling quantitative analogue model results to nature or for making comparisons with numerical models. The frictional behavior of sand is highly sensitive to small variations in material state or experimental set-up, and hence, it will remain difficult to scale quantitative results such as number of thrusts, thrust spacing, and pop-up width from model to nature. 相似文献
57.
采用塑化松香作为岩石圈延性下层的相似材料，进行了板内塑性流动网络及多层构造变形的物理模拟实验。延性单层模型的实验表明，在边界挤压或“高原”重力势的作用下，依赖于延性层粘度的高低不同，主要形成剪切网络、压性褶皱以及二者过渡型式等一级构造。在延性／脆性双层模型中（脆性上层和延性下层分别相当于岩石圈上、下层），边界驱动力的远程传递，主要借助于延性下层的网络状流动，岩石圈下层（含下地壳和岩石圈地幔）的剪切网络，即塑性流动网络，控制着板内构造变形，导致脆性上层内剪切破裂网络、逆推断裂、纵向张裂以及其它次级断裂和褶皱的发育。实验还表明，上、下层之间非连续分布的软弱夹层（模拟壳内低速、高导层）并不妨碍下层塑性流动网络的扩展，但影响牵引力的向上传递及上层构造变形的强弱分布 相似文献
58.
Weak Zone Related Seismic Cycles in Progressive Failure Leading to Collapse in Brittle Crust 总被引：2，自引：0，他引：2
Until quite recently our understanding of the basic mechanical process responsible for earthquakes and faulting was not well known. It can be argued that this was partly a consequence of the complex nature of fracture in crust and in part because evidence of brittle phenomena in the natural laboratory of the earth is often obliterated or obscured by other geological processes. While it is well understood that the spatial and temporal complexity of earthquakes and the fault structures emerge from geometrical and material built-in heterogeneities, one important open question is how the shearing becomes localized into a band of intense fractures. Here we address these questions through a numerical approach of a tectonic plate by considering rockmass heterogeneity both in microscopic scale and in mesoscopic scale. Numerical simulations of the progressive failure leading to collapse under long-range slow driving forces in the far-field show earthquake-like rupture behavior. En Echelon crack-arrays are reproduced in the numerical simulation. It is demonstrated that the underlying fracturing induced acoustic emissions (or seismic events) display self-organized criticality—from disorder to order. The seismic cycles and the geometric structures of the fracture faces, which are found greatly depending on the material heterogeneity (especially on the macroscopic scale), agree with that observed experimentally in real brittle materials. It is concluded that in order to predict a main shock, one must have extremely detailed knowledge on very minor features of the earth's crust far from the place where the earthquake originated. If correct, the model proposed here seemingly provides an explanation as to why earthquakes to date are not predicted so successfully. The reason is not that we do not understand earthquake mechanisms very well but that we still know little about our earth's crust. 相似文献
59.
不同温压条件下居庸关花岗岩脆塑性转化与失稳型式的实验研究 总被引：9，自引：0，他引：9
为研究花岗岩的脆塑性转化和失稳型式，在固体围压介质三轴实验系统上进行了3组高温高压实验，结果表明，温度小于300℃时花岗岩为脆性破裂，大于800℃时为塑性变形，在300-600℃，花岗岩为半脆性破裂和碎裂流动，在600-800℃，花岗岩为半脆性流动，花岗岩的渐进破坏发生在低压区域；突发失稳发生在室温高压（≥300MPa)和高温高压（550℃600MPa-650℃700MPa)两个区域；在突发失稳与渐进破坏区域之间存在大范围的准突发失稳区，在实验温压范围内，影响花岗岩脆塑性转化的首要因素是温度，其次是围压；而花岗岩的失稳型式同时取决于围压和温度。 相似文献
60.
遥感图象的解译结果表明，环形构造与中强地震的关系密切。通过对环形构造控震作用的研究，指出了环形构造的控震模式及环形构造对地震构造环境的分析和地震预报的意义。 相似文献