共查询到20条相似文献，搜索用时 579 毫秒
1.
Jin-Qi Hao Lynn M. Hastie Frank D. Stacey 《Physics of the Earth and Planetary Interiors》1982,28(2):129-140
Transient magnetic anomalies accompanying seismic stresses are more elusive than had been anticipated. We have, therefore, undertaken a more rigorous calculation than hitherto of the piezomagnetic effect accompanying representative seismic strain fields. We present a numerical method of treating faults of arbitrary area and orientation with fault displacement graded to zero at the fault boundaries to avoid stress discontinuities. The effect of grading the displacement in a realistic way is to give a more restricted and generally smaller piezomagnetic anomaly field than is indicated by simpler models. Seismomagnetism remains important in the search for earthquake prediction methods, but is more difficult to observe than had been hoped. 相似文献
2.
Mrinal K. Paul 《Pure and Applied Geophysics》1965,62(1):105-117
Summary The effect of slightly curved boundaries (free surfaces and interfaces) of the elastic mediums on the components of displacement of a particle in a medium due to the propagation of the surface waves has been investigated in this paper. It has been found that along with the usual displacement components for stratified boundaries (designated here as primary components), there exist secondary displacement components arising from the presence of curvature in the boundaries. They are constituted of different harmonic components with their amplitudes proportional to the parameters which measure the extent of curvature of the boundaries. The wave numbers of these harmonic constituents are related to those of the primary components in a definite way decided by the shapes of the boundaries. 相似文献
3.
Duhee Park Myung Sagong Dong-Yeop Kwak Chang-Gyun Jeong 《Soil Dynamics and Earthquake Engineering》2009,29(11-12):1417-1424
Various components including wave scattering, wave passage, and site amplification effects cause the ground motion to vary spatially. The spatially varying ground motion can significantly influence the dynamic response of longitudinal structures such as bridges and tunnels. While its effect on bridges has been extensively studied, there is a lack of study on its effect on underground tunnels. This paper develops a new procedure for simulating the tunnel response under spatially varying ground motion. The procedure utilizes the longitudinal displacement profile, which is developed from spatially variable ground motion time histories. The longitudinal displacement profile is used to perform a series of pseudo-static three-dimensional finite-element analyses. Results of the analyses show that the spatially variable ground motion causes longitudinal bending of the tunnel and can induce substantial axial stress on the tunnel lining. The effect can be significant at boundaries at which the properties of the ground change in the longitudinal direction. 相似文献
4.
In this study, a theoretical approach is used to investigate the scattering problem of circular holes under a scalene triangle on the surface. The wave displacement function is obtained by solving the Helmholtz equation that meets the zero-stress boundary conditions by adopting the method of separation of variables. Based on the complex function, multi-polar coordinate method, and region-matching technique, algebraic equations are established at auxiliary boundaries and free boundaries conditions in a complex domain. The auxiliary circle is used to solve the singularity of the reflex angle at the triangle corner. Then, according to sample statistics, the least squares method is used instead of the Fourier expansion method to solve the undetermined coefficient of the algebraic equations by discrete boundary. Numerical results show that the continuity of the auxiliary boundaries and the accuracy of the zero-stress boundaries are adequate, and the displacement of the free surface and the stress of the circular hole are related to the shape of the triangle, the position of the circular hole, the direction of the incident wave, and the frequency content of the excitation. Finally, time-domain responses are calculated by FFT based on the frequency domain theory, and the results reveal the wave propagation mechanism in a complicated structure.
相似文献5.
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针对地下工程抗震分析中边界条件和地震动输入方式选择问题,对一地下半无限体模型在一剪切波垂直入射条件下进行不同边界条件和不同地震动输入方法的算例试算。结果发现:两侧采用竖直向位移约束、底部采用黏弹性边界、并在模型底部用等效节点力输入地震动的方法,与三边均采用黏弹性边界条件和三边均采用等效节点荷载输入地震动的方法可以获得同样的结果。该方法易于在ANSYS中通过APDL编程实现,可为地下工程抗震分析中黏弹性边界的使用提供便利。 相似文献
7.
