复合周期钢结构随机地震动波响应与控制

基于固体物理周期结构的基本理论,将其应用于结构隔震来研究地震动波在周期结构中的传播。首先构造复合周期钢结构模型,以两两单元之间相位差为参数:设钢结构中至少含2个有方向的周期单元,将这些单元两两黏合。首先固定第一个格子,按照黏合映射与方向复合的等距映射,它和第二个格子形成两格子周期结构,且其中2个周期结构方向之间有正的相位差。这2个格子向两端延伸,构成一维复合周期结构,且包含不少于2个有方向的周期结构。在一维复合周期结构中,每个格子再向平面内、空间内按照黏合映射与方向复合的等距映射延伸,组成二维、大于二维的复合周期结构。黏合映射与方向复合构成两两黏合后周期结构之间公共部分的映射,将地震动波从第一个单元传播到第二个单元,再依次传播到整个复合周期钢结构。接着计算地震动波在复合周期结构中的响应,影响参数有:波数、黏合映射数、周期结构的尺度和相位差。假设响应是线性的,首先分别讨论单个参数影响,最后求和得到复合周期结构总响应。由于地震动波具有随机性,服从给定的随机微分方程,结构响应也是可能取值的集合。故先讨论2个周期单元情形、一维情形的地震动响应。在两格子复合周期钢结构中,先在第一个格子输入给定的随机微分方程、初始条件和边界条件,应用集值随机过程和鞅理论计算,得到第一个格子的响应;再由相位差和三角函数性质,计算第二个格子的响应、一维结构中每一个格子的响应。最后实施结构地震动响应的Markov控制,选择最优相位角,实现一类多项式函数响应目标:根据周期单元响应的集值随机过程性质,表示为扩散过程,由它的无穷小生成元构造对应的Dirichlet-Poisson方程,进而构造Hamilton-Jacobi-Bellman(HJB)方程,解得最优相位角,代回Dirichlet-Poisson方程,再求解得到控制结果。该响应随地震动波传播时间、初始幅值增大而降低。应用Monte Carlo模拟给定的随机地震动波,生成平稳分布,再采样。该采样序列分布服从该平稳分布,计算采样序列和Markov控制的方差,再比较随机地震动波示性函数和Markov控制的期望,表明Markov控制序列的波动性小于采样序列,Markov控制也降低了地震动响应的期望值。该方法实现了复合周期钢结构地震动波响应的随机过程表示及Markov控制,为复合周期钢结构地震动波响应随机预测提供参考。

PGMD选波时规范反应谱局部场地效应参数研究

在地震动选波的谱匹配环节,规范反应谱是最常用的目标谱,此时应尽可能反应预期工程场地地震的统计特征.在规范谱与场地效应相关的参数中,场地地震动峰值加速度调整系数、罕遇地震反应谱特征周期增加值可按各个行业规范选取,且差异较大.基于PGMD选波数据库,比选出我国规范考虑的因素吻合性最好的地震动衰减关系BSSA 14,按我国规范地震动峰值加速度分区值的规定,建立基于BSSA 14计算的场地地震动峰值加速度调整系数、罕遇地震反应谱特征周期增加值,并与我国规范的相关规定做对比.研究表明Ⅰ类场地细分成Ⅰ0与Ⅰ1两个亚类、场地地震动峰值加速度调整系数、罕遇地震反应谱特征周期增加值,各个行业跨规范参照《参数区划图》2015版选取,则会得到与PGMD数据库自身统计规律适应性强的规范反应谱参数.

基于地震动信号的目标预警系统

针对现代智能弹药系统低功耗的需求,提出一种基于地震动信号的低功耗预警系统电路。通过分析地震动波的特点,合理选择预警系统的地震动传感器;在自适应浮动门限与目标通过特性提取原理的基础上,设计低功耗硬件电路实现的震动预警系统;给出电路的系统结构组成框图和主要环节电路的工作原理。试验结果表明:该电路系统具有低功耗(<5 mW)、低虚警(<6次/24 h)和目标的预警距离远(装甲目标350 m)等特点,并能够抗战场爆炸等冲击干扰。

