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921.
922.
Introduction Richter and Mckenzie (1978) supposed that there is a small-scale convection system in the mantle. For a long time lots of research provides observational data to infer the possibility of a small-scale convection in the upper mantle. For example, Haxby and Weissel (1986) discussed the relationship between SEASAT map and small-scale convection. Baudry and Kroenke (1991), Maia and Diament (1991) found that the geoid and bathymetry exhibit peaks in the 400~650 km range in the Pa… 相似文献
923.
电测深法在漠河地区探测永久冻土层的应用 总被引:1,自引:0,他引:1
用电测深方法研究永久冻土带的空间分布规律,为东北天然气水合物远景调查的进一步研究提供依据。通过在漠河地区南北剖面(20 km)和东西剖面(13 km)电阻率测深法的探测研究,实测电测深曲线多数为HK、K或Q型,对应的地电结构大致为:第一层为地表干燥松散碎石层,该层电阻率很高(几百~几千Ω.m),但厚度较小,一般不超过2 m;第二层为无冰冻含水碎石堆积层(部分测点无此层),电阻率一般小于100Ω.m,厚度不超过2~5 m;第三层为推断的永久冻层,电阻率一般大于300Ω.m,该层厚度变化较大,从20几m到100多m;推断永冻层下为一低阻层,电阻率一般小于200Ω.m。 相似文献
924.
The Dhanbad district in Jharkhand faces acute water scarcity and is chronically drought-prone. The groundwater resources in
the area have not been fully exploited. The present study was undertaken to evaluate the groundwater prospective zones. Landsat-5
Multi Spectral Scanner (MSS) data of band 2 and band 4 and false colour composite (FCC) of band 2, 3, 4 were interpreted visually
to differentiate different hydromorphogeological units and to delineate the major trends of lineaments. The different geomorphic
features identified are linear ridges, residual hills, and pediplain, buried pediment and dissected pediplain, besides lineaments.
The study shows that the pediplain and buried pediments are promising zones for groundwater prospecting. The occurrence and
movement of groundwater is restricted to the unconsolidated material, weathered and fractured rocks. For the selection of
tube well sites, geoelectrical resistivity investigations have been carried out at the sites, which were found suitable based
on hydrogeomorphological and hydrogeological studies. Twenty-six Vertical Electrical Soundings (VES) have been carried out
by using Schlumberger electrode configuration, which have brought out 3 to 7 layered sub-surface layers. The resistivity of
water-bearing weathered/fractured rocks varies from 120–150 ohm m. The integrated studies have revealed that the blue colour
zones are most promising for groundwater exploration and dug wells may be dug up to depths of 30±5m. 相似文献
925.
926.
Seismogenic zone structure beneath the Nicoya Peninsula, Costa Rica, from three-dimensional local earthquake P- and S-wave tomography 总被引:3,自引:0,他引:3
927.
928.
929.
A three-dimensional radially anisotropic model of shear velocity in the whole mantle 总被引:4,自引:0,他引:4
We present a 3-D radially anisotropic S velocity model of the whole mantle (SAW642AN), obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on Non-linear Asymptotic Coupling Theory (NACT). The model is parametrized in level 4 spherical splines, which have a spacing of ∼ 8°. The model shows a link between mantle flow and anisotropy in a variety of depth ranges. In the uppermost mantle, we confirm observations of regions with VSH > VSV starting at ∼80 km under oceanic regions and ∼200 km under stable continental lithosphere, suggesting horizontal flow beneath the lithosphere. We also observe a VSV > VSH signature at ∼150–300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast-spreading segments. In the transition zone (400–700 km depth), regions of subducted slab material are associated with VSV > VSH , while the ridge signal decreases. While the mid-mantle has lower amplitude anisotropy (<1 per cent), we also confirm the observation of radially symmetric VSH > VSV in the lowermost 300 km, which appears to be a robust conclusion, despite an error in our previous paper which has been corrected here. The 3-D deviations from this signature are associated with the large-scale low-velocity superplumes under the central Pacific and Africa, suggesting that VSH > VSV is generated in the predominant horizontal flow of a mechanical boundary layer, with a change in signature related to transition to upwelling at the superplumes. 相似文献
930.