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781.
基于择优的块体模型解算南北地震带中南段主要断层滑动速率 总被引:1,自引:1,他引:0
利用1999 ~2007期GPS速度场数据,通过块体模型择优得到了南北地震带中南段主要块体边界带变形的适用模型,并给出了块体边界主要断层的滑动速率.结果表明,龙门山断裂带宝兴-汶川段张压速率较小,为0.5 ~ 1.8mm·a-1;汶川-茂县压性相对显著,速率达1.8~3.8mm·a-1;鲜水河断裂带张压及走滑速率存在一定的空间差异性特征,即炉霍以北张性滑动速率(8.1mm·a-1)比左旋走滑速率(4.8mm·a-1)大,炉霍-道孚段张压速率与走滑速率基本相同,道孚-康定段呈现出左旋走滑速率减小、张性速率增大的变化趋势,康定-石棉段表现出较明显的左旋走滑性质;小江断裂带走滑速率明显大于张压速率;红河断裂带空间分段性较为明显,北西段滑动量较小,但存在一定的张压分量(景东段速率4.7 mm·a-1),南东段(个旧以西)以走滑为主(速率4.5mm·a-1). 相似文献
782.
The influence of the mesoscale eddy on seismic wave propagation and seismic imaging in deep sea is investigated. Based on fundamental fluid equations, an appropriate partial differential equation is derived for the acoustic pressure field in water with eddies, including current effects. Seismic wavefields and synthetic seismograms in the center of the eddy are simulated. Numerical experiments demonstrate that velocity variations caused by the eddy can lead to traveltime perturbations. Further, in seismic images, the reflectors below the water layer are positioned incorrectly due to the perturbation of the eddy and this image perturbation depends linearly on the migration velocity of the layer below the corresponding reflector. The zero-offset seismic profiling throughout the affected area of the eddy shows that the maximum traveltime perturbation appears at the center of the eddy and the structure of horizontal reflectors below the water layer are distorted. 相似文献
783.
Eduard Petrovský Radek Zbořil Tomáš Matys Grygar Bohumil Kotlík Jiří Novák Aleš Kapička Hana Grison 《Studia Geophysica et Geodaetica》2013,57(4):755-770
Magnetic measurements of deposited atmospehric dust can serve as an additional parameter in assessing environmental pollution. This method is based on the assumption that atmospherically deposited particles contain significant portion of ferrimagnetic iron oxides of anthropogenic origin, which can be easily detected. Aim of this paper is to identify clearly magnetic fraction of daily samples of particulate matter less than 10 μm (PM10), routinely used for air quality assessment and monitoring. We used combination of thermomagnetic analyses and other physical and chemical methods, including scanning electron microscopy (SEM) and Mössbauer spectroscopy. Our results show that daily samples of PM10, collected at sites with different degree of atmospheric pollution, contain magnetite of spherical shape, which is presumably of industrial origin. Thus, magnetic methods can be applied directly to the same substances, which are used routinely in air quality assessment and monitoring. 相似文献
784.
785.
为掌握火电厂新型主厂房框排架结构中异型节点的抗震性能,对由两侧梁高不等、柱截面突变及错层引起的异型节点进行了6个1/5比例试件拟静力试验研究及含有该类节点的空间结构试验研究。研究了节点的受力破坏模式、滞回耗能性能、强度和刚度退化规律及承载力计算方法。结果表明:该类节点初裂与极限荷载较常规节点显著降低,易发生小核心剪切破坏和柱端压弯剪复合破坏;异型节点中剪力墙的设置可以有效改善节点的抗震性能,提高其延性和耗能能力;通过分析节点受力机理并根据不同的破坏形态,提出针对SRC异型节点的承载力计算方法,为该类节点的实际设计提供参考。 相似文献
786.
应用芦山MS7.0地震震中附近跨断层及连续形变观测资料, 分析了芦山地震前不同阶段地形变变化的特点, 讨论了震中附近区域异常时空演化过程. 结果表明: ① 自2013年1月起, 沿鲜水河断裂带一些跨断层基线观测到显著的加速转折变化, 沿安宁河、 则木河断裂带个别场地的跨断层水准基线, 2010年以来出现的巨幅异常等是突出的场兆变化; 沿龙门山断裂带一些水准观测在汶川MS8.0地震后持续的调整变化具有近震源区变形特征. ② 鲜水河、 龙门山和安宁河3条主要断裂围成的三叉口地区, 地倾斜、 应变、 重力及断层水准和蠕变观测临震前均未有显著的异常变化, GPS水平、 垂直位移年速率最小, 该地区是形变变化或形变异常分布的“空区”. ③ 在对近场与远场多种连续形变数据通过傅里叶变换提取年周期成分后发现, 临震前2—3年近震源区域的地倾斜、 重力年变化幅度不是增大, 而是减小. 芦山MS7.0地震前观测到的形变前兆现象特征与汶川MS8.0地震等震前的前兆现象较为接近. 因此, 芦山地震前近震源区及外围形变异常分布特征不是个别的现象. 相似文献
787.
788.
Abstract Conventional methods of deriving global or continental vegetation maps from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR) time series data are based on two‐value Boolean logic, which cannot properly model the so‐called ecotone, the transition zone between adjacent ecosystems. New methods and data models that have been developed on the basis of fuzzy logic to address the “mixed pixel” issue in multi‐spectral imagery can also be used with multi‐temporal imagery to handle the mixture of vegetation types within an ecotone. This study introduces the concept of semantic space and its transformation from spectral feature space, which utilizes a fuzzy logic approach to characterize the continuum of vegetation communities in the African continent from AVHRR multi‐temporal (12 months for three years from 1986 to 1988) NDVI data. The fuzzy procedure was based on the Fuzzy c‐Means (FCM) algorithm with significant modifications to improve processing speed for handling large volumes of data. A second‐order mapping approach was also devised to explicitly represent subdominant vegetative coverage in ecotones and other heterogeneous regions. Comparisons between a Sub‐Saharan African Vegetation Map compiled by the International Union for Conservation of Nature (IUCN) in 1986 and the maps derived from this study demonstrated that fuzzy modeling and classification might provide a better and more realistic representation of the vegetative characteristics of the region. 相似文献
789.
790.
It is still not well understood if subseasonal variability of the local PM2.5 in the Beijing-Tianjin-Hebei (BTH) region is affected by the stratospheric state. Using PM2.5 observations and the ERA5 reanalysis, the evolution of the air quality in BTH during the January 2021 sudden stratospheric warming (SSW) is explored. The subseasonal variability of the PM2.5 concentration after the SSW onset is evidently enhanced. Stratospheric circumpolar easterly anomalies lasted for 53 days during the January–February 2021 SSW with two evident stratospheric pulses arriving at the ground. During the tropospheric wave weakening period and the intermittent period of dormant stratospheric pulses, the East Asian winter monsoon weakened, anomalous temperature inversion developed in the lower troposphere, anomalous surface southerlies prevailed, atmospheric moisture increased, and the boundary layer top height lowered, all of which favor the accumulation of pollutant particulates, leading to two periods of pollution processes in the BTH region. In the phase of strengthened East Asian winter monsoon around the very beginning of the SSW and another two periods when stratospheric pulses had reached the near surface, opposite-signed circulation patterns and meteorological conditions were observed, which helped to dilute and diffuse air pollutants in the BTH region. As a result, the air quality was excellent during the two periods when the stratospheric pulse had reached the near surface. The increased subseasonal variation of the regional pollutant particulates after the SSW onset highlights the important role of the stratosphere in the regional environment and provides implications for the environmental prediction. 相似文献