An alternative scenario for earthquake prediction experiments     

Stuart Crampin 《Geophysical Journal International》1991,107(1):185-189

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Current earthquake prediction experiments investigate behaviour before potentially large earthquakes. There is some evidence that comparatively small typical events in isolated swarms of earthquakes may have precursory behaviour similar to that before much larger earthquakes in more complicated areas of seismicity. Such typical events in isolated swarms frequently recur with similar magnitudes in similar locations with repetition times sometimes as little as a few days. It is argued that monitoring such typical events in isolated swarms could be an effective way to gain experience of precursory activity, and might well be a good guide for investigations of precursors to large earthquakes.  相似文献   

Laboratory analogy of crystalline enstatite grain formation in plasma field     

T. Sato  K. Kamitsuji  Y. Kimura  O. Kido  Y. Saito 《Planetary and Space Science》2006,54(6):617-620

Crystalline enstatite (MgSiO₃) grains were produced by the simultaneous evaporation of SiO grains and Mg vapor in a plasma field. The MgSiO₃ grains were spherical or needlelike. The necessity of a plasma field in astromineralogy is suggested in the present study.  相似文献   

季节背景对ENSO循环过程中SSTA增/减幅作用的数值试验研究     

管兆勇  周铁汉 《气象学报》2001,59(6):659-673

利用热带太平洋地区 2层区域海洋模式和再分析资料探讨了大气 /海洋的季节背景对ENSO时间尺度上海温异常的增幅或减幅作用。结果表明 :不论什么季节背景下 ,就海洋变化而言 ,El Nino/La Nina事件均可存在 ,说明 El Nino/La Nina事件的存在和维持并没有季节性选择 ;模式海洋的西太平洋赤道地区次表层海水温度异常变化位相明显超前于东太平洋SSTA且在空间上自西向东传播 ,同时有位相超前的量还包括模式第 1层厚度异常及热容量异常 ,这些对 ENSO的预测和机制研究具有重要意义。 SSTA的振幅在不同的季节背景下可受到不同的调节。以春季为背景 ,同样的异常风应力作用于海洋 ,可使 NINO3区 SSTA较正常季节背景下该区的 SSTA振幅明显增大 ;而在冬季背景下可使 SSTA受到一定程度的减幅 ,这说明 El Nino/L a Nina现象的发生和消亡有季节选择倾向。与春季背景下 NINO 3区SSTA的增幅倾向相反 ,模式第 1层厚度异常的振幅则受到削弱。而西太平洋赤道地区 ,模式海洋混合层的厚度异常则有所增强。这种与 SSTA增 /减幅反相关的现象需要进一步研究  相似文献   

STABILITY OF GRAVEL BED RIVERS BASED ON SIEVE ANALYSIS DATA   总被引：1，自引：0，他引：1  

Andreas DITTRICH Institute of Water Resources Management  Hydraulic  Rural Engineering  University of Karlsruhe  Germany. 《国际泥沙研究》2001,16(2)

the or are rm me un'.ox rm as n^nAndreas mlimcrbo was - ou at the -- of Karlsruh in the las l0 pe to meq esistingwt and wt our W on tbe bo Of th6 stabmp of bo edconSsting Of graVe and stones. Sbo in the ds mOuntain wt with tyPbo sbo Of I== 0.05% tO 0.8% as well as those with distinct ~ strUCtUres and slpe of I > 4% and I Sl0% were investipe. host ot the -- were conot in the bo--. bo som Of the results that bad bo for under tw COntwcoul be eded with ealsting field data. In the followin,…  相似文献   

A flume design for the study of slope length effects on runoff     

T. J. Stomph  N. De Ridder  N. C. Van De Giesen 《地球表面变化过程与地形》2001,26(6):647-655

Recent publications from field and simulation studies indicate that runoff per unit area decreases as the length of the slope being observed is increased. This scale effect has been observed and documented for slopes with a uniform infiltration capacity as well as for slopes along which infiltration capacity is variable. This paper presents the design and testing of a laboratory flume for the study of the processes that lead to this scale effect, particularly for the case of slopes covered with crops. The features of the flume include reliable experimental control of soil water content prior to rainfall, high intensity rainfall without erosion, uniform crop growth along the slope, and the option of varying the infiltration rate independently of rainfall and soil characteristics. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Theme Issue on Confining Units     

