场地效应研究的传递台站线性反演法——以芦山地震为例

采用线性反演法研究了地震动的场地效应,并针对线性反演法的局限性,提出了“传递台站”的方法来扩展其应用.通过传递台站,地震事件不再局限于必须被参考台记录到,台站也不再局限于须与参考台站同时获取到地震记录,改进后可大大增加数据样本,使得结果更趋稳定.同时,对于原来难以参与分析的台站,也可得到其场地反应.研究中,还采用了基于遗传算法的非参考台方法,进一步分析了场地反应和验证所提方法的合理性.将所提方法应用于2013年芦山7.0级地震周边区域,分析了这一地区的强震台站的场地反应和地震波衰减因子Q_s值.研究结果显示,当采用一个和二个传递台站进行分析时,所能利用的地震事件和所能求解场地反应的台站数目逐步增加,随着数据样本的增加,分析结果趋于稳定.研究区域的Q_s值拟合结果为Q_s（f）=334.16f^0.73.遗传算法结果表明,线性反演法中所选取的参考台站有其自身的场地反应.当利用遗传算法获得的参考场的场地反应去校正线性反演法的结果时,对于多数场地,两者的结果符合得很好,说明了遗传算法的结果可以合理地认为是场地较为真实的反应.

     

Effect of structural characteristics distribution on strength demand and ductility reduction factor of MDOF systems considering soil-structure interaction

It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings.The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades.However,no investigation has yet been carried out for the case of soil-structure systems.In the present study,through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns,including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils,the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated.The results of this study show that depending on the level of inelasticity,soil flexibility and number of degrees-of-freedoms(DOFs),structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems.It is also found that at high levels of inelasticity,the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.     

太原基准地震台地电阻率干扰形态特征分析

分析太原基准地震台2001年至2011年地电阻率观测中常见干扰因素,着重分析因不同干扰引起的图像变化特征,并就存在的问题提出合理化改进建议,力求对观测场地的选择、线路架设、资料分析、异常的判断及地震预测预报具有一定指导意义。     

乌加河地震台地电阻率干扰形态识别

选取乌加河地震台2015-2018年地电阻率观测资料,分析数据异常变化,结合观测环境及实地调查,发现存在降雨、雷电、金属管线、农田灌溉、设备漏电等影响因素,对比分析并总结各类干扰曲线形态、变化幅度、影响时间、干扰频次等特征,以便正确认识并排除地电阻率干扰,为地震异常信息识别提供帮助。     

网格剖分及其精度和计算量分析

网格剖分程度直接影响着地震波正演数值模拟的计算精度及其计算量.以均匀介质模型为例,分析不同网格大小对波场模拟精度和计算量的影响,得出精细化网格剖分是实现高精度地震波正演模拟的有效方法,然而其计算量较大.以均匀倾斜介质模型为例,探讨倾斜地层网格剖分问题,数值实例分析不同震源频率对不同网格剖分方案引起的波场传播精度的影响,...     

Vulnerability of floating tunnel shafts for increasing earthquake loading

Fragility curves constitute the cornerstone in seismic risk evaluations and performance-based earthquake engineering. They describe the probability of a structure to experience a certain damage level for a given earthquake intensity measure, providing a relationship between seismic hazard and vulnerability. In this paper a numerical approach is applied to derive fragility curves for tunnel shafts built in clays, a component that is found in several critical infrastructure such as urban metro networks, airport facilities or water and waste water projects. The seismic response of a representative tunnel shaft is assessed using tridimensional finite difference non-linear analyses carried out with the program FLAC^3D, under increasing levels of seismic intensity. A hysteretic model is used to simulate the soil non-linear behavior during the seismic event. The effect of soil conditions and ground motion characteristics on the soil-structure system response is accounted for in the analyses. The damage is defined based on the exceedance of the concrete wall shaft capacity due to the developed seismic forces. The fragility curves are estimated in terms of peak ground acceleration at a rock or stiff soil outcrop, based on the evolution of damage with increasing earthquake intensity. The proposed fragility models allows the characterization of the seismic risk of a representative tunnel shaft typology and soil conditions considering the associated uncertainties, and partially fill the gap of data required in performing a risk analysis assessment of tunnels shafts.     

