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A variety of lacustrine sediments from the Devonian Caithness Flagstone Group in northern Scotland has been subjected to palaeomagnetic and mineralogical analysis. In general, the sediments show little evidence of a Devonian magnetization although this is partly seen in the Spital Flagstones. The magnetization seems to be dominated by Mesozoic overprints of normal and reversed polarity. The different sub-components of the magnetizations cannot be resolved thermally because of the difficulty of applying thermal demagnetization techniques above 400°C. At and above this temperature, sulphide oxidation results in laboratory magnetizations which obscure the NRM.Mineralogical studies show that the overprint is carried by Fe hydroxides in association with pyrite and marcasite grains (dolostones) or hematite in association with Cr-spinels (Achanarras Limestone). In the Spital Flagstones the relict Devonian magnetization and the normal Mesozoic overprint appears to be carried by magnetite. Our results show the importance of mineralogical studies in making realistic interpretation of the origin of magnetizations in ancient sediments. 相似文献
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根据共振声谱原理,建立了气液两相介质中圆柱共振腔共振声谱的实验测量系统,研究了共振腔体中不同含量的气体对共振声谱的幅度和共振频率的影响.实验结果表明：共振幅度和共振频率随着气体流量的增加都呈指数衰减变化趋势,但共振幅度比共振频率的衰减速度快,都可反映气体流量的变化.另外,在理论上,推导了均匀流体模型气液两相介质中的圆柱共振腔的共振频率计算公式,并模拟计算了共振频率和气体含量的变化规律曲线.理论研究结果表明,随着持气率的增加,共振频率减小;当持气率较小时,共振频率衰减较快.这一结论已经被本文实验测量结果所验证.理论和实验研究表明,利用共振声谱法可以检测气液混相介质中气体含量,它为发展生产井中气液两相流分相含量检测方法提供一种可能的途径. 相似文献
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等效力控制方法在拟动力试验中的应用 总被引：2，自引：0，他引：2
为了避免用复杂的迭代求解拟动力试验隐式逐步积分方法的非线性运动方程,作者提出了一种用反馈控制求解的方法—等效力控制方法。这篇文章首先介绍等效力控制方法的原理;然后通过数值模拟和试验验证此方法的有效性。数值模拟和试验的结果都表明,当选用合理的等效力控制器参数时,此方法可以取得非常好的稳定性和精度。数值模拟的结果还表明尽管等效力控制方法是以力作为反馈控制的对象,此方法能有效完成对具有负刚度试件的加载。 相似文献
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微动探测技术是一种经济环保、可靠实用并广泛应用于资源勘探及工程地质领域的新型物探技术。为了探讨测线方位对线形台阵探测结果的影响,研究利用武汉中心地震台实测的小尺度密集台阵数据,对比分析了多时段双重圆形、T形和不同方向线形台阵微动探测结果。研究发现不同方向的线形台阵探测结果具有明显差异,测线方位从北向东变化时实测相速度逐渐增加,且在NE45°角左右时与双重圆形结果最接近。数值模拟结果也显示当测线与主噪声源中心线夹角在30°～55°范围内时,线形台阵探测效果较好,且随着夹角增加实测相速度逐渐增加。在测区周边存在主噪声源时,实测和模拟结果均表明有限地增长观测时间难以弥补线形台阵方位分布的不足。因此,在微动探测实践前应考虑测区周边可能存在的噪声源分布,选择合适的台阵形式进行探测。 相似文献
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以华北地区1980——2010年资料为例,以单位边长的网格覆盖研究区,考察中小地震空间分布非空网格数的变化．网格尺度足够小则非空网格数趋于该时段的地震数,网格尺度足够大则非空网格数为1．实际资料显示,当空间网格尺寸大于0.5deg;之后,对结果稳定性的影响逐渐减弱．中小地震空间分布非空网格数的变化与ldquo;背景rdquo;地震活动的空间扩展（增强）或收缩（平静）有关．不同网格尺寸条件下的非空网格数有基本一致的变化趋势,可能间接反映了区域应力的短时扰动或起伏．小地震有更高的丛集特性,随着震级下限的提高,不同网格尺寸非空网格数之间差异逐渐变小．华北地区小震活动非空网格数的频次分布符合统计正态分布,因而给定置信概率、依据正态分布密度函数可计算非空网格数的ldquo;正常rdquo;分布范围,超出此范围的数据可视为异常．统计显示,就华北地区而言,中小地震非空网格数ldquo;平静rdquo;型异常的预测效率最低,ldquo;增强rdquo;型异常具有最高的报警对应率,而同时考虑ldquo;增强rdquo;及ldquo;平静rdquo;的异常判据则具有最高的预报评分．这也意味着,华北中强地震前以ldquo;增强rdquo;型的中小地震活动异常为主．研究结果还显示,小地震时空活动格局的改变与后续中强地震似乎具有更强的统计关联特性． 相似文献
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Discharge of groundwater from a limestone aquifer through floodplain sediments is associated with a large decrease in the nitrate concentration of the water. Results are presented to show that only a small amount of this reduction is caused by dilution of groundwater by water already present within the floodplain sediments; most of the effect is an active reduction process, most probably biological denitrification. The nitrate reduction process appears to operate independently of surface vegetation type and tends to be focused in specific regions of the floodplain where sediments are anaerobic and carbon-rich. The results suggest that active denitrification can operate throughout the winter, when nitrate concentrations in groundwater are at their highest and that the process remains effective even during periods of maximum run-off. The results show that undrained floodplains can be used as buffer zones to protect surface waters from groundwater polluted with agriculturally derived nitrate. 相似文献
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Deyan Draganov Ranajit Ghose Elmer Ruigrok Jan Thorbecke Kees Wapenaar 《Geophysical Prospecting》2010,58(3):361-373
