Preliminary palaeomagnetic study of loess from the Wucheng section,North China     

Huamei Li  Zhisheng An  Junda Wang 《中国地球化学学报》1982,1(1):82-95

One hundred and seventeen oriented specimens of loess (in the form of cubes with an edge of 4 cm) were collected from the Wucheng loess section in Xixian County, Shanxi Province. After magnetic cleaning in an alternating field the remanent magnetization of specimens was measured with an astatic magnetometer (sensitivity 4×10^?3 emu/cm³). The normally magnetized zone of the Brunhes normal epoch is recorded in upper Pleistocene Malan loess and middle Pleistocene Lishi loess which contain typical Zhoukoudian fauna. The reversely magnetized zone of the Matuyama reversed epoch is observed in lower Pleistocene Wucheng loess, whose fossils are found corresponding to Villafranchian Nihowan fauna.  相似文献   

基于加权信息量模型的湖南省麻阳县地质灾害危险性评价与区划     

王国卫  李明波  蒋明光  罗冠枝  陈全明  王迪 《地质与资源》2020,29(3):266-272

以麻阳县1：5万地质灾害详细调查数据为基础，选择地质灾害点密度、地形地貌、岩土体结构类型、地质构造、降雨、植被、人类工程活动、受威胁人数和潜在经济损失等9个因素作为评价指标，采用层次分析法对不同指标的重要性进行排序与赋权.最后基于加权信息量模型进行麻阳县地质灾害危险性评估及分区评价.研究结果表明：麻阳县主要处于地质灾害低-中等危险区，其中低、中危险区面积分别为984.44 km²和414.08 km²，极低危险区和高危险区分别为81.11 km²和86.57 km².  相似文献   

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong <Emphasis Type="Italic">M</Emphasis>=8 earthquake     

Gao Meng-tan  Jin Xue-shen  An Wei-ping  Lü Xiao-jian 《地震科学（英文版）》2004,17(4):398-404

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed.  相似文献   

Lichens as Biomonitors of Depleted Uranium in Kosovo     

S. Loppi  L. A. Di Lella  L. Frati  G. Protano  S. A. Pirintsos  F. Riccobono 《Journal of Atmospheric Chemistry》2004,49(1-3):437-445

This paper reports the results of a study using lichens as biomonitors to investigate the environmental distribution of depleted uranium (DU) at selected Kosovo sites as a consequence of the use of DU ordnance during the conflict of 1999. The results suggested that the use of DU ammunitions did not cause a diffuse environmental contamination in such a way to have caused a detectable U enrichment in lichens. Also isotopic ²³⁵U/²³⁸U measurements did not indicate the presence of DU particles in lichens, except for some samples at a heavily shelled site, which resulted contaminated by DU.  相似文献   

Volcanic hazard assessment at the restless Campi Flegrei caldera   总被引：1，自引：0，他引：1  

Giovanni?OrsiEmail author  Mauro?Antonio?Di?Vito  Roberto?Isaia 《Bulletin of Volcanology》2004,66(6):514-530

Eruption forecasting and hazard assessments at the restless Campi Flegrei caldera, within the Neapolitan volcanic area, have been performed using stratigraphical, volcanological, structural and petrological data.On the basis of the reconstructed variation of eruption magnitude through time, we hypothesize that the most probable maximum expected event is a medium-magnitude explosive eruption, fed by trachytic magma. Such an eruption could likely occur in the north-eastern sector of the caldera floor that is under a tensile stress regime, when the ongoing deformation will generate mechanical failure of the rocks. A vent could open also in the western sector, at the intersection of two fault systems contemporaneously activated, as happened in the last eruption at Monte Nuovo. The eruption could likely be preceded by precursors apparent to the population, such as ground deformation, seismicity and increase in gas emissions. It will probably alternate between magmatic and phreatomagmatic phases with the generation of tephra fallout, and dilute and turbulent pyroclastic currents. During and/or after the eruption, the re-mobilization of ash by likely heavy rains, could probably generate mud flows.In order to perform a zoning of the territory in relation to the expected volcanic hazards, we have constructed a comprehensive hazard map. On this map are delimited (I) areas of variable probability of opening of a new vent, (II) areas which could be affected by variable load of fallout deposits, and (III) areas over which pyroclastic currents could flow. The areas in which a vent could likely open have been defined on the basis of the dynamics of the ongoing deformation of the caldera floor. To construct the fallout hazard map we have used the frequency of deposition of fallout beds thicker than 10 cm, the frequency of load on the ground by tephra fallout and the direction of dispersal axes of the deposits of the last 5 ka, and the limit load of collapse for the variable types of roof construction. The pyroclastic-current hazard map is based on the areal distribution and frequency of pyroclastic-current deposits of the last 5 ka.Editorial Responsibility: T. Druitt  相似文献   

Role of conduit shear on ascent of the crystal-rich magma feeding the 800-year-<Emphasis Type="SmallCaps">b.p.</Emphasis> Plinian eruption of Quilotoa Volcano (Ecuador)     

M.?Rosi  P.?LandiEmail author  M.?Polacci  A.?Di Muro  D.?Zandomeneghi 《Bulletin of Volcanology》2004,66(4):307-321

