共查询到20条相似文献，搜索用时 15 毫秒
1.
Okada (1992) provided expressions for the displacement and strain fields due to a finite rectangular source in an elastic, homogeneous and isotropic half-space. Starting with these results, we applied the correspondence principle of linear viscoelasticity to derive the quasi-static displacement, strain and stress fields in a viscoelastic, homogeneous and isotropic half-space. We assume that the medium deforms viscoelastically with respect to both the shear and the normal stresses but keeps a constant bulk modulus; in particular, the shear modulus relaxes as Maxwell fluid. We presented the viscoelastic effect on displacement, displacement gradient and stress fields, for a choice of parameter values. The viscoelastic effect due to the sudden dislocation reaches a limit value after about 10 times the Maxwell time. The expressions obtained here provide tools for the study of viscoelastic relaxation of lithosphere associated with seismic and volcanic phenomena. 相似文献
2.
Summary. A microplate is modelled as an elastic plate with two long strike-slip boundaries, lying over a Maxwell-type viscoelastic asthenosphere. The microplate is subjected to a constant and uniform shear strain rate by the opposite motions of two adjoining larger plates. After the occurrence of an earthquake at one of the microplate boundaries, the time evolution of shear stress at the other boundary is studied. It is found that stress build-up at the second boundary is delayed due to stress diffusion governed by the asthenosphere relaxation. Earthquake occurrence at this latter boundary would be delayed depending upon both the microplate width and the ratio between the Maxwell relaxation time of the asthenosphere and a characteristic time required for tectonic strain to recover rupture conditions. It turns out that the parameters which determine the occurrence of seismic activity along the microplate boundaries are more strictly constrained in the presence of a viscoelastic asthenosphere than in the case of an elastic half-pace model. 相似文献
3.
水分胁迫条件下棉花生理变化及其高光谱响应分析 总被引：19，自引：4，他引：15
利用ASD地物光谱仪,测定水分胁迫条件下棉花不同生育时期内叶片的光谱反射率,应用微分技术处理棉花的反射光谱,并结合棉花叶面积指数(LAI)、叶绿素(a b)含量(Chlt)、叶片全氮(TN)含量等生物参数进行分析,研究棉花水分胁迫情况下的高光谱特征,结果表明,一阶微分光谱720nm波段的数值与LAI的正相关(R=0．7656);750nm处一阶微分值与叶绿素含量呈显著正相关关系(R=0．7774);微分光谱690nm～740nm数值积分面积与TN含量呈正相关(R=0．7669),采用比值反射率对反射光谱1300nm～1500nm波段范围内最小值与棉花叶片的含水量作相关分析,达到极显著水平(R^2=0．8298),验证了一阶微分光谱数据与棉花的生理参数有很好的相关性,可见光和近红外波段光谱反射率能够反映出棉花生长发育的动态特征;证明了棉花的花铃期是高光谱遥感对棉花长势和生理参数定量诊断的最佳时期。本研究通过建立一系列线性光谱模型对棉花生理参数进行估测,为基于高光谱数据的棉花生长模型和棉花长势的遥感监测提供了理论依据。 相似文献
4.
Summary. The method proposed by Mendiguren to determine the source parameters from free oscillation data is applied to the 1970 July 31 deep Colombian earthquake. The results indicate a source propagating horizontally for about 150 km along the lithosphere and cutting across its width. The slab behaves as a guide for source propagation. The horizontal propagation velocity is determined as 3.8 km/s. The intensity of the source grew proportionately to the second power of the propagation distance. This rate of source intensity growth may be interpreted either by a fan-shaped fault model or by a cone-shaped volume source. The average slip and stress drop are estimated as 360 cm and 300 bar for the fault model. For the volume source model the transformational shear strain and stress are estimated as 11 × 10−5 and 160 bar. There is no evidence of a double couple radiation preceding the P origin time. It is shown that the isotropic and deviatoric components of the moment tensor cannot be uniquely resolved when only observations of a single mode are available. It is observed that, from a statistical basis, the available 0 Sn data for Colombian shock can be equally well explained by a pure deviatoric source model or by a source model including an isotropic component. Numerical experiments indicate that the inclusion of higher mode data does not change this situation. But, on the other hand, numerical experiments show that the available data and the scheme used for the inversion would not result in a solution including an artificial implosive component if the actual source were pure deviatoric. If the departure from a pure deviatoric source is produced by noise, it has to be non-random, as it could be produced by lateral heterogeneities not included in the inversion scheme. 相似文献
5.
