力平衡式加速度计仪器响应误差的校正方法

本文通过对数字强震仪系统使用的力平衡加速度计的仪器响应误差进行分析,提出了一个校正仪器响应失真的处理方法(微分-微分方法),即对未校正记录做低通滤波后运用近似理想微分器做两次微分得到校正加速度记录。针对大亚湾核电站地震仪表系统(K IS)给出了仪器校正示例,并编制了相应计算软件。该方法适用于我国强震动台网数字强震仪获取的加速度记录的仪器响应误差校正处理。     

Response of three Athens metro underground structures in the 1999 Parnitha earthquake

The M_s 5.9 earthquake of 1999 produced valuable records in three underground structures, as follows: (a) in the just completed cut-and-cover station of Sepolia two accelerographs recorded the free-field and the station-base motion; (b) in the still under-construction tunnelled station of Monastiraki an accelerograph recorded the ground surface motion, and (c) in the nearby Kerameikos station, abandoned for non-technical reasons, the temporary prestressed-anchor piled (PAP) wall was still in place and produced a record of total seismic displacement at its top. Directly or indirectly utilising these records, the article outlines the results of numerical analyses aimed at ‘recovering’ the complete seismic response of the three underground structures. Particular emphasis is given to Sepolia station, where the developed accelerations (with PGA of about 0.17 g at the station base and 0.43 g at the station roof) are shown to have been almost exactly equal to the design accelerations according to the seismic code under the assumption that the station responds as an aboveground structure. The successful performance of the two temporary structures, in Monastiraki and Kerameikos (which had been designed against minimal acceleration levels but experienced ground-surface high-frequency accelerations of the order of 0.50 g) is explained through dynamic response analyses.     

Approximate recovery of coseismic deformation from Taiwan strong-motion records

Since 1990, digital strong-motion accelerographs and global positioning system (GPS) instruments have been widely deployed in the Taiwan region (Shin et al. 2003; Yu et al. 2001). The 1999 Chi-Chi, Mw 7.6 earthquake and the 2003 Chengkung, Mw 6.8 earthquake were well recorded by both digital accelerographs and GPS instruments. These data offer a good opportunity to determine coseismic displacements from strong-motion records and to compare the results with those derived from GPS measurements. As noted by Boore (2001), a double integration of the acceleration data often leads to unreasonable results, and baseline corrections are therefore required in most cases before the integration. Based on the works of Iwan et al. (1985) and Boore (2001), we developed an improved method for baseline correction and validated it using an extensive set of data from shake-table tests of a known “step” displacement on 249 accelerographs. Our baseline correction method recovered about 97% of the actual displacement from the shake-table data. We then applied this baseline correction method to compute coseismic displacements from the strong-motion data of the Chi-Chi and Chengkung earthquakes. Our results agree favorably with the coseismic displacements determined by the GPS measurements at nearby sites. The ratio of seismic to geodetic displacement varies from 0.78 to 1.41, with an average of about 1.05.     

Spatial correlation of earthquake ground motion: non-parametric estimation

A non-parametric method, called multidimensional correlation mapping (MCM), is used to describe the local spatial correlation of different components of earthquake ground acceleration. The method estimates spatial correlation without presuming homogeneity or isotropy of the phase-aligned local ground motion fields. For selected events recorded by the SMART1 accelerograph array, we obtain contour plots of equal correlation of ground acceleration, with respect to the center of the array. Displacement time-histories are also computed from the accelerograms and the spatial correlation of the displacements is estimated for comparison with that of the accelerations.     

带SRC桁架转换层及钢加强层高层建筑抗震性能研究

本文对一座设置钢骨混凝土桁架转换层及两道钢桁架加强层的超高层建筑结构模型振动台试验结果进行了分析,发现Ⅶ度小震和中震阶段在下部转换层和中部加强层加速度突变较大,而上部加强层突变较小：在Ⅶ度大震阶段由于转换层及其附近楼层裂缝的出现,地震能量转嫁到中部加强层,致使中部加强层加速度突变出现大幅度的增长,该层及附近楼层核心筒墙肢出现一定程度的破坏。采用SAP2000有限元程序对该结构模型进行了小震阶段三维分析,并与试验值进行了对比：从动力特性来看,前几阶周期比较吻合,高阶周期误差较大;从动力反应来看,侧移曲线、加速度包络图、地震作用包络图在整体上符合较好,但在中部加强层和转换层处突变幅度计算值偏小;从层间剪力包络图来看,试验值与有限元计算值都呈现近似直线分布。     

A note on an instrumental comparison of the modified mercalli (MMI) and the Japanese meteorological agency (JMA) intensity scales,based on computed peak accelerations

