Bilateral recursive restitution of true ground motion from near-field and far-field seismograms

Summary A two-sided recursive inverse filtering procedure, originally proposed by R. Vích, is used to restore the true ground motion from digital records of inertial electromagnetic seismographs. Numerical simulations of far-field and near-field P-wave seismograms are used to test the performance of the procedure and to derive criteria for recognizing successful restorations. The procedure is applied to seismograms of local microearthquakes as well as of teleseismic events, and the restored signals are compared with those obtained by causal (one-sided) inverse filtering. In all cases the two-sided approach proved to have fundamental advantages: a higher accuracy of the approximation of the true ground motion, a faster convergence to the best attainable approximation, a lower sensitivity to incoherent noise, and a more reliable discrimination between veracious and dubious results.     

Analysis of exceptionally large tremors in two gold mining districts of South Africa

An investigation of ground motion, recorded using broad-band, wide dynamic-range digital seismographs, of large mine tremors from two South African mining districts with different geologic settings, reveals some essential differences in both seismic source and ground motion parameters. In the Klerksdorp district where the strata are offset by major throughgoing normal faults, the largest tremors, with magnitudes ranging as high as 5.2, tend to be associated with slip on these pre-existing faults. Moreover, the seismic source and ground motion parameters are quite similar to those of natural crustal earthquakes. In the Carletonville district, by contrast, where substantial faults do not exist, the large-magnitude tremors appear to result from the failure of relatively intact rock and cause seismic stress drops and ground motion parameters higher than normally observed for natural shocks. Additionally, there appears to be an upper magnitude limit of about 4 in the Carletonville district. Detailed analyses of an exceptionally large event recorded locally from each of these districts serve to highlight these contrasts.Presented at the Fred Leighton Memorial Workshop on Mining Induced Seismicity, Montreal, Canada, August 30, 1987.     

用复曲线拟合方法确定DD-1和DK-1型电子放大地震仪的传递函数、频率特性和时间特性

地震仪的动力学特性通常是用频率域中的幅频特性和相频特性表示的,但是,合成地震图和由地震图恢复地面的真实运动都是在时间域中进行的,这就需要知道地震仪的时间特性（脉冲响应特性）。从理论上讲,可以由实测地震仪的幅频与相频特性通过快速傅里叶变换（FFT）用数值方法把时间特性计算出来,但是,计算结果表明,误差很大,尤其是在初动部分。因此,计算地震仪的时间特性应该从地震仪的传递函数出发,通过拉普拉斯反变换求得。 目前,我国基准地震台上使用三种类型地震仪:直接耦合地震仪、电流计记录地震仪和电子放大地震仪。前两种地震仪,它们的运动方程和传递函数已知,传递函数系数可以通过经典的分段标定方法求得。但是,对于电子放大地震仪,由于引入电子线路,首先必须确定电子线路部分的传递函数及其系数,然后再求出它们的频率特性和时间特性的解析表达式。 作者根据DD-1和DK-1型电子放大地震仪的分段标定结果,用复曲线拟合方法求出了它们的传递函数,并由传递函数导出了频率特性和时间特性的解析表达式,计算出了DD-1和DK-1型地震仪的幅频特性曲线、相频特性曲线和时间特性曲线。     

Orientation error estimation of buried seismographs in array observation

Array observation is an efficient tool to investigate various characteristics of earthquake ground motion. However, seismographs used in arrays may involve unexpected errors in their orientations. Methods of orientation error estimation were developed in three-dimensional space by comparing recorded ground motions at a reference point with those at a checking point. A maximum cross-correlation method and a maximum coherence method were proposed and their accuracy was demonstrated. The earthquake ground motions recorded in the Chiba array and in two other arrays were used in numerical examples. Non-trivial orientation errors were detected for all these arrays. The cross-correlation coefficients and the coherence values between two points increased significantly by correcting the estimated orientation errors.     

Estimation of Sedimentary Thickness in Kachchh Basin, Gujarat Using SP Converted Phase

An inexpensive method using natural earthquake data is utilized for determining the sedimentary thickness in Kachchh. The Institute of Seismological Research (ISR) is operating a network of broadband seismographs and strong motion accelerographs in Gujarat. We used data from 13 broadband seismographs and two strong motion accelerographs in the study. The stations are within 5 to 80?km from the epicenters. In this study the S-to-P converted phase, S_P, is used. This phase is generated due to large impedance contrast between sediments and basement. This phase is clear in the vertical component. The difference in the travel times of S and S_P phases and velocities of P and S waves is used for determining the sedimentary layer thickness. The thickness of sediments beneath each of these 15 stations was determined covering an area of 23,500?sq km.     

