Simple analytical Green's functions for ray perturbations in layered media     

Beverley J. Moore 《Geophysical Journal International》1993,115(3):1137-1142

The total Green's function for two-point boundary-value problems can be related to the propagator for initial-value problems. A very simple expression for the Green's function is obtained when the unperturbed medium may be described by material with a constant gradient in quadratic slowness. The derivation requires a correct understanding of assumptions made in the propagator solution. Expressions are also obtained for Green's function in multilayered media.  相似文献   

Observations of geomagnetic pulsations and variations with a new borehole magnetometer down to depths of 3000 m   总被引：1，自引：0，他引：1  

K. Spitzer 《Geophysical Journal International》1993,115(3):839-848

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A triaxial magnetometer has been developed for investigating the in situ skin effect of horizontal geomagnetic pulsations and variations in deep boreholes. The observations were carried out in the pilot borehole of the Continental Deep Drilling Program of Germany (KTB) down to depths of 3000 m and up to temperature of 90 C. A weak skin effect, due to the known very low conductivity of the penetrated crystalline rocks, of 90 to 95 per cent in amplitude and -5 to -10 rotation in phase has been observed at periods of 10 s and magnetometer depth of 2400 m.
An essential prerequisite for all calculations is the accurate determination of the orientation of the downhole magnetometer. It is demonstrated how oriented record samples of temporal variations at depth correlate precisely with those from the surface.
Results from surface magnetotelluric (MT) investigations show strong local distortions of the telluric field. The distortion of the MT tensor response has been determined by means of newly introduced skin-effect transfer functions, which are assumed to be undistorted.  相似文献   

Late Quaternary kinematics of the Pallatanga strike-slip fault (Central Ecuador) from topographic measurements of displaced morphological features   总被引：2，自引：0，他引：2  

Thierry Winter  Jean-Philippe Avouac  Alain Lavenu 《Geophysical Journal International》1993,115(3):905-920

The northeast-trending Pallatanga right-lateral strike-slip fault runs across the Western Cordillera connecting N50E-N70E trending normal faults in the Gulf of Guayaquil with N-S reverse faults in the Interandean Depression. Over most of its length, the fault trace has been partly obscured by erosional processes and can be inferred in the topography only at the large scale. Only the northern fault segment, which follows the upper Rio Pangor valley at elevations above 3600 m, is prominent in the morphology. Valleys and ridges cut and offset by the fault provide an outstanding record of right-lateral cumulative fault displacement. The fault geometry and kinematics of this particular fault segment can be determined from detailed topographic levellings. The fault strikes N30E and dips 75 to the NW. Depending on their size and nature, transverse morphological features such as tributaries of the Rio Pangor and intervening ridges, reveal right-lateral offsets which cluster around 27 ± 11m, 41.5 ± 4 m, 590 ± 65 m and 960 ± 70 m. The slip vector deduced from the short-term offsets shows a slight reverse component with a pitch of about 11.5 SW. The 41.5 ± 4 m displacements are assumed to be coeval with the last glacial termination, yielding a mean Holocene slip-rate of 2.9- 4.6 mm yr⁻¹. Assuming a uniform slip rate on the fault in the long term, the 27 m offset appears to correlate with an identified middle Holocene morphoclimatic event, and the long term offsets of 590 m and 960 m coincide with the glacial terminations at the beginning of the last two interglacial periods.  相似文献   

Reciprocity theorem to compute the static deformation due to a point dislocation buried in a spherically symmetric earth   总被引：4，自引：0，他引：4  

Shuhei Okubo 《Geophysical Journal International》1993,115(3):921-928

Intriguing reciprocity relations exist between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. Coseismic deformations can be rewritten as follows: (1) potential change in terms of the tide deformation field, (2) radial displacement in terms of the load and tidal deformation fields, and (3) tangential displacement in terms of shear and torsional deformation fields. The relations greatly reduce the effort to compute the coseismic crustal deformation in a spherically symmetric earth.  相似文献   

Inference of core-mantle boundary topography from ISC PcP and PKP traveltimes     

Arthur Rodgers  John Wahr 《Geophysical Journal International》1993,115(3):991-1011

