Evidence for a seismic activity mainly constituted of hybrid events at Cayambe volcano,Ecuador. Interpretation in a iced-domes volcano context     

Bertrand Guillier  Jean-Luc Chatelain 《Comptes Rendus Geoscience》2006,338(8):499-506

The high activity level of Hybrid Events (HE) detected beneath the Cayambe volcano since 1989 has been more thoroughly investigated with data from a temporary array. The unusual HE spectral content allows separating a high-frequency signal riding on a low-frequency one, with a probable single source. HEs are interpreted as high frequency VT events, produced by the interaction between magmatic heat and an underground water system fed by thaw water from the summital glacier, which trigger simultaneous low-frequency fluid resonance in the highly fractured adjacent medium. Pure VTs are interpreted as ‘aborted’ HEs occurring probably in the oldest and coldest part of the volcano complex. To cite this article: B. Guillier, J.-L. Chatelain, C. R. Geoscience 338 (2006).  相似文献   

Abrupt climate change: An alternative view   总被引：2，自引：0，他引：2  

Carl Wunsch 《Quaternary Research》2006,65(2):191-203

Hypotheses and inferences concerning the nature of abrupt climate change, exemplified by the Dansgaard-Oeschger (D-O) events, are reviewed. There is little concrete evidence that these events are more than a regional Greenland phenomenon. The partial coherence of ice core δ¹⁸O and CH₄ is a possible exception. Claims, however, of D-O presence in most remote locations cannot be distinguished from the hypothesis that many regions are just exhibiting temporal variability in climate proxies with approximately similar frequency content. Further suggestions that D-O events in Greenland are generated by shifts in the North Atlantic ocean circulation seem highly implausible, given the weak contribution of the high latitude ocean to the meridional flux of heat. A more likely scenario is that changes in the ocean circulation are a consequence of wind shifts. The disappearance of D-O events in the Holocene coincides with the disappearance also of the Laurentide and Fennoscandian ice sheets. It is thus suggested that D-O events are a consequence of interactions of the windfield with the continental ice sheets and that better understanding of the wind field in the glacial periods is the highest priority. Wind fields are capable of great volatility and very rapid global-scale teleconnections, and they are efficient generators of oceanic circulation changes and (more speculatively) of multiple states relative to great ice sheets. Connection of D-O events to the possibility of modern abrupt climate change rests on a very weak chain of assumptions.  相似文献   

和田地区近40年气温变化特征分析     

玉苏甫·阿布都拉  艾力·买买提明  热依汗古丽 《沙漠与绿洲气象(新疆气象)》2005,28(5):16-17

利用和田地区4个代表站1961～2000年的气温资料，对和田地区近40a来的气温变化作了分析。得出近40年来和田地区年平均气温呈上升趋势，春季气温和于田县的年平均气温却呈下降趋势。特别是上世纪90年代增温十分明显，1999年是近40a来和田地区最暖的一年。  相似文献   

Regional characteristics of dust events in China     

WANG Shigong  WANG Jinyan  ZHOU Zijiang  SHANG Kezheng  YANG Debao  ZHAO Zongsuo 《地理学报》2003,13(1):35-44

