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1.
Summary. Palaeomagnetic measurements have been carried out on one Cretaceous and five Cenozoic sedimentary sequences of Australia; of those, one is in the Carnarvon Basin of north-western Australia, and the others are in the Otway Basin of south-eastern Australia. The new results are used together with those published previously to define a revised late Mesozoic–Cenozoic apparent polar wander path for Australia. This path differs from earlier, basalt-derived paths by the absence of a large westward excursion and zig-zag irregularities. It is characterized instead by a substantially straight Cenozoic trajectory, a sharp bend in the Late Cretaceous, and a non-uniform rate of apparent polar wander.
The early Tertiary segment of the new path lies north of the original paths, thus eliminating a discrepancy that has been noted previously between the Indian and Australian palaeomagnetic data (Luyendyk & Rennick, Peirce and Klootwyk & Peirce). A re-examination of the original data suggests that this discrepancy, as well as two others in the Australian results, may have been caused principally by incomplete time-averaging of remanence directions, because the volcanics on which the results were based had been extruded episodically.  相似文献   

2.
Summary. A complete method of solution of linear inverse problems with non-negativity constraints has been given previously. Here, problems with more particular applications in geophysics are discussed. First, we describe the evolution of the set of solutions when a statistical distribution of the errors is assumed. The theory of ideal bodies, which has been introduced recently by Parker, is then discussed. Conjectures of Parker's are proved. Algorithms to construct ideal bodies for any data set are given. To finish, we study planar diagrams, which nicely illustrate the extent of the set of equivalent solutions by showing two moments of a solution versus each other for all possible solutions. The evolution of these diagrams when a new measurement is made gives a good idea of the interest of this measurement. Three-dimensional diagrams can be managed in the same way and used for the gravity interpretation.  相似文献   

3.
The Nama Group of southern Namibia is a candidate for the Terminal Proterozoic Global Stratotype Section and Point (GSSP). Desirable characteristics of a GSSP include a well-preserved index-fossil assemblage, little deformation or metamorphism. well-constrained isotopic ages, stable-isotope records and magnetostratigraphic control. The age of the Nama Group sediments is now constrained to between 570 and 510 Ma. Assuming the Gondwana assembly was nearly complete at this same time, there is a discrepancy between the previously published Nama poles, a revised 550-510 Ma apparent polar wander path for Gondwana and the preceding supercontinental assemblages of Rodinia and Panottia. For these reasons, the Nama Group sediments were resampled in an effort to evaluate the potential of detailing the magnetostratigraphy of the Nama Group and resolving the discrepancy between the Nama poles and the APWP of Gondwana. Collectively, both the previous studies of the Nama Group and this one show a complex series of overprints and no easily discernible primary direction of magnetization. We therefore urge caution in using the Nama Group poles in any tectonic models of the Neoproterozoic-Early Palaeozoic. Specifically, the N1 component of magnetization, previously identified as a primary magnetization, was discovered in a younger suite of samples. Therefore, previous tectonic models that used the N1 magnetization direction as representative of the time of Nama deposition should be revised in light of these recent findings.  相似文献   

4.
The representation of women on geography faculties did not increase appreciably between 1971 and 1977, but women in other academic disciplines have fared somewhat better. The latter have improved their status primarily as a result of actions taken by professional associations representing their fields. When a professional association ignores its female constituency or refuses to commit itself to improving their circumstances, federal agencies now offer alternative channels for obtaining redress.  相似文献   

5.
Abstract

Geography is one of the subjects offered toward a diploma of the International Baccalaureate Organization. Like the others, its syllabus is regularly reviewed and revised to remain current. The advent of a revised syllabus brings overlap that can be challenging for teachers. The syllabus that is now coming to an end was described in 107(4–5) of the Journal of Geography. The present article compares that syllabus with the new one and, particularly, the demands the new syllabus will place on teachers and students alike.  相似文献   

