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本文根据唐山震区的地质构造模拟制作光弹模型,以N60°E方向加压进行唐山震前应力场的光弹性模拟实验。用打孔的方法模拟强震的应力释放。实验结果表明:1.在N60°E方向压缩时,唐山—丰南一带、滦县、野鸡坨和卢龙等地区是最大剪应力集中区,与唐山7.8级、滦县7.1级地震及强余震的震中分布基本吻合。说明唐山大震及余震的发生是近东西向压应力场作用的结果。2.当唐山7.8级地震应力释放后,震前具有高应力背景值的其它地区,应力进一步加强。说明唐山地震的发生导致了应力场的重新调整,增强了强余震发震的动力条件。3.实验结果证明,在断裂带两侧、端部或几条断裂的复合部位,其主应力方向与区域应力场的总体方向比较,大致有10°～25°的偏转。强震的应力释放导致震中区附近的主应力方向与震前相比也发生约10°～20°的偏差。 相似文献
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Ho KT Burgess RM Pelletier MC Serbst JR Ryba SA Cantwell MG Kuhn A Raczelowski P 《Marine pollution bulletin》2002,44(4):286-293
The identification of toxicants affecting aquatic benthic systems is critical to sound assessment and management of our nation's waterways. Identification of toxicants can be useful in designing effective sediment remediation plans and reasonable options for sediment disposal. Knowledge of which contaminants affect benthic systems allows managers to link pollution to specific dischargers and prevent further release of toxicant(s). In addition, identification of major causes of toxicity in sediments may guide programs such as those developing environmental sediment guidelines and registering pesticides, while knowledge of the causes of toxicity which drive ecological changes such as shifts in benthic community structure would be useful in performing ecological risk assessments. To this end, the US Environmental Protection Agency has developed tools (toxicity identification and evaluation (TIE) methods) that allow investigators to characterize and identify chemicals causing acute toxicity in sediments and dredged materials. To date, most sediment TIEs have been performed on interstitial waters. Preliminary evidence from the use of interstitial water TIEs reveals certain patterns in causes of sediment toxicity. First, among all sediments tested, there is no one predominant cause of toxicity; metals, organics, and ammonia play approximately equal roles in causing toxicity. Second, within a single sediment there are multiple causes of toxicity detected; not just one chemical class is active. Third, the role of ammonia is very prominent in these interstitial waters. Finally, if sediments are divided into marine or freshwater, TIEs perforMed on interstitial waters from freshwater sediments indicate a variety of toxicants in fairly equal proportions, while TIEs performed on interstitial waters from marine sediments have identified only ammonia and organics as toxicants, with metals playing a minor role. Preliminary evidence from whole sediment TIEs indicates that organic compounds play a major role in the toxicity of marine sediments, with almost no evidence for either metal or ammonia toxicity. However, interpretation of these results may be skewed because only a small number of interstitial water (n = 13) and whole sediment (n = 5) TIEs have been completed. These trends may change as more data are collected. 相似文献
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McKay CP Grunthaner FJ Lane AL Herring M Bartman RK Ksendzov A Manning CM Lamb JL Williams RM Ricco AJ Butler MA Murray BC Quinn RC Zent AP Klein HP Levin GV 《Planetary and Space Science》1998,46(6-7):769-777
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants. 相似文献