基于IDA方法的悬索桥地震破坏机理分析中地震输入合理选择

以非线性时程分析为基础的IDA方法可作为展现以桥塔为主要目标的悬索桥地震破坏模式研究的有力工具。地震动输入的不确定性是时程分析结果离散性大的决定性因素。因此首先需为以IDA为工具的悬索桥地震破坏模式研究选择恰当的地震动记录以及IM指标。基于地震动记录选波研究现状,明确恰当的选波数量、选波方法及采用的工具和数据库。以悬索桥为对象,根据悬索桥桥塔高阶振动和非线性软化效应的地震响应特点,讨论谱匹配参数设置。以PGMD开放程序为工具,采用两级选波方法在PEER-NGA数据库中选出40条地震动记录,通过对比Sa(T1,5%)和PGA调幅下桥塔地震响应离散性,最终选定18条地震动记录以及PGA为合理的IM指标,并通过悬索桥IDA分析曲线验证选波的合理性。研究详细展示了如何利用现有开放强震数据库,以IDA为工具进行某一特定结构抗震性能研究时,选择合理地震动记录及IM指标的方法及过程,也可为悬索桥地震破坏模式的研究提供基础。

An automatic seismic signal detection method based on fourth-order statistics and applications

Real-time, automatic, and accurate determination of seismic signals is critical for rapid earthquake reporting and early warning. In this study, we present a correction trigger function（CTF） for automatically detecting regional seismic events and a fourth-order statistics algorithm with the Akaike information criterion（AIC） for determining the direct wave phase, based on the differences, or changes, in energy, frequency, and amplitude of the direct P- or S-waves signal and noise. Simulations suggest for that the proposed fourth-order statistics result in high resolution even for weak signal and noise variations at different amplitude, frequency, and polarization characteristics. To improve the precision of establishing the S-waves onset, first a specific segment of P-wave seismograms is selected and the polarization characteristics of the data are obtained. Second, the S-wave seismograms that contained the specific segment of P-wave seismograms are analyzed by S-wave polarization filtering. Finally, the S-wave phase onset times are estimated. The proposed algorithm was used to analyze regional earthquake data from the Shandong Seismic Network. The results suggest that compared with conventional methods, the proposed algorithm greatly decreased false and missed earthquake triggers, and improved the detection precision of direct P- and S-wave phases.

The anti-correlation method for removing harmonic distortion in vibroseis slip-sweep data

The slip-sweep technique is one of the high-efficiency, high-fidelity, and environmental vibroseis seismic prospecting techniques which consists of a vibrator group sweeping without waiting for the previous group＇s sweep to terminate. The cycle time can be reduced drastically and hence the production efficiency can be increased significantly but harmonic distortion of one sweep will leak into the record of the other sweep. In this paper, we propose an anti-correlation method for removing harmonic distortion in vibroseis data. This method is based on decomposition of the ground force signal into fundamental and harmonic components. Then the corresponding anti-correlation operator can be computed to estimate the energy of each harmonic after correlating the vibroseis data with the corresponding harmonic component. Finally, the vibroseis harmonic noise to be removed can be obtained by subtracting the extracted harmonic noise from the traces of the previous group＇s sweep. The advantage of the proposed method is that it can process both uncorrelated and correlated vibroseis seismic data. Moreover, the algorithm is simple, stable, and computationally fast. Especially, the significant contribution of this method is a considerable reduction in the harmonic without any alteration of the desired signals. The method was tested on both synthetic and field data sets to validate the good harmonic noise suppression results.

One-way wave equation seismic prestack forward modeling with irregular surfaces

Mathematical geophone （MG） and equal-time stacking （ETS） principles are used to implement seismic prestack forward modeling with irregular surfaces using the oneway acoustic wave-equation. This method receives seismic primary reflections from the subsurface using a set of virtual MGs. The receivers can be located anywhere on an irregular observing surface. Moreover, the ETS method utilizes the one-way acoustic wave equation to easily and quickly image and extrapolate seismic reflection data. The method is illustrated using high single-noise ratio common shot gathers computed by numerical forward modeling of two simple models, one with a flat surface and one with an irregular surface, and a complex normal fault model. A prestack depth migration method for irregular surface topography was used to reoroduce the normal fault model with high accuracy.

