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1.
Summary The analysis of palaeomagnetic data where only inclinations are available is considered. Maximum likelihood estimates for the mean inclination I 0 and Fisher's precision parameter k are derived. It is shown that they are in all cases biased although the bias is small for low inclinations. The case of steep inclinations and small values of k is examined and it is shown that in this region I 0 and k are not separable as distinct variables, because the lack of declination information in this region leads to fundamental ambiguities. Unbiased estimates for I 0 and (1/ k ) are derived for the case where the portion of the distribution folded about the vertical is insubstantial. A worked example of the method, with calculation of confidence limits, is appended. 相似文献
2.
近地表气温直减率是推测近地表气温空间分布的重要参数。中国幅员辽阔,气候和地形地貌条件复杂,直接使用反映对流层平均状况的单一气温直减率(0.65℃/100 m)很难表征中国近地表气温直减率的季节和类型差异。本文利用中国839个国家气象站点2000-2013年的近地表气温数据,分别在国家尺度和综合自然区划尺度上使用多元回归分析方法计算各个季节的平均气温直减率(lrmeanT)、平均最低气温直减率(lrminT)和平均最高气温直减率(lrmaxT),并借助空间插值算法对气温直减率的可靠性进行了验证,最后分析了其季节和类型的差异。结果表明：①在国家尺度上,3种气温直减率均小于0.65℃/100 m;lrminT、lrmeanT和lrmaxT的季节差异分别为0.05、0.13和0.24℃/100 m,且一般有夏季最大、冬季最小的季节规律;春、夏、秋、冬季气温直减率的类型差异分别为0.12、0.05、0.11和0.26℃/100m,且有lrminT>lrmeanT>lrmaxT的规律。②在综合自然区划尺度上,气温直减率大多低于0.65℃/100 m,且存在明显的地域差异;夏季气温直减率一般大于冬季气温直减率,季节差异大多超过0.10℃/100 m;气温直减率类型差异半数区域超过或等于0.10℃/100 m,在春、夏、秋季,半数左右的区域lrmaxT >lrminT,在冬季,多数区域的lrminT >lrmaxT,lrmeanT一般处于lrmaxT和lrminT之间。 相似文献
3.
Summary. Six submarine rocks dredged from guyots in the western Pacific were dated by means of 40 Ar–39 Ar step heating dating technique. All ages show mid- to late-Cretaceous ages in accordance with the generally supposed age of the ocean crust estimated from the magnetic anomaly pattern.
The back-tracked paths were calculated for the guyots with the use of their absolute ages, for both the Pacific plate movements proposed by Morgan and by Clague & Jarrard. In both cases these show birth places for the guyots, which are located near the equator.
Fossil ages are nearly concordant with the40 Ar–39 Ar ages for the guyots which are older than 95 Myr, whereas the fossil ages are considerably younger than the 40 Ar–39 Ar ages for the guyots younger than 90 Myr. This contrast may be due to the world-wide marine transgression, whose climax is believed to have occurred at about 85 Myr BP. 相似文献
The back-tracked paths were calculated for the guyots with the use of their absolute ages, for both the Pacific plate movements proposed by Morgan and by Clague & Jarrard. In both cases these show birth places for the guyots, which are located near the equator.
Fossil ages are nearly concordant with the
4.
The tidal dynamics of the Irish and Celtic Seas 总被引：1，自引：0，他引：1
I. S. Robinson 《Geophysical Journal International》1979,56(1):159-197
Summary. Current meter data collected over periods of more than 14 day from the Irish and Celtic Seas are harmonically analysed and presented in maps of tidal stream information. Making use of the analysed current data, and by constructing time series of frictional and inertial stresses which are also harmonically analysed, harmonic constituents of the surface tidal slopes at current meter stations are obtained. Using these with data collected from offshore tide gauges, and in conjunction with coastal tide data, cotidal maps are drawn with some confidence for M 2 , S 2 , O 1 and K 1 , the M 2 chart resolving the discrepancy which exists between the different charts of the Celtic Sea already produced. Cotidal maps for M 3 and M 4 are also presented.