Seismic interferometry is the process of generating new seismic traces from the cross‐correlation, convolution or deconvolution of existing traces. One of the starting assumptions for deriving the representations for seismic interferometry by cross‐correlation is that there is no intrinsic loss in the medium where the recordings are performed. In practice, this condition is not always met. Here, we investigate the effect of intrinsic losses in the medium on the results retrieved from seismic interferometry by cross‐correlation. First, we show results from a laboratory experiment in a homogeneous sand chamber with strong losses. Then, using numerical modelling results, we show that in the case of a lossy medium ghost reflections will appear in the cross‐correlation result when internal multiple scattering occurs. We also show that if a loss compensation is applied to the traces to be correlated, these ghosts in the retrieved result can be weakened, can disappear, or can reverse their polarity. This compensation process can be used to estimate the quality factor in the medium. 相似文献
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在地震序列的早期阶段获得科学可靠的余震预测结果,始终是地震预测研究的前沿课题.针对新近发展的Omi-R-J方法的适用性问题,以及相比于传统的Reseanberg-Jones （R-J）模型在地震序列参数拟合、余震预测效能上的差异等问题,本文以2017年四川九寨沟MS7.0地震序列为例,利用多时间窗的连续滑动拟合、预测和检验,以及通过构建重采样随机地震序列目录的系统检验等方式,开展了应用研究和比较研究.结果表明：相比于R-J模型,Omi-R-J方法可在余震记录较不完整的地震序列早期阶段获得稳定、可靠的序列参数,p值、c值和b值的标准差相比于R-J模型参数明显减小.N-test方法检验结果表明,在R-J模型等传统方法无法获得预测结果的地震序列早期阶段,Omi-R-J方法预测结果可以较高的比例通过N-test检验,在后续时段的预测效果也明显优于R-J模型.利用随机地震序列目录的测试结果表明,余震记录完整性下降对Omi-R-J方法预测结果的影响相对较小,在全部时段的完整性下降的影响高于在部分时段的完整性下降.上述结果对进一步地将Omi-R-J方法应用在震后早期余震预测中具有一定科学借鉴意义. 相似文献
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本文对高宽比为2.5的普通钢框架隔震结构模型,采用多种不同的地震动进行了水平向和竖向双向地震输入的振动台试验研究,并利用时程分析法完成了模型结构地震反应的数值分析。试验结果表明,高宽比隔震结构在水平向和竖向双向输入情况下隔震层基本上不会进入拉伸应力状态,即使在9度大震E l Centro和Hach inohe波输入时,隔震层支座仍以受压为主。因此小高宽比隔震结构在场地好的情况下,结构不会出现倾覆,仅需考虑软弱土场地的受拉情况。试验发现竖向地震输入对小高宽比隔震结构水平反应的影响相当小;对小高宽比隔震结构进行水平向地震反应分析时,可以忽略竖向地震对结构的影响。 相似文献
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The seismic response of light secondary systems in a building is dependent on the response of the primary structural system to the seismic ground motion with the result that very high accelerations can be induced in such secondary systems. This response can be reduced through the use of aseismic base isolation which is a design strategy whereby the entire building can be decoupled from the damaging horizontal components of seismic ground motion by the use of some form of isolation system. The paper presents a theoretical analysis of the response of light equipment in isolated structures and a parallel experimental programme both of which show that the use of base isolation can not only attenuate the response of the primary structural system but also reduce the response of secondary systems. Thus, the design of equipment and piping in a base-isolated building is very much simpler than that for a conventionally founded structure: inelastic response and equipment-structure interaction need not be considered and multiple support response analysis is rendered unnecessary. Although an isolation system with linear elastic bearings can reduce the acceleration of the structure, it may be accompanied by large relative displacements between the structure and the ground. A system using lead-rubber hysteretic bearings, having a force-displacement relation which is approximately a bilinear loop, can reduce these displacements. A parallel experimental programme was carried out to investigate the response of light equipment in structures isolated using lead-rubber bearings. The experimental results show that these bearings can dissipate energy and limit the displacement and acceleration of the structure but are less effective in reducing the accelerations in the internal equipment. The results of both the analysis and the tests show that base isolation is a very effective method for the seismic protection of light equipment items in buildings. 相似文献
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震源深度是地震学研究的关键参数,也是难以准确测定的参数之一。由于Pn和Pg震相的路径特征,其走时差对震源深度的变化较敏感,Pn和Pg震相是地震台网观测报告中数量较丰富且精度较高的震相数据,因此Pn-Pg方法为震源深度测定提供了简便且可行的方式。本文讨论了使用Pn-Pg走时差测定震源深度的实现方式,使用模拟数据评估了该方法的误差,结果表明,震相到时误差在一定范围时,此方法可以给出较可靠的深度结果。使用Pn和Pg走时差计算了内蒙古地区地震的震源深度,重新测定的深度频次分布更加合理,区域差异也比较明显,东部和西部的震源深度较深,中部地区震源深度较浅。 相似文献
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We demonstrate that the idea of symmetropy can be used for quantification of earthquake patterns. The symmetropy can be considered
as a measure of asymmetry. A pattern is richer in asymmetry when the symmetropy is smaller. The specific results of its applications
are obtained as follows. In a discrete model of a seismic source with self-organized criticality, the spatial patterns of
earthquakes during critical states and sub-critical states are distinguished by the behaviour of the symmetropy: sub-critical
patterns show that the symmetropy is approximately a constant but this has various values during critical states. The critical
patterns show asymmetric property without any asymmetric force from the outside and without asymmetric intracellular rule.