6.
Summary. A direct calculation is made of the effect on the Chandler wobble of 1287 earthquakes that occurred during 1977–1983. The hypocentral parameters (location and origin time) and the moment tensor representation of the best point source for each earthquake as determined by the 'centroidmoment tensor' technique were used to calculate the change in the Chandler wobble's excitation function by assuming this change is due solely to the static deformation field generated by that earthquake. The resulting theoretical earthquake excitation function is compared with the 'observed' excitation function that is obtained by deconvolving a Chandler wobble time series derived from LAGEOS polar motion data. Since only 7 years of data are available for analysis it is not possible to resolve the Chandler band and determine whether or not the theoretical earthquake excitation function derived here is coherent and in phase with the 'observed' excitation function in that band. However, since the power spectrum of the earthquake excitation function is about 56 dB less than that of the 'observed' excitation function at frequencies near the Chandler frequency, it is concluded that earthquakes, via their static deformation field, have had a negligible influence on the Chandler wobble during 1977–1983. However, fault creep or any type of aseismic slip that occurs on a time-scale much less than the period of the Chandler wobble could have an important (and still unmodelled) effect on the Chandler wobble.  相似文献   

7.
Climatic water budget principles provide an analytical basis for expressing drought severity as the cumulative moisture deficiency in biologic and hydrologic systems. This conceptual framework emphasizes the disparity between real-time and expected precipitation, soil moisture, and runoff in quantifying the cumulative moisture deficiency, and it facilitates incorporation of spatial characteristics in assessing drought severity. Comparison of the temporal and spatial properties of the severe 1924 and 1977 droughts in the Sacramento River Basin illustrate the procedure. The 1924 drought has a larger average water deficiency, or magnitude, but the 1977 drought has a longer duration and its cumulative moisture deficiency, or severity, is 1.4 times greater than the 1924 drought. Expressed volumetrically, the greater cumulative moisture deficiency for the 1977 drought is 13.3 times larger than the moisture deficit difference indicated by calculations of natural runoff for water years 1924 and 1977.  相似文献   

8.
Interpretations of a decline in foreign-area specialization have raised concerns about the capacity of geography in the United States to serve the expected increase in demands for foreign-area expertise. An assessment of foreign-area dissertations awarded by U.S. geography programs over a 15-year period (1977–1991) fails to support the concerns raised. No significant declines, if any at all, are found for early career interest and research in foreign areas. Several caveats are warranted, however. Geography has lost three doctoral programs with strong foreign-area dissertation records for the period in question. Also, non-U.S. citizens, many of whom do not remain in the United States after completion of their doctorate work, account for a significant proportion of foreign-area dissertations. Various questions that must be addressed to analyze the capacity question more broadly are identified.  相似文献   

9.
New Zealand's policy goal to preserve coastal natural character was first incorporated into planning legislation in 1973 and protected area legislation in 1977. An evaluation of 100 relevant Resource Management Act Court decisions determined the Courts' interpretations of this policy goal. The Courts have repeatedly found that natural character is of nature (not culture), including natural elements, patterns, and processes. There is a continuum of naturalness from pristine indigenous ecosystems to the urban environment. A 2014 Supreme Court decision has upheld the use of environmental bottom lines for natural character and the importance of protection as part of sustainable management.  相似文献   

10.
We selected four typical glaciers in the Qilian Mountains and investigated their movements and variation using advanced technologies such as remote sensing,photographic measurements,and global positioning systems.The velocity of glacier movements in the Qilian Mountains is relatively low,and there has been no significant variation during the past 50 years.Glacier motion has maintained a normal style.The movement velocity of Laohugou Glacier No.12 presented a decreasing trend(by 48%) from 1960 to 2012.The movement velocity of the Qiyi Glacier also presented a decreasing trend(by 48.1%) from 1958 to 2012; it decreased by 29.4% from 1958 to 1977 and by 26.5% from 1977 to 2012.Therefore,the Qiyi Glacier's movement velocity varied greatly over the earlier 20 years(1958–1977),but presented a small decreasing trend during the latter 30 years(1977–2012).By comparing the movement velocity variation of these typical glaciers,we determined that the extent of variation was consistent among large glaciers(such as Laohugou Glacier No.12) and small glaciers(such as the Qiyi Glacier and Yanglonghe Glacier No.5),despite their different sizes.  相似文献   

