排序方式： 共有36条查询结果，搜索用时 15 毫秒
21.
2008年汶川M_S8.0强震过去已十几年,这期间,震源区发生了大量的余震,震源周边地区发生了多次中强震.本研究利用大量震源机制解资料系统地研究汶川地震对其周边中强震及其余震触发作用,并将研究结果与先前研究结果进行了对比和分析,获得以下结论:(1)汶川地震对其周边发生的中强震存在一定的触发作用;(2)当等效摩擦系数为0.4时,由三种震源破裂模型获得的余震触发率均为65%左右(以0.01 MPa为阈值);(3)随着等效摩擦系数的增大,余震震源机制解节面上ΔCFS为正的地震数增多,反映主震触发作用增强,这与等效摩擦系数增大地震难以发生并不矛盾,而是反映等效摩擦系数增大时,断层面上正应力对ΔCFS的贡献增大,同时表明在分析库仑应力触发作用时,合理选取等效摩擦系数是至关重要的;(4)统计余震震源机制解节面上受到的库仑应力大于某一数值和小于其相反数的地震数之比时,随着统计阈值的增大,比值呈现出增大的趋势,同时比值也变得离散,该现象还有待于进一步研究. 相似文献
22.
The Climate Forecast Systems （CFS） datasets provided by National Centers for Environmental Prediction （NCEP）, which cover the time from 1981 to 2008, can be used to forecast atmospheric circulation nine months ahead. Compared with the NCEP datasets, CFS datasets successfully simulate many major features of the Asian monsoon circulation systems and exhibit reasonably high skill in simulating and predicting ENSO events. Based on the CFS forecasting results, a downscaling method of Optimal Subset Regression （OSR） and mean generational function model of multiple variables are used to forecast seasonal precipitation in Guangdong. After statistical analysis tests, sea level pressure, wind and geopotential height field are made predictors. Although the results are unstable in some individual seasons, both the OSR and multivariate mean generational function model can provide good forecasting as operational tests score more than sixty points. CFS datasets are available and updated in real time, as compared with the NCEP dataset. The downscaling forecast method based on the CFS datasets can predict three seasons of seasonal precipitation in Guangdong, enriching traditional statistical methods. However, its forecasting stability needs to be improved. 相似文献
23.
YRY�����Ӧ�������ݲɼ��ĸ߾���ʵ�� 总被引：1，自引：1，他引：0
??????????????????YRY????????????????????????6λ???????????????24λ??-????ADC ADS1201?????????????????·??????????????Χ??????????????????????????????????????????????????????????????????????????????Ч???? 相似文献
24.
How accurately do coupled climate models predict the leading modes of Asian-Australian monsoon interannual variability? 总被引：1，自引：0，他引：1
Bin Wang June-Yi Lee I.-S. Kang J. Shukla J.-S. Kug A. Kumar J. Schemm J.-J. Luo T. Yamagata C.-K. Park 《Climate Dynamics》2008,30(6):605-619
Accurate prediction of the Asian-Australian monsoon (A-AM) seasonal variation is one of the most important and challenging tasks in climate prediction. In order to understand the causes of the low accuracy in the current prediction of the A-AM precipitation, this study strives to determine to what extent the ten state-of-the-art coupled atmosphere-ocean-land climate models and their multi-model ensemble (MME) can capture the two observed major modes of A-AM rainfall variability–which account for 43% of the total interannual variances during the retrospective prediction period of 1981–2001. The first mode is associated with the turnabout of warming to cooling in the El Niño-Southern Oscillation (ENSO), whereas the second mode leads the warming/cooling by about 1 year, signaling precursory conditions for ENSO. The first mode has a strong biennial tendency and reflects the Tropical Biennial Oscillation (Meehl in J Clim 6:31–41, 1993). We show that the MME 1-month lead prediction of the seasonal precipitation anomalies captures the first two leading modes of variability with high fidelity in terms of seasonally evolving spatial patterns and year-to-year temporal variations, as well as their relationships with ENSO. The MME shows a potential to capture the precursors of ENSO in the second mode about five seasons prior to the maturation of a strong El Niño. However, the MME underestimates the total variances of the two modes and the biennial tendency of the first mode. The models have difficulties in capturing precipitation over the maritime continent and the Walker-type teleconnection in the decaying phase of ENSO, which may contribute in part to a monsoon “spring prediction barrier” (SPB). The NCEP/CFS model hindcast results show that, as the lead time increases, the fractional variance of the first mode increases, suggesting that the long-lead predictability of A-AM rainfall comes primarily from ENSO predictability. In the CFS model, the correlation skill for the first principal component remains about 0.9 up to 6 months before it drops rapidly, but for the spatial pattern it exhibits a drop across the boreal spring. This study uncovered two surprising findings. First, the coupled models’ MME predictions capture the first two leading modes of precipitation variability better than those captured by the ERA-40 and NCEP-2 reanalysis datasets, suggesting that treating the atmosphere as a slave may be inherently unable to simulate summer monsoon rainfall variations in the heavily precipitating regions (Wang et al. in J Clim 17:803–818, 2004). It is recommended that future reanalysis should be carried out with coupled atmosphere and ocean models. Second, While the MME in general better than any individual models, the CFS ensemble hindcast outperforms the MME in terms of the biennial tendency and the amplitude of the anomalies, suggesting that the improved skill of MME prediction is at the expense of overestimating the fractional variance of the leading mode. Other outstanding issues are also discussed. 相似文献
25.
