共查询到10条相似文献，搜索用时 109 毫秒
1.
Pavel Vyskoc&#x;il 《Tectonophysics》1979,52(1-4)
Preliminary analysis of the new results of repeated levellings within the territory of the Bohemian Massif and its border with the Carpathians is made, and the correlation between horizontal gradients of vertical movements and main fault zones discussed. The results indicated the continuance of the main movement's tendencies, determined by the foregoing measurements. Also discussed are the vertical and horizontal crustal movements between the Bohemian Massif and the Carpathians. The active zones are connected with the main fault systems, and the horizontal movements indicated the spreading tendencies between both geological structures. These results are in accord with the tendencies of horizontal movements in the Soviet Carpathians. 相似文献
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Geodetic measurements in the Rhinegraben area are discussed. Repeated levellings, together with horizontal control data, torsion-balance measurements, very dense gravity coverage, tiltmeter observations and a high-precision gravity test net were available in order to test present concepts of the Rhinegraben structure and sources of recent crustal movements. The ambiguities of levelling data are stressed, but investigations of high-precision levelling data clearly indicate subsidence of several centimetres in the graben area, whereas multivariate studies of the data available on the graben shoulders do not indicate any significant movement on the shoulders themselves. 相似文献
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Wolfgang Torge 《Tectonophysics》1986,130(1-4):385-393
Through recent developments in absolute and relative techniques, gravimetry has reached an accuracy of a few hundredths to a few tenths of μm s−2 *in small or large-scale networks, respectively. Consequently, gravimetric techniques can now be employed as one efficient tool for detecting vertical crustal movements. Gravity data are necessary for converting the results of geometric levelling to heights defined in the gravity field, and—by repeated surveys—to control time variations of the height-reference surface. More important is the use of repeated gravity surveys for strengthening and partly replacing levelling, being a time-consuming procedure with unfavourable error propagation over larger distances. The successful application of observed gravity variations with time in the detection of vertical crustal movements depends on the reliability of the conversion factor between gravity and height changes, and on the accuracy of the gravity measurements. The conversion factor should be determined through simultaneous levelling and gravimetry, in representative parts of the survey region. Strategies for establishing gravimetric control are changing now with the availability of transportable absolute gravity meters, and the possibility of accurately calibrating relative instruments and observing small gravity differences with feed-back-systems. Consequently, more attention has to be given now to disturbing effects of environmental character, such as microseismics, atmospheric pressure and groundwater table variations, and to periodic effects such as gravimetric earth tides and polar motion. 相似文献
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L.N. Kailasam 《Tectonophysics》1979,52(1-4)
Recent crustal movements have been observed and studied in several parts of India including the Himalayan and sub-Himalayan regions, the Precambrian shield of peninsular India and also the coastal tracts. The results of studies of Holocene deformation and crustal movements in two type areas are presented, one in the extreme southeastern part of the peninsula and the other in northeastern India.The Precambrian shield in the extreme southeastern part is characterised by a major NE—SW trending fault zone in the Tirupattur—Mattur areas of Tamil Nadu with some major extended faults, one of which apparently cuts through the entire crust and Moho as indicated by gravity data and which is associated with occurrences of alkaline and basic intrusions and carbonatite complex. Evidence of Recent crustal movements in this zone is afforded by geomorphic features and recent and current seismicity of a mild nature which is apparently to be attributed to slow movements along the fault plane.The Shillong plateau in northeastern India occurs as block-uplifted horst, comprising for the most part Archaean crystalline rocks with plateau basalts and Cretaceous and Tertiary sediments occurring on its southern margin. The plateau is bounded by major faults and is located in a zone of high seismicity lying astride and parallel to the eastern Himalayas intervened by the alluvium of the Brahmaputra Valley. Geomorphic features such as raised terraces, straight-edged scarps, etc., provide evidence for Recent crustal movements with dominant vertical movements along the fault planes which have continued through Tertiary and Recent times. Repeated precision levelling measurements conducted by the Survey of India indicate a rate of uplift of 4–5 cm per 100 years during the period 1910–1975.The gravity data pertaining to this region are also discussed in relation to the crustal movements. 相似文献
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A significant drop in seismic travel times of up to 1.0% occurred in the Charlevoix region between 1979 and 1980, possibly related to the M = 5.0 (Aug., 1979) earthquake in the vicinity. A travel-time drop of this magnitude could have been produced either by the closing of dry or saturated cracks in the upper crustal material or by the saturation of dry or partly saturated cracks. However, the anisotropy of travel-time changes in this area supports the view that this travel-time drop was caused by the closing of water-saturated aligned vertical cracks in the crustal material. Three different crack directions with respect to north were resolved: 0 ° or 90 ° in the Precambrian rocks underneath the St. Lawrence River, −18° or 72° in the shallow rocks (< 5 km) of the Charlevoix crater, region, and +35° or 125° in the Paleozoic cover rocks. Crack closure would require a decrease in the pore volume of the rocks which would be expected to produce subsidence in the Charlevoix area. Since repeated levellings restrict the vertical crustal motion during this time interval to less than 2 cm, we conclude that either the effective aspect-ratio of cracks is less than 0.0001 or the process of crack closure occurred in a number of unconnected regions. More specifically the crack deformation would have to occur in isolated inclusions less than 1 km in diameter and no deeper than about 6 km. The process of crack closure may have been triggered by the passage of seismic waves from the M = 5.0 earthquake. 相似文献
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G. Gerstbach 《Tectonophysics》1986,130(1-4):427-436
In mountainous regions, the effect of vertical deflections vastly exceeds the accuracy of most geodetic measurements and causes systematic errors of some cm per km at steep sightings. Therefore, crustal movements may be veiled by the enlarged error ellipses.
This paper shows how to compute local vertical deflections to ± 1–2″ within 5 minutes per point, using a parabolic formula and a raw topographical map. For very asymmetrical peaks, by-valleys and irregular slopes, a simple correction is given. No astronomical observations or digital height models are necessary. 相似文献
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袁兆亿 《大地构造与成矿学》1991,15(1):7-13
通过分析东南、华北及藏北三个地洼区的重力、地震、地热等深部和浅部地球物理资料所表现出来的不同特征及其存在的差异,论述了上述三个地洼区现阶段的大地构造运动中,东南地洼区地壳运动最弱,藏北地洼区地壳运动最强,华北地洼区的地壳运动强度居于前两者之间。研究表明,地壳运动的强弱变化与地幔有着密切联系。 相似文献