In many parts of the world, subjectively based earthquake intensity scales similar to those of the Modified Mercalli Intensity (MMI) are applied regularly. Although the characteristics of these scales are quite similar, it is often difficult to convert an estimate of strong ground shaking measured by the MMI scale into its equivalent on other scales. In this paper, an instrumental correlation of the Japanese Intensity scale (JMA) with the MMI scale is described. Currently, one common yardstick that is available for both Japan and the United States is the statistic of peak accelerations. The correlation is done by comparing the JMA for sites where the ‘peak acceleration’ is known in Japan with the MMI for sites in the United States where the peak acceleration is also known. To ensure a direct correspondence of peak accelerations in these two countries, the peak values recorded in the U.S. are corrected by determining the peak acceleration as recorded by the Japanese accelerograph, the SMAC, while it is subjected to the excitation recorded in the United States.     

航空重力测量中载体运动加速度的确定

航空重力测量是使用重力仪、GPS及其他传感器测定地球重力场的一种新型技术，其基本原理是利用重力仪测定包括重力加速度、载体运动加速度以及其他一些加速度在内的总加速度，从观测值中减去利用GPS确定的载体运动加速度，再加上一些改正，得到了重力加速度. 本文推导了确定载体运动加速度的直接解算法的公式，利用某次航空重力测量数据，分别在静态、动态两种情况下，分析了确定载体运动加速度精度. 结果表明：在静态、60s的平滑间隔条件下，载体加速度的确定精度是0.4—0.9mGal；在动态、90s的平滑间隔条件下，整个飞行测段载体运动加速度的确定精度是1—3mGal.     

利用近场加速度记录确定近震震源参数的研究

本文对利用强震近场加速度记录确定时,空、强三个完整的震源参数。文中给出一种利用计算机自动识别地震记录的Ｐ波初动到时和Ｓ波震相到的算法。根据新近发表的Ｗｏｏｄ－Ａｎｄｅｒｓｏｎ地震仪器的最新参数,修牍正唐山地区量规函数。利用唐 山数字震观测台阵得到的近场加速度数据,计算了１０次地震的震源位置和震级,并对定位误差进行了综合分析,将强震台网测定的震源参数与地震台     

SMA-1强震仪原理及特殊故障维修

美国生产的SMA—1强震仪在我国的应用较为广泛，因使用多年，故障率逐年递增。从仪器的工作原理入手，简略介绍了常见故障的维修和仪器的改进方法。改进的仪器，经三年多的考验，运行正常。     

Earthquake strong motions recorded by a large near-source array of digital seismographs

Specially designed arrays of strong-motion seismographs near to the earthquake source are required for seismological and engineering studies of the generation and near-field properties of seismic waves. The first such large digital array, called SMART 1 (with radius 2 km and 37 accelerometers), to record substantial ground motion (up to 0·24g horizontal acceleration) became operational in late 1980 in a highly seismic region of Taiwan. During the first 6 months of operation, SMART 1 recorded nine earthquakes with magnitudes ranging from M_L 3·8 to 6·9. Three were located directly below the array at focal depths of 59 to 76 km. The remaining six had shallow depths and epicentral distances from 7 to 193 km. Digital records from 27 three-component accelerographs were obtained from a magnitude 6·9 (M_L) local earthquake on 29 January 1981. Representative measurements are described of seismic wave coherency and power spectrum as a function of wave number, frequency, azimuth of propagation and wave type. Acceleration waveforms varied significantly across the array for each event. On average, peak acceleration of horizontal components was about three times that of the vertical component. Relative spectral changes from earthquake to earthquake were large.     

Horizontal rotation signals detected by “G-Pisa” ring laser for the M w = 9.0, March 2011, Japan earthquake

We report the observation of the ground rotation induced by the M _w = 9.0, 11th of March 2011, Japan earthquake. The rotation measurements have been conducted with a ring laser gyroscope operating in a vertical plane, thus detecting rotations around the horizontal axis. Comparison of ground rotations with vertical accelerations from a co-located force balance accelerometer shows excellent ring laser coupling at periods longer than 100?s. Under the plane wave assumption, we derive a theoretical relationship between horizontal rotation and vertical acceleration for Rayleigh waves. Due to the oblique mounting of the gyroscope with respect to the wave direction of arrival, apparent velocities derived from the acceleration/rotation rate ratio are expected to be always larger than or equal to the true wave propagation velocity. This hypothesis is confirmed through comparison with fundamental mode, Rayleigh-wave phase velocities predicted for a standard Earth model.     

