Characteristics of seismic activity before the M_S8.0 Wenchuan earthquake          下载免费PDF全文

Yan Xue  Jie Liu  Shirong Mei  Zhiping Song 《地震科学（英文版）》2009,22(5):519-529

The characteristics of spatio-temporal seismicity evolution before the Wenchuan earthquake are studied. The results mainly involve in the trend abnormal features and its relation to the Wenchuan earthquake. The western Chinese mainland and its adjacent area has been in the seismically active period since 2001, while the seismic activity shows the obvious quiescence of M≥?7.0, M≥?6.0 and M?≥5.0 earthquakes in Chinese mainland. A quiescence area with M?≥7.0 has been formed in the middle of the North-South seismic zone since 1988, and the Wenchuan earthquake occurred just within this area. There are a background seismicity gap of M?≥5.0 earthquakes and a seismogenic gap of M_L?≥4.0 earthquakes in the area of Longmenshan fault zone and its vicinity prior to the Wenchuan earthquake. The seismic activity obviously strengthened and a doughnut-shape pattern of M?≥4.6 earthquakes is formed in the middle and southern part of the North-South seismic zone after the 2003 Dayao, Yunnan, earthquake. Sichuan and its vicinity in the middle of the doughnut-shape pattern show abnormal quiescence. At the same time, the seismicity of earthquake swarms is significant and shows heterogeneity in the temporal and spatial process. A swarm gap appears in the M4.6 seismically quiet area, and the Wenchuan earthquake occurred just on the margin of the gap. In addition, in the short term before the Wenchuan earthquake, the quiescence of earthquake with M_L≥?4.0 appears in Qinghai-Tibet block and a seismic belt of M_L?≥3.0 earthquakes, with NW striking and oblique with Longmenshan fault zone, is formed.  相似文献   

青海湖地区植被覆盖及其与气温降水变化的关系   总被引：9，自引：2，他引：7  

陈晓光  李剑萍  李志军  韩颖娟  陈葆德 《中国沙漠》2007,27(5):797-804

使用1981年到2003年月NDVI(归一化植被指数）资料,计算了青海湖地区植被覆盖度,分析了该地区植被覆盖度的历史演变,发现其值在增大,尤其是从1996到2003年,青海湖地区的植被覆盖度都为正距平,NDVI年平均增长率为1.07×10-3。四季的植被覆盖度均为增加趋势,夏季增加最多。月平均温度与月植被覆盖度、春夏季降水与夏秋季植被覆盖度显著正相关。因此,热量条件和春夏季降水是影响青海湖地区植被生长的关键性因素。  相似文献   

THE EVOLUTIONARY HISTORY OF THE WEST KUNLUN MOUNTAINS: A TECTONIC RECONSTRUCTION BASED ON STUDIES OF MAGMATISM     

Yuan Chao    Sun Min  Li Jiliang WT  ”BX 《地学前缘》2000,(Z1)

THE EVOLUTIONARY HISTORY OF THE WEST KUNLUN MOUNTAINS: A TECTONIC RECONSTRUCTION BASED ON STUDIES OF MAGMATISM  相似文献   

On the form factor scale effect     

A. García-Gmez 《Ocean Engineering》2000,27(1):403

Four geosim families, with fully available resistance test results, have been re-analyzed to check the possible scale effect on the form factor. The form factor determined by Prohaska's method, with exponent n=4 and ITTC'57 correlation line, increases with the model size in all four cases analyzed. Because of its high correlation coefficient, a linear variation of the form factor with the scale is assumed. It is possible to have a first estimation of the ship's form factor extrapolating for λ=1 in the regression line. Form factor Reynolds number dependency will always be associated with a friction line. Using the ITTC'57 correlation line, the following equation K_S−K_M=1.91·(λ−1)·10⁻³ can be used to estimate the scale effect on the form factor. Calculations carried out, for axisymetric bodies, with some CFD codes are in good agreement with the experimental findings.  相似文献   

鲎血细胞提取物生物活性的初步研究   总被引：7，自引：0，他引：7  

张海涛  梁景耀  翁云  祝其锋 《海洋科学》2000,24(10):48-50

采用酸抽提法和Ｓｅｐｈａｄｅｘ Ｇ－５０凝胶层析从鲎血细胞中分离出含有一低分子量组分的提取物,ＳＤＳ－ＰＡＧＥ显示一条区带。提取物可以抑制内毒素诱导的鲎试剂（ＴＡＬ）反应,抑制金色葡萄菌和大肠杆菌的生长,并发现２５ｍｇ／Ｌ的提取物对ＨＬ－６０细胞的生长有强烈的抑制作用。  相似文献   

