Stable isotope values of Costa Rican surface waters   总被引：3，自引：0，他引：3  

Matthew S. Lachniet  William P. Patterson 《Journal of Hydrology》2002,260(1-4):135-150

Stable isotope data of surface waters from the humid tropics in general, and Costa Rica in particular, are scarce. To improve our understanding of the spatial distribution of stable isotopes in surface waters, we measured δ¹⁸O and δD in river and lake (n=63) and precipitation (n=3) samples from Costa Rica. We also present data from the IAEA/WMO isotopes in precipitation network as context for our study. Surface water isotope values do not strongly correlate with elevation, stream head elevation, stream length, distance from Caribbean Sea, or estimated mean annual precipitation for the country as a whole. However, the data show distinct regional trends. The δ¹⁸O and δD values downwind of mountain ranges are inversely related to the altitude of the ranges the air masses traverse. In the lee of the high Talamanca Range, δ¹⁸O values are 6–8‰ lower, while in the lee of the lower Tilarán Range δ¹⁸O values are 2–3‰ lower than upwind sites along the Caribbean Slope. An altitude effect of −1.4‰ δ¹⁸O/km is present on the Pacific slope of southern Costa Rica, equivalent to a temperature effect of −0.3‰/°C. The Nicoya and Osa Peninsulas have higher values than upwind sites, suggesting input of Pacific-sourced moisture, evaporative enrichment, or decreased condensation temperatures. Elevated and increasing d-excess values inland along the Nicaragua Trough suggest a recycled component may be an important contributor to the water budget. These data provide preliminary stable isotope information for Costa Rica, and will benefit paleoclimatic research in the region. More detailed studies would be beneficial to our understanding of the controls on stable isotope composition of tropical waters.  相似文献   

Predicting average annual groundwater levels from climatic variables: an empirical model   总被引：8，自引：0，他引：8  

Zhuoheng Chen  Stephen E. Grasby  Kirk G. Osadetz 《Journal of Hydrology》2002,260(1-4):102-117

On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment.  相似文献   

Interpretation of charging on fracture or frictional slip surface of rocks     

Akihiro Takeuchi  Hiroyuki Nagahama 《Physics of the Earth and Planetary Interiors》2002,130(3-4):285-291

Fracturing and frictional sliding of quartz and granite under dry condition generates fractoluminescence, charged particle emission and electromagnetic radiation. Various kinds of experiments indicate that surface charge density on fracture or frictional slip surface of quartz and granite is 10⁻⁴ to 10⁻² C/m² which is larger than bound charges induced by the disappearance of piezoelectricity due to the release of stress. Hole and electron trapping centers, which is found in semiconductor devices with the Si–SiO₂ system, are causes of surface charging on fracture or frictional slip surface of quartz crystal. The quantity of the surface charge is enough to cause corona discharge that can generate earthquake lights. The mechanism considering the hole and electron trapping centers has a probability to explain why non-piezoelectric minerals or rocks generate electromagnetic phenomena. It can be one of origins of seismo-electromagnetic phenomena (SEP).  相似文献   

结构动力反应分析的三阶显式方法   总被引：14，自引：6，他引：14  

张晓志  程岩  谢礼立 《地震工程与工程振动》2002,22(3):1-8

本通过对传统动力反应分析方法的总结，阐明了建立隐式和显式方法的一般思路及数学本质，提出了使用系统位移反向向量三阶导数的隐工和实用显式积分方法－3阶显式方法，分析了该显式方法的精度和稳定性，并对建立更高阶隐式和显式方法以及方法的精度和稳定性作了初步讨论。最后，通过算例对本方法、献[1]方法和经典的常平均加速度法（隐式方法、视为精确解）的精度和稳定性进行了比较分析。结果表明，本方法具有明显的优点。  相似文献   