Crustal attenuation characteristics of S-waves beneath the Eastern Tohoku region,Japan

An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan.Accelerograms from 85 shallow crustal earthquakes up to25 km depth and magnitude range between 3.5 and 5.5were analyzed to estimate the seismic quality factor Q_s. A homogeneous attenuation model Q_s for the wave propagation path was evaluated from spectral amplitudes, at 24 different frequencies between 0.5 and 20 Hz by using generalized inversion technique. To do this, non-parametric attenuation functions were calculated to observe spectral amplitude decay with hypocentral distance. Then, these functions were parameterized to estimate Q_s. It was found that in Eastern Tohoku region, the Q_s frequency dependence can be approximated with the function 33 f~(1.22) within a frequency range between 0.5 and 20 Hz. However,the frequency dependence of Q_s in the frequency range between 0.5 and 6 Hz is best approximated by Q_s(f) = 36f~(0.94) showing relatively weaker frequency dependence as compared to the relation Q_s(f) = 6 f~(2.09) for the frequency range between 6 and 15 Hz. These results could be used to estimate source and site parameters for seismic hazard assessment in the region.     

Changes of P, Ca, Al and Fe contents in fringe marshes along a pedogenic chronosequence in the Pearl River estuary, South China

Soil and plant samples were collected in four fringe marsh zones (i.e., A, B, C and D zones) along a pedogenic chronosequence in the Pearl River estuary in the Spring of 2009. Samples were subjected to a total digestion technique and analyzed for P, Ca, Al and Fe in order to study the changes of nutrient contents, storages in soils and their bioavailabilities to wetland plants (e.g. Cyperus malaccensis) in four zones. Results showed that soil Ca increased with depth along soil profiles, while P, Al and Fe generally kept constant in soil profiles in four zones. Al and Fe contents in the top 10 cm soils showed significant decreases from D to A zone, while a significant increase in Ca contents (P<0.05). Significant increases along pedogenic chronosequence for P, Al and Fe at 30-40 cm soil horizons were also observed. Ca was mainly accumulated in plant aboveground parts; Al and Fe were accumulated in the belowground parts; while P was homogenously distributed among the tissues of C. malaccensis. C. malaccensis in D zone had lower Bio-concentration factors (BCFs) of P in the shoots and Al and Fe in the roots, and higher values of Ca in the shoots than those in older zones (P<0.05). Compared to Al and Fe, both Ca and P had relatively higher translocation capacities for C. malaccensis, while only lower TFs for P and higher values for Al and Fe in D zone were observed than those in A and B zones (P<0.05). Except for Al with no significant changes, the total BCFs for P and Fe showed an increasing trend with soil ages, while a decreasing trend for Ca. The total bio-storage factors (TBSFs) of P and Ca declined with the pedogenic time, whereas an increase for Fe. The results of this study can contribute to the wetland conservation and management in the Pearl River estuarine region.     

基于因子分析的地震综合指数在辽宁地区地震预测中的应用

将辽宁地区按照地震活动特点划分为辽北、辽南、辽西三个主要区域,应用因子分析的方法,选取地震活动性参量中的11个参量(地震频次N、b值、η值、A(b)值、Mf值、Ac值、C值、D值、Rm值、能量E、响应比),进行数据的综合和再次挖掘,得到包含地震时、空、强及地下介质信息的综合指数。综合指数Wfa中涵盖了众多参量中80~90%的信息,并有效规避了各参量在地震预测中的不一致性。结果显示,在研究区域影响范围内发生较大地震前的1~2年时间内,综合指数Wfa都有明显的异常变化,说明综合指数可以较好反映地震活动异常特征。