The mean over a tidal cycle of the energy flux for M2 , S 2 and O 1 is also presented in the form of the total energy flux in these constituents which crosses different sectional lines. A flux of 44 × 106 kW is observed to enter the Celtic Sea from the Atlantic and this is compared with previous estimates. An energy budget is also performed for M 2 , including all the effects of astronomical forcing and Earth tides to enable comparison to be made between the true energy inflow and the estimated frictional dissipation. Finally, comparison is made between the mean of the instantaneous energy flux and the sum of the energy fluxes associated with the major harmonics. 相似文献
The mean over a tidal cycle of the energy flux for M
5.
Toshikazu Odaka 《Geophysical Journal International》1984,76(2):497-513
Summary. A ray-theoretical approach is successfully employed for obtaining the relations between the intrinsic dissipation factors of P - and S -waves, Q α and Q β , and the apparent dissipation factors of toroidal and spheroidal oscillations, Q Tor and Q Sph These are given in quite simple forms and are expressed, to zero-order approximatiom which neglects the effect of reflection of waves at an interface and/or at a free surface), as where α and β are the P - and S -wave velocities and the integrals are evaluated long the surface to surface P - and S -rays.
Some numerical comparisons support the validity of these formulae for higher modes of toroidal and radial oscillations of a realistic earth model.
A first-order approximation reveals that the existence of a discontinuity in an earth induces a systematic fluctuation in normal-mode Q values for any given phase velocity as a function of frequency (or radial mode number). 相似文献
Some numerical comparisons support the validity of these formulae for higher modes of toroidal and radial oscillations of a realistic earth model.
A first-order approximation reveals that the existence of a discontinuity in an earth induces a systematic fluctuation in normal-mode Q values for any given phase velocity as a function of frequency (or radial mode number). 相似文献
6.
Tidal gravity in Britain: tidal loading and the spatial distribution of the marine tide 总被引：1，自引：0，他引：1
T. F. Baker 《Geophysical Journal International》1980,62(2):249-267
Summary. Tidal gravity measurements have been made at six sites in Britain with two nulled LaCoste and Romberg Earth tide gravitymeters. The M 2 observations from these and two further sites are compared with calculations of the tidal loading from the seas around the British Isles and the major oceans. Models of the M 2 marine tides are convolved with Green's functions for appropriate radially stratified Earth models. The differences between the M 2 observations and the theoretical calculations are less than 0.6 μ gals and it is shown that these differences contain further information concerning the errors in the marine tide models. The M 2 marine tides on the north-west European continental shelf are reasonably well known and this allows a useful test of the feasibility of using tidal gravity measurements for the inverse ocean tide problem in areas where the ocean tides are less well known. The differential gravity loading signal between pairs of gravity stations is shown to be important for considerations of the uniqueness and accuracy of the inverse problem. M 2 tidal gravity loading maps for the British Isles and Europe have been produced which are of use in making corrections to various geodetic measurements. 相似文献
7.
Thomas M. Hearn Suyun Wang Shunping Pei Zhonghuai Xu James F. Ni Yanxiang Yu 《Geophysical Journal International》2008,174(1):223-234
Amplitude tomography reconstructs seismic attenuation directly from recorded wave amplitudes. We have applied the tomography to amplitude data reported in the 'Annual Bulletin of Chinese Earthquakes' and interpreted the regionally varying crustal attenuation in terms of tectonics. The seismic amplitudes were originally recorded for determining the M L and M S magnitudes. They generally correspond to the maximum amplitudes of the horizontal components of the short-period S waves and intermediate-period Rayleigh waves. Both sets of measurements are sensitive to crustal structure. The peak amplitudes from M L amplitudes spread spherically with significant dispersion and scattering. M S amplitudes show cylindrical spreading with little dispersion. Average crustal Q values for attenuation at 1 Hz are 737 and 505 for M L and M S , respectively, with substantial regional variations. Frequency dependence in the attenuation is also indicated. Regions with the lowest attenuation (high Q values) are beneath the south China Block, Sichuan Basin, Ordos Platform, the Daxinganling and the Korea Craton. These tend to be tectonically inactive regions, which are generally dominated by intrusive and cratonic rocks in the upper crust. Regions with the highest attenuation (low Q values) are beneath Bohai Basin, Yunnan, eastern Songpan-Ganzi Terrain, margins of the Ordos platform and the Qilian Shan. These are predominantly active basins, grabens and fold belts. The continental margin also highly attenuates both S and surface waves. 相似文献
8.
