Assessment of nutrient sources and paleoproductivity during the past century in Longgan Lake,middle reaches of the Yangtze River,China   总被引：3，自引：0，他引：3  

Yanhong Wu  Andreas Lücke  Sumin Wang 《Journal of Paleolimnology》2008,39(4):451-462

Total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were determined in combination with stable isotope ratios of carbon and nitrogen (δ¹³C_Org, δ¹⁵N) in a 63 cm sediment core from Longgan Lake, located in the middle reaches of the Yangtze River, China. These geochemical and isotopic records provide a continuous history of lake productivity and trophic state of Longgan Lake since 1890. Variations of δ¹³C_Org, TOC, TN and TP indicate that primary productivity of Longgan Lake increased continuously during the last century and that the trophic state of the lake shifted from oligotrophic to mestrotrophic conditions accordingly. Anthropogenic sources of organic carbon (OC), nitrogen (N) and phosphorus (P) were distinguished from their natural background in the sediments using mass accumulation rates. Element mass accumulation rates suggested increased human activities in the lake’s catchment since 1950s, were especially the utilization of artificial fertilizers amplified the anthropogenic input of N and P into the lake. In the course of the improved availability of dissolved nutrients also primary productivity of Longgan Lake increased, resulting in an increase of the Suess-effect corrected organic carbon isotope ratios. δ¹⁵N of bulk sediments show a marked shift towards lower values around 1950 that has been attributed to the input of nitrogen from chemical fertilizers characterized by relatively depleted isotopic signatures into the lake.  相似文献   

On the use of satellite altimetry to infer the earthquake rupture characteristics: application to the 2004 Sumatra event     

A. Sladen  H. Hébert 《Geophysical Journal International》2008,172(2):707-714

Standard data and methods, such as the inversion of seismic and GPS data, have been used extensively to infer the details of the 2004 December 26 earthquake. The unprecedented large size of this event gave the opportunity to modern altimeters to provide the first clear records of a tsunami in deep ocean, therefore allowing us to study the rupture history from an independent perspective. We invert the Jason-1 and Topex–Poseidon altimetry records, considering the new constraints available on the geometry of the fault plane, and taking them into account in a 3-D rupture model. The data are corrected for the non-negligible effect of satellite motion during measurements. Our results show that the rupture propagated over the 1500 km of subduction zone initially identified by the aftershock distribution, with a magnitude of   M _w= 9.1  . Our solution compares well with the latitudinal distribution of slip inferred from other data sets, with a maximum of energy release north of Sumatra, and two other slip patches near the Nicobar and Andaman islands. Based on waveform comparison, we assert that the shallow portion of the megathrust offshore Banda Aceh had slip amplitudes of more than 20 m. Also, we find that significant amounts of slip (about 10 m) concentrated below the Andaman islands and did not propagate on the shallow portion of the interface. Although synthetic tests tend to show less resolution in the northern part of the rupture, this solution is compatible with the near-field data (GPS, coral heads and imagery), and would allow one to explain the apparent paradox between the large local displacements and the moderate tsunami observed locally. Finally, we demonstrate the rapidly dominating effect of propagation and slip distribution over the rupture velocity, and how it precludes the direct estimate of this latter parameter.  相似文献   

The reflection seismic survey of project TIPTEQ—the inventory of the Chilean subduction zone at 38.2° S     

K. Groß  U. Micksch  TIPTEQ Research Group  Seismics Team 《Geophysical Journal International》2008,172(2):565-571

We describe results of an active-source seismology experiment across the Chilean subduction zone at 38.2°S. The seismic sections clearly show the subducted Nazca plate with varying reflectivity. Below the coast the plate interface occurs at 25 km depth as the sharp lower boundary of a 2–5 km thick, highly reflective region, which we interpret as the subduction channel, that is, a zone of subducted material with a velocity gradient with respect to the upper and lower plate. Further downdip along the seismogenic coupling zone the reflectivity decreases in the area of the presumed 1960 Valdivia hypocentre. The plate interface itself can be traced further down to depths of 50–60 km below the Central Valley. We observe strong reflectivity at the plate interface as well as in the continental mantle wedge. The sections also show a segmented forearc crust in the overriding South American plate. Major features in the accretionary wedge, such as the Lanalhue fault zone, can be identified. At the eastern end of the profile a bright west-dipping reflector lies perpendicular to the plate interface and may be linked to the volcanic arc.  相似文献   

Bayesian inference of kinematic earthquake rupture parameters through fitting of strong motion data     

D. Monelli  P. M. Mai 《Geophysical Journal International》2008,173(1):220-232

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Non-parametric seismic data recovery with curvelet frames   总被引：12，自引：0，他引：12  

Felix J. Herrmann  Gilles Hennenfent 《Geophysical Journal International》2008,173(1):233-248

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A non-linear geodetic data inversion using ABIC for slip distribution on a fault with an unknown dip angle   总被引：1，自引：0，他引：1  

Yukitoshi Fukahata  Tim J. Wright 《Geophysical Journal International》2008,173(2):353-364

