Slow mass movement in the Kangchenjunga area, eastern Nepal Himalaya     

Dhananjay  Regmi  Teiji  Watanabe 《Island Arc》2005,14(4):400-409

Abstract   The rates of the accumulated and continuous displacement of solifluction lobes in the Kangchenjunga area, eastern Nepal Himalaya, were determined using glass fiber tubes and a strain probe. Ground temperature, precipitation and soil moisture were monitored at two sites, whose altitude differed by approximately 100 m, to understand the solifluction process. The average movement rate of the glass fiber tubes on a 31° slope at altitudes of 5412–5414 m a.s.l. was approximately 11 mm/year, being almost threefold greater than that observed on a 22° slope at 5322–5325 ma.s.l. There was no significant difference in the depth of displacement at these sites. The continuous displacement measurement near the ground surface at 5414 m showed permanent downslope movement from early July. Such movement may be attributed to additional moisture supply during the monsoon season. The amplitude of the displacement cycle was highest at the ground surface, and decreased to virtually zero at and below 20 cm in depth. Probable factors leading to the relatively slow rates of downslope displacement at the surface and depth at the studied altitudes are the lack of concurrence of the freeze–thaw cycles and the high moisture condition in the soil, and the low moisture retention capacity of the soil because of steep slopes and superficial desiccation. The rate of displacement may be more pronounced at altitudes above 5600 m because of the freeze–thaw cycles during the summer season.  相似文献   

2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region     

LIU Zhi  ZHANG Xian-kang  WANG Fu-Yun  DUAN Yong-Hong  LAI Xiao-Ling 《地震学报(英文版)》2005,18(3)

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.  相似文献   

Refining the pre-industrial atmospheric Pb isotope evolution curve in Europe using an 8000 year old peat core from NW Spain   总被引：1，自引：0，他引：1  

M.E. Kylander  D.J. Weiss  A. Martínez Cortízas  R. Garcia-Sanchez 《Earth and Planetary Science Letters》2005,240(2):467-485

Pb pollution has existed for several millennia and remains relevant today. By using peat cores as environmental archives it is possible to reconstruct this long history on a regional scale. This is a significant contribution to the findings from ice core records, the only other archive recording purely atmospheric additions. Without information that allows linking and comparison between sites regionally, within Europe and elsewhere, our ability to make coherent global models of the natural Pb cycle, and anthropogenic forcing of this cycle, is limited. In this respect, the characteristics of the Pb pre-pollution aerosol (PPA) are important to define globally. We characterize for the first time a PPA in Southern Europe with [Pb] = 0.78 ± 0.86 μg g^− 1, net Pb accumulation rates of 0.032 ± 0.030 mg m^− 2 y^− 1 and a ²⁰⁶Pb / ²⁰⁷Pb signature of 1.25470 ± 0.02575. This PPA Pb isotope signature is more radiogenic than that found thus far in Western and Northern Europe. Spain is a historically important mining site. Using three-isotope plots and a pool of potential Pb isotope signatures, a detailed source appointment of both natural and anthropogenic Pb sources was made. We found evidence of Saharan aridification and its termination ∼4400 BP and/or agricultural signals and strong local control (from rock and soil) of the Pb PPA. Human impact is first recorded at 3210 BP but does not exceed 50% of deposited Pb until 3005 BP. Mines in SE Spain dominate early Pb pollution history at this site. During the rise of Roman rule, contributions come from mines in N, NW and SW Spain with no strong indication of other European mining activities. In Medieval and Industrial times local contributions to the peat bog are reduced.  相似文献   

A detailed receiver function image of the sedimentary structure in the Bohai Bay Basin   总被引：5，自引：0，他引：5  