J. P. Poirier 《Geophysical Journal International》1986,85(2):315-328
Summary . Dislocation theories of melting provide a possibility of calculating the melting temperature, from first principles, as the temperature at which the free energy of a crystal saturated with dislocations becomes equal to that of the dislocation-free crystal. After a brief review of the physical bases of the dislocation melting theories, Ninomiya's theory is used to determine the melting temperature as well as the volume and entropy of melting and the slope of the melting curve for iron at atmospheric pressure and under conditions prevailing at the Earth's inner core boundary. The necessary parameters (elastic moduli, Grüneisen parameter) are drawn from seismological earth models. We find a melting temperature of the material of the inner core of about 6150 K, independent of shock-wave experiments but in good agreement with them and with extrapolations using Lindemann's law. With usually accepted values of the melting point depression due to light elements in solution, the temperature at the inner core boundary is found to be T ICB ≅ 5000 K. This temperature is compatible with a temperature of the outer core at the core-mantle boundary T CMB ≅ 3800 K. Dislocation melting theories can thus help constrain the temperature profile in the Earth's core. 相似文献
6.
流拖曳系数是海冰动力学模型中的重要参数,实际海冰运动时受到水流的底面剪切作用和侧面正压力作用,相应的拖曳系数分别为摩拖曳系数和形拖曳系数。利用实验室波流水槽设备,对长方平底、长方粗糙底和圆饼型淡水冰试样进行拖曳运动试验,获得26组冰样运动数据。根据这些试验数据,利用动量法原理和数学优化方法构造了摩拖曳系数和形拖曳系数的辨识模型,将摩拖曳系数和形拖曳系数两项分开。在此基础上,分析了冰样粗糙度指标(支承长度率和冰厚均方根偏差)对这两个系数的影响;发现了摩拖曳系数同冰样水平尺寸和垂直尺寸之比的关系,该关系能将冰山和浮冰的摩拖曳系数归结到同一条曲线上。 相似文献
7.
流变是控制岩体稳定的主要因素之一。流变试验结果显示,新近系红层软岩蠕变和松弛曲线具有明显的三阶段变化特征。对比研究新近系粉砂质泥岩和泥质粉砂岩的流变结果,得出粉砂质泥岩较泥质粉砂岩强度低,蠕变量大,达到稳定需要的时间长。经过模型辨识,认为红层软岩流变符合伯格斯模型（Burgers model）。利用改进后的麦夸托（Marquardt）算法求取了红层软岩的流变参数。结果显示,反映岩石流变特性的两个主要指标弹性模量和黏滞系数远低于硬岩的同类指标,充分说明新近系红层软岩具有显著的流变性。获取的流变参数可用于伯格斯模型计算。 相似文献
8.
We investigated time dependent piezomagnetic fields due to volcanic sources embedded in a viscoelastic, homogeneous half-space. Especially in volcanic areas, the presence of inhomogeneous materials and high temperatures produce a lower effective viscosity of the Earth's crust that calls for considering anelastic properties of the medium. Piezomagnetic properties are carried by grains of titano-magnetite, which occupy only a small fraction of ordinary rock volume and are supposed to be elastic, while the non-magnetic surrounding matrix is assumed to be viscoelastic. From all the possible rheological models, we investigated two cases in which the bulk modulus is purely elastic and the shear modulus relaxes as: (i) a Maxwell solid and (ii) a standard linear solid (SLS). We applied the Correspondence Principle to the analytical elastic solutions for pressurized spherical sources and dislocation sources in order to determine the time dependent piezomagnetic fields in a viscoelastic medium. The piezomagnetic field completely vanishes after the relaxation process for a Maxwell rheology, whereas it is found to decrease over time and reach some finite offset value for a SLS rheology. These different behaviours provide helpful hints in understanding the temporal evolution of piezomagnetic anomalies in volcanic regions. 相似文献
9.