Scale of seismic and rock burst hazard in the Silesian companies in Poland

Presently the seismic and rock burst hazard appears still to be important in most of hard coal mines in Poland. Recently, there was a significant increase of seismic activity of the Silesian rock massive, when compared with the previous years. In the period 1999-2008 the hard coal mines experienced 34 rock bursts. The causes of rockburst occurrence are presented based on the analysis of the rockbursts occurring in the Polish hard coal mines. The scale of the rockburst hazard has been characterized with respect to the mining and geological conditions of the existing exploitation. Of the factors influencing the state of rockburst hazard, the most essential one is considered the depth interval ranging from 600 m to 900 m. The basic factors that promote the rockburst occurrence are as follows： seismogenic strata, edges and remnants, goal, faults, pillars and excessive paneling.

Experimental Research on the Low Frequency Wave That Radiates into the Air before the Failure of Rock

Experiments on sonic transmission show that a slabstone can directly transmit part of the energy of a wave excited by knocking or by a transducer into the air. The other part of the wave energy can generate the normal mode of vibration on the slabstone and excite measurable acoustic signals in the air. The dominant frequency is related to the size of the slabstone. These results indicate that the acoustic emission (AE) in rock also displays similar behavior if the source is shallow. It is demonstrated that with the nucleation and propagation of cracks, the dominant frequency of the radiated wave will be lower. When the frequency becomes very low, the wave can be transmitted through the rock into the air and be received by a microphone. According to the theory of similarity of size, there will be low-frequency waves before strong earthquakes because of nucleation of cracks, which can be received by special low-frequency transducers or infrasonic detectors. Before earthquakes, the mechanism of precursors could be very complicated. They might be produced by plastic creep or attributed to liquids but not brittle fracture in most cases. So the periods of the produced waves will be longer. This perhaps accounts for the lack of foreshocks before many strong earthquakes.

Dynamic response law about gravity retaining wall to seismic characteristics and earth fill properties

In order to find the dynamic response laws of retaining walls affected by certain earthquake loads,the influence of the seismic wave characteristics and sub-grade fill parameters(including the foundation surface slope) were focused on,and a series of tests were performed.The results show that the maximum stress of the retaining wall decreases as internal friction angle,foundation slope,filled soil cohesion and the biggest dynamic elastic modulus increase,while it increases with the seismic frequency and seismic input peak dropping.The addition value of dynamics earth pressure increases when seismic frequency and seismic input peak are reduced,while it decreases when the filled soil cohesion and internal friction angle rise.Meanwhile,dynamic elastic modulus and foundation slope have no obvious influences on addition value of dynamics earth pressure.The slope will be instable if the seismic input peak exceeds 0.5g and be disruptive if seismic frequency is larger than 2.5 Hz.The mid-lower parts of retaining walls are in most heavy and obvious response to these factors,which reveals the mechanism of "belly burst" in retaining wall that appears commonly in practical projects.

Plastic-Flow Waves (“Slow-Waves") and Seismic Activity in Central-Eastern Asia

The results inferred from experiments with analogue models carried out previously have shown that two types of plastic-flow waves, “fast-waves" and “slow-waves", are induced in the lower lithosphere (including the lower crust and lithospheric mantle) under driving at plate boundaries and both of them are viscous gravity waves formed by the superposition of major and subsidiary waves. The major waves are similar to solitary waves and the subsidiary waves are traveling waves. The plastic-flow waves in the lower lithosphere control seismic activities in the overlying seismogenic layer and result in the distribution of earthquakes along the wave-crest belts. “Fast-waves" propagated with velocities of orders of magnitude of 100～102km/a have been verified by wave-controlled earthquake migration, showing the “decade waves" and “century waves" with the average periods of 10.8 and 93.4 a, respectively, which originate from the Himalayan driving boundary. According to the recognition of the patterns of the belt-like distribution of strong earthquakes with M S≥7.0, it is indicated further in this paper that the “slow-waves" with velocities of orders of magnitude of 100～101 m/a also originated under compression from the Himalayan driving boundary. Strong earthquakes with M S≥7.0 are controlled mainly by subsidiary waves, because the major waves with a duration of up to 106 a for each disturbance cannot result in the accumulation of enough energy for strong earthquakes due to the relaxation of the upper crust. The subsidiary waves propagate with an average wave length of 445 km, velocities of 0.81～2.80 m/a and periods of 0.16～0.55 Ma. The wave-generating time at the Himalayan driving boundary is about 1.34～4.59 Ma before present for the “slow-waves", corresponding to the stage from the Mid Pliocene to the Mid Early-Pleistocene and being identical with one of the major tectonic episodes of the Himalayan tectonic movement. It is shown from the recognition of the wave-controlled belts of strong earthquakes that two optimal patterns of wave-crest belts originated simultaneously from the eastern and western segments of the Himalayan arc, respectively. The overlap of wave-crest belts of these two systems is responsible for the relative concentration of energy and forms the seismic-energy-background zones for strong earthquakes with M S≥7.0.