Vicki Remenda 《Hydrogeology Journal》2001,9(1):3-4

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In situ and laboratory investigations of fluid flow through an argillaceous formation at different scales of space and time, Tournemire tunnel, southern France     

Jean-Yves Boisson  Lucien Bertrand  Jean-François Heitz  Yann Golvan 《Hydrogeology Journal》2001,9(1):108-123

In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron, France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10^–12 to 2×10^–11 m²/s) and hydraulic conductivities derived from different types of laboratory tests (10^–14 to 10^–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements) were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10^–13 to 10^–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling, based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture network do not permit reduction of uncertainties on these estimations at this stage. Electronic Publication  相似文献   

Neighbor competition modifies demographic responses of desert dune annuals to gradients in sand stability     

Ronen Kadmon 《Journal of Arid Environments》1997,36(4):557-564

A field experiment was conducted to test the hypothesis that competitive interactions affect demographic responses of desert dune annuals to gradients in sand stability. The experiment was based on a three-way factorial design with two types of neighbor treatments (complete neighbor removalvs. control), two types of habitats (stablevs. unstable sands) and two species which characterize sandy areas of the western Negev Desert (Neurada procumbensandBromus fasciculatus). Each of the eight treatment/habitat/species combinations was characterized by three demographic variables: seedling survival to reproduction, fruit number per reproductive plant and fruit number per seedling. All of these variables exhibited significant interactions between the effects of neighbor removal and habitat type, indicating that neighbor conditions were important in determining the observed patterns of demographic variation. Moreover, while plants ofNeurada procumbensgrowing without neighbors suffered more mortality on unstable sands, conspecific plants growing at natural density conditions suffered more mortality on stable sands. In the case ofBromus fasciculatus, individuals growing in the absence of competitive effects produced more fruits on stable sands, but conspecific plants growing at natural density conditions exhibited higher fruit production on unstable sands. These findings indicate that competitive effects not only modify, but may even reverse demographic responses of desert dune annuals to gradients in sand stability. Based on these results and evidence from two other studies it is suggested that seed dispersal from abiotically favorable into less favorable habitats may increase fitness of desert annuals by reducing the average effect of competition.  相似文献   

Prediction Model for Vortex-Induced Vibration of Circular Cylinder with Data of Forced Vibration     

潘志远崔维成  刘应中 《中国海洋工程》2007,21(2):239-254

A model based on the data from forced vibration experiments is developed for predicting the vortex-induced vibrations (VIV) of elastically mounted circular cylinders in flow. The assumptions for free and forced vibration tests are explored briefly. Energy equilibrium is taken into account to set up the relationship between the dynamic response of self-excited oscillations and the force coefficients from forced vibration experiments. The gap between these two cases is bridged straightforwardly with careful treatment of key parameters. Given reduced mass m and material damping ratio ζ of an elastically mounted circular cylinder in flow, the response characteristics such as amplitude, frequency, lock-in range, added mass coefficient, cross-flow fluid force and the corresponding phase angle can be predicted all at once. Instances with different combination of reduced mass and material damping ratio are compared to investigate their effects on VIV. The hysteresis phenomenon can be interpreted reasonably. The predictions and the results from recent experiments carried out by Williamson's group are in rather good agreement.  相似文献   

Violent breaking wave impacts. Part 1: Results from large-scale regular wave tests on vertical and sloping walls     

G.N. Bullock  C. Obhrai  D.H. Peregrine  H. Bredmose 《Coastal Engineering》2007

As part of an investigation into the detailed characteristics of wave impacts, experimental data are presented for the impact pressures and forces generated by waves up to 1.7 m high breaking onto a vertical wall and a wall inclined at 27° to the vertical. Particular attention is given to the influence of entrained and entrapped air and, by selecting regular wave conditions that produce impacts, trends are identified for highly variable phenomena that could easily be missed when masked by the even greater variability associated with irregular waves.  相似文献