豫北平原的沙质草地分布于黄河多次泛滥改道冲积形成的沙丘、沙地。其主要类型有:①以白茅、达乌里胡枝子为主的草从草地;②刺槐、杨树等林地下层以藜、白茅、茜草等为主的林下草地;③以碱茅、狗牙根等为主的低湿草地。沙质草地的主要特征为种类组成简单,牧草产量低(<2 000 kg·hm-2)且利用过度。但多种优良栽培牧草在沙地生长良好,可获较高产量。在沙地开发中,应针对各草地类型采取相应措施改造为人工、半人工草地。同时应结合沙地多种林木、果树和经济作物种植,建设农牧林复合经营的系统。畜牧业开发应以产业化为主导,发展适应市场需求的优良畜种,实行适度规模经营。 相似文献
9.
M. Amin 《Geophysical Journal International》1982,68(1):57-78
Summary. Long-period tidal records from eight ports on the west coast of Great Britain are analysed, using both the harmonic method and the response function. Time series up to 9.5 yr were used so that fine structure of certain regions of high energy in the tidal residual spectrum may be examined. This also assisted in accurate separation of tides from surges. According to the currently accepted formulation of M1 , its composition is not compatible with its actual composition in the real tide and, as such, has no useful purpose to serve in computation of predictions. Constituents Sa, Ssa, MA, and MB, are adversly affected by weather and long records are essential for their accurate separation. It has been observed that annual perturbations of S2 , similar to those confirmed in recent years for M2 , also exist but these are not readily recognisable because their speeds are the same as those of constituents T2 and R2 . These perturbations, being highly sensitive to meteorological forces, are mainly responsible for cusps or humps in the vicinity of major tidal constituents in tidal residual spectra. The relationship of radiational and gravitational tides is found to be in very good agreement with theoretical results. In summer months non-predictable variance reduces to about half of the annual variance, reflecting the regional weather conditions of summer and winter. 相似文献
10.
沙尘气溶胶中硝酸盐的含量和来源对于全球氮排放估算具有重要意义。为了探讨格尔木沙尘气溶胶中硝酸盐的含量和来源,我们在格尔木2008年沙尘过程多发期1-6月进行了连续观测,并对收集的沙尘气溶胶样品进行了详细的水溶性离子色谱分析。结果显示:沙尘天气的大气总悬浮颗粒物(TSP)平均浓度及NO3-平均浓度分别为2 015.94 μg·m-3和1.8 μg·m-3,非沙尘天气两者平均浓度分别为274.68 μg·m-3和0.74 μg·m-3。观测期间,格尔木NO3-浓度和TSP浓度存在明显的季节变化,NO3-和TSP浓度变化均为春季>夏季>冬季。TSP与NO3-浓度的相关系数为0.67,春季两者相关系数为0.71,且Ca2+与NO3-浓度显著相关,推测格尔木沙尘气溶胶中NO3-离子可能主要来源于干旱区的地表物质。非沙尘天气期间NO3-/TSP浓度比值高于沙尘天气,且分布较为分散,表明非沙尘天气NO3-浓度受到人为源或气象条件的影响。 相似文献
11.
Summary. Refraction diagrams are drawn for 6-sec microseisms when they approach the British Isles from the SW, WSW, W, WNW and NW directions. Refraction diagrams are also drawn for 4-s and 8-s microseisms approaching from a westerly direction. The diagrams show that all the westerly microseisms are very much reduced. This effect is confirmed by measurement of the vertical component of the microseisms due to sixteen storms which occurred during the period 1945–53. 相似文献
12.