The regional characteristics of dust events in China has been mainly studied by using the data of dust storm, wind-blown sand and floating dust from 338 observation stations through China from 1954 to 2000. The results of this study are as follows: (1) In China, there are two high frequent areas of dust events, one is located in the area of Minfeng and Hotan in the South Xinjiang Basin, the other is situated in the area of Minqin and Jilantai in the Hexi Region. Furthermore, the spatial distributions of the various types of dust events are different. The dust storms mainly occur in the arid and semiarid areas covering the deserts and the areas undergoing desertification in northern China. Wind-blown sand and floating-dust not only occur in the areas where dust storms occur, but also extend to the neighboring areas. The range of wind-blown sand extends northeastward and southeastward, but floating-dust mainly extends southeastward to the low-latitude region such as the East China Plain and the area of the middle and lower reaches of the Yangtze River. Compared with wind-blown sand, the floating-dust seldom occurs in the high latitude areas such as North Xinjiang and Northeast China. (2) The affected areas of dust storms can be divided into seven sub-regions, that is, North Xinjiang Region, South Xinjiang Region, Hexi Region, Qaidam Basin Region, Hetao Region, Northeastern China Region and Qinghai-Xizang (Tibet) Region. The area of the most frequent occurrence of dust storms and floating-dust is in South Xinjiang Region, and of wind-blown sand in the Hexi Region. In general, the frequency of dust events in all the seven regions shows a decreasing tendency from 1954 to 2000, but there are certain differences between various dust events in different regions. The maximum interannual change and variance of dust events during this time happened in South Xinjiang Region and Hexi Region. The dust events generally occur most frequently in April in most parts of China. The spring occurred days of dust events occupied 60-70% of the whole year in Hetao Region and Northeastern China Region. However, in South Xinjiang Region and North Xinjiang Region, which was less affected by monsoon climate, dust events may occur at any time of the year, less than 50% of the events in this region occur during spring. In the remaining three regions 50-60% of the dust events occur in spring of a year.  相似文献   

华南热水成因硅质岩建造的稀土元素地球化学特征   总被引：11，自引：2，他引：11  

杨海生  周永章  杨志军  张澄博  付伟 《矿物岩石地球化学通报》2003,22(1):61-64

本文在华南地区若干个重要层位热水成因硅质岩建造的稀土元素地球化学数据的基础上,讨论了热水成因硅质岩的REE特征及其与形成环境的关系。指出典型热水沉积建造的δCe为负异常,而δEu为正异常,且LREE>HREE;这种热水成因的硅质岩REE总量普遍较低,且有从热水喷口向外REE总量增高的趋势。热水成因硅质泥岩与正常沉积成因硅质泥的混合存在使稀土元素分布状况变得更复杂。  相似文献   

Recurrence characteristics of late-quaternary strong earthquakes on the major active faults along the northern border of Ordos block   总被引：1，自引：0，他引：1  

冉勇康  陈立春  杨晓平  韩竹军 《中国科学D辑(英文版)》2003,46(Z2)

Through study on trenches, analysis of recurrence characteristics and recurrence interval cluster/gap of strong earthquakes along the major active faults on the northern border of Ordos block, we found 62 paleoearthquakes that occurred in the late Quaternary, including 33 earthquakes occurring in the Holocene. The recurrence characteristics of the paleoearthquakes are different at three levels, segments, faults, and fault zones. The strong seismic sequence on the independent segments is mostly characterized by long- and short-interval recurrences, while that on the faults and in fault zone is characterized clearly by random and cluster recurrences. Results of the moving window test indicate that the probabilities of "temporal cluster or gap", caused by random coincidence as opposed to intersegment contagion, are 64% and 70% for the Serteng piedmont fault and for the south-border fault of Wula Mountains, respectively, no clear interaction among the segments of each fault; while the probability is 26.8% for the whole fault zone, suggesting a clear interaction among the faults of this fault zone. These recurrence characteristics may imply an effect of the entire block motion on the recurrence of strong earthquakes. Moreover, the elapsed time for the Wujumeng Pass-Dongfeng Village segment of Serteng piedmont fault and the Tuzuo Banner-Wusutu and the Hohhot segments of Daqingshan piedmont fault has exceeded the average recurrence interval, hence these three segments may be the possible places for future strong earthquakes.  相似文献   

四川呷村黑矿型矿床硅质岩的硅、氧同位素组成及其与现代海底硅质烟囱比较研究   总被引：14，自引：0，他引：14  

侯增谦  吴世迎  T.Urabe 《地质论评》1996,42(6)