Jiang Changsheng 《中国地震研究》2007,21(2):156-162
Considering the controversy over whether the Taipei 101 skyscraper has induced an increase of local seismicity, we reanalyzed the local earthquake catalogue before and after the construction to investigate whether the reported seismicity increase related to the construction is statistically significant. Statistical tests obtained a positive conclusion about the apparent seismicity increase. However, the calculation of maximum ΔCFS shows that at most a 2.2×10-4 bar Coulomb Failure Stress change was produced by the construction. Therefore, whether the construction of Taipei 101 really triggered the increase of seismicity still remains an open question: Statistically-yes; physically-no. 相似文献
26.
研究区延长组沉积为陆相三角洲沉积,主要含油气层位为长6油层组.受沉积环境及泥岩中有机质含量的影响,该区非渗透层段测井曲线响应差异较大,使得测井曲线标准化效果不佳.针对此情况,在借助自然伽马、井径测井、声波测井、感应测井等曲线构建"视标准层"的基础上,利用ΔlgR方法剔除受有机质影响明显的非渗透层段,进而选取不受井眼条件、岩性、物性、含油气性等因素影响的非渗透层段作为"视标准层",最后采用直方图法对研究区测井曲线进行标准化,并结合孔隙度计算模型进行了检验.研究结果表明,ΔlgR方法可以较为有效地消除非渗透层段有机质含量的影响,提高陆相地层中"视标准层"构建的质量,为后期储层参数的确定奠定基础. 相似文献
27.
28.
2014年10月《地球物理学报》出版的陶玮等(2014)"紫坪铺水库造成孔隙弹性耦合变化及其对2008年汶川地震触发作用"一文基于完全耦合孔隙弹性理论,采用二维有限单元法模拟了紫坪铺水库蓄水造成的库区应力场和孔隙压力场的变化.该文模拟计算原则和思路是正确的,但仍然采用二维模型是一个不足.真实三维模型中水库是有限的一定面积内的载荷;而二维计算模型,却把水库载荷作为无限长的带状载荷,夸大了水库的作用.如果考虑三维模型,该研究得到的震源处库仑应力增长2~25kPa的结论可能只能解读为0.7~8.0kPa.对于紫坪铺水库是否对汶川地震有触发作用,目前各个研究组估计的库仑应力变化恰好处在是否可以触发的边缘.取得进一步认识的关键有赖于对地下结构、状态和物性认识的突破性进展. 相似文献
29.
A growing body of research suggests that the marine environments of south Florida provide a critical link between the tropical and high-latitude Atlantic. Changes in the characteristics of water masses off south Florida may therefore have important implications for our understanding of climatic and oceanographic variability over a broad spatial scale; however, the sources of variability within this oceanic corridor remain poorly understood. Measurements of ΔR, the local offset of the radiocarbon reservoir age, from shallow-water marine environments can serve as a powerful tracer of water-mass sources that can be used to reconstruct variability in local-to regional-scale oceanography and hydrology. We combined radiocarbon and U-series measurements of Holocene-aged corals from the shallow-water environments of the Florida Keys reef tract (FKRT) with robust statistical modeling to quantify the millennial-scale variability in ΔR at locations with (“nearshore”) and without (“open ocean”) substantial terrestrial influence. Our reconstructions demonstrate that there was significant spatial and temporal variability in ΔR on the FKRT during the Holocene. Whereas ΔR was similar throughout the region after ∼4000 years ago, nearshore ΔR was significantly higher than in the open ocean during the middle Holocene. We suggest that the elevated nearshore ΔR from ∼8000 to 5000 years ago was most likely the result of greater groundwater influence associated with lower sea level at this time. In the open ocean, which would have been isolated from the influence of groundwater, ΔR was lowest ∼7000 years ago, and was highest ∼3000 years ago. We evaluated our open-ocean model of ΔR variability against records of local-to regional-scale oceanography and conclude that local upwelling was not a significant driver of open-ocean radiocarbon variability in this region. Instead, the millennial-scale trends in open-ocean ΔR were more likely a result of broader-scale changes in western Atlantic circulation associated with an increase in the supply of equatorial South Atlantic water to the Caribbean and shifts in the character of South Atlantic waters resulting from variation in the intensity of upwelling off the southwest coast of Africa. Because accurate estimates of ΔR are critical to precise calibrations of radiocarbon dates from marine samples, we also developed models of nearshore and open-ocean ΔR versus conventional 14C ages that can be used for regional radiocarbon calibrations for the Holocene. Our study provides new insights into the patterns and drivers of oceanographic and hydrologic variability in the Straits of Florida and highlights the value of the paleoceanographic records from south Florida to our understanding of Holocene changes in climate and ocean circulation throughout the Atlantic. 相似文献
30.
阿尔及利亚Chelif盆地中—新生界烃源岩研究 总被引：1，自引：0，他引：1
Chelif盆地的勘探在近半个世纪一直没有突破,是否存在有效烃源岩成为制约勘探决策的主要因素。在分析Chelif盆地地表和钻井样品地球化学特征的基础上,研究和预测了中—新生界烃源岩性质与分布,并且采用ΔlogR技术计算TOC含量以弥补露头采样的不足。研究显示,Chelif盆地是阿尔及利亚西北部的中—新生界叠合盆地。在白垩纪Chelif盆地处于被动大陆边缘的拉张构造环境,属于海相盆地;到新生代盆地演变为山间盆地,经历断坳演化过程,形成了快速充填的沉积特征。盆地发育上白垩统、下中新统和上中新统3套烃源岩,有机质丰度显示,该烃源岩为中等—好烃源岩,含Ⅱ型干酪根,有机质热演化处于低成熟—成熟阶段。上白垩统泥灰岩为盆地的主力烃源岩,盆地油气源较丰富,具有较好的勘探前景。 相似文献