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利用山东区域地震数字台网提供的数据,通过三维层析成像方法结合山东地质构造实际情况,对山东区域进行联合走时反演地壳速度结构,获得该区分辨率较高的三维速度结构图像。结果表明:不同深度上的速度分布反映出山东地区深部构造的某些重要信息,为进一步研究该区的活动构造及地震参数计算提供科学依据。在地壳速度结构与中强地震活动的关系上,再次显示出中强震多发生在速度结构高速单元与低速单元的过渡带附近,说明中强震的孕育与震源区周围介质的不均匀性有关。 相似文献
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采用更加符合长期变形和震后短期变形的Burgers流变模型,模拟了华北地区1303年以来6.5级以上地震引起的同震和震后库仑应力演化.结合华北地区历史地震期幕活动特征,分析了不同活跃期之间、同一活跃期内不同地震之间的库仑应力加卸载效应.结果表明:华北地区不同活跃期的强震主体活动区受控于历史强震的库仑应力加载作用;每个活跃期内强震活动主体区在空间上的迁移与该活跃期内首个7.5级以上地震的触发作用有关;华北地区每个活跃期内强震活动在时间上表现出的"平静期—活跃警告期—高潮期—剩余释放期"应该是区域动力加载过程的一种表现.岩石圈流变松弛效应引起的库仑应力变化对华北地区强震活动时空演化有显著的促进作用.本研究讨论了库仑应力变化在华北地区历史地震活动时空演化过程中可能扮演的角色,为探索华北地区强震活动空间迁移和韵律特征蕴含的构造动力学过程,以及与之相关的地震危险性判定提供参考依据. 相似文献
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《地球物理学报》2020,(9)
采用更加符合长期变形和震后短期变形的Burgers流变模型,模拟了华北地区1303年以来6.5级以上地震引起的同震和震后库仑应力演化.结合华北地区历史地震期幕活动特征,分析了不同活跃期之间、同一活跃期内不同地震之间的库仑应力加卸载效应.结果表明:华北地区不同活跃期的强震主体活动区受控于历史强震的库仑应力加载作用;每个活跃期内强震活动主体区在空间上的迁移与该活跃期内首个7.5级以上地震的触发作用有关;华北地区每个活跃期内强震活动在时间上表现出的"平静期—活跃警告期—高潮期—剩余释放期"应该是区域动力加载过程的一种表现.岩石圈流变松弛效应引起的库仑应力变化对华北地区强震活动时空演化有显著的促进作用.本研究讨论了库仑应力变化在华北地区历史地震活动时空演化过程中可能扮演的角色,为探索华北地区强震活动空间迁移和韵律特征蕴含的构造动力学过程,以及与之相关的地震危险性判定提供参考依据. 相似文献
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利用江浙沪区域地震台网53个台站在1983-2015年间记录的1595个中小地震事件,筛选出54248个直达P、S震相,采用双差层析成像方法,同时获得了下扬子地区三维地壳P、S波速度结构和地震精定位结果,然后对该区地震活动与速度结构分布的关系进行了研究.检测版测试显示,除边缘区域外,0.5.大小网格可以对研究区内部进行较好的分辨.速度结构分布图像结果显示研究区西部陆域和东北部海域的中下地壳存在明显的低速层.此处也是历史上多次强震活跃的地方,如1984如东近海M6.2、6.1地震,1979溧阳M6.0,1996长江口外M 6.1地震.综合分析认为,下扬子地区强震活动区域与该区中上地壳速度结构异常体分布相关,强震发生在高速区与低速区交界处. 相似文献
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一、前言晋冀蒙交界地区(E111°—116°,N39°—41°30′)位于山西断陷地震带与阴山—燕山地震带交汇地区,构造上具有强震背景,是历史上强震活动的主要场所之一。近年来该区先后发生了和林格尔6.3级地震和丰镇5.8级地震,地震形势引人瞩目。本文侧重研究了上述两个地震震前地震活动和测震学指标的前兆特征,并粗略分析了怀来地5.4级地震的一些特点。 相似文献
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卡方检验在华北强震前的应用 总被引:1,自引:0,他引:1
用卡方检验的数理统计方法,结合华北地区活断层、震源机制解等地震地质构造,对华北地区3次强震前的地震活动进行了时间及空间上的检验.认为,卡方检验不仅揭示了中强震前地震的丛集特性,而且体现了强震与地震地质背景之间的密切关系,揭示了构造体系与地震的某些联系. 相似文献
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本文在研究了华北地区强震发生的深部构造资料基础上,总结出7项标志.并以1679年三河、平谷8级地震和1976年唐山7.8级地震为例,对深部构造条件进行了分析.认为强震受深部构造控制. 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. 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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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