Analysis of the spatial variation of seismic waves and ground movements from smart-1 array data

Specially designed arrays of strong motion seismographs located near earthquake sources are required for engineering studies of the near-source properties and the spatial variation of seismic waves. The SMART-1 array in Taiwan provides good records for this type of study. Careful study of the observed strong motion data permits the identification of wave types, directions and apparent wave velocities. In this paper, a principal direction ratio R (f,α) is defined; this indicates the principal direction of the motion (along a nearly straight line) within the range 0 < R < 1. Vertical motion of the ground is also included in this study. Orbit spectrum analysis is used to verify the identification of wave directions and wave types. The spatial variation of seismic waves along the principal direction is studied. From frequency-domain analysis, mathematical models of the spatial variation of ground displacement are developed using a wave-number spectrum and the cross-spectral density function between two spatial coordinates; these models in turn can provide two alternative models for the random vibration analysis of extensive structures subject to multiple point seismic excitation. The SMART-1 array data gathered during the January 29, 1981 earthquake also are used to demonstrate calculation of the ground strains and differential movements of the array site. From time-domain analysis, the spatial variation of seismic waves is defined for ground motion along the identified principal direction. The time variation of evolutionary spectra characterized by frequency-dependent parameters is used for this formulation. The SMART-1 array data again form the basis for discussion of the spatial variation of model parameters.     

Some suggestions for the construction of a flat response seismograph

Summary A new circuit is suggested which allows the seismographs to afford a flat response to the ground displacement and to the ground velocity. The circuit is based on a rigorous integrator and it fits to any pendulum's damping.     

An approach to digitize analog form of accelerograms recorded at Tarbela—Pakistan

Pakistan has a long history of seismological activity. The devastation caused by Kashmir earthquake has been administered all over the world. In Pakistan first seismological network, consisting of analog accelerograms and seismographs, was setup in early 1969 at Tarbela, where the largest water reservoir of the country is located. An approach to convert analog ground motion records into digital form is explained using a simple technique. The digitized data was compared with the original analog record and found in good agreement. The data has been used to plot response spectra. The digitized data will be available for seismic response analysis of structures and seismic risk analysis of the region.     

Estimating the size of an earthquake using short-period seismograms of the first three seconds: A simulated experiment using the 1999 Chi-Chi earthquake sequence

Most of the present earthquake early warning systems are based on broadband or strong motion recordings. How-ever, the short-period instruments are still deployed. It is well-known that short-period recordings have saturation problems for large earthquakes when estimating the size of an earthquake. Thus, it is necessary to make clear the magnitude at which saturation starts to occur for the commonly used τc and Pd measurements, respectively. To investigate the possibility of using short-period seismic recordings for earthquake early warning, we conducted a simulated experiment using the strong motion data of the 1999 Chi-Chi earthquake sequence including its main shock and 31 aftershocks, with magnitude span from 4 to 7.6. The strong motion acceleration recordings were convolved with the instrument response of short-period seismographs in northern China to simulate short-period seismograms. Parameters τc and Pd from the first-three-second seismograms were calculated for the simulated short-period recordings and compared with that obtained by the original strong ground motion recordings. The result showed that to some extent, short-period recordings can be used for threshold earthquake early warning, while the magnitude saturation of Pd estimation can be up to 6.5, better than τc estimation.     

乌鲁木齐附近地区小爆破识别判据的研究

采用新疆乌鲁木齐地区多个地震台的位移仪及速度仪记录，探讨了人工小爆破记录与天然地震记录的差异及其识别判据。结果发现，爆破记录与地震记录在震相、P波垂直向初动符号分布、振幅衰减、振幅比As^-/Ap^-等方面具有不同的特征，据此我们制定出了识别爆破的单项判据和综合判据。     

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.     

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。     

Review on the study of topographic effect on seismic ground motion

Topographic effect study is a very important research topic in seismology, seismic engineering,earthquake engineering, engineering earthquake construction and engineering seismology. This paper focuses on its present development status. Post-earthquake investigation has found that the existence of topography caused more serious earthquake damage. The actual seismographs also recorded the topographic amplification effect of 6 to 7 times and even more than 10 times. Numerical simulation is an important technique to study topographic effect, which complements the lack of observed records. However researches on 3-D topographic effect are not enough and need to be studied deeper. To find the main influence factors and the quantitative relationship between topography and ground motion are required very urgently. Obviously the achievements not only can be applied in the earthquake resistant design, but also can provide the quantitative pre-earthquake disaster prediction and quantitative post-earthquake disaster evaluation.     

地震仪器的瞬态响应ht

本文主要讨论观测仪器的质量问题, 着重讨论影响初动的有关仪器部件和它们的参数.提出用升起时间ts作为评价仪器记录初至波质量好坏的特性参数.给出升起时间ts和仪器频带之间的关系.对我国地震台站上常用地震仪器的升起时间作了比较.      