中纬度造山带地区的长期化学风化——中亚和北美的对比研究     

孙晨  朱秉启 《地质学报》2024,98(6):1880-1892

长期化学风化速率（LCWR）和化学风化剥蚀率（CDF）是表征区域化学风化程度和揭示地貌和气候系统演变的重要依据。全球尺度上,中纬度地区的长期化学风化研究远比低纬地区争议更多,原因之一是其风化机制在理论认识上仍存在不确定性,特别是造山带地区的长期化学风化与物理侵蚀、构造、气候之间的关系等。本文利用地球化学质量平衡方法,针对北半球中纬度典型造山带（中亚黑河流域和北美内华达山脉）开展了相关数据和资料的系统整理与再分析,估算了黑河流域的LCWR值和物理侵蚀速率（E）值并与内华达山脉进行了对比研究。分析结果表明,黑河流域、内华达山脉的LCWR分别为17. 4~895 t/km2/a、1~173 t/km2/a,CDF分别为0. 17~0. 81、0. 02~0. 61,LCWR与E均显著正相关,与海拔高度、年均温度、年均降水量等仅局部相关。研究区的长期化学风化主要表现为“供应受限型”风化,但黑河流域局部地区已处于“供应受限”与“动力学受限”过渡的风化阶段。结合回归分析结果和已有成果的综合分析,中纬度造山带地区的长期化学风化速率受到地质、气候等因素的协同影响,但主控因素为地质因素,而化学风化剥蚀率则主要受控于其他因素。  相似文献   

长江经济带城乡居民福祉测度及其差异     

贺艳华  刘聪  周国华  陈妍 《热带地理》2021,41(2):327-339

通过构建城乡居民客观发展指数、主观幸福感指数和福祉差异系数,分析了2005-2015年长江经济带城镇、乡村居民福祉水平及其差距的动态变化过程和空间差异,探讨其影响因素与作用机制.结果表明:1)长江经济带及各省城乡居民福祉均呈上升趋势,区域城镇和乡村居民福祉指数分别由2005年的0.6653、0.5704提高至2015年...  相似文献   

A symplectic mapping approach to the study of the stochasticity in asteroidal resonances     

S. Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》1996,65(4):421-437

In the case of the 2:1 and 3:2 resonances with Jupiter, it has not been yet possible to have a complete identification of all chaotic diffusion processes at work, mainly because the time scale of some of them are of an order still out of the reach of precise integrations. A planar Hadjidemetriou's mapping, using expansions valid for high eccentricities and scaled in order to accelerate the diffusion processes, was derived. The solutions obtained with the mapping show huge eccentricity variations in all orbits starting in the middle of the 2:I resonance, when the main short-period perturbations of Jupiter's orbit are considered. The solutions starting in the middle of the 3:2 resonance do not show any important diffusion.  相似文献   

夏季西藏4个站点大气向下长波辐射观测分析   总被引：1，自引：0，他引：1       下载免费PDF全文

刘梦琪  郑向东  赵春生 《应用气象学报》2018,29(5):596-608

对2011—2016年部分夏季时段分别在西藏那曲、拉萨、林芝和阿里观测的大气向下长波辐射（L_↓）进行分析,结果显示:L_↓具有明显的日变化,最大值出现在北京时间15:00前后,而最低值出现在凌晨至10:00,日平均值林芝最高（368 W·m-2）,其次是拉萨（319 W·m-2）、阿里（305 W·m-2）和那曲（299 W·m-2）。晴天L_↓ ?ngstr?m（1915）的经验公式最适合林芝,而Konzelmann（1994）的公式则适合那曲、拉萨和阿里;随着人工观测总云量的增加,L_↓增强趋势明显,满云（云量7~10成）情形4个站点云增强效应均从20 W·m-2上升至50 W·m-2以上,低云量对L_↓的增强效应明显高于总云量。云份额数（C_F）上升所对应天顶方向平均云底高度下降,但云增强效应上升。在晴天（C_F为-5%~5%、平均云底高度大于4 km）时,云增强效应仅为5 W·m-2左右（林芝接近20 W·m-2）,但当C_F为90%以上（云底高度小于3.5 km）时,云增强效应则上升到60 W·m-2（林芝接近50 W·m-2）。固定云底高度,C_F与L_↓云增强效应呈显著相关（r2为0.91~0.97）,远高于云底高度与L_↓云增强效应的相关（r2为0.32~0.58）。  相似文献   

Seasonal dynamics of N:P ratio stoichiometry and Ca fraction for four dominant plants in the Alxa Desert     

JianTan Guo  XingDong He  HongJuan Jing  YuTing Liang 《寒旱区科学》2018,10(4):326-332

Desert plants take on unique physiologically adaptive mechanisms in response to an adverse environment. In this study, we determined the concentrations of leaf nitrogen(N), phosphorus(P), and calcium(Ca) fraction for dominant species of Artemisia ordosica, A. frigida, Calligonum mongolicum, and Oxytropis aciphylla in the Alxa Desert and discussed seasonal changes of their leaf N:P ratio and Ca fraction. The results showed that, from May to September, the N:P ratios of A. ordosica and C. mongolicum gradually and significantly increased, while those of A. frigida, and O. aciphylla had an increase trend that was not significant; the physiologically active Ca of A. ordosica and A. frigida increased significantly,while that of C. mongolicum and O. aciphylla decreased significantly. The physiologically inert calcium of C. mongolicum increased extremely significantly, while that of others was not significant. There was a significantly positive correlation between the N:P ratio and physiologically active Ca for A. ordosica, and the N:P ratio was significantly and negatively correlated with physiologically active Ca for O. aciphylla. These findings revealed that the physiological regulation mechanism was different for the plants either in earlier stage or later stage of plant-community succession.  相似文献