浅埋圆柱形弹性夹杂附近等腰三角形凸起地形引起的SH波的散射 总被引：4，自引：0，他引：4
文章利用“契合”思想,给出了地下弹性夹杂与地面上的等腰三角形凸起地形引起的SH波散射问题的解析解答。利用复平面下坐标移动,通过区域Ⅰ和区域Ⅱ以及区域Ⅱ和区域Ⅲ的“公共边界”位移应力连续条件,建立起求解该问题的无穷代数方程组并截断有限项进行求解,最后通过具体算例及结果分析得出相应结论。 相似文献
8.
本文采用有限元方法,对直立的、无限长的二维走滑断层上的地震不稳定性的滑动弱化模型进行分析,研究断层参数对失稳的影响,从理论上探索当断层强、弱区均有弱化现象时,断层破裂的前兆信息,进而分析摩擦应力弱化规律与地震预报的关系,讨论失稳前后位移场、应变场和应力场的演变过程。 相似文献
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Vincent W Lee 《地震学报(英文版)》2010,(1):5-12
This paper presents a closed-form solution for diffraction of plane SH waves by a semi-circular cavity in half-space by using wave function expansion method. Accuracy of the solution is checked by the displacement residual and stress residual along the boundaries. Numerical results show that there are notable differences for response amplitudes between a semi-circular cavity and a whole-circular cavity in a half-space. 相似文献
11.
《Journal of Volcanology and Geothermal Research》1999,91(1):65-78
The tectonic stresses can significantly affect the propagation of a magma-filled crack. It has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress. However, it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states. We have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow. The stress profiles were estimated by a simple model of lithospheric deformation. We employed a three-layer model of the lithosphere; the upper crust, the lower crust and the upper mantle have different rheological properties. A constant horizontal force is applied to the lithosphere, and the horizontal strain is assumed to be independent of depth. When realistic tectonic forces (>1011 N/m) are applied, the rheological boundaries mainly control the emplacement of magma. The emplacement is expected at the MOHO, the upper–lower crust boundary, and the brittle–ductile boundary. For lower tectonic forces (<1011 N/m), the tectonic stress no longer plays an important role in the emplacement of magmas. When the tectonic stress controls the emplacement, the roles of rheological boundaries strongly depend on the surface heat flow. When the surface heat flow is relatively high (>80 mW/m2), the stress in the mantle is quite low and the MOHO cannot trap ascending magmas. For relatively low heat flow (<80 mW/m2), on the other hand, the MOHO acts as a magma trap, and the upper–lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high. Our results suggest that the emplacement depth can change responding to the change in the tectonic force and/or that in the surface heat flow. This may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and/or thermal history. 相似文献
12.
A study of stress accumulation in seismic gaps and of stress transfer along linear plate boundaries is presented. Time-dependent reloading of plate boundaries following seismic ruptures is modeled by a modified Elsasser model of a coupled lithosphere/asthenosphere plate system. This model is applied to study a series of large earthquakes in the Aleutian Islands and the Alaska peninsula in 1938–1965. It is found that the Rat Island earthquake and the 1948 earthquake in the central Aleutians are likely to have been triggered by adjacent ruptures, in the sense that their occurrence would have come at a later time had their neighboring segments not been ruptured. Stresses in the Unalaska Gap and the Shumagin gap are at a relatively high level and these segments of the plate boundary may be expected to rupture in the near future. In general, in the ten years (about 16% of the earthquake cycle for the Aleutians) following an earthquake, the stress recovery in the rupture zone is highly nonlinear, resulting in a much more rapid stress accumulation than the linear case. Even at a later stage of an earthquake cycle, adjacent ruptures can cause an acceleration of loading rate in addition to the coseismic stress jump. A good example is the influence of the 1964 Alaska earthquake on the 1938 rupture zone. A general conclusion of this work is that long term earthquake prediction models must take into account the nonlinear stress accumulation behavior in seismic gaps. Also, we have shown the interaction of adjacent plate boundary segments, which suggests that some large earthquakes may have been triggered by nearby ruptures. 相似文献
13.