Advanced sensitivity calibration of the Los Angeles strong motion array

Results are presented of recent sensitivity calibration of 76 accelerographs (SMA-1) of the Los Angeles Strong Motion Array. These have pendulum-like transducers and optical recording system. One characteristic of their design is off-axis sensitivity, which is magnified by transducer misalignment. A new calibration procedure was applied, which considers off-axis sensitivity and measures the angles of misalignment (φ and ψ), as well as the incident angle of the light beam onto the film (θ₀). These are required (1) for accurate estimation of sensitivity, and (2) for proper instrument correction of recorded accelerograms which considers also cross-axis sensitivity and misalignment. These effects are important near large acceleration peaks (approaching and exceeding 1g), e.g. like the ones recorded near the source of the 1994 Northridge earthquake (M_L=6·4). This earthquake was recorded by 65 stations of the Los Angeles Strong Motion Array, at epicentral distances from 2 to 85 km. Histograms showing distribution of the misalignment angles, light beam incidence angle θ₀ (for unloaded position) and the transducer sensitivities are presented. These indicate that the misalignment angles are typically 1–1·5°, but may also be 3–4°. Angle θ₀ (usually neglected), is mostly between ±8°, but may reach ±12°. Assuming θ₀=0 leads to systematically smaller values of the measured sensitivity (e.g. by ∼3% for θ₀=8° and ∼4% for θ₀=12°). Comparison of the newly measured sensitivities with those measured prior to installation (in 1979/1980), s^old, shows that, in general, the new values are systematically smaller. The difference is typically within 5 per cent, but in some cases is as large as 10 per cent. Other principal sources of the observed differences and their mechanisms are discussed. Those include long-term changes in the transducers (e.g. change of stiffness, reflected in changes of the natural frequency) and differences in the calibration procedure (e.g. errors associated with manual reading film records with tilt test data, and with transducer and instrument housing misalignment). The presented results may be considered typical of similar strong motion arrays worldwide. © 1998 John Wiley & Sons, Ltd.     

Measurement of six degree-of-freedom ground motion by using eight accelerometers

A new integrated measuring system with eight force-balance accelerometers is proposed to obtain a direct measurement of six degree-of freedom （DOF） ground motions, including three rotational and three actual translational acceleration components without gyroscopes. In the proposed measuring system, the relationship between the output from eight force-balance accelerometer and the six DOF motion of the measuring system under an earthquake are described by differential equations. These equations are derived from the positions and directions of the eight force-balance accelerometers in the measuring system. The third-order Runge-Kutta algorithm is used to guarantee the accuracy of the numerical calculation. All the algorithms used to compute the six DOF components of the ground motion are implemented in a real-time in Digital Signal Processor （DSP）. The distortion of the measured results caused by position and direction errors of the accelerometers in the measuring system are reduced by multiplying a compensation coefficient C to the output and subtracting static zero drift from the measured results, respectively.     

Synthetic earthquake ground motions on an array

Linear and especially non-linear analyses of spatially extended structures, such as pipelines and bridges, often requires specification of time histories of ground motion at an array of closely spaced points. As the number of dense accelerograph arrays worldwide is small, and the number of earthquake observations is limited, synthetic motions with desired characteristics become necessary. This paper presents a method for synthesizing such motions, which is an extension of the SYNACC method, developed first in the early 1970s for synthetic accelerations, velocities and displacements at a point, and later extended to synthetic near surface strains, rotations and curvatures of ground motion at a point. It consists of unfolding in time a site specific Fourier amplitude spectrum of ground acceleration, obtained by an empirical scaling model, by representing the ground motion as a superposition of traveling wavelets of Love and Rayleigh waves and body waves, which propagate with phase and group velocities consistent with the dispersion characteristic of the site geology, approximated by parallel layers. Uniform hazard Fourier spectra or any specified target Fourier spectrum can also be used. Derivations of the point strains, rotations and curvatures are also presented. The method is illustrated for scenario M6.5 and M7.5 earthquakes and three dispersion models.     

Cross-axis sensitivity of accelerographs with pendulum like transducers—mathematical model and the inverse problem

A mathematical model for a three-component accelerograph is presented that accounts for the effects of transducer misalignment and cross-axis sensitivity. The former refers to departures in the alignment of the transducer penduli (typically of the order of few degrees) from an ideal orthogonal system, and the latter to a transducer recording components of motion in directions other than its principal sensitivity axis. Transducer misalignment magnifies the effects of cross-axis sensitivity. These effects are significant only for large amplitude recordings (peak acceleration close to 1g), for example in the near-field of the 1994 Northridge, California, earthquake. The misalignment angles and the angular amplification constant can be determined by a static tilt test, performed in the field, and solving a generalized inverse problem. This paper presents an algorithm for solution of this inverse problem on a routine basis. Practical implementation of the algorithm and results for 76 instruments of the Los Angeles Strong Motion Array are presented in a separate paper. © 1998 John Wiley & Sons, Ltd.     