Spatial variation and stochastic modelling of seismic differential ground movement

Specially designed arrays of strong motion seismographs located near earthquake sources are required for engineering studies of near-source earthquake properties as well as spatial variation of seismic waves. The SMART-1 array in Tath provides good records for this type of study. Based on the SMART-1 array data, the analysis of the principal direction wave propagation and the space-time correlation of some events recorded by SMART-1 have been studied. A stoce model for predicting the differential ground movement was also developed. This stochastic model includes the effect of source characteristics, attenuation of wave passage and spatial correlation characteristics. The performance of this more discussed and compared with the ground movement recorded by the SMART-1 array. From the present study, it is that spatial correlations do exist as seismic waves propagate across the array site. Generally, the loss of coherence is direction of propagation can be explained by energy at the same frequency exhibiting a slightly different velocity with the measurement intervals. It is also concluded that the phase velocity of seismic waves and the corner frequency of the grep displacement spectrum are controlling factors in the prediction of the root mean square of differential grep displacement.     

Ionospheric response to the entry and explosion of the South Ural superbolide

The South Ural meteoroid (February 15, 2013; near the city of Chelyabinsk) is undoubtedly the best documented meteoroid in history. Its passage through the atmosphere has been recorded on videos and photographs, visually by observers, with ground-based infrasound microphones and seismographs, and by satellites in orbit. In this work, the results are presented of an analysis of the transionospheric GPS sounding data collected in the vicinity of the South Ural meteoroid site, which show a weak ionospheric effect. The ionospheric disturbances are found to be asymmetric about the explosion epicenter. The received signals are compared, both in shape and amplitude, with the reported ionospheric effects of ground level explosions with radio diagnostics. It is shown that the confident registration of ionospheric effects as acoustic gravity waves (AGWs) by means of vertical sounding and GPS technologies for ground explosions in the range of 0.26–0.6 kt casts doubt on the existing TNT equivalent estimates (up to 500 kt) for the Chelyabinsk event. The absence of effects in the magnetic field and in the ionosphere far zone at distances of 1500–2000 km from the superbolide explosion epicenter also raises a question about the possibility of an overestimated TNT equivalent. An alternative explanation is to consider the superposition of a cylindrical ballistic wave (due to the hypersonic motion of the meteoroid) with spherical shock waves caused by the multiple time points of fragmentation (multiple explosions) of the superbolide as a resulting source of the AGW impact on ionospheric layers.     

Sensitivity of the Sharpe and Worden gravity meters to vertical motion

Summary Using the least-squares method the constants of both gravity meters — seismometers — were derived from the amplitude responses, observed under vertical motion on a vibrating table in the 0.3–30 s range. The values of the seismogram amplitudes, above which seismic waves cause an observable displacement of the gravity meter reading beam, were determined for the SKD and Press-Ewing station seismographs.     

P. G.-Seismographen und ihre Eichung

Zusammenfassung Es wird die Theorie der Pendel-Galvanometer-Seismographen (P. G.-Seismographen) ergänzt, eine neue Eicheinrichtung beschrieben und als Beispiel einHiller-Askania-Seismograph geeicht.

---

Summary A contribution to the theory of the galvanometric seismographs is given. Two new shaking tables are described and as an example aHiller-Askaniaseismograph is calibrated.

     

Seismic response evaluation of retrofitted Vincent Thomas bridge under spatially variable ground motions

In this study, a three dimensional finite element (FE) model of the Vincent Thomas bridge is developed using a widely used software. In order to show the appropriateness of the model, the eigenproperties of the bridge model are evaluated and compared with the results of system identification from ambient vibration and the 2008 Chino Hills earthquake response data. A new simulation technique is developed to generate spectrum-compatible spatial variable ground motions. The response of Vincent Thomas bridge under spatially varying ground motion is evaluated by nonlinear time history analysis. Using spatially variable motions, it is found out that the response in some locations on the bridge girder, may be under-predicted even if the motion with maximum intensity is uniformly applied at all supports.     

2017年6月3日内蒙古阿拉善左旗5.0级地震强震记录及特征分析

2017年6月3日内蒙古阿拉善左旗发生5.0级地震,位于甘肃天祝-古浪一带的"西部烈度衰减台阵"得到充分触发,甘肃强震动台网的50台强震仪获得了主震加速度记录。本文首先对150条强震动记录进行常规处理,计算出近场强震动记录的加速度峰值随震中距的分布情况;根据4个典型台站的加速度时程记录及其加速度反应谱,分析本次地震的基本特征;然后将实际观测数据与意大利新一代地震动衰减公式对比,分析峰值加速度（PGA）及谱加速度衰减关系;最后结合已有的工程场地地质资料,采用H/V谱比法对4个不同类别的典型台站进行分析,发现该方法能很好地反映实际台站场地的反应特征。