Application of Seismic Inversion Using Logging Data as Constraints in Coalfield

Seismic inversion and basic theory are briefly presented and the main idea of this method is introduced. Both non-linear wave equation inversion technique and Complete Utilization of Samples Information (CUSI) neural network analysis are used in lithological interpretation in Jibei coal field. The prediction results indicate that this method can provide reliable data for thin coal exploitation and promising area evaluation.

Study on Dynamic Response of the “Dualistic” Structure Rock Slope with Seismic Wave Theory

Currently, scant attention has been paid to the theoretical analysis on dynamic response mechanism of the ＂Dualistic＂ structure roek slope. The analysis presented here provides insight into the dynamic response of the ＂Dualistie＂ structure rock slope. By investigating the principle of energy distribution, it is shown that the effect of a joint plays a significant role in slope stability analysis. A dynamic reflection and transmission model （RTM） for the ＂Dualistic＂ structure rock slope and explicit dynamic equations are established to analyze the dynamic response of a slope, based on the theory of elastic mechanics and the principle of seismic wave propagation. The theoretical simulation solutions show that the dynamic response of the ＂Dualistic＂ structure rock slope （soft-hard） model is greater than that of the ＂Dualistic＂ strueture rock slope （hard-soft） model, especially in the slope crest. The magnifying effect of rigid foundation on the dynamic response is more obvious than that of soft foundation. With the amplitude increasing, the cracks could be found in the right slope （soft-hard） crest. The crest failure is firstly observed in the right slope （soft-hard） during the experimental process. The reliability of theoretical model is also investigated by experiment analysis. The conclusions derived in this paper could also be used in future evaluations of Multi-layer rock slopes.

Seismic Waves in a Layered Half-Space from an Arbitrary Buried Source

In this paper, a transfer matrix and a three-dimensional dynamic response of a layered half-space to an arbitrary buried source are derived with the aid of a technique which combines the Laplace and two-dimensional Fourier transforms in a rectangular coordinate system. This method is clear in concept, and the corresponding formulas given in the paper are simple and convenient for marine seismic prospecting and other fields' applications. An example is presented and the calculated results are in good agreement with those of the finite element method (FEM).

Discussion on the Relationship between Different Earthquake Magnitude Scales and the Effect of Seismic Station Sites on Magnitude Estimation

Based on the earthquake catalog reported by the Chinese digital seismic network in recent years,we select the earthquakes with both surface wave magnitude and local magnitude and fit them into a relationship between the two magnitudes.The systematic difference is found from the formula which has been used for 30 years.Because of a large dynamic range and wide frequency range of the current digital observation system,in addition to a larger number of stations and earthquakes being used compared to before,the relation obtained in this paper seems more reliable.Our calculation shows that there is no significant difference before and after magnitude conversion so we suggest the abandonment of magnitude conversion.The site response of a station consists of amplification at different frequencies.The amplification is equal to about 1 and changes little with frequency at stations located on basement rock,and it is greater than 1 at low frequency ranges and less than 1 at high frequency ranges at stations located on sediment layers.The difference between magnitudes from single station located on sediment layer and the average magnitude from the whole network increases from negative to positive with period.It seems that there is no fixed station correction factor and the station correction method does not work to improve the accuracy and magnitude estimates.

Effect of Shear Wave Velocity on the Ground Motion Parameters of Site Surface

Based on the data from typical sites in the Jianghuai region,many kinds of soil layer seismic response are modeled by increasing and decreasing the measured values of shear velocity to a certain scale. The seismic response of soil layer sites are calculated using the one-dimensional equivalent linear method in the frequency domain by choosing the Taft,Kobe and El-centro records as the ground motion input. The results show that the impact of shear velocity variability on the surface ground motion is in relation to the soil layer structure and ground motion input parameters such as amplitude and spectral characteristic. With the increase of shear velocity,the PGA( peak ground acceleration)on the surface of site will increase,however,the characteristic period of the acceleration response spectra is decreasing.