11.
Little Ice Age (LIA) moraines along the margins of Skálafellsjökull and Heinabergsjökull, two neighbouring outlet glaciers flowing from the Vatnajökull ice‐cap, have been re‐dated to test the reliability of different lichenometric approaches. During 2003, 12 000 lichens were measured on 40 moraine fragments at Skálafellsjökull and Heinabergsjökull to provide surface age proxies. The results are revealing. Depending on the chosen method of analysis, Skálafellsjökull either reached its LIA maximum in the early 19th century (population gradient) or the late 19th century (average of five largest lichens), whereas the LIA maximum of Heinabergsjökull occurred by the mid‐19th century (population gradient) or late‐19th century (average of 5 largest lichens). Discrepancies (c. 80 years for Skálafellsjökull and c. 40 years for Heinabergsjökull) suggest that the previously cited AD 1887 LIA maxima for both glaciers should be reassessed. Dates predicted by the lichen population gradient method appear to be the most appropriate, as mounting evidence from other geochronological reconstructions and sea‐ice records throughout Iceland tends to support an earlier LIA glacier maximum (late 18th to mid‐19th century) and probably reflects changes in the North Atlantic Oscillation. These revised chronologies shed further light on the precise timing of the Icelandic LIA glacier maximum, whilst improving our understanding of glacier‐climate interactions in the North Atlantic.  相似文献   

12.
The Hazar Basin is a 25 km‐long, 7 km‐wide and 216 m‐deep depression located on the central section of the East Anatolian Fault zone (eastern Turkey) and predominantly overlain by Lake Hazar. This basin has been described previously as a pull‐apart basin because of its rhombic shape and an apparent fault step‐over between the main fault traces situated at the southwestern and northeastern ends of the lake. However, detailed structural investigation beneath Lake Hazar has not been undertaken previously to verify this interpretation. Geophysical and sedimentological data from Lake Hazar were collected during field campaigns in 2006 and 2007. The analysis of this data reveals that the main strand of the East Anatolian Fault (the Master Fault) is continuous across the Hazar Basin, connecting the two segments previously assumed to be the sidewall faults of a pull‐apart structure. In the northeastern part of the lake, an asymmetrical subsiding sub‐basin, bounded by two major faults, is cross‐cut by the Master Fault, which forms a releasing bend within the lake. Comparison of the structure revealed by this study with analogue models produced for transtensional step‐overs suggests that the Hazar Basin structure represents a highly evolved pull‐apart basin, to the extent that the previous asperity has been bypassed by a linking fault. The absence of a step‐over structure at the Hazar Basin means that no significant segmentation boundary is recognised on the East Anatolian Fault between Palu and Sincik. Therefore, this fault segment is capable of causing larger earthquakes than recognised previously.  相似文献   

13.
在有关养老的老年学和地理学研究中,“就地养老”是一个广泛使用的概念,并一直被认为是解决老龄人口养老需求的有效政策手段。迄今为止,关于就地养老的研究主要关注了很多能够让老年人健康就地(或在家)养老的物质方面的因素,比如住房条件或家庭照护。有些老年学研究者们认识到,就地养老受到居住环境中实体环境和社会、情感因素的共同影响。但我们认为,在养老体验研究中,要更加深入地审视“人”和“地方”之间的复杂关系。特别是,我们主张就地养老成功的因素是地方具有维持良好关系的潜力。提到“地方(place)”一词的时候,人们过分局限于关注老年人身体上接近的地理空间,或是具有实体边界的地方,例如房子或社区。而我们通过回顾现有文献发现,对许多选择就地养老的人来说,更具有意义的是随着时间的推移,他们在不同空间尺度上所建立起来的多元的、网络化的社会和非社会关系。基于这个新的视角,可以更好地理解老年人与地方的多层次的联系,以及从不同尺度和不同类型的人与地方的关系来考察就地养老的意义。  相似文献   

14.
Jacobsen, N. Kingo, 1977: Recreation on the Danish Wadden Sea Coasts. Geografisk Tidsskrift 76: 52–58. København, June 1, 1977.