Summary. Kirchhoff's time-dependent surface integral representation of a scalar wavefield is applied to the problem of computing synthetic seismograms for P -waves in the Earth. By means of an appropriate parameterization, the Kirchhoff integral is transformed into a convolution of a weight function with the derivative of the source function in the time domain. The weight function is calculated using simple ray theory. The method extends the applicability of simple ray theory to caustics and other diffraction phenomena and allows certain kinds of departures from spherical symmetry to be taken into account. The method is illustrated in detail by application to the PKP -wavefield in the Earth. 相似文献
10.
Rosa M. Carrasco Javier Pedraza David Domínguez‐Villar Jane K. Willenbring Javier Villa 《Geografiska Annaler: Series A, Physical Geography》2013,95(3):211-226
During the deglaciation stages of the last glacial period a rock avalanche took place on the glacier that occupied the upper sector of the Cuerpo de Hombre Valley (Sierra de Béjar). The material displaced during the avalanche fell onto the ice, was transported by the glacier and later deposited as supraglacial ablation till. The cause of the avalanche was the decompression of the valley slopes after they were freed from the glacier ice (stress relaxation). Reconstruction of the ice masses has been carried out to quantify the stress relaxation that produced the collapse. The rock avalanche took place on a lithologically homogeneous slope with a dense fracture network. The avalanche left a 0.4 ha scar on the slope with a volume of displaced material of 623 ± 15 × 103 m3. The deposit is an accumulation of large, angular, heterometric boulders (1–100 m3 in volume) with a coarse pebble‐size matrix. The avalanche can be explained as a relaxation process. This implies rock decompression once the glacier retreat left the wall ice free (debuttressing). Calculations show that the avalanche took place where the decompression stresses were highest (130–170 kPa). In the Spanish Central System paleoglaciers the largest accumulation of morainic deposits occurred after the glacial maximum and the earliest stages of the ice retreat. The process described here is used as an example to formulate a hypothesis that the largest accumulations of tills were formed in relation to enhanced slope dynamics once some glacier retreat had occurred. 相似文献
11.
A new experiment method is introduced to study the relations between frost heaving strain and stress of soil or fracture rock under different moisture contents, temperatures and stress states. Based on experiments, a new triaxial frost heaving stress-strain relation is presented aiming at tunnel in cold regions. The experimental equipments are strain-controlled and low temperature buildup, and different restrained conditions are controlled by changing the stiffness of a test-force-ring. Then the frost heaving strain and stress of soil or fracture rock can be obtained under different restrained conditions, and the frost heaving stress-strain relation can be got by regression analysis of some feature points. Experiments of saturated sandy soil conducted by this method show that the triaxial frost heaving stress-strain relation could be expressed by logarithmic curves, and the frost heaving stress changes linearly with the logarithm of the frost heaving strain. The stronger the constraint, the smaller the frost heaving strain and the larger the frost heaving stresses. The frost heaving stresses would tend to a limit value with increasing the constraint intensity. The larger the confining pressure, the larger the frost heaving strain and stress. 相似文献
12.
大型振动台试验相似材料研究 总被引：2，自引：0，他引：2
在分析总结近几年岩土工程物理模拟试验中常用的岩质相似材料研究现状的基础上,采用重晶石粉、石英砂、石膏、甘油配制振动台模型试验相似材料,通过不同配比的材料力学试验,考虑相似材料的含水率,分析研究了各种材料含量以及含水率变化对相似材料物理力学性质的影响规律,发现含水率对材料的抗压强度、粘聚力、弹性模量、摩擦角有较大影响,根据试验结果最终确定了振动台试验相似材料配比.试验结果证明,该相似材料力学指标稳定,能很好地满足相似材料的选材要求,便于一次性浇注较大尺寸规模的模型试件,适用于大型振动台等物理模拟试验. 相似文献
13.