青海湖流域沙柳河下游沉积物中重金属污染风险评价 总被引：6，自引：0，他引：6
对青海湖流域沙柳河下游沉积物中As、Cd、Pb、V、Cr、Mn、Ni、Cu和Zn 9种重金属元素的含量进行了分析测定,采用污染系数、富集系数、地累积指数和潜在生态危害指数评估了其污染程度。结果表明：无论在横向还是纵向上,重金属元素含量均低于青海湖土壤背景值;重金属元素污染系数和富集系数均小于2,且大多数样品的值低于1（高于1者多为Cd、Cu、Ni、Zn,且具高值）;地累积指数均为负值（除QB-19中Cd和Cu分别为0.10和0.02）;潜在生态风险因子大多低于30,潜在生态危害指数大多低于70。沙柳河下游沉积物尚未出现重金属污染,具有低的生态风险,但该流域重金属的人为排放确实存在（主要是Cd、Cu、Ni、Zn等）,而且在近代排放更为显著。 相似文献
13.
为准确刻画资料缺乏、地表水–地下水转换频繁的泽令沟盆地地表水?地下水不同时空尺度上的转换关系,利用河道径流数据、遥感蒸散发数据、地下水位观测数据等对SWAT-MODFLOW耦合模型进行率定和验证,在此基础上对泽令沟盆地水循环过程进行模拟分析。结果显示：① SWAT-MODFLOW耦合模型模拟效果较好,率定期和验证期月径流量的R2≥0.73,NSE≥0.67,PBIAS在?20%~20%。其各子流域实际蒸散发的R2均大于0.91,NSE均大于0.85,PBIAS在?10%~10%。此外,模拟地下水位与实测值误差在0.6 m以内,R2为0.94。② 地表水补给地下水的河道占整个河道长度90.31%,年平均补给量占年总交换水量的50.20%;季节尺度上,补给的最大值出现在7月,为331043.31 m3/d,最小值出现在12月份,为41208.33 m3/d。地下水对地表水的补给量较为稳定,季节性变幅在?2.5%~2.5%,年际变幅处于?6.5%~0.6%之间。 相似文献
14.
The results of the geochemical investigation on bulk sediment fromthree cores collected in Albano crater lake (Central Italy) are reported, andthe main markers of the palaeoenvironmental changes in the last 26ka are discussed. The sediment of Lago Albano consists of greysilt and mud, and is made of volcanogenic, calcareous, siliceous and organicmaterial. Some tephra layers provide a chronological framework for thesequence. The chemical features of the sediments are strongly impacted by theAlban Hills volcanism (Roman volcanic area), but there are also strong changesof organic/inorganic matter ratios, owing to variations in biologicalproductivity and terrigeous supply from the catchment. Six chemostratigraphiczones record the main steps of the transition from the cold and dry climate ofGlacial Maximum to the warmer and more humid Holocene climate. The most usefulgeochemical indices are: biogenic silica, CO2, Br and organiccontent (OM) for biological productivity; Al, Y, CIA (Chemical Index ofAlteration), Al/Rb, Ti/Zr and Y/Al ratios for terrigenous clasticmaterial; OM/Al ratio for organic/terrigenous ratio; S/Fe andMo/Fe ratios and Authigenic U for redox diagenetic conditions of the lakesediment. The geochemical records agree rather well with those of thelithological and paleomagnetic studies, and despite the information obtainedare less detailed than those acquired by the study of biological remains, thepalaeoenvironmental significance inferred is consistent. A comparison of thechemostratigraphic results of Lago Albano with those obtained on coevalsediments from Central and Southern Italy lakes supports the role of thegeochemical investigation as important complement to more sophisticatedtechniques in the palaeoenvironmental reconstructions. 相似文献
15.
Summary. A simple normal approximation is given for the joint probability density function of the polar coordinates (θ, φ) of a random vector following the Fisher distribution with arbitrary mean direction (θ0 , φ0 ). Two important applications of this approximation are discussed, and conditions for the validity of the approximation are investigated and summarized. 相似文献
16.