Statistical Analysis on the Corner Period of Site-Related Design Spectra

According to the results of site seismic hazard analysis accomplished in the past decades, 96 site-related design spectra are selected as samples in this study. The result shows that the value of the corner period (T g) of the design spectrum in GBJ11-89 (China Seismic Building Code, issued in 1989) is lower than the value obtained by site seismic hazard analysis. The same situation exists when we compare the design spectra of the Codes to the spectra according to the earthquake records. The value in current seismic design code, GBJ50011-2001 issued in 2001, is greater than that in GBJ11-89, but still less than the value obtained by site seismic hazard analysis. If we accept the value got by site seismic hazard analysis, we have a suspicion that 2/3 of buildings built according to GBJ11-89 will not be safe when an earthquake with 2% probability of exceedance in 50 years occurs.

INFLUENCE OF UNCERTAINTY OF ROCK PROPERTIES ON SEISMIC RESPONSES OF REACTOR BUILDINGS

The influence of the dispersion and uncertainty of the dynamic shear wave velocity and Poisson＇s ratio of soil in a hard rock site was investigated on the seismic response of reactor building structure. The analysis is performed by considering the soil-structure interaction effects and based on the model of the reactor building in a typical pressurized water reactor nuclear power plant （NPP）. The numerical results show that for the typical floor selected, while the relative increment ratio of the dynamic shear wave velocity varies from -30% to 30% compared to the basis of 1 930 m/s, the relative variation of the horizontal response spectra peak value lies in the scope of ±10% for the internal structure, and the relative variation of the frequency corresponding to the spectra peak is 0.0% in most cases. The relative variation of the vertical response spectra peak value lies in the scope of - 10% to 22%, and the relative variation of the frequency corresponding to the Spectra peak lies in the scope of - 22% to 4%. The analysis indicates that the dynamic shear wave velocity and the Poisson＇s ratio of the rock would affect the seismic response of structure and the soil-structure interaction effects should be considered in seismic analysis and design of NPP even for a hard rock site.

An evaluation of deep thin coal seams and water-bearing/resisting layers in the quaternary system using seismic inversion

Non-liner wave equation inversion,wavelet analysis and artificial neural networks were used to obtain stratum parameters and the distribution of thin coal seams.The lithology of the water-bearing/resisting layer in the Quaternary system was also predicted.The implementation process included calculating the well log parameters,stratum contrasting the seismic data and the well logs,and extracting,studying and predicting seismic attributes.Seismic inversion parameters,including the layer velocity and wave impedance,were calculated and effectively used for prediction and analysis.Prior knowledge and seismic interpretation were used to remedy a dearth of seismic data during the inversion procedure.This enhanced the stability of the inversion method.Non-linear seismic inversion and artificial neural networks were used to interpret coal seismic lithology and to study the water-bearing/resisting layer in the Quaternary system.Interpretation of the 1～2 m thin coal seams,and also of the water-bearing/resisting layer in the Quaternary system,is provided.The upper mining limit can be lifted from 60 m to 45 m.The predictions show that this method can provide reliable data useful for thin coal seam exploitation and for lifting the upper mining limit,which is one of the principles of green mining.

Focal Mechanism Solution of the 2011 M_S4.8 Anqing Earthquake Determined from the CAP Method

In this article, we have inverted local broadband waveform data to determine the focal mechanism of the 2011 Ms4.8 Anqing earthquake. Our results show that the best double couple solution of the Ms4.8 event is 16°, 74° and 120° for strike, dip and rake angles of one nodal plane respectively, and 131 °, 33°, 30° for the other nodal plane. The estimated focal depth is about 3kin. Both strikes of the two nodal planes differ significantly to the strike of Susong-Zongyang fault, along which seismic activity has been at a low level since the Late Quaternary. This implies that this earthquake may not have occurred on the Susong-Zongyang fault, and we infer that a buried fault with strike of NNE may be the seismogenic structure of this event.