城市化水平增长曲线的类型、分段和研究方法 总被引：2，自引：0，他引：2
城市化水平增长曲线可以分为S形和J形2大类别,其变化特征、动力学背景及研究方法也不尽相同。城市化曲线研究可以分为唯象分析和唯理分析2大途径,唯理研究包括城一乡人口异速生长、城一乡人口替代以及城乡人口迁移和转换3种路径,目前这些方法主要用于S形曲线研究,对J形曲线的探索不够深入。S形曲线是一种奇对称曲线,其模型导数却是一... 相似文献
14.
2012年11月—2013年4月中国第29次南极科学考察期间,针对南极夏季固定冰单轴压缩性质开展了研究。使用冰芯钻直接在平整冰层钻取力学试样,取样冰厚为149 cm,其中颗粒冰、柱状冰和片状冰分别占采样冰芯总长度的15.4%、72.5%和12.1%;单轴压缩试样只采用柱状冰部分,加工好的力学冰样尺寸为直径9 cm,长度为18 cm;共设置5个试验温度(-2、-4、-6、-8和-10℃),加载应变速率在10-6—10-2s-1。利用统计方法分析试验结果,建立了南极夏季海冰单轴压缩强度与孔隙率和应变速率的关系式,以及综合考虑应变速率和温度影响下的单轴压缩强度定量表达式;同时,基于分形理论对单轴压缩试样破碎块分布规律进行了分析,结果显示碎块长度分形维数随着温度和应变速率的降低有增大趋势。在特别低应变速率下海冰试样整体发生蠕变时,无法采用分形方法讨论海冰内部破碎程度。 相似文献
15.
The creep behavior of microbiotic crust at room temperature was revealed by the creep bending tests of cantilever beam under constant-load conditions.The variation in the deflection with time can be depicted well by a standard creep curve.Creep rupture is a fundamental failure mechanism of microbiotic crust due to creep.A simple theory was then applied to describe this new me-chanical behavior.The existence of creep phenomenon brings into question the validity of widely used methods for measuring the strength of microbiotic crust. 相似文献
16.
Summary We consider a long strike-slip fault in a lithosphere modelled as an elastic slab. To the base of the slab a shear stress distribution is applied which simulates the viscous drag exerted by the asthenosphere. The resulant stress on the fault plane may directly fracture the lithosphere in its brittle upper portion; alternatively it may give rise at first to a stable aseismic sliding in the lower portion. In the latter case, stress concentration due to the deep aseismic slip is the relevant feature of the pre-seismic stress acting on the upper section of the lithosphere. The two cases are examined by use of dislocation theory and their observable effects compared. Different depths of the aseismic slip zone and the presence or absence of a uniform friction on the seismic fault are allowed for. If the model is applied to the San Andreas fault region, where a steady sliding condition actually seems to be present at shallow depth, it turns out that the slip amplitudes commonly associated with large earthquakes are consistent with average basal stress values which can be substantially lower than a few bars, a value often quoted as the steady state basal stress due to a velocity gradient in the upper asthenosphere. 相似文献
17.
Calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor 总被引：3，自引：0，他引：3
Earthquakes potentially serve as abundant and cost-effective gauges of tectonic stress provided that reliable means exist of extracting robust stress parameters. Several algorithms have been developed for this task, each of which typically provides information on the orientations of the three principal stresses and a single stress magnitude parameter. A convenient way of displaying tectonic stress results is to map the azimuth of maximum horizontal compressive stress, which is usually approximated using the azimuth of the larger subhorizontal principal stress. This approximation introduces avoidable errors that depend not only on the principal stress axes' plunges but also on the value of the stress magnitude parameter. Here we outline a method of computing the true direction of maximum horizontal compressive stress ( S H ) and show that this computation can be performed using only the four stress parameters obtained in routine focal mechanism stress estimation. Using theoretical examples and new stress inversion results obtained with focal mechanism data from the central Grímsey lineament, northern Iceland, we show that the S H axis may differ by tens of degrees from its commonly adopted proxy. In order to most appropriately compare tectonic stress estimates with other geophysical parameters, such as seismic fast directions or geodetically measured strain rate tensors, or to investigate spatiotemporal variations in stress, we recommend that full use be made of the routinely estimated stress parameters and that a formal axis of maximum horizontal compression be calculated. 相似文献
18.
粒度特征是沉积物的基本特征之一.计算沉积物粒度参数的方法主要有矩法和图解法两种,其中图解法必须通过手工作图求累积曲线,是一项相当繁杂的劳动,不利于计算大量样品.文中提出的方法将图解求沉积物样品的累积曲线百分位数的过程转化为不等区间的一维函数内插值问题,然后利用通用程序MATLAB的函数功能求解百分位数和计算粒度参数.计算结果和验算表明MATLAB计算相当可靠,完全可以代替手工作图.该方法原理简单,使任何懂或不懂编程的沉积分析人员,都能在计算机的帮助下无须作图用图解法计算样品的粒度参数,既能使粒度分析从繁杂 相似文献
19.
Frost heave is an upward swelling of soil during cryogenic conditions in cold regions. It is caused by the accumulation of ice crystals in subgrade soil, which grow upwards when freezing temperatures penetrate into the subgrade. This study establishes the allowable soil subgrade frost heave based on the roughness standard of asphalt pavement in China, and aims to balance the pavement design and frost heave resistance of subgrades in cold regions. We formulated a mechanical model of pavement supported by the boundary conditions of differential frost heave, based on the elastic layered system theory. The differential soil subgrade frost heave was modeled as a sinusoidal function, and the allowable frost heave and the roughness index were modeled as the displacement boundaries for the top and bottom of the pavement structure. Then the allowable frost heave was back-calculated according to the roughness standard. Numerical results show that the allowable frost heave depends on the pavement structure, material properties, the highway grade, and other factors. In order to ensure that the actual soil subgrade frost heave is lower than the allowable frost heave, pavement structures and materials need to be selected and designed carefully. The numerical method proposed here can be applied to establish the frost heave resistance of subgrade when the pavement structure and materials are determined. 相似文献
20.
Estimate of the stress field in Kilauea's South Flank, Hawaii 总被引：1，自引：0，他引：1
We estimated stress and seismic strain tensors for the Kilauea volcano's south flank. the stress orientation inversion and the seismic strain calculation were performed using fault-plane solutions. the principal stress and seismic strain directions are approximately uniformly distributed in space and time during the interval covered by the data. However, the σ1, σ3 plane is approximately orthogonal to the 1, 3 plane. Therefore, a weak layer may exist beneath the south flank. σ1 has a plunge of 59° and an azimuth of 152°, with a 10° 95 per cent confidence range. We also developed a stress magnitude inversion to estimate magnitudes of boundary and interior stresses. In this inversion, the principal stress directions were taken as constraints in the seismic volume, and surface geodetic observations were used as data. the maximum magmatic pressure in Kilauea's rift zone is about 160 MPa. the direction of σ1 can be interpreted as the superposition of hydrostatic stress ( pgh ) and magmatic pressure. Without the constraint imposed by the direction of σ1, the estimated pressure is only 60MPa, the distribution of magmatic pressure may be similar to that of pgh . In contrast, the upper rift zone may be in tension. the shear stress in the rift zone is about one order of magnitude smaller than the maximum compressive stress, supporting the interpretation of magmatic flow as fluid in dikes or channels. the combination of stress orientation inversion, seismic strain calculation, and stress magnitude inversion performed in this study provides a means by which to estimate the stress state in seismic areas. 相似文献