本文研究了有限长度含有单一粗糙面的垂直走滑断层的滑动弱化不稳定性.我们假定断层强度在其深度方向是均匀的,而在走滑方向是不均匀的,即存在一个高强度段.并假定断层上的粗糙段及断层上的其它部分具有相同类型的本构律,只是峰值应力不同.断层周围的地壳材料用上、下表面应力自由的弹性平板来模拟.我们用有限元方法研究了理论位移场、应力场和应变场随远场位移的演变情况.此时,断层位移和摩擦应力并不是预先给定的,而是在求解过程中同时确定的.根据计算结果,我们比较了理论位移场及断层上摩擦应力分布在稳定和不稳定滑动情况时的差别.并与内部含有低强度段的走滑断层的场合做了比较. 相似文献
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16.
Jay Melosh 《Pure and Applied Geophysics》1977,115(1-2):429-439
This paper is a review of the theoretical and observational evidence bearing on the magnitude of the shear stress which acts on the base of a lithospheric plate. Estimates based on the viscosity of the upper mantle do not yield useful limits. Arguments based on the thermal stability of the upper mantle indicate that the basal shear stress is no larger than a few bars. An indirect measurement of the rheology and shear stress can be made by studying the diffusion of stress and displacement following a large decoupling earthquake. When applied to the 1965 Rat Island Earthquake, this method yields a basal shear stress of about 2 bars. These results indicate that for small plates the forces produced by basal shear stress are probably small in comparison with forces acting on plate boundaries. To a first approximation, the smaller plates act as if they were decoupled from the mantle below. These stress estimates lead to a model in which the motion of the smaller lithospheric plates is governed almost entirely by the forces acting on their edges. Forces due to basal shear stress may be comparable to forces acting on the edges of large lithospheric plates. Thus, complete decoupling may not be a good approximation for such plates. 相似文献
17.
Abstract Structures developed in metamorphic and plutonic blocks that occur as knockers in the Mineoka Ophiolite Belt in the Boso Peninsula, central Japan, were analyzed. The aim was to understand the incorporation processes of blocks of metamorphic and plutonic rocks with an arc signature into the serpentinite mélange of the Mineoka Ophiolite Belt in relation to changes in metamorphic conditions during emplacement. Several stages of deformation during retrogressive metamorphism were identified: the first faulting stage had two substage shearing events (mylonitization) under ductile conditions inside the crystalline blocks in relatively deeper levels; and the second stage had brittle faulting and brecciation along the boundaries between the host serpentinite bodies in relatively shallower levels (zeolite facies). The first deformation occurred during uplift before emplacement. The blocks were intensively sheared by the first deformation event, and developed numerous shear planes with spacing of a few centimeters. The displacement and width of each shear plane were a few centimeters and a few millimeters, respectively, at most. In contrast, the fault zone of the second shearing stage reached a few meters in width and developed during emplacement of the Mineoka Ophiolite. Both stages occurred under a right-lateral transpressional regime, in which thrust-faulting was associated with strike-slip faulting. Such displacement on an outcrop scale is consistent with the present tectonics of the Mineoka Belt. This implies that the same tectonic stress has been operating in the Boso trench–trench–trench-type triple junction area in the northwest corner of the Pacific since the emplacement of the Mineoka Ophiolite. The Mineoka Ophiolite Belt must have worked as a forearc sliver fault during the formation of a Neogene accretionary prism further south. 相似文献
18.
