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11.
应用GPS观测青藏高原东北缘应力场变化 总被引:2,自引:0,他引:2
采用各向同性弹性地球模型推导了地面位移场速率与地壳内任意点应力场变化的边界积分关系,同时利用青藏高原东北缘1999~2001年观测的GPS资料对观测区地壳深度为5 km和25 km的主应力和最大剪应力进行了计算分析.结果表明,青藏高原东北缘的主应力变化主要集中在祁连山断裂、海原断裂等,在1920~1954年间历史上发生过多次震级为7.0~8.5级强震的断裂附近,并具有主应力变化沿断层走向分布、最大剪应力沿断层走向交替变化等特征. 相似文献
12.
T. Masuda T. Shibutani T. Ochiai S. Akagi H. Yamaguchi Y. Kugimiya N. Kimura T. Miyake 《Journal of Metamorphic Geology》2004,22(3):199-205
Evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains (p) in a quartz matrix in metacherts. It is proposed that p is a practical indicator of relative differential stress. Analysis of 123 metacherts from the 800 km long Sambagawa metamorphic belt, Japan, reveals that p‐values range from < 0.01 to 0.7 in this region. Most samples from Wakayama in the mid‐belt area have p‐values of 0.4–0.6, whereas those from western Shikoku have p‐values of < 0.1. This difference cannot be explained by variations in metamorphic temperature, and is instead attributed to a regional, lateral variation in differential stress during metamorphism. 相似文献
13.
Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a... 相似文献
14.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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16.
Interplanetary field enhancements were first discovered in the vicinity of Venus. These events are characterised by an increase in the magnitude of the heliospheric magnetic field with a near-symmetrical, sometimes thorn-shaped profile, and last from minutes to hours. Surveys of the events near Venus and Earth indicated clustering of the events in inertial space, which suggested that their sources were Solar System objects other than the Sun. A survey is presented of strong events of this type detected by the Ulysses spacecraft from 1990 to late 2001. Most of the events are accompanied by a discontinuity in the field direction near the events' centres. Other discontinuities are often symmetrical about the enhancement. The majority of events last less than two hours. When examined as a whole, the events tend to be accompanied by subtle changes in some plasma parameters. The majority of the enhancements are accompanied by magnetic holes on their fringes. The enhancements' occurrence rate increases with decreasing heliocentric distance. Possible formation mechanisms are discussed. No link was found with solar, or solar wind sources. Several aspects of the survey results are consistent with an origin related to cometary dust trails. Possible processes associated with a dust-solar wind interaction are discussed. 相似文献
17.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
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19.
Univariate and multivariate stress release models are fitted to historical earthquake data from North China. It is shown that a better fit is obtained by treating separately the Eastern part of the region, including the North China Plain and Bohai Sea, and the Western part of the region, including the Ordos Plateau and its Eastern boundary. Further improvement is obtained by fitting the large events (M7.6) and smaller events in the Western region by different stress release models. The comparisons are made by computing the likelihoods of the fitted models and discounting the number of parameters used by Akaike's AIC criterion. The models are used to develop long-term risk scenarios for the East and West regions. 相似文献
20.
A theoretical model for wind‐sand flow is developed by considering the coupling between wind flow and sand particle motion, the latter subject to the Magnus effect, under different atmospheric stability conditions. Using this model, the characteristics of the wind‐sand flow are discussed in detail. The results show that the atmospheric stability and the Magnus effect both have a strong influence on wind profiles and on the trajectories of sand particles. This approach produces results with characteristics that differ from those previously reported; the latter only applying to atmospheric conditions of neutral stability. The saltating sand reaches a greater height under non‐neutral stability than under neutral stability, while the maximum horizontal distance is greater under unstable conditions and is smaller under stable conditions than under conditions of neutral stability. 相似文献