The traveltime perturbation equations for the quasi-compressional and the two quasi-shear waves propagating in a factorized anisotropic inhomogeneous (FAI) media are derived. The concept of FAI media simplifies considerably these equations. In the FAI medium, the density normalized elastic parameters a ijkl ( X i ) can be described by the relation a ijkl ( X i ) = f 2 ( x i ) A ijkl , where A ijkl are constants, independent of coordinates x i and f 2 ( x i ) is a continuous smooth function of x i . The types of anisotropy ( A ijkl ) and inhomogeneity [ f ( x i )] are not restricted. The traveltime perturbations of individual seismic body waves ( q P , qS 1 and qS 2) propagating in the FAI medium depend, of course, both on the structural pertubations [δ f 2 ( x i )] and on the anisotropy perturbations (δ A ijkl ), but both these effects are fully separated. The perturbation equations for the time delay between the two qS -waves propagating in the FAI medium are simplified even more. If the unperturbed (background) medium is isotropic, the perturbation of the time delay does not depend on the structural perturbations (δ f 2 ( x i ) at all. This striking result, valid of course only in the framework of first-order perturbation theory, will simplify considerably the interpretation of the time delay between the two split qS -waves in inhomogeneous anisotropic media. Numerical examples are presented. 相似文献
17.
Oasisization is a process of converting a natural desert into a man-made oasis in order to satisfy social needs under certain economical and technical conditions. This paper substitutes space for time in order to study physical property changes of oasis soil along the oasisization in about a 1,000-year period. This research focuses on providing the bases for better understanding the process of oasisization. The results show: (1) In about 1,000-year chronological scale, the bulk density and the saturated soil hydraulic conductivity of the surface layer (0-20 cm) significantly reduced with the increase of land reclamation time, while soil porosity, stability of aggregates, and silt content significantly increased. The soil bulk density of the unreclaimed filed (0 year) and the reclaimed field (about 1,000 years) in the surface layer (0-20 cm) are 1.51 g/cm3 and 1.35 g/cm3, the total porosity are 43.16% and 49.27%, the capillary porosity are 38.73% and 47.10%, the water-stable aggregate (0.25 mm) content are 24.60% and 49.59%, the sand content are 85.42% and 61.56%, the clay content are 3.93% and 4.80%, the specific surface area are 128 cm2/g and 231 cm2/g, and the saturated hydraulic conductivity are 0.74 cm/h and 0.34 cm/h, respectively. (2) In the first 30 years of the oasis reclamation, the changes are relatively fast, and the rates of the saturated soil hydraulic conductivity, dry aggregate (0.25 mm), water-stable aggregate (0.25 mm) content, and specific surface area are 0.01 cm/h·yr, 0.58%/yr, 0.50%/yr, and 1.48 cm2/g yr, respectively. 相似文献
18.
19.
河北坝上风蚀沙化地区固沙造林植物种的选择 总被引：3，自引：0，他引：3
通过对河北坝上沙地植被的调查和固沙造林植物种的引种栽植试验,指出适于坝上沙地固沙造林的植物种有9种。适应性强的有褐沙蒿、山竹子两个乡土植物种和华北落叶松、樟子松、沙棘、黄柳;适应性中等的有小叶锦鸡儿、沙柳、花棒;适应性弱的有沙地柏、紫穗槐。 相似文献
20.
Summary. Geomagnetic time-variations observed at several sites on the island of Hawaii are analysed for the effects of island bathymetry as well as for the inductive response of the deeper mantle. The data are generally consistent with the deep conductivity profile derived using lower frequency, electromagnetic data from the Island of Oahu. Hawaii data fit better if that model is modified to give the upper 200 km of the mantle a lower conductivity of 0.02 S/m compared to 0.1 S/m for Oahu. The data are represented by a complex, frequency-dependent function of location, T u , relating the vertical variation Z to a component U of the horizontal variation ( Tu = Z/U ). The direction of U is nearly frequency independent at each site but is different for each site. Below a frequency of about 30 cycles per day, the functions, T u , at any two sites are found to be related by a real constant. This suggests that the deeper conductivity structure is the same beneath each site. This result is consistent with quasi-static induction in a non-uniformly conducting thin sheet above a stratified conductivity structure. The response of such a model can be written as T u = Aq , where q is a quasi-uniform, complex, frequency-response function characterizing the effect of the deep conductivity and A is a spatially dependent parameter parameterizing the effect of variable conductivity in the thin sheet. The parameter A may be estimated by fitting observational estimates of T u to models of deep conductivity structure. 相似文献