The staggered grid finite-difference method is a powerful tool in seismology and is commonly used to study earthquake source
dynamics. In the staggered grid finite-difference method stress and particle velocity components are calculated at different
grid points, and a faulting problem is a mixed boundary problem, therefore different implementations of fault boundary conditions
have been proposed. Viriuex and Madariaga (1982) chose the shear stress grid as the fault surface, however, this method has
several problems: (1) Fault slip leakage outside the fault, and (2) the stress bump beyond the crack tip caused by S waves
is not well resolved. Madariaga et al. (1998) solved the latter problem via thick fault implementation, but the former problem remains and causes a new issue;
displacement discontinuity across the slip is not well modeled because of the artificial thickness of the fault. In the present
study we improve the implementation of the fault boundary conditions in the staggered grid finite-difference method by using
a fictitious surface to satisfy the fault boundary conditions. In our implementation, velocity (or displacement) grids are
set on the fault plane, stress grids are shifted half grid spacing from the fault and stress on the fictitious surface in
the rupture zone is given such that the interpolated stress on the fault is equal to the frictional stress. Within the area
which does not rupture, stress on the fictitious surface is given a condition of no discontinuity of the velocity (or displacement).
Fault normal displacement (or velocity) is given such that the normal stress on the fault is continuous across the fault.
Artificial viscous damping is introduced on the fault to avoid vibration caused by onset of the slip. Our implementation has
five advantages over previous versions: (1) No leakage of the slip prior to rupture and (2) a zero thickness fault, (3) stress
on the fault is reliably calculated, (4) our implementation is suitable for the study of fault constitutive laws, as slip
is defined as the difference between displacement on the plane of z = + 0 and that of z = − 0, and (5) cessation of slip is achieved correctly. 相似文献
19.
A three-layer elastic-gravitational fault displacement model using dislocation theory has been developed and used to examine the effect of layering of earth elastic moduli on surface and subsurface displacement fields for a vertical strike-slip fault. The model has been used to examine the effect of depth variation of elastic properties at coseismic and postseismic time scales. For pure strike-slip motion the effect of gravity on coseismic and postseismic horizontal deformation is negligible. For coseismic deformation the model predicts that (for constant Poisson's ratio) an increase in elastic moduli with depth attenuates the displacements within the upper layers with respect to displacement distribution for a uniform half-space, while an inclusion of a soft layer between the top layer and lower half-space amplifies upper layer displacements. The effect of variation in Poisson's ratio on surface and subsurface displacements has also been examined.The effect of postseismic stress relaxation on surface and subsurface displacements for a three-layer model has been calculated and compared with that of a uniformly relaxed half-space model. Layer 1 is assumed to correspond to the upper crust, layer 2 the lower crust and layer 3 the upper mantle. The effect of postseismic stress relaxation within a uniform half-space and within just the lower crust and upper mantle has been examined. Stress relaxation within the whole half-space decreases the amplitude and shortens the wavelength of displacements, while stress relaxation within the lower two layers increases the amplitude and broadens the wavelength of displacements. The difference between uniform and layered postseismic relaxation is particularly pronounced at the base of the crust.Coseismic and postseismic normal and volumetric strains for a vertical strike-slip fault have also been examined. For a uniformly relaxed half-space model, an increase in normal strains is shown with respect to the coseismic elastic solution, whereas the postseismic volumetric strain is effectively zero. For a three-layer model with stress relaxation in the lower layers only, the normal and volumetric strains within the top elastic layer resemble coseismic strains, while in the lower layers which suffer a rigidity decrease, the postseismic volumetric strain is effectively zero. 相似文献
20.
六棱山北麓断裂新活动特征 总被引：6，自引：1，他引：6
通过对六棱山北麓活动断裂的几何结构、分段活动特征及段落边界等方面的地质地貌调查与研究，认为该活动断裂可分为４段，除东段在早更新世有过活动外，其他３段均为晚更新世晚期～全新世活动段，段落长度１０～３９ｋｍ。该断裂在晚中生代表现为逆冲性质，至新生代随区域构造应力场的变化而转变为倾滑正断层。各段落上垂直位移量分布呈包络线状，而且各段平均滑动速率不同，西大东小，显示断裂新活动强度自西向东变弱 相似文献