Tianyu Zheng 《Physics of the Earth and Planetary Interiors》2005,152(3):129-143

If the site at which receiver functions are constructed is filled by sediments, then the waveforms from these receiver functions are dominantly controlled by the sedimentary structures within the first few seconds after the direct P arrival. Based on this observation, waveform data collected at 44 temporary seismic stations have been used to image the sedimentary structure of the Bohai Bay Basin, a major continental petroliferous basin in Eastern China. An adapted hybrid global waveform inversion method was applied to the receiver functions to extract structural information beneath each of the stations. The derived S-velocity structure provides for the first time, a basin-scale seismic image of detailed sedimentary stratification. The sedimentary cover of the basin is about 2-12 km thick, consisting of Cenozoic, Mesozoic, and Paleozoic strata from top to bottom. The structural features presented in the S-velocity image coincide quite well with the depression-uplift type of tectonic system in the Bohai Bay Basin. The reconstructed morphology of the sedimentary layers provides seismological evidence for the two-stage evolution of the intracontinental basin that were caused by an intensive tectonic regime transition in late Mesozoic immediately following the lithospheric reforming of the Eastern China continent.  相似文献   

Curie-point depth from spectral analysis of magnetic data in central-southern Europe   总被引：3，自引：0，他引：3  

P. Chiozzi  Y. Okubo  M. Verdoya 《Physics of the Earth and Planetary Interiors》2005,152(4):267-276

The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29-33 km deep in the stable areas (central Europe Variscan units, Corsica-Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea-Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C).  相似文献   

Magnetotelluric data inversion with seismic data constraint     

宋维琪  孙山 《地震学报(英文版)》2005,18(6):678-685

Introduction The research on the structure and physical property of ancient hidden hill, igneous rocks and basement is relatively difficult by using seismic data only. If we combine seismic data, magneto-telluric (MT) data and geophysical data together, better results can be obtained for the above problem. A number of geophysicists at home and abroad, such as CHEN and WANG (1990), Siri-punvarapor and Egbert (2000) have tried many methods to solve the problem by the inversion of seismic da…  相似文献   

格尔木井水温异常特征及其与地震关系分析   总被引：1，自引：1，他引：1  

邱鹏程  刘学领  王永刚  白占孝  常振广 《地震地磁观测与研究》2005,(Z1)

简要介绍了格尔木井水温动态观测的环境与条件,在研究正常动态特征和影响因素的基础上,对水温异常的映震关系进行了分析,并成功地进行了一次短临地震趋势预测。探讨了水温异常的形成原因。  相似文献   

Inversions for MT data in 2D symmetrical anisotropic media     

杨长福  林长佑  孙崇赤  李清河 《地震学报(英文版)》2005,18(3):361-367

Introduction Ready and Renkin (1971) were the first to make the research on anisotropy problems in magnetotellurics (MT). The progress in the research is not evident because it is more complex and difficult than isotropic problems. Now, the one-dimensional (1D) anisotropy problems in MT have been well solved, while for the two-dimensional (2D) cases, the numerical solutions have only been obtained for some particular conditions (Ready and Renkin, 1975). As to the three-dimensional (3D) ani…  相似文献   

The lacustrine sedimentary records of coal-burning atmospheric pollution     

E. Appel  V. Hoffmann 《中国科学D辑(英文版)》2005,48(10)

With the acceleration of industrialization, coal- burning atmospheric pollution is getting more and more serious in many regions in China. However, there are only about ten odd years literature records about pollution in some large and mid-sized cities, where the atmosphere has perhaps been polluted for several decades, and therefore it is difficult to know the process and characteristic of pollution, and diffi-cult to evaluate its damage to environment. Lacustrine sediment, a natural record w…  相似文献   

2-D crustal Poisson’s ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region   总被引：1，自引：0，他引：1  

Liu Zhi  Zhang Xian-kang  Wang Fu-yun  Duan Yong-hong  Lai Xiao-ling 《地震学报(英文版)》2005,18(3):345-353

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L ₁ are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson’s ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson’s ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson’s ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson’s ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson’s ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson’s ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region. Foundation item: Key Project from China Earthquake Administration and the Project (95-11-02-01) from Ministry of Science and Technology (2001DIA10003). Contribution No. RCEG200401, Geophysical Exploration Center, China Earthquake Administration.  相似文献