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901.
The lithospheric models obtained for the Baltic Shield by using deep seismic soundings are discussed and results from different parts of the shield are compared with models achieved by the investigation of surface waves and of P to S converted waves. The results are found to agree rather well with each other particularly with regard to the first interface (at a depth of 10–15 km) and the whole thickness of the crust (c. 40 km). The macroseismic focal depth determinations of regional earthquakes are correlated with lithospheric structure. The main maximum in the focal depth distributions of Finnish earthquakes occur at a depth of 10–12 km. The geographical distribution of the earthquake epicentres suggests several seismo-active zones in the northern Baltic Shield. One new finding in this field concerns the Lapland zone, which runs in a north-westerly direction.  相似文献   
902.
Thin section, SEM, and TEM analyses have indicated that the red ‘teri’ sands of southeast India have formed from weathering in situ of coastal dune sands. The data does not support a detrital origin for the red sands. C14 dates indicate that dune deposition and weathering, to a maximum depth of 10 m, leading to the formation of a hematite, koalinite and illite rich matrix has taken place rapidly over the past 25,000 years. It is postulated that garnet was a major source of hematite (ferric oxide).  相似文献   
903.
The results of seismic measurements along the deep seismic sounding profile VII and terrestrial heat flow measurements used for construction of heat generation models for the crust in the Paleozoic Platform region, the Sudetic Mountains (Variscan Internides) and the European Precambrian Platform show considerable differences in mantle heat flow and temperatures. At the base of the crust variations from 440–510°C in the models of Precambrian Platform to 700–820°C for the Paleozoic Platform and the Variscan Internides (Sudets) are found. These differences are associated with considerable mantle heat flow variations.The calculated models show mantle heat flow of about 8.4–12.6 mW m–2 for the Precambrian Platform and 31 mW m–2 to 40.2 mW m–2 for Paleozoic orogenic areas. The heat flow contribution originating from crustal radioactivity is almost the same for the different tectonic units (from 33.5 mW m–2 to 37.6 mW m–2). Considerable physical differences in the lower crust and upper mantle between the Precambrian Platform and the adjacent areas, produced by lateral temperature variations, could be expected. On the basis of carbon ratio data it can be concluded that the Carboniferous paleogeothermal gradient was much lower in the Precambrian Platform area than in the Paleozoic Platform region.  相似文献   
904.
Some results of induced polarisation surveys carried out for the exploration of sulphide mineralisation in parts of Rajasthan and Gujarat, employing both frequency-domain and time-domain techniques, are presented. A few typical examples of I.P. results along with borehole sections and results of conventional geophysical surveys have been incorporated. Frequency-domain and time-domain I.P. data have been compared for selected areas.Borehole data pertaining to several areas investigated have corroborated the I.P. results fairly well.  相似文献   
905.
Elastic wave velocities and the ratiov P/v S were studied for dry and initially saturated samples of carbonate and crystalline rocks at pressures to 2 kbar. In initially saturated samplesv P increases in crystalline rock, whereas in sedimentary rock it may either increase or decrease with increasing pressure. Under the same conditionsv S remains approximately constant in crystalline rocks and decreases in sedimentary samples. The ratiov P/v S as a function of pressure increases in dry rocks and decreases in saturated ones. Saturated samples always have higherv P/v S ratios than dry ones. It appears that the geometry of the pore space influences the acoustic properties of saturated crystalline rocks.  相似文献   
906.
Phase velocities of Rayleigh waves for the Adriatic Sea area are obtained in the period range 25–190 sec along the path (l'Aquila-Trieste) AQU-TRI and 20–167 sec along the path (Trieste-Bari) TRI-BAI.The phase velocities are systematically higher than the known values for the surrounding regions. The data inversion indicates the presence of a lithosphere typical of stable continental areas with clear high-velocity lid (V s 4.6 km/sec) overlying a well developed low velocity zone (V s 4.2 km/sec).P. F. Geodinamica C.N.R., Roma Pubbl. N. 189.  相似文献   
907.
This paper examines the evidence for the model of a small cumulus cloud represented as a quasi static but turbulent entity, growing on the upshear side and decaying on the downshear side. While the air just outside the cloudy outline is, on average, stationary relative to the embedding airmass, there is a slight flow, upwards and forward as though the updraft has induced upward motion in the clear air outside the cloud, on the growing side. On the decaying side the motion is downwards and away from the cloud.This is a flow pattern which is not consistent with the air flowing around the cloud as it moves forward but it agrees well with the picture given. Decayed remnants of cloud are found throughout the air previously occupied by the cloud. The cloud outline moves through the embedding air at a velocity which is almost as large as the relative motion of the subcloud feeding airflow (which is almost free from internal wind shear in strong convection).The mixing of dry air from above the inversion yields the observed diluted liquid water content in small cumuli, if such mixing is allowed to proceed until the cloud density equals that of the surrounding air. Quantitative conditions relating the liquid water to inversion temperature and moisture changes, and to the stability of the environment are presented. The strong vertical mixing from the top of the cloud downwards is important to microphysical processes.  相似文献   
908.
An examination is made of the hypothesis that internal cloud properties are determined by the mixing of dry air from above the cloud top and cloud base air in such a way that the mixture is neutrally buoyant with respect to the clear air environment at each level. It is concluded that the resulting mixture is much drier than is actually observed. Comments are made about observed cloud properties which need to be taken into account in any model of the mixing process.  相似文献   
909.
云南民族语地名探析   总被引:1,自引:0,他引:1  
云南有25种世居的少数民族,是全国少数民族最多的省,也是民族语地名语种最多的省。云南被称为“地名博物馆,,民族语地名有其典型性。云南的民族语地名有很多特点,但并不特殊,在其他地方也似曾相识。本文以一个省为单元,对少数民族语地名进行全面综合研究,探讨民族语地名与地理环境、历史发展的关系及各种民族语地名之间的关系。  相似文献   
910.
对流层高层偏北气流在梅雨暴雨中的作用   总被引:11,自引:0,他引:11  
翟国庆 《气象学报》1998,56(1):68-76
文中对江淮梅雨暴雨过程中的高低空流场特征及物理过程进行分析.结果表明:对流层上部青藏高原东侧常有高空偏北大风轴汇入南亚东风急流中.在这支强北风轴北端发现高空辐散和辐散的增长.亦即有利于低层辐合上升的持续、发展和加强;表明了低层西南急流与高空青藏高压东侧的偏北强风轴之间的次级环流圈,有利于梅雨暴雨的持续.  相似文献   
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