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在较详细分析华东地区1970年以来中等地震活动规律的基础上,对华东地区中等地震活动条带及迁移规律进行了研究,发现该地区的中等地震活动具有由西向东的整体性迁移特征,其迁移速率约25 km/a,可能起源于地幔应力波.对华东地区而言,目前东部的北西向条带北部,是未来最有可能出现"关门"地震的区域.该项研究为地震趋势的判断提供了一种参考. 相似文献
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本文分析了部分地震学指标的物理意义。通过对华东地区1970年以来14个指标的全时间扫描,并使用华东地区Ms≥5.0地震进行对应,结果表明,选取Rm值、b值和AC值进行同步异常分析,能显著提高华东地区的有震报震率,但有漏报。对目前华东地区异常集中区(南黄海及其沿岸地区)进行时间扫描,结果显示该异常集中区未出现同步异常,认为该区域短期内发生中强地震的可能性不大。 相似文献
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用统计学上的χ~2检验方法对华东地区M_L≥4.0地震平静进行了统计检验,得出在较高的置信概率下可以将平静时间T≥140天作为平静异常的判别标准。总结了华东地区自1970年以来出现的平静异常,并分析了其对应中强地震的情况。研究表明,M_L≥4.0地震平静异常是华东地区中强震前的一种普遍现象。62.5%的平静异常后发生了M_S≥4.5地震;绝大多数平静异常前存在着地震活动的增强过程,多次活动增强后连续发生了平静异常且之后发生了M_S≥5.0地震。 相似文献
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应用应力调制图像法对辽宁地区1970年以来的21次ML≥5.0地震进行了检验。结果显示,有18次地震的震前出现了S值异常单元,虚报地震11次,漏报3次,R值评分0.58。 相似文献
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四川地区综合预报判据和指标的研究 总被引:1,自引:1,他引:1
一、概论四川地区地震活动频度较高,强度较大.自公元前111年至1988年6月10日,境内共发生7.0~7.9级地震13次,6.0~6.9级地震42次,5.0~5.9级地震143次.其中1970年以来就发生了7.0~7.9级地震3次,6.0~6.9级地震9次,5.0~5.9级地震63次.1970年以来6级以上地震的空间分布如图1所示。1970年大邑6.3级地震以后,四川省成立地震监测机构,陆续布设了一批地震前兆观测台网。至1984年底,共建成专业地震台30个(其分布见图1),具有包括测震、视电阻率、地磁、水氡,地倾斜,定点重力,电感应力等共计73项前兆观测项目。还建有15个 相似文献
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M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
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Gtz Schroth Luciana Ferreira Da Silva Marc‐Andree Wolf Wenceslau Geraldes Teixeira Wolfgang Zech 《水文研究》1999,13(10):1423-1436
The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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M. A. Kahn 《洁净——土壤、空气、水》2000,28(2):95-101
Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate. 相似文献