2008年汶川大地震震源机制的时空变化   总被引：23，自引：7，他引：16       下载免费PDF全文

张勇  许力生  陈运泰 《地球物理学报》2009,52(2):379-389

本文提出了一种基于恒定破裂速度和固定子事件震源时间函数的假定、利用远场地震波形资料获取大地震震源机制的时空变化图像的线性反演方法,并利用这种方法及全球范围内48个台站的长周期波形资料反演建立了2008年汶川M_S8.0地震的震源机制随时间和空间变化的图像.根据这个图像可知,汶川大地震断层的西南端震源机制接近于逆冲,随着破裂向东北方向延伸,震源机制的走滑分量逐渐增大,走滑分量超过逆冲分量的转折点在震中东北大约190 km的位置.为了检验反演方法的有效性和反演结果的可靠性,我们特别设计了一个数值试验对反演结果进行了检验.检验结果表明,我们在本文中提出的反演方法是有效的,关于汶川大地震的反演结果也是可靠的（除长周期信号较弱的一段外).通过比较发现,反演结果与震后野外考察的结果也相当吻合.  相似文献   

强烈地震震源破裂和深层过程与地震短临预测探索   总被引：11，自引：5，他引：6       下载免费PDF全文

滕吉文  张永谦  闫雅芬 《地球物理学报》2009,52(2):428-443

强烈地震震源区和其周边地域的介质,在力源作用下开始破裂,即微破裂,而当其在应力不断积累、逐渐发展并形成具有一定规模的“破裂链”时,即应力集中达到临界状态时,震源介质所积累的巨大能量以波动的形式瞬间释放,并冲出地表发生地震,且在地表产生一系列的破坏和大型断裂.在强烈地震发生后依据设定的初始模型和远、近地震台网记录,通过震源机制解计算,可求得震源介质的破裂长度和破裂过程.事实表明,一系列大地震的“孕育”、发生和发展,由震源深处到地表均呈现出强烈的破裂效应,其破裂长度可由几公里、几十公里、乃至千余公里长.有的地震在发生前确亦存在着破裂响应和迹象.为此,若在地表和深井中能进行破裂效应的观测,以捕捉初始微破裂和其形成“破裂链”的动力过程,这对于短临地震预测可能是一个十分重要的途径.  相似文献   

复杂场地条件下震源参数对断层附近长周期地震动的影响   总被引：2，自引：0，他引：2       下载免费PDF全文

刘启方  金星  丁海平 《地球物理学报》2008,51(1):186-196

基于显式有限元方法和运动学震源模型并利用昆明盆地三维地下构造模型,本文研究了震源参数对断层附近长周期地震动的影响.结果表明,断层的破裂方式、埋藏深度、破裂速度以及断层面上位错的不均匀分布对断层附近长周期地震动有重要影响.不同破裂方式下,破裂的方向性强的区域分布不同,由于破裂的方向性效应和复杂场地条件的共同作用,导致不同破裂方式的断层附近地震动分布差别很大.随着破裂速度的增加,方向性效应更加明显,断层附近的长周期地震动也随之增大;对于浅源地震,随着断层埋深的增加,地震动明显下降.对于埋藏深度很浅的断层,当Asperity靠近断层上沿时,会显著增大其在地表投影附近的长周期地震动.能否合理地估计这些基本震源参数,是预测未来发震断层周围地震动场的关键.  相似文献   

不同饵料及添加剂对中国对虾幼体的影响   总被引：1，自引：0，他引：1  

朱丽岩  郑家声  王梅林  祁自忠  徐怀恕 《海洋科学》2000,24(11):41-45

在连续两年春季中国对虾育苗期间,采用几种不同的饵料－人工饵料为主、活饵料和两种强化饵料分别培育中国对虾幼体,以存活率、体长、体重、抗感染力的缺氧耐受力等指标检验育苗效果。结果表明,人工饵料为主的喂养方式各项指标均显著劣于活饵料;强化与未强化的活饵料效果相近;强化的人工饵料在体长和耐缺氧方面显著优于人工饵料,存活率略低于后者,增重和抗感染方面与后者相近。  相似文献   

Experimental Determination of the Roughness Length for Temperature Over a Field of Tall Grass in Central Sweden     