地震次生毒气泄漏与扩散的数值模拟与动态仿真   总被引：16，自引：1，他引：16  

赵振东  余世舟  钟江荣 《地震工程与工程振动》2002,22(5):137-142

文章对破坏性地震中可能发生的次生毒气泄漏与扩散灾害进行了数值模拟与动态仿真研究，设定了几种有实际意义的数值分析模型，分别进行了结构地震破坏，有毒有害气体泄漏，在一定泄漏和气象条件下的向周围空间扩散的动态仿真研究，给出了典型毒气扩散过程中可致人员死亡，严重危险和有感区域的范围的动态变化结果，作者认为地震次生毒气泄漏与扩散研究对大地震应急、城市和大型企业防灾都有重要的意义和广阔的应用前景。  相似文献   

2001年11月14日新疆-青海交界8.1级地震   总被引：3，自引：0，他引：3  

陈学忠  许力生 《国际地震动态》2002,(3):1-4

简要介绍了2001年11月14日新疆－青海交界8．1级地震的预测情况，给出了中、美、日等对此次地震的震源参数测定和震源机制，以及余震的分布和加卸载响应比随时间的变化。进而对震区近期地震趋势进行预测。  相似文献   

科技形变资料的管理模式     

宋雯  辛德兰 《国际地震动态》2002,(5):7-9

科学的进步使地形变监测事业得到长足发展，市场经济的繁荣催生出形变监测行业独有的管理之道。形变监测行业是个介于科研、IT及服务行业三者之间的特殊行业，因此，它的发展必须具有一定的科学性、前瞻性和服务性。  相似文献   

Erosion and Sediment Disaters in Cambodia     

Bun Hean  Vin Bun Pov 《中国地震研究》2002,16(3):207-209

  相似文献   

The experimental studies on electrical con-ductivities and P-wave velocities of anortho-site at high pressure and high temperature   总被引：1，自引：0，他引：1  

白利平  杜建国  刘巍  周文戈 《地震学报(英文版)》2002,15(6):667-676

Introduction The measurements of the compressional wave velocity and electrical conductivity of minerals and rocks are of fundamental importance to look into the earths interior, including composition, geotherm, generation and distribution of fluids and melts. Hydrous minerals formed by metamatu-siom are abundant within the earth. Previous studies have been carried out on the dehydration effect on the electrical conductivity and wave velocity of rocks such as serpentine, amphibole, most of whi…  相似文献   

Lithium and lithium isotope profiles through the upper oceanic crust: a study of seawater-basalt exchange at ODP Sites 504B and 896A     

Lui-Heung Chan  Jeffrey C Alt 《Earth and Planetary Science Letters》2002,201(1):187-201

Ocean Drilling Program (ODP) Hole 504B near the Costa Rica Rift is the deepest hole drilled in the ocean crust, penetrating a volcanic section, a transition zone and a sheeted dike complex. The distribution of Li and its isotopes through this 1.8-km section of oceanic crust reflects the varying conditions of seawater alteration with depth. The upper volcanic rocks, altered at low temperatures, are enriched in Li (5.6-27.3 ppm) and have heavier isotopic compositions (δ⁷Li=6.6-20.8‰) relative to fresh mid-ocean ridge basalt (MORB) due to uptake of seawater Li into alteration clays. The Li content and isotopic compositions of the deeper volcanic rocks are similar to MORB, reflecting restricted seawater circulation in this section. The transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization. Li enrichment in this zone is accompanied by relatively light isotopic compositions (−0.8-2.1‰) which signify influence of basalt-derived Li during mineralization and alteration. Li decreases with depth to 0.6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high-temperature reaction zone. Rocks in the dike complex have variable isotopic values that range from −1.7 to 7.9‰, depending on the extent of hydrothermal recrystallization and off-axis low-temperature alteration. Hydrothermally altered rocks are isotopically light because ⁶Li is preferentially retained in greenschist and amphibolite facies minerals. The δ⁷Li values of the highly altered rocks of the dike complex are complementary to those of high-temperature mid-ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage. The inventory of Li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of Li in the ocean. On balance, the upper 1.8 km of oceanic crusts remains a sink for oceanic Li. The observations at 504B and an estimated flux from the underlying 0.5 km of gabbro suggest that the global hydrothermal flux is at most 8×10⁹ mol/yr, compatible with geophysical thermal models. This work defines the distribution of Li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle.  相似文献