We show that the emergence of asymmetric patterns is a generic feature of dynamic ruptures in our model. Such a generic asymmetry
results from the model which is an inherently discrete system consisting of finite-sized cells. These cells may represent
geometrical disordered fault zones. We further discuss rotational motions that generate seismic rotational waves. In micromorphic
continuum theory, such rotations are attributed to dynamic ruptures in disordered systems. We note that the concept of disorder
in this theory is expressed by a set of finite-sized microstructures and is consistent with the concept of disorder modelled
in the present study. Thus, we suggest that the spatially asymmetric patterns of earthquakes might be related to the rotational
motions, because both come from dynamic ruptures in a discrete fault zone without a well-defined continuum limit. 相似文献
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The results of experiments discussed in this paper show that some characteristics of gravity waves in finite-depth water can be used in the case of steady flows with a pronounced nonuniformity in open channels. In particular, in addition to the classical critical velocity and depth, the higher (second) critical velocity and (second) critical depth can be used. 相似文献
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Hydrological model sensitivity to climate change can be defined as the response of a particular hydrological model to a known quantum of climate change. This paper estimates the hydrological sensitivity, measured as the percentage change in mean annual runoff, of two lumped parameter rainfall-runoff models, SIMHYD and AWBM and an empirical model, Zhang01, to changes in rainfall and potential evaporation. These changes are estimated for 22 Australian catchments covering a range of climates, from cool temperate to tropical and moist to arid. The results show that the models display different sensitivities to both rainfall and potential evaporation changes. The SIMHYD, AWBM and Zhang01 models show mean sensitivities of 2.4%, 2.5% and 2.1% change in mean annual flow for every 1% change in mean annual rainfall, respectively. All rainfall sensitivities have a lower limit of 1.8% and show upper limits of 4.1%, 3.4% and 2.5%, respectively. The results for potential evaporation change are −0.5%, −0.8% and −1.0% for every 1% increase in mean annual potential evaporation, respectively, with changes rainfall being approximately 3–5 times more sensitive than changes in potential evaporation for each 1% change in climate. Despite these differences, the results show similar correlations for several catchment characteristics. The most significant relationship is between percent change in annual rainfall and potential evaporation to the catchment runoff coefficient. The sensitivity of both A and B factors decreases with an increasing runoff coefficient, as does the uncertainty in this relationship. The results suggest that a first-order relationship can be used to give a rough estimate of changes in runoff using estimates of change in rainfall and potential evaporation representing small to modest changes in climate. Further work will develop these methods further, by investigating other regions and changes on the subannual scale. 相似文献
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Scattering of elastic waves by a three‐dimensional transversely isotropic basin of arbitrary shape embedded in a half‐space is considered using an indirect boundary integral equation approach. The unknown scattered waves are expressed in terms of point sources distributed on the so‐called auxiliary surfaces. The sources are expressed in terms of the full‐space Green's functions with their intensities determined from the requirement that the boundary and the continuity conditions are to be satisfied in the least‐squares sense. Steady‐state results were obtained for incident plane pseudo‐P‐, SH‐, SV‐, and Rayleigh waves. Using the Radon transform the Green's functions are obtained in the form of finite integrals over a unit sphere or a unit circle which can be numerically evaluated very efficiently. Detailed analysis of the method includes the discussion on the shape of the auxiliary surfaces and the distribution of the collocation points and sources. The convergence criteria is defined in terms of transparency tests, isotropic limit test, and minimization of a certain norm. The isotropic limit tests show excellent agreement with the isotropic results available in literature. For anisotropic materials the numerical results are given for a semispherical basin. The results show that presence of an anisotropic basin may result in significant amplification of surface motion atop the basin. While the amplitude of peak surface motion may be similar to the corresponding isotropic results, the difference in the displacement patterns may be quite different between the two. Therefore, this study clearly demonstrates that material anisotropy may be very important for accurate assessment of surface ground motion amplification atop basins. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献