M. Mölder  A. Lindroth  & A. Grelle 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):87-100

The aim of this study was to analyse wind, temperature and humidity profiles, surface radiation temperature, and eddy correlation fluxes of momentum and heat over a grass field in order to obtain a better parameterisation of exchange processes over such a surface. The study was performed under summer conditions over a formerly cultivated, uniform and well-watered field of tall grass in central Sweden. An unusually low displacement height, d, was found, at 0.25 times the maximum canopy height h. The roughness length for wind speed could be approximated with the relation z_ou = 0.15(h–d). The relations of d and z_ou would be closer to the traditional ones if a mean canopy height, which is about half of the height used here, had been used in the analysis. The estimation of the quantity kB^–1 required accurate determination of the surface temperature. The radiometric surface temperature was measured by two different radiometers, one collecting thermal radiation at angles 0–45° and measuring effectively at 30° from nadir, and the other having a field of view of 15° and being tilted at 45° from nadir. The detected directional variations in the surface radiation temperature were within ± 1K, and the former radiometer, which was judged to be more accurate, was used for further analysis. The quantity kB^–1 was expressed through the roughness-sublayer Stanton number and drag coefficient. Methodologically, the most accurate determination of the Stanton number was to plot the air-surface temperature difference versus the temperature scale multiplied by any other relevant parameter. The quantity kB^–1 showed a dependence on the roughness Reynolds number, Re_o, and it took the form kB^–1 = 0.08 Re_o^0.5–1.9; its value varied between 0 and 4 for the present range of Re_o. These results are judged to be in good agreement with theory, considering the complexity of natural surfaces and the simplifications used in the theoretical deductions.  相似文献   

上海软弱地基的超长钻孔灌注桩施工技术   总被引：1，自引：0，他引：1  

张蛮庆  游维忽 《福建地质》1999,18(1):27-33

根据８个上海软弱地基的超长钻孔灌注桩工程项目的施工技术资料,总结了超长桩的概念,施工难度和施工方法。  相似文献   

岩体表面节理迹长与节理真实长度尺寸的概率关系     

袁绍国  王震 《水文地质工程地质》1999,(1)

空间节理长度不能直接进行测量,只能通过岩石暴露面上节理迹线长度来量测,但是节理迹线是节理面与岩面交切的结果,迹长在多大程度上能代表节理真实长度是值得研究的,本文利用计算机模拟的方法分析了迹长与节理真实长度的统计关系。  相似文献   

Study on a boundary-layer numerical model with inclusion of heterogeneous multi-layer vegetation     

Zeng Xinmin  Zhao Ming  Su Bingkai  Wang Hanjie 《大气科学进展》1999,16(3):431-442

On the basis of improving the algorithm of the mixing length in and above forest canopies, a PBL numerical model including the multi-layer, heterogeneous vegetation is developed. Simulations indicate that different treatments of mixing length can make a great difference in the wind field especially for dense forest, and results from the improved mixing length scheme are in better agreement with observations than those from the original scheme. It may be expected that the improved mixing length scheme can lead to more ra-tional turbulent transfer than the original one. From the sensitivity experiments, we obtain the characteris-tics of both wind and temperature profiles in and above plant canopies, e.g., during the daytime, a stable thermal stratification exists near the surface in the canopies, but a neutral or slightly unstable condition ap-pears above plant canopies, while at night the reverse situations occur; the increase of the temperature of the dense-forest case is less than that of the sparse-forest case; the windspeed is reduced within the canopy lay-er and the large wind shear occurs near the treetop, etc.  相似文献   

A Roughness Sublayer Wind Profile Above A Non-Uniform Surface   总被引：2，自引：0，他引：2  

D. T. Mihailović  Branislava Lalić  B. Rajković  I. Arsenić 《Boundary-Layer Meteorology》1999,93(3):425-451

In atmospheric models for different scales the underlying surface consists of patches of bare soil and plant communities with different morphological parameters. Experimental evidence indicates that there is a significant departure of the wind profile above a vegetative surface from that predicted by the logarithmic relationship, which gives values that are greater than those observed. This situation can seriously disturb the physical picture concerning the transfers of momentum, heat and water vapour from the surface into the atmosphere.The intention of this paper is to generalise the calculation of exchange of momentum between the atmosphere and a non-homogenous vegetative surface, and to derive a general equation for the wind speed profile in a roughness sublayer under neutral conditions. Furthermore, these results are extended to non-neutral cases. The suggested expression for the wind profile is compared with some earlier approaches and the observations obtained above a broad range of plant communities.  相似文献   

Stochastic Doppler shift and encountered wave period distributions in Gaussian waves     

G. Lindgren  I. Rychlik  M. Prevosto 《Ocean Engineering》1999,26(6):2300

We show how to calculate the encountered wave period distribution for a ship traveling with constant speed on a Gaussian random sea with a directionally distributed frequency spectrum.  相似文献