含煤层地质环境下地震波场的数值模拟   总被引：3，自引：2，他引：1  

潘冬明  杨顶辉 《地球物理学进展》1997,12(1):74-83

本文对含低速煤层地质环境下弹性波场多波多分量地震资料进行了二维数值模拟研究,对人工边界反射进行了有效处理,频散效应得到了有效的压制,对几种不同激发与观测排列方式下的弹性波资料进行了模型计算与分析。  相似文献   

扬子地台前寒武纪－寒武纪界线地层的微体植物化石群   总被引：10，自引：2，他引：8  

尹磊明 《地层学杂志》1995,(4)

前寒武纪一寒武纪界线地层在扬子地台发育良好、分布广泛,并有包括微体植物群、海藻、瓶形原生物、具硬体动物及‘澄江动物群’等化石的发现。因而,扬子地台成为研究前寒武纪－寒武纪界线生物地层的代表地区之一。基于对扬子地台前寒武纪－寒武纪界线地层已知微体植物化石记录的回顾和论定,总结概括了下寒武统微体植物化石组合：寒武系最底部硅质磷块岩中的Ｍｉｃｒｈｙｓｔｒｉｄｉｕｍ－Ｐａｒａｃｙｍａｔｉｏｓｐｈａｅｒａ－Ｍｅｇａｔｈｒｉｘ组合和较高层位页岩的Ｓｋｉａｇｉａ－Ａｎｎｕｌｕｍ－Ａｒｃｈａｅｏｄｉｓｃｉｎａ组合。它们分别与Ａｎａｂａｒｉｔｅｓ－Ｃｉｒｃｏｔｈｅｃａ－Ｐｒｏｔｏｈｅｒｔｚｉｎａ小壳动物化石带和Ｐａｒａｂａｄｉｅｌｌａ及Ｅｏｒｅｄｌｉｃｈｉａ三叶虫带相对应。与东欧地台疑源类生物地层相对照,扬子地台Ｍｉｃｒｈｙｓｔｒｉｄｉｕｍ－Ｐａｒａｃｙｍａｔｉｏｓｐｈａｅｒａ－Ｍｅｇａｔｈｒｉｘ组合的纵向分布大体和东欧地台Ａｓｔｅｒｉｄｉｕｍｔｏｒｎａｔｕｍ－Ｃｏｍａｓｐｈａｅｒｉｄｉｕｍｖｅｌｖｅｔｕｍ组合带相一致,而以上两地台的化石组合产出层位可能都略高于纽芬兰东部剖面,依据Ｐｈｙｃｏｄｅｓｐｅｄｕｍ所厘定的寒武系底界?  相似文献   

Measurements of peroxyacetylnitrate in the marine boundary layer over the Atlantic     

K. P. Müller  J. Rudolph 《Journal of Atmospheric Chemistry》1992,15(3-4):361-367

The atmospheric concentration of peroxyacetylnitrate (PAN) was measured during a cruise of the R.S. Polarstern from Bremerhaven (Germany) to Rio Grande do Sul (Brazil) in September/ October 1988. The measurements were made in-situ by a combination of electron capture gaschromatography with a cryogenic preconcentration step. The theoretical lower limit of detection (3) was 0.4 ppt. The mixing ratios of PAN varied by more than three orders of magnitude from 2000 ppt in the English Channel to less than 0.4 ppt south of the Azores (38° N). South of 35° N, PAN levels were below the detection limit, except at 30–31° S off the eastern coast of South America. Here, PAN mixing ratios of 10 to 100 ppt were detected in continentally influenced air masses. Detectable levels of PAN were mostly observed in air masses of continental or high northern origin. Changes in the wind directions were usually associated with substantial changes in the PAN mixing ratios.  相似文献   

短周期仪器记录在远震分析中的应用     

许康生 《地震地磁观测与研究》1992,13(2):15-19

地震泼由多种频率成份组成,在其传播过程中。由于地球介质的滤波作用,随着传播距离的增大。高频成份逐渐被衰减。周期越大的成份传播越远。因此,在地震观测上,不同频带的地震仪用于观测不同震中距范围的地震,使仪器较好地响应,就我国台网而言,短周期仪用于地方震、近震的监测,中长周期仪和长周期仪用于远震,极远震的监测,其中长周期仪偏重于记录极远震。但作者在实际分析工作中注意到,短周期仪的记录应用于远震,极远震的分析,显示出独特的作用,充分挖掘和利用短仪资料,将会更加丰富远震、极远震的震相资料。本文以高台地震台的资料为依据,从震中距和震级角度,与中长仪和长仪作比较,对短仪记录远震、极远震的震相及特征作了统计分析与初步探讨,并对新疆地区“影区”地震S波的记录、日本地区地震_PPcP等震相的出现提出了现象的存在,给出了相应的观测结果,以待步一步研究。  相似文献   

Transmission and reflection of Rayleigh waves at a thin low velocity vertical layer: A laboratory and theoretical study     

P. F. Biagi  T. S. Gegechkory  E. N. Its  P. Manjgaladze  V. Sgrigna  D. Zilpimiani 《Pure and Applied Geophysics》1990,133(2):317-327

A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling.  相似文献   

西安南郊丰水年秋季土壤水分研究   总被引：4，自引：0，他引：4  

李艳花  赵景波 《中国沙漠》2006,26(1):113-116

 通过对西安南郊丰水年秋季土壤含水量的测定，研究了地下0~6 m之间土壤含水量的变化与土壤干层的恢复问题。研究结果表明，丰水年西安南郊人工林下2~3 m的土壤含水量在20％左右，远远高于正常年份的土壤含水量，而且大于表层和深层的土壤含水量。分析得出，土壤干层发育较弱的地区在降水丰富的年份可以得到一定程度的恢复；西安地区基本适合进行人工造林；通过人工措施，增强降水入渗和土壤含水量，对树木成活和长期的生长应当具有明显的作用。  相似文献   