AUTOMATED STATIC CORRECTIONS*

The widespread use of common depth point techniques has emphasized the need for accurate static corrections. Manual interpretation methods can give excellent results, but a computer technique is desirable because of the great volumn of data recorded in common depth point shooting. The redundancy inherent in common depth point data may be used to compute a statistical estimate of the static corrections. The corrections are assumed to be time-invarient, surface-consistent, and independent of frequency. Surface consistency implies that all traces from a particular shot will receive the same shot static correction and all traces from a particular receiver position will receive the same receiver correction. Time shifts are computed for all input traces using crosscorrelation functions between common depth point traces. The time shift for each trace is composed of a shot static, a receiver static, residual normal moveout if present, and noise. Estimates of the shot and receiver static corrections are obtained by averaging different sets of the measured time shifts. Time shifts which are greatly in error are detected and removed from the computations. The method is useful for data which has a moderate to good signal to noise ratio. Residual normal moveout should be corrected before estimating the statics. The program estimates the statics for correctly stacking common depth point traces but it is not sensitive to constant or very slowly changing static errors.     

2008年汶川地震近断层竖向与水平向地震动特征

选取分布在北川—映秀中央断裂两侧断层距120 km以内的40个强震动台站的记录,对汶川地震近断层地震动竖向和水平向加速度峰值、速度峰值、竖向和水平向加速度反应谱及谱比值进行了统计分析.研究表明:(1)地震动加速度峰值有显著的上盘效应,经验衰减模型的结果表明,在距地表破裂3~60 km的范围内,龙门山发震断层上盘一侧竖向与水平向的加速度峰值要比衰减模型得到的平均值大30%~40%.上盘的加速度峰值残差大部分是正值,而断层下盘残差大部分为负;水平地震动的东西分量幅值总体要大于南北分量,东西分量衰减相对较慢.(2)地震动长周期成分较弱,加速度反应谱值随周期增大而迅速减小,在周期1.0 s 时,即使在靠近中央断裂的最大加速度反应谱值也只有0.5 g;地震动加速度反应谱谱比值(竖向/水平向)沿龙门山断层周围的分布,在较长周期(T=0.2 s, 0.5 s, 1.0 s)与短周期(T=0.05 s, 0.1 s)有明显的不同.(3)近断层竖向地震动显著,地震动加速度峰值比在(竖向/水平向)可达1.4.在龙门山发震断层的上盘,地震动加速度峰值比整体上比下盘要大,竖向地震动尤为剧烈.部分近断层记录的地震动谱比值(竖向/水平向)在短周期(< 0.1 s)甚至超过1.5,统计分析还表明谱比值在短周期段(< 0.1 s)随断层距的增大而减小.     

甘肃岷县漳县6.6级地震强震动观测记录与初步分析

2013年7月22日甘肃省定西市岷县漳县交界(东经104.2°,北纬34.5°)发生M6.6地震。甘肃强震动台网在该地区覆盖良好,获得了丰富的主震加速度记录。本文收集整理了此次地震中各强震动台站获得的加速度记录资料并进行了基本处理;经统计分析绘出了峰值加速度分布图。     

The study and analysis of floating datum selection for rugged terrain

We analyze the characteristics of different floating datums for static corrections and discuss the methods for determining them. The effect of different floating datum corrections was studied using theoretical model experiments, resulting in the conclusion that the velocity obtained after the floating datum correction with the minimum static correction errors depends on the velocity of the layer below the low velocity layer （LVL） lower boundary and is not related to topographic relief and LVL structure. For the real data processing case, wave equation numerical model experiments were conducted which resulted in a new method for calculating objective functions based on the waveform and modifications to the calculation equation for minimum static correction errors to make the method suitable for real data static correction processing using inhomogeneous velocity models with lower velocity boundary relief. Real data processing results demonstrate the method＇s superiority.     

1985年8月23日新疆乌恰地震6.7级强余震频谱分析

在1985年8月23日新疆乌恰7.4级地震后二十天,即9月12日04点45分53秒发生了一次6.7级的强余震,在距微观震中约4公里处获得了强震记录。其最大水平向加速度值为123.8伽,是最大竖向加速度值的四倍。这次地震的反应谱峰值周期比海城、唐山、松潘地震都长。因此,虽然在微观震中处地震动强度相当于烈度7°,但震害却仅是6°。