Fine three-dimensional P-wave velocity structure beneath the capital region and deep environment for the nucleation of strong earthquakes

A detailed 3-D P-wave velocity model of the crust and uppermost mantle under the capitol region is determined with a spatial resolution of 25 km in the horizontal direction and 4-17 km in depth. We used 48750 precise P-wave arrival time data from 2973 events of local crustal earthquakes, controlled seismic explosions and quarry blasts. These events were recorded by 123 seismic stations. The data are analyzed by using a 3-D seismic tomography method. Our tomographic model provides new information on the geological structure and complex seismotectonics of this region. Different patterns of velocity structures show up in the North China Basin, the Taihangshan and the Yanshan Mountainous areas. The velocity images of the upper crust reflect well the surface geological, topographic and lithological features. In the North China Basin, the depression and uplift areas are imaged as slow and fast velocity belts, respectively, which are oriented in NE-SW direction. The trend of velocity anomalies is the same as that of major structure and tectonics. Paleozoic strata and Pre-Cambrian basement rocks outcrop widely in the Taihangshan and Yanshan uplift areas, which exhibit strong and broad high-velocity anomalies in our tomographic images, while the Quaternary intermountain basins show up as small low-velocity anomalies. Most of large earthquakes, such as the 1976 Tangshan earthquake (M 7.8) and the 1679 Sanhe earthquake (M 8.0), generally occurred in high-velocity areas in the upper to middle crust. However, in the lower crust to the uppermost mantle under the source zones of the large earthquakes, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids, just like the 1995 Kobe earthquake (M 7.2) and the 2001 Indian Bhuj earthquake (M 7.8). The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes.     

有限元-界面元混合模型及其应用

推导得出了一个简化过渡界面单元的单元刚度矩阵．采用界面元-有限元的混合模型来模拟三堆土-结构体系，并采用一致边界来模拟波向无穷远城地基的传播作用．然后壕制了一个可用于进行三堆土-结构非线性地震反应分析的程序，并用谊程序对一框架结构进行了考虑土-结构相互作用影响的地震反应分析．最后总结了各种非线性因素和土-结构相互作用效应时结构地震反应的影响规律．图11。参9．     

基于小波变换的爆破地震信号去噪的应用

运用小波变换在不同的尺度下观察信号局部化特征。由于信号和噪声具有不同的奇异性，它们的二进小波变换模的极大值在不同尺度下的传播特性也不相同。在相邻模极小构成的待选通域中分析出噪声局部极大值所在的选通域进行平滑处理，从而得到局部信号的小波系数，将其反变换重建出去噪后的信号。将该方法用于爆破地震信号去噪声，结果表明：这种方法计算简单，且去噪效果较好。     

竖向排列地下硐室群动力稳定性的数值模拟分析

以竖向排列地下硐室群为研究对象，将爆破地震波简化为谐波形式，运用三维有限差分程序FLAC^10研究不同速度、不同动荷载频率以及不同硐室间距条件下硐室群隔板位移和围岩塑性区面积的变化规律，以及上方硐室跨度变化对隔板位移和下方硐室稳定性的影响，通过工程实例分析爆破震动作用下地下硐室群的稳定性。研究结果表明：动荷栽速度对地下硐室群稳定性的影响最明显，隔板位移和围岩塑性区面积随爆破地震波速度增大而增大；随着爆破地震波频率的增大，隔板位移先增大后减小；随着硐室间距的增加，隔板位移减小，有利于地下硐室群的稳定；随着上方硐室跨度增加，隔板位移增大；地下硐室群围岩中出现多处应力集中，但最大拉应力小于岩体的抗拉强度，不会出现拉裂破坏；分析结果与实际观测结果相吻合。     

单自由度体系地震能量反应的计算

在地震中，结构吸收地震波输入的能量，并以阻尼耗能和滞回耗能的形式消耗能量。通过结构弹塑性地震反应分析的时程分析法，可以计算出结构地震总输入能及结构阻尼耗能和滞回耗能的时程曲线。这些曲线可以为结构抗震分析提供依据。简要介绍了计算单自由度体系弹塑性地震能量反应的基本过程，并以算例说明。     

准噶尔盆地阜东斜坡带石树沟群地震相分析及沉积体系预测

对准噶尔盆地阜东斜坡带石树沟群首次进行了系统地震相分析,根据地震相单元的内部反射结构和外部几何形态及其他参数,划分出6种具有重要指相意义的地震相.依据沉积体系展布的基本模式以及少量井孔资料,将地震相转换为沉积相,预测了石树沟群沉积体系的分布,指出三角洲前缘相带是最有利的岩性圈闭发育带.     

CFRP加固RC框架结构振动台试验及损伤机理分析

通过对两个缩尺比为1/4的两层单跨钢筋混凝土框架结构模型的加固、未加固及其震坏后再加固的3次振动台对比试验,探讨了其动力特性、地震反应和损伤破坏情况.同时运用有限元程序建模进行了计算,分析了不同试验模型的损伤机理,对比了根据不同损伤机理进行抗震加固的效果.试验研究及计算分析表明:根据损伤机理的不同,用碳纤维布(CFRP)有针对地加固钢筋混凝土框架结构能够提高其抗震能力,并满足抗震规范要求.     

大型复杂钢结构厂房的抗震性能的有限元分析

利用通用有限元程序ANSYS建立了某大型复杂钢结构厂房的三维空间有限元模型，完成了其整体结构的动力学特性分析，还根据现有7级地震记录对其施加了横向、纵向和斜向地震激励，分别做时间历程分析，并对计算结果做了相应的对比．最后结合结构抗震规范的相关条文，对该钢结构厂房的抗震性能进行了综合评定，结果表明其满足7级抗震要求．分析结果可为工程师们设计类似结构提供相应的依据．     

层间隔震底层框架砌体房屋动力计算方法

底层框剪结构多层砖房在城市建设中应用广泛，这种房屋的特点是由2种承重和抗侧力体系构成的，但是这类房屋的抗震性能较差．为此，提出把隔震橡胶垫放置在上部砌体与底层框架结构之间的隔震措施，它依靠隔震层较大的变形和耗能能力，大大削弱了地震对建筑结构的影响．由于上部砖房的刚度比隔震垫与底层框架的刚度大得多，因此可以将隔震房屋模拟成具有2个自由度的系统．并分析了此类房屋的动力特性，与隔震振型的参与系数相比，非隔震振型的参与系数非常小，隔震振型控制了系统的反应，得到了用来求解此类房屋动力计算的实用方法．为建立实用设计方法、推广层间隔震结构的应用提供了有效途径．     

Ability to detect weak effective seismic signals by utilizing chaotic vibrator system

Taking the advantage of CVS (Chaotic Vibrator System) sensitivity of large-scale periodic phase-state response to quasi-periodic or periodic signals,a series of numerical experiments were made to understand the ability of CVS to detect weak effective seismic signals in the common-shot seismic record distorted by strong stochastic noise. The re-sults demonstrate that the large-scale periodic phase-states of CVS are correlated with the signal composition of the quasi-periodic wavelet sequence constructing from horizontal moveout of seismic events,noise strength and the noise distortion de-gree to signal. For the same kind of events,the higher the noise distortion degree is,the lower the detectable SNR can be reached by CVS. For seismic data with the same noise distortion degree,the closer the scanning seismic velocity (the trial moveout ve-locity) approaches to the accurate velocity,the higher the detectable SNR can be reached by CVS. More-over,the truncating scanning velocities form an asymmetric belt,which indirectly makes CVS achieve a large-scale periodic phase-state and then the ratio of wavelet distortion coefficients in events can be a biggish variable scope.