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Stable inversions for complete moment tensors   总被引：5，自引：0，他引：5  

Sarah E. Minson  Douglas S. Dreger 《Geophysical Journal International》2008,174(2):585-592

The seismic moment tensors for certain types of sources, such as volcanic earthquakes and nuclear explosions are expected to contain an isotropic component. Some earlier efforts to calculate the isotropic component of these sources are flawed due to an error in the method of Jost & Herrmann. We corrected the method after Herrmann & Hutchensen and found great improvement in the recovery of non-double-couple moment tensors that include an isotropic component. Tests with synthetic data demonstrate the stability of the corrected linear inversion method, and we recalculate the moment tensor solutions reported in Dreger et al. for Long Valley caldera events and Dreger & Woods for Nevada Test Site nuclear explosions. We confirm the findings of Dreger et al. that the Long Valley volcanic sources contain large statistically significant isotropic components. The nuclear explosions have strikingly anomalous source mechanisms, which contain very large isotropic components, making it evident that these events are not tectonic in origin. This indicates that moment tensor inversions could be an important tool for nuclear monitoring.  相似文献   

青藏高原发现大型冻胀丘群   总被引：4，自引：2，他引：2  

吴吉春  盛煜  曹元兵  李静  冯子亮  王新斌 《冰川冻土》2015,37(5):1217-1228

在青藏高原黄河源地区多格茸盆地内发现大型冻胀丘群,这些冻胀丘外观多呈穹窿状,有些呈脊状、新月状.盆地内的冻胀丘隆起高度多在3~6 m,最高不超过10 m,水平扩展范围数十米到上百米,最大超过300 m.冻胀丘在盆地内密集分布,众多小型湖塘嵌于其中,分布密度估计5~8个·km^-2,局部区域内可达10个·km^-2以上.从外观看,多数冻胀丘形态较完整,但有的已经部分塌陷,有的几乎完全塌陷,不同塌陷阶段的冻胀丘在盆地内均有发现.冻胀丘顶部钻孔岩芯揭示高含冰地层从丘顶以下5 m左右一直延续到20多米,局部发育厚层地下纯冰层,厚度可达2 m以上.根据外观形态、地下冰类型判断,这些多年生的冻胀丘属冰土丘(lithalsa),和常见的冰核丘(pingo)有所区别.初步判断,这些冻胀丘形成于全新世大暖期以后的新冰期时期.多格茸盆地冻胀丘群的发现对现行的工程建设及工程建筑物的运营安全、区域古环境、流域水文等方面的研究都具有重要意义.  相似文献   

黄河源区玛多县沙漠化成因与发展过程     

姚正毅  李晓英  董治宝 《冰川冻土》2015,37(5):1245-1256

通过分析黄河源区玛多县沙漠化的成因和过程,结果表明,玛多县沙漠化成因类型有三种,分别为固定沙丘/古沙丘活化、滑塌陡坎及风蚀斑块,其形成都与多年冻土退化相关.在固定沙丘或古沙丘分布区,冻土退化导致热融沉陷,形成沉陷坑,沉陷坑边缘形成拉裂缝或陡坎,使下伏松散沙露出.在斜坡上,冻土退化形成滑塌陡坎,使底层土壤从侧面暴露.在平坦的冲积平原,差异性冻胀和融沉导致草皮拉裂,形成积水坑洼,冻土退化导致土壤变干,土壤的底层暴露.下伏风成沉积物暴露后,遭受风蚀,形成侧向凹槽,致使上部土体坍塌,使更多的风成沉积物暴露,这些过程的不断重复,使风蚀坑、陡坎、风蚀斑块扩大相连,最终形成流动沙丘、风蚀劣地、戈壁等地貌.  相似文献   

渗透作用下多孔介质中循环浓度污染物的迁移过程研究     

李华伟  白冰  王梦恕  许韬 《岩土力学》2015,36(5):1306-1312

根据饱和多孔介质中考虑释放效应的一维渗透作用的可溶性污染物的迁移控制方程,通过Laplace变换和Fourier变换及其逆变换求得相应的通解形式。根据半无限体表面可溶性污染物点源注入情形下的基本解,通过积分方法得到半无限体表面圆形区域上作用循环浓度污染物后,在多孔介质内部污染物迁移过程的求解方法。作为一个典型算例,对渗透作用下循环浓度污染源引起的多孔介质中的迁移过程进行分析。算例表明,当污染源浓度为周期变化时,多孔介质内部污染物的浓度随时间增长由不稳定的周期变化过程逐渐过渡到稳定的循环过程,而某一深度处污染物浓度的相位则相应滞后。此时,稳定后的污染物浓度周期与污染源浓度周期相同。实际上,随多孔介质表面污染源浓度的周期变化,在靠近多孔介质表面一定深度范围内的污染物浓度在深度方向也呈增大或减小的交替变化过程。另一方面,在污染源循环变化过程中污染物不断向深处推进,而最终其影响范围限定在某一深度内。  相似文献