We invert ISC PcP and PKP absolute and differential traveltimes in an attempt to infer the long-wavelength topography of the core-mantle boundary (CMB). The data selection and processing methods are described and evaluated. These travel-time data are very noisy and the geographic distribution of the data is highly non-uniform, inhibiting reliable inference of CMB topography. Spatial averaging enhances the coherent component of the residual variance (related to heterogeneity), however, the random component of the variance is much larger than the coherent component. We show that for PcP data the coherent signal due to mantle heterogeneity overshadows that arising from the CMB, and that the effects of mantle heterogeneity are mapped into our inferred CMB solutions. The PcP data are not correlated across the spatial averaging bins and seem to have a strong bias due to small-scale structure and/or noise. The non-uniform geographic sampling of the data plays a role in the mapping of mantle heterogeneity onto the CMB. Spatial patterns of CMB models inferred from different phases do not agree. Amplitudes of seismically inferred CMB undulations vary greatly. The sensitivity of inferred CMB models to the processing, spatial averaging procedure, and inversion techniques are investigated. Topographic amplitudes increase strongly with increasing input residual variance. The power spectrum of inferred topography indicates that there are unmodelled heterogeneities that must be described with spherical harmonics of degree 6 and higher. Based on this work, we conclude that reliable inference of long-wavelength CMB topography is not likely with the current ISC data set or with a spherical harmonic expansion truncated to degree and order 6.  相似文献   

Personal Narratives as Interactive Texts: Collecting and Interpreting Migrant Life-Histories*     

Miranda Miles  Jonathan Crush 《The Professional geographer》1993,45(1):84-94

Life-history or personal narrative techniques have considerable potential as a way of recovering hidden histories, contesting academic androcentrism, and reinstating the marginalized and dispossessed as makers of their own past. Drawing on a large methodological literature on life-history collection, and applications of these techniques in Africa, we argue that geographers might explore these methodologies as a means of recovering lost geographies and venting alternative voices in academic texts. Drawing on our own project on Swazi migrant women, we suggest that life-histories cannot, however, be seen purely as vehicles for the delivery of uncontaminated fact about the past. Rather personal narratives should be viewed and interpreted as interactive texts. This leads us to a consideration of a number of methodological and interpretive issues surrounding life-history collection: the positional advantages of insider status, the “terrible assymetries” of the interview process, and the power (and pitfalls) of narrative forms of representation.  相似文献   

开展灾害学研究 保障人类生存与发展     

陈荫祥 《遥感学报》1990,(3)

灾害是人类面临的最严重的威胁。本文简要列述了各类灾害对国民经济建设和人类生存的危害性,论述了灾害的分类和体系特征,探讨了灾害形成的科学机理,强调了开展多学科、大体系研究的重要意义。同时结合国土环境遥感调查,提出了开展灾害学研究、监测防御、减灾抗祸的对策和建议,以期发挥现代地球科学理论与遥感技术的潜力,为促进灾害学的研究、保障人类更好地生存与发展作出贡献。  相似文献   

铀矿层真实厚度的确定和最佳测井点距          下载免费PDF全文

秦积庚  谭庆江 《地球物理学报》1990,33(4):468-479

本文讨论了最佳测井点距的选择原理,其最佳值大致为8-12.5cm.并从原理上分析了矿层解释厚度增大的主要原因:根据离散测量值所作的分层解释结果必然导致矿层解释厚度的增大.大量的模型测量结果完全证实了理论分析的正确性,并且还提出了合适的解决办法.  相似文献   

Reliability level III method in design of square pillar resting on weak floor stratum     

W. M. Pytel 《Geotechnical and Geological Engineering》1990,8(2):149-162

Summary Current methods of design of pillars resting on weak floor strata involve only a deterministic, conventional safety factor calculation, based on material parameters treated as the mean values taken from observations. In a case where high parameters variability occurs, these methods may lead to fatal design errors resulting in excessive pillar settlement and roof falls. Therefore, to include the influence of parameters quality, the new approach based on reliability level III method was developed. Consideration was given to the identification of the system parameters importance, and to density function for the safety factor treated as a random variable. Design procedure involving floor probability of failure was illustrated by numerical examples.  相似文献   

用时间序列模拟和预报天山乌鲁木齐河源1号冰川年径流总量     

宋强  陈靖 《冰川冻土》1990,(2)

本文把1958—1984年天山乌鲁木齐河源1号冰川的融水径流总量的时间序列X(t),分解为趋势项L(t)、周期项P(t)、平稳项S(t)、随机项ε(t),使该时间序列表示为X(t)=L(t)+P(t)+S(t)+ε(t)。采用非线性回归提取L(t),用谱分析和Fourier级数提取P(t),余差用自回归方程建模,用上述项的叠加作出预报,按相关指数公式计算R=0.90,效果良好。  相似文献