本文首次报道了川西呷村黑矿型矿床硅质岩的硅、氧同位素组成,其δ~(18)O为12.8‰-18.3‰纵,形成温度约99-120℃,δ~(30)Si为0.0‰-1.5‰,与Mariana和GalaPagos热液硅质烟囱的δ~(30)Si值范围基本相当,揭示两者具相似的形成机制。硅质岩和硅质烟囱δ~(30)Si最大值与相伴火山岩δ~(30)Si值一致,反映硅质来自被热液淋滤交代的火山岩系。根据SiO_2溶解度-温度关系提出,来自海底之下1-2km处的水-岩反应带、温度高于320℃的初始流体,通过绝热上升或传导冷  相似文献   

湘中南二叠系孤峰组硅质岩的成因属性及其地球动力学指示意义   总被引：5，自引：0，他引：5  

付伟  周永章  杨志军  何俊国  张澄博  杨海生 《矿物岩石地球化学通报》2004,23(4):292-300

华南二叠系底部的硅质岩及同一层位对应于华南重要的地幔强活动期和成矿期，有非常重要的动力学指示意义。研究表明，孤峰组剖面的岩性可划分为三段：泥页岩段、厚层状硅质岩段和薄层状硅质岩段。沿剖面自下而上，Al2O3、K2O和TiO2含量逐渐降低，MnO、TFe等组分逐渐升高；稀土元素显示出一定的铈负异常，∑REE偏低，且向上∑REE逐渐减少而HREE／LREE逐渐增高；一些热水沉积诊断性微量元素如As、Sb、Hg等也显示出一定程度的异常。这些特征均表明硅质岩的成岩过程中包含有正常沉积和热水沉积的共同作用，且自下而上热水沉积作用逐渐增强的趋势。这种成岩作用的演化特征，代表了下扬子地台拉张裂陷盆地对晚古生代伸展背景的沉积响应，对于探讨裂谷盆地阶段性发育的动力学特征有一定的指示意义。  相似文献   

Meteorological Office, Pune-411 005     

U. S. De  Medha Khole  M. M. Dandekar 《Natural Hazards》2004,31(2):487-497

Natural disasters like floods, tornadoes, tropicalcyclones, heat and cold wavewreak havoc and cause tremendous loss ofproperty all over the world. Most ofthe natural disasters are either dueto weather or are triggered due toweather related processes.Extreme weather events claimed thousands oflives and caused damage on vastscale. Recent super cyclone which affectedOrissa in 1999, Bangladesh cyclone of1970 and Hurricane Andrew in 1992 areexamples of some of the more damagingtropical cyclones which affected developingas well as the developed world. Heatand cold waves are also extreme events,which cause enormous losses in terms oflives lost and human discomfort and ailmentsarising out of them. The heat waveof 1995 and 1998 are still fresh in the mindof the Indian public. The estimated lossof human lives due to heat wave in 1998 was morethan 15,000. Economic losses asa result of these disasters and in particular inassociation with tropical cyclones haveincreased enormously over the last three decades.During 1961–1991, total loss oflives from drought alone was 1,333,728 overthe whole world. In terms of economiclosses, there is 8–10 fold increase from thebase figure of 1960. The socio-economicimpact of natural disaster is complex dependingupon the vulnerability of the placeand mitigation strategies that are put in place.Meteorology plays a crucial role in forewarningpeople about the severe/extremeweather systems and a constant endeavour by themeteorological services worldover has gone a long way towards minimizing thelosses caused by natural disasters.The paper summarises the natural disasterstatistics over south Asia and the possibleprediction strategies for combating theirsocio-economic impacts.  相似文献   

孟湾槽在百色市异常降雪天气中的作用     

邓海光  唐毓勇 《云南地理环境研究》2004,(Z1)

通过对1983年12月28日、2002年12月26日百色市两次异常降雪天气过程的对比分析,发现冬季孟加拉湾槽的发展东移在其中起到了关键性的作用。由于孟加拉湾槽前暖湿气流强盛,这种强盛的西南暖湿气流在低空冷空气堆(冷锋)上发生强烈的系统性上升运动,从而导致百色市及其邻近地区出现异常的雨雪天气。  相似文献