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991.
北京市CORS网络是由多家单位共建、共享的GNSS综合应用服务系统,随着连续运行基准站系统应用领域的不断发展和在一些高精度监测领域的应用,其稳定性越发显得重要。本文简要介绍了基准站网稳定性监测流程,包括基线的精密解算、秩亏网平差、拟稳分析,并最终得到可靠的监测成果。文章重点讨论了海洋潮汐、大气荷载对区域GPS基线应用GAMIT软件精密解算的影响,并对基线数据和坐标结果进行了分析,对后续稳定性分析工作具有一定的指导作用。 相似文献
992.
G.?Han J.?Yans M.?Goudalier F.?Lacquement R.?M.?Corfield J.?L.?Mansy F.?Boulvain A.?PréatEmail author 《International Journal of Earth Sciences》2003,92(3):348-363
Illite Kübler index (KI) and oxygen isotope (brachiopods and micrites) investigations have been performed on more than 300 Frasnian limestones sampled in one borehole and numerous outcrops in the Dinant Synclinorium (Belgium, northern France) of the northern Variscan front. The illite Kübler index and 18O data of a 3-km-thick, tectonically repeated Frasnian series from the Focant borehole are compared with their surrounding surface correspondents and document in-situ reheating induced by Variscan tectonic loading, which post-dated sedimentary burial alteration. The boundary between these two thermal processes (sedimentary burial and tectonic loading) on the Focant profile corresponds to an important location where the heat induced by the tectonic loading was equivalent to that Frasnian strata suffered during maximum sedimentary burial. Mainly based on this knowledge and on a former conodont colour alteration index study, the thickness of the eroded thrust sheet in the Focant area is estimated to be around 3,000 m. Oxygen isotopic exchange in these Frasnian closed carbonate systems, occurring under highest-grade diagenesis and anchimetamorphism, records two events. Brachiopods present a quite different and more homogeneous pattern, due to their higher resistance to heat alteration. These thermal events caused both 18O records to become increasingly lighter than the presumed original seawater signature. The comparison between KI and 18O profiles indicates that illite KI analysis is more appropriate than 18O in highlighting the temperature variations in the burial metamorphism at the periphery of orogenic belts. 相似文献
993.
Contributions of phosphatase and microbial activity to internal phosphorus loading and their relation to lake eutrophication 总被引:3,自引:2,他引:3
Phosphatase may accelerate the process of lake eutrophication through improving phosphorus bioavailability. This mechanism was studied in three Chinese eutrophic shallow lakes (Lake Taihu, Lake Longyang and Lake Lianhua). Phosphatase activity was related to the concentration of soluble reactive phosphorus (SRP) and chlorophyll a. Stability of dissolved phosphatase in reverse micelles may be attributed to molecular size, conformation and active residues of the enzyme. At the site with Microcystis bloomed in Lake Taihu, dissolved phosphatase activity was higher and more stable in micelles, SRP concentrations were lower in interstitial water, the contents of different forms of phosphorus and the amounts of aerobic bacteria were lower while respiration efficiency was higher in sediments. Phosphobacteria, both inorganic and organic and other microorganisms were abundant in surface water but rare in sediments. Therefore, internal phosphorus may substantially flux into water column by enzymatic hydrolysis and anaerobic release, together with mobility of bacteria, thereby initiating the bloom. In short, biological mechanism may act in concert with physical and chemical factors to drive the internal phosphorus release and accelerate lake eutrophication. 相似文献
994.
Cyclic shear response of channel-fill Fraser River Delta silt 总被引:2,自引:0,他引:2
The cyclic shear response of a channel-fill, low-plastic silt was investigated using constant-volume direct simple shear testing. Silt specimens, initially consolidated to stress levels at or above the preconsolidation stress, displayed cyclic-mobility-type strain development during cyclic loading without static shear stress bias. Liquefaction in the form of strain softening accompanied by loss of shear strength did not manifest regardless of the applied cyclic stress ratio, or the level of induced excess pore water pressure, suggesting that the silt is unlikely to experience flow failure under cyclic loading. The cyclic shear resistance of the silt increased with increasing overconsolidation ratio (OCR) for OCR>1.3. The silt specimens that experienced high equivalent excess cyclic pore water pressure ratios (ru>80%) resulted in considerable volumetric strains (2.5%–5%) during post-cyclic reconsolidation implying potentially significant changes to the particle fabric under cyclic loading. 相似文献
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Crustal Stress Evolution over the Past 700 Years in North China and Earthquake Occurrence 总被引:1,自引:0,他引:1
Wan Yongge 《中国地震研究》2006,20(3):244-261
INTRODUCTIONThe effect of the Coulomb failure stress change (CFSC) caused by large earthquakes on thelocation and time of subsequent earthquake occurrence have attracted much attention in theseismological community during recent years ( Harris , 1998 ; Stein, 1999) . Many studies ofearthquake cases showedthat the increase in Coulombfailure stress (CFS) could obviously encouragethe occurrence of subsequent moderate-strong earthquakes (Deng and Sykes ,1997 ; Stein,et al .,1997 ;Nalbant… 相似文献
998.
999.
The error contributions within the ocean tide loading (OTL) convolution integral computation were determined to be able to estimate the numerical accuracy of the gravity OTL values. First, the comparison of four OTL programs by different authors (CONMODB, GOTIC2, NLOADF and OLFG/OLMPP) at ten globally distributed gravity stations using exactly the same input values shows discrepancies between 2% and 5%. A new program, called CARGA, was written that is able to reproduce the results of these programs to a level of 0.1%. This has given us the ability to state with certainty the cause of the discrepancies among the four programs. It is shown that by choosing an appropriate interpolation of the Green’s function, refinement of the integration mesh and a high-resolution coastline, an accuracy level of better than 1% can be obtained for stations in Europe. Besides this numerical accuracy, there are errors in the ocean tide model such as a 1% uncertainty in the mean value of the sea-water density and the lack of conservation of tidal water mass, which can produce offsets of around 0.04 μgal. 相似文献
1000.
地震构造是强震发生的必要基础,强震的孕育和发生与构造密切相关。强震的孕育和发生不仅与震中周围构造有关,而且与孕震区所在的整个构造带有关。这就表明整个构造带的地震活动性与未来强震都有关联,因此,我们在做测震学参数异常预测地震时,必须考虑整个构造带的地震活动。过去我们常以震中周围地区的地震活动资料来做测震学参数的异常分析,可能会丢失部分信息。本文进行了地震构造分区和构造单元的划分,把加卸载响应比参数和张家口一渤海边界带有机结合,对基于活动地块边界带的加卸载响应比参数在海城地震预测中的应用进行了研究,结果预测效果很好。这种方法对边界带的地震危险性判定有某种参考价值。 相似文献