Preliminary analysis of the shear-wave splitting observations from the Qiaojia seismic array*          下载免费PDF全文

Hao Liang  Zhen Fu  Chunlai Li  Lisheng Xu 《地震科学（英文版）》2020,33(2):82-97

A total of 351 shear-wave splitting results at 25 stations were obtained from the seismic data recorded in period of January, 2013 to December, 2016, by a broadband seismic array deployed in the northern segment of Xiaojiang Fault Zone (n-XJFZ). Meanwhile, the stress field of the n-XJFZ was determined by inverting 140 focal mechanism solutions of the small earthquakes within the study area which were recorded in the same period. This determination confirmed a compressive stress in NW-SE orientation and an extensional stress in the NE-SW orientation, with little difference from those released by previous studies. The shear-wave splitting results show a spatial complexity in polarization orientation, different from one site to another. However, the polarization orientations integrated for the subareas suggest that the fault trends seemingly played important roles. All the subareas bear two dominant orientations, N10°E and N90°E, both of which are different from the azimuths of the principal compressive stress, due to the fault distribution. The time delay averaged over the entire region is 4.56 ms/km, close to that of the upper boundary of the generally accepted interval worldwide but larger than those in most of the investigated regions in the Chinese mainland, which probably implies an alignment of more micro-cracks in the n-XJFZ. Interestingly, the 2014 M_S6.5 Ludian earthquake was found to have caused a variation in the time delays of the slow shear waves within the study area though its epicenter was outside. This earthquake resulted in an evident drop of the time delays remaining for 4 months, however, lifted a bit the time-delay level with respect to that prior to the earthquake.  相似文献   

Dynamic microplasticity manifestation in consolidated sandstone in the acoustical frequency range          下载免费PDF全文

E.I. Mashinskii 《Geophysical Prospecting》2017,65(1):266-279

Microplasticity manifestations caused by acoustical wave in the frequency range of about 4.5 kHz–7.0 kHz are detected in consolidated artificial sandstone. Equipment was tested by means of comparison of data obtained for a standard material (aluminium) and sandstone. Microplasticity manifestations in acoustic records are present in the form of the ladder‐like changes in the amplitude course. The stress plateaus in the acoustic trace interrupt the amplitude course, transform the wavefront, and shift the arrival time along the time axis. Microplasticity contribution to the acoustic record changes with the increase in the strain amplitude value. The combined elastic–microplastic process conditions the wavefront steepness and its duration. Stress plateaus exert influence on the waveform and, accordingly, on pulse frequency response. These results confirm the earlier data obtained for weakly consolidated rock. This contribution to wave propagation physics can be useful in solving applied problems, as, for instance, the reservoir properties prediction by means of wave attenuation in acoustic logging and seismic prospecting.  相似文献   

龙门山断裂带域上地壳各向异性及其变化          下载免费PDF全文

陈安国  高原  石玉涛 《地球物理学报》2019,62(8):2959-2981

龙门山断裂带上发生了2008年汶川8.0级和2013年芦山7.0级地震,为了研究芦山地震前后该区域地壳各向异性的空间分布和变化,以及较大地震对快剪切波偏振方向造成的影响,本文运用剪切波分裂系统分析方法,结合固定地震台网（2010-01—2017-10）和川西流动地震台阵（2006-10—2009-07）的小震波形数据,得到了龙门山断裂带及邻近地区上地壳各向异性参数.结果表明,慢剪切波时间延迟主要分布在0.65~7.39 ms·km^-1之间,横向上具有不均匀性,地壳20 km以上的介质对各向异性的贡献较大.快剪切波优势偏振方向主要为NW或NWW和NE向,具有明显的分区特性.位于龙门山断裂带附近台站的快剪切波偏振方向自北向南由NWW转变为NW、NE向,在南段又变为NWW、NE向,指示了龙门山断裂带的分段特性是其构造属性.根据得到的有效事件数据,本文使用的49个台站中有19个台站的各向异性参数与反方位角、深度、震级和路径长度等显示出一定的相关性.研究区内的芦山地震及其他较大地震可能影响了局部快剪切波偏振方向.研究表明,更多的有效事件数据将有益于定量分析局部构造应力场和断裂属性的变化情况,从而有益于断裂带地震学特性及地震预测研究.  相似文献   

Linear dynamic modeling of a uni‐axial servo‐hydraulic shaking table system     

J. P. Conte  T. L. Trombetti 《地震工程与结构动力学》2000,29(9):1375-1404

This paper focuses on the development of a linear analytical model (even though servo‐hydraulic actuation systems are inherently non‐linear, especially for large amplitude simulations — near the performance capacity of the system — linearized models proved experimentally to be quite effective overall in capturing the salient features of shaking table dynamics) of a uni‐axial, servo‐hydraulic, stroke controlled shaking table system by using jointly structural dynamics and linear control theory. This model incorporates the proportional, integral, derivative, feed‐forward, and differential pressure gains of the control system. Furthermore, it accounts for the following physical characteristics of the system: time delay in the servovalve response, compressibility of the actuator fluid, oil leakage through the actuator seals and the dynamic properties of both the actuator reaction mass and test structure or payload. The proposed model, in the form of the total shaking table transfer function (i.e. between commanded and actual table motions), is developed to account for the specific characteristics of the Rice University shaking table. An in‐depth sensitivity study is then performed to determine the effects of the table control parameters, payload characteristics, and servovalve time delay upon the total shaking table transfer function. The sensitivity results reveal: (a) a potential strong dynamic interaction between the oil column in the actuator and the payload, and (b) the very important effect of the servovalve time delay upon the total shaking table transfer function. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

复杂网络中考虑不完全免疫的病毒传播研究          下载免费PDF全文

王亚奇  蒋国平 《海洋学报》2010,32(10):6734-6743

提出一种新的流行病传播模型,基于平均场理论,研究传染媒介和传播延迟同时存在对网络中流行病传播行为的影响.理论分析和仿真结果表明,传染媒介和传播延迟同时存在显著增强了网络中流行病爆发的危险性,并加速了流行病的传播.研究还发现,对于给定的有效传播率,均匀网络中流行病的感染程度分别与传染媒介的传染概率和传播延迟呈对数关系,无标度网络中流行病的感染程度与传染媒介的传染概率呈幂率关系,而与传播延迟之间则存在线性关系.  相似文献   

基于无记忆状态观测器的多时滞不确定非线性系统的自适应控制          下载免费PDF全文

郭鹏  胡慧  刘国荣  胡俊达 《海洋学报》2010,32(9):5925-5929

针对一类多时滞不确定非线性系统,研究了基于无记忆状态观测器的自适应控制问题.时滞状态扰动的上界未知,在控制中通过自适应律估计未知参数,并利用估计值设计了不依赖于时滞的无记忆状态观测器和控制器,基于Lyapunov-Krasovskii函数证明了观测误差渐近收敛到零.最后仿真结果说明了该方法的有效性.  相似文献