A comparison is made between the quite different positions of the Danish Wadden Sea coasts as to recreational pattern. This is mostly due to the ever varying accessiblility. The Blåvand-Skallingen area can be reached by land. The islands partly by ebbroads (Mandø, Lungli), partly by ferry (Fanø), and partly by a road-dam (Rømø).  相似文献   

15.
Landform–sediment assemblages associated with two ice-dammed lakes, one active and one fossil, at Heinabergsjökull in southeast Iceland are described. The current ice-dammed lake (Vatnsdalur) is dominated by a large aggradational terrace, as well as an excellent suite of shorelines. The second fossil ice-dammed lake dates from the Neoglacial maximum of Heinabergsjökull ( c . 1887) and drained during the late 1920s. This lake is associated with a suite of shorelines and ice-marginal glaciolacustrine fans. The sedimentology of one of these fans is described. Between 50 and 70% of the sediment succession is dominated by ice-rafted sediment, although rhythmites, matrix-rich gravels, sands and graded sand–silt couplets are also present. A range of intra-formational, soft-sediment deformation structures are present, consistent with liquefaction and deformation associated with loading, current shear, and iceberg calving. The landform–sediment assemblages described from Heinabergsjökull provide important data for the interpretation of Pleistocene ice-dammed lakes.  相似文献   

16.
本文对地理研究所三十年的科研工作进行了回顾。其中对科研工作的发展按四个时期作了简要分析。重点介绍了为生产和建设服务的工作,扼要总结了地理学基础理论研究方面的工作,最后阐述了实验技术的发展与新技术的应用。  相似文献   

17.
Summary. The method of stochastic inversion, previously applied to secular variation data, is applied to main field data. Adaptations to the method are required: non-linear, as well as linear, data are used; allowance is made for crustal components in the observatory data; and the prior information is specified differently. The requirement that the models should satisfy a finite lower bound on the Ohmic heating in the core provides strong prior information and gives finite error estimates at the core—mantle boundary.
The new method is applied to data from the epochs 1969.5 and 1980.0. The resulting field models are very much more complex than other models, such as the IGRF models extrapolated to the core, and show considerable small-scale detail which, on the basis of the error analysis, can be believed.
The flux integral over the northern hemisphere is computed at each epoch; the difference between the two epochs is approximately one standard deviation, suggesting that the question as to whether the decay of the dipole is consistent with the frozen-flux hypothesis has been resolved in favour of the hypothesis.  相似文献   

18.
Summary. A method is given which completely solves linear inverse problems with positive constraints. Equivalent solutions form a convex combination (i.e. with barycentric coefficients) of a special set of solutions, called the extremals. Conversely, the set of all linear convex combinations of the extremals coincide with the set of equivalent solutions. Thus the extremals completely define the set of solutions, exactly like the vertices of a triangle define the whole triangle. A strategy is given to obtain these extremals in a natural order, through several applications of well-known algorithms, taking into account all physical information. Similar methods are given to evaluate the range of the set of equivalent solutions, and to manage numerical uncertainties. The choice of a solution inside the set is discussed. In the Appendix B, several typical choices are given, and should meet physicists requirements in most of these problems.  相似文献   

19.
Summary. This paper discusses the inverse (downward) continuation of a wavefield into a medium, as a means of estimating seismic velocities and the imaging of the geometry of reflecting objects. The notion of a kinematically equivalent (K-equivalent) operator of the field continuation is introduced, which allows both the possibility of replacing the initial Lamé equation by a simpler one (for example, a wave equation) and also the existence of an infinite set of continuation operators which permit us to construct a wavefield with proper characteristics. Any of the K-equivalent operators can be used in the task of imaging of reflectors given the known velocities. If velocities are unknown and reflectors are irregular, it is possible to improve the regularity of reflections by continuing the field downward to a fictitious surface in the media with a velocity Vo, that differs from the true velocity V . The conditions needed to untie loops in the true patterns in the continued field are also given.
Another approach is connected with calculations of dynamic sections using different values of velocity (say, an extremal velocity) under which the amplitudes of reflectors on sections are brought to a maximum due to the phenomena of focusing. Extremal velocities can be also used for solving inverse kinematical problems.  相似文献   

20.
<正>Profile Prof. Fang Chun-hui,as the Second Grade Professor and Doctoral Supervisor,was born in Xianyang City,Shaanxi Province,China,in 1957.He was admitted to the Chemistry Department,Northwestern University,China,after resumed the college entrance examination in 1977,He has been engaged in sci-  相似文献   

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