We have characterized pumice products belonging to the climactic phase of the 800-year-b.p. Quilotoa eruption. Bulk rock compositions, petrography, mineral, and glass chemistry and textural investigations were performed on the three end-member pumice types, namely white, gray, and mingled pumices. All the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage, but glass compositions and bulk textures change according to different pumice types. White pumice has higher crystallinity (~48 wt%), abundant euhedral pheno/microphenocrysts, no groundmass microlites, the most evolved glass compositions (74–78 wt% SiO₂), and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls. Gray pumice exhibits lower crystallinity (29–36 wt%), abundant broken and/or resorbed crystals, ubiquitous groundmass phenocryst fragments and microlites, the widest range of glass compositions (69–78 wt% SiO₂), and quite homogeneous poorly deformed and coalesced vesicles with thicker walls. Mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics. We attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface. In particular, the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls. The less viscous gray magma, therefore, would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal-rich dacitic magmas.Editorial responsibility: D. Dingwell  相似文献   

Carbon assimilation characteristics of plants in oasis-desert ecotone and their response to CO<Subscript>2</Subscript> enrichment     

Peixi Su  Huaishun Chen  Lizhe An  Xinmin Liu 《中国科学D辑(英文版)》2004,47(1):39-49

Six species of more than 20-year-old desert woody plants in the oasis-desert ecotone were selected for study. The results showed that: (1) in different growing seasons δ¹³C values of assimilating organ varied between -14%. and -16%. for Haloxylon ammodendron (HA),-14%. - -15%. for Calligonum mongolicum (CM) and -25%. - -28%. for Caragana korshinskii (CK), Nitraria sphaerocarpa (NS) and Hedysarum scoparium (HS). (2) The net photosynthetic rate (Pn) of HA and CM was significantly higher than those of the other species. With the decrease in Pn for the six species, their intercellular CO₂ concentration increased, but stomatal limitation value decreased under the intensive light. At the same time, the photochemical efficiency of PS II dropped to different degrees. (3) The CO₂ enrichment experiment demonstrated that, Pn of HA and CM increased to different extent under 450 μmol/mol, but their Pn reduced or approximated to the current condition under 650 μmol/mol. Under 450 μmol/mol the efficiency for solar energy utilization of CK and HS significantly reduced and under 650 μmol/mol their respiration rate exceeded photosynthesis rate. It can be concluded that HA and CM have some function of pathway for C₄ but the other three species have the function for C₃. The decline in their Pn is mainly caused by non-stomatal factors. HA, CM, CK and HS exhibited photoinhibition, which disappeared in a short time. This is a kind of positive readjustment to adapting to the desert environment. HA and CM can adapt to the high CO₂ environment, but CK and HS cannot. With the rise in atmospheric CO₂ concentration and climate warming, the latter two species in the oasis-desert ecotone may be gradually degraded or even disappear.  相似文献   

Provenance of Oligocene synorogenic sediments of the Ligurian Alps (NW Italy): inferences on belt age and cooling history     

Chiara?Barbieri  Barbara?Carrapa  Andrea?Di GiulioEmail author  Jan?Wijbrans  Glen?R.?Murrell 《International Journal of Earth Sciences》2003,92(5):758-778

Mineral chemistry, ⁴⁰Ar/³⁹Ar geochronology on white micas and Apatite Fission Track Thermochronology (AFTT), are applied here to study the provenance of the synorogenic Molare Formation (lowermost unit of the Tertiary Piedmont Basin clastic sequence). The Molare Formation was deposited during transgression onto the Ligurian Alps nappe stack in the Early Oligocene. Depositional facies show that clastic distribution remained transversal, with local sources located just landward from the coastline. Phengite mineral chemistry together with ⁴⁰Ar/³⁹Ar data clearly shows two distinctive source areas, each one mirroring the composition of the basement directly beneath the clastic sequence. Amphibole mineral chemistry allows second order provenance distinctions within each sector, reflecting heterogeneous metamorphic evolution of the bedrock complexes. Integrated ⁴⁰Ar/³⁹Ar dating and AFTT suggest that, following a fast cooling/exhumation episode of the Ligurian Alps during the Oligocene, very little net uplift has since occurred. This is due to a period of general subsidence from the Oligocene–Late Miocene followed by comparable uplift from Late Miocene–Pliocene to the present. In general our data provide an image of the Ligurian Alps during the Oligocene, which is very similar to the present-day one.This revised version was published online in September 2003.  相似文献   

东北亚地区夏季850 hPa南风异常与东北旱涝的关系   总被引：12，自引：3，他引：9  

孙力  安刚  唐晓玲 《大气科学》2003,27(3):425-434

利用东北地区均匀分布的80个测站40年(1961～2000年)夏季月降水资料和同一时期北太平洋海温及NCEP/NCAR月平均再分析等资料,首先分析了东北亚地区夏季850 hPa南风异常特征,然后讨论了这种异常与东北降水的关系及其物理意义,最后给出了东北亚地区夏季南风异常的某些前兆特征.结果表明,东北亚地区夏季南风的强弱变化不仅与东北旱涝存在着十分密切的关系,而且对大范围大气环流异常也具有非常敏感的反应,东北亚地区南风异常的出现还具有前冬和前春北太平洋海温和500 hPa大气环流异常的前兆信号.  相似文献   

谈编制、更新1∶1万地形图     

安文梅 《地理空间信息》2004,2(1):48-50

阐述了河南省遥感测绘院近几年更新11万基础地形图的成图方法、作业工序和作图过程中的体会。  相似文献