Mantle plumes from top to bottom   总被引：5，自引：0，他引：5  

Norman H. Sleep 《Earth》2006,77(4):231-271

Hotspots include midplate features like Hawaii and on-axis features like Iceland. Mantle plumes are a well-posed hypothesis for their formation. Starting plume heads provide an explanation of brief episodes of flood basalts, mafic intrusions, and radial dike swarms. Yet the essence of the hypothesis hides deep in the mantle. Tests independent of surface geology and geochemistry to date have been at best tantalizing. It is productive to bare the current ignorance, rather than to dump the plume hypothesis. One finds potentially fruitful lines of inquiry using simple dynamics and observations. Ancient lithospheric xenoliths may reveal heating by plumes and subsequent thermal equilibration in the past. The effect at the base of the chemical layer is modest 50-100 K for transient heating by plume heads. Thinning of nonbuoyant platform lithosphere is readily observed but not directly attributable to plumes. The plume history in Antarctica is ill constrained because of poor geological exposure. This locality provides a worst case on what is known about surface evidence of hotspots. Direct detection of plume tail conduits in the mid-mantle is now at the edge of seismic resolution. Seismology does not provide adequate resolution of the deep mantle. We do not know the extent of a chemically dense dregs layer or whether superplume regions are cooler or hotter than an adiabat in equilibrium with the asthenosphere. Overall, mid-mantle seismology is most likely to give definitive results as plume conduits are the guts of the dynamic hypothesis. Finding them would bring unresolved deep and shallow processes into place.  相似文献   

Tectonic relation between northeastern China and the Korean peninsula revealed by interpretation of GRACE satellite gravity data   总被引：2，自引：0，他引：2  

Sungchan Choi  Chang-Whan Oh  Herrmann Luehr 《Gondwana Research》2006,9(1-2):62

The major continental blocks in northeastern Asia are the North China block and the South China block, which have collided starting from the Korean peninsula. Geologic and geophysical interpretations reveal a well defined suture zone in northeastern China from Qinling through Dabie to Jiaodong. The discovery of high-pressure metamorphic rocks in the Hongseong area of the Korean peninsula, prominent evidence for the collision zone, indicates extension of the collision zone in northeastern China into the Korean peninsula. Interpretation of the GRACE satellite gravity dataset shows two prominent structural boundaries in the Yellow Sea. One extends from the Jiaodong Belt in eastern China to the Imjingang Belt in the Korean peninsula. The other extends from near Nanjing, eastern China, to Hongseong. Tectonic movement in or near the suture zone may be responsible for seismic activity in the western Korean peninsula and the development of the Yellow Sea sedimentary basin.  相似文献   

Seismic lamination and anisotropy of the Lower Continental Crust   总被引：2，自引：3，他引：2  

Rolf Meissner  Wolfgang Rabbel  Hartmut Kern 《Tectonophysics》2006,416(1-4):81

Seismic lamination in the lower crust associated with marked anisotropy has been observed at various locations. Three of these locations were investigated by specially designed experiments in the near vertical and in the wide-angle range, that is the Urach and the Black Forrest area, both belonging to the Moldanubian, a collapsed Variscan terrane in southern Germany, and in the Donbas Basin, a rift inside the East European (Ukrainian) craton. In these three cases, a firm relationship between lower crust seismic lamination and anisotropy is found. There are more cases of lower-crustal lamination and anisotropy, e.g. from the Basin and Range province (western US) and from central Tibet, not revealed by seismic wide-angle measurements, but by teleseismic receiver function studies with a P–S conversion at the Moho. Other cases of lamination and anisotropy are from exhumed lower crustal rocks in Calabria (southern Italy), and Val Sesia and Val Strona (Ivrea area, Northern Italy). We demonstrate that rocks in the lower continental crust, apart from differing in composition, differ from the upper mantle both in terms of seismic lamination (observed in the near-vertical range) and in the type of anisotropy. Compared to upper mantle rocks exhibiting mainly orthorhombic symmetry, the symmetry of the rocks constituting the lower crust is either axial or orthorhombic and basically a result of preferred crystallographic orientation of major minerals (biotite, muscovite, hornblende). We argue that the generation of seismic lamination and anisotropy in the lower crust is a consequence of the same tectonic process, that is, ductile deformation in a warm and low-viscosity lower crust. This process takes place preferably in areas of extension. Heterogeneous rock units are formed that are generally felsic in composition, but that contain intercalations of mafic intrusions. The latter have acted as heat sources and provide the necessary seismic impedance contrasts. The observed seismic anisotropy is attributed to lattice preferred orientation (LPO) of major minerals, in particular of mica and hornblende, but also of olivine. A transversely isotropic symmetry system, such as expected for sub-horizontal layering, is found in only half of the field studies. Azimuthal anisotropy is encountered in the rest of the cases. This indicates differences in the horizontal components of tectonic strain, which finally give rise to differences in the evolution of the rock fabric.  相似文献   

Large igneous provinces generated from the margins of the large low-velocity provinces in the deep mantle     

Trond H. Torsvik  Mark A. Smethurst  Kevin Burke  Bernhard Steinberger 《Geophysical Journal International》2006,167(3):1447-1460

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