Comparison of point and array-computed rotations for the TAIGER explosions of 4 March 2008

Two large explosions were recorded by a dense array of strong-motion accelerometers and rotational seismometers in northeastern Taiwan associated with a Taiwan Integrated Geodynamics Research long-range refraction experiment. The objective of this experiment was to test the response of the experimental eentec rotational seismometers against calculated array rotations. Computed array rotation rates are seen to have little variation across the array, but point rotation rate measurements obtained from individual rotational seismometers show significant deviations with each other and with the array rotation rates in the ranges of 3?C5?Hz and, especially, 3?C50?Hz. A cross-correlation method was used to compare array-computed rotation rates and point rotation rate measurements in the frequency band of 3?C5?Hz with the result that the absolute value of the normalized maximum correlation coefficient for each station set varied from 0.45 to 0.97 with an average of 0.84. Amplitude differences of the point rotation rate measurements are seen to be factors of 0.2 to 1.8 times the array rotations as well. It is not likely that the differences seen in the point and array-computed rotation rates are due to nonlinear or heterogeneous site conditions under each array element since these effects should also be seen in the acceleration data used to determine rotation rate. A rigorous method for accurately calibrating rotation rate instruments is needed to understand their response in the field.     

地震科学探测台阵无线监控技术

地震科学探测台阵是开展地震学综合研究的大型野外观测系统,可根据观测目的布置在一定区域内进行连续观测。其特点是数量大、分布广,台站工作状况易受外部环境的影响。实际工作中迫切需要掌握流动地震仪的工作状态,而人工巡台工作量大,时效性不能保证。流动地震仪器工作状态的监控对于野外流动观测具有重要意义。我们采用虚拟网络（VPN）技术,通过无线（CDMA／GPRS）通讯方式组成局域网,实现了科学探测台阵总控中心一流动监控中心一观测仪器间的实时通讯,可方便、快速地对大量流动观测台进行实时监控和数据传输,显著提高了远程仪器维护的工作效率,便于提高观测质量。     

正弦标定自动处理算法研究

由于种种原因, 地震计的周期、 阻尼、 灵敏度等参数在仪器运行的过程中会发生变化, 这些参数的变化直接影响到地震计的性能和观测数据的质量。 为了掌握地震计参数的变化, 通常采用定期标定的方法, 对运行中仪器的参数进行跟踪监测, 通过分析标定数据得到仪器的运行状态。 目前, 对于标定数据的处理通常采用人工分析的办法。 随着台站数量的增加, 对标定数据的处理工作变得日益繁重。 该文介绍一种正弦标定自动处理算法, 利用这种算法编写的自动处理程序, 在标定数据处理过程中不需要人工干预, 计算机可以自动提取有效的波形数据进行测量计算, 并可以对效果不好的数据进行修复, 最终给出仪器的频率响应特性。     

Intrinsic noise of seismometers at frequencies from 0.01 to 0.1 Hz

The paper presents a comparative analysis of the intrinsic noises of seismometers operating at Kamchatka seismic stations: CMG-3TB (GURALP), CMG-5TD (GURALP), CMG-6TD (GURALP), GMS-AC-73i HHV (GeoSIG), SM3os (GEOTECH+), S5Sos (KF GS), and SM3kv. It is shown that the dynamic range of the seismometers is narrower at low frequencies in the area of weak signals.     

Spin and twist motions in the earthquake preparation processes: Analysis of records

Three seismic events in L’Aquila region and one in western Greece have been chosen for comparative analysis of two kinds of seismic motions, spin and twist. These torque components of the seismic field were detected in horizontal plane with the rotational seismometers. Homologous parts were sought in the signals of spin and twist components — curve of one component was compared to the other directly and after transformations: phase-shifting and sign reversal. To achieve better clarity, these operations were done on the data divided into several descendant signals with the use of band-pass filtration. Conformities of spin and twist, revealed in this way, are assumed to be results of distant processes in the source, where relations between rotational and shear motions include retardations.     

井下地震计的P波接收函数正演计算及其稳定性研究——以首都圈地区为例

井下地震计波形记录的P波垂向分量存在频谱极小（spectrum null）现象,导致接收函数的结果不稳定.本文以首都圈地区为例,基于平面波入射的传播矩阵理论,发展了用于计算井下地震计的接收函数正演方法.在此基础上,分析了井下地震计波形垂向分量频谱极小现象,研究其对接收函数稳定性的影响.结果表明,井下地震计波形记录垂向分量的频谱极小开始出现的频率和地震计的埋深相关.该现象可造成反卷积提取的接收函数不稳定,且不稳定情况出现在频谱极小附近的频段,可通过选择合适的高斯因子压制其对接收函数的影响.     

地震勘探組合法对传播方向随机改变干扰的压制作用

地震勘探組合法中,采用很小的組內检波器間距离吋,組合法仅只起提高接收仪器灵敏度的作用;检波器間距較大情况下,微震干扰可以看作相互独立的随机干扰来研究;但在間距不太大但也不能认为等于零时,組合方法的效果却是个尚待討論的問題。本文假定微震是由传播方向随机改变的平面波形成的,用概率論方法討論了組合地震法对徽震干扰的压制效果。     

Some sources of plasma inhomogeneities in the solar wind in front of the Earth’s magnetosphere

The origination of various plasma inhomogeneities in the magnetosheath in front of the Earth’s magnetosphere is analyzed within classical magnetohydrodynamics. The effect of directional discontinuities or tangential and rotational discontinuities of the solar wind on plasma is studied. The origination of inhomogeneities of the type of secondary MHD waves in the magnetosheath is shown; the former equalize plasma parameters when restoring the stationary state. The effect of a rotational discontinuity on the bow shock–Earth’s magnetosphere system is of special interest, with distinguishing of plasma inhomogeneities of the plateau type observed in the near-Earth space.     

台阵地震计程控化正弦标定系统设计

为满足台阵地震计标定要求,通过对程控化标定测控仪和标定测控软件的研究,采用一种适用于台阵地震计的程控化正弦标定方法,对中国地震局地球物理勘探中心负责管理的台阵地震计进行标定。台阵地震计标定实验结果显示,采用程控化正弦标定方法,在缩短标定时长、提高标定效率方面具有显著效果。     

安徽六安井下地震计与地表地震计观测质量对比

将安徽六安2015年安装的2台GL-S60B井下地震计记录数据,分别与在各自井口架设的BBVS-60地表地震计记录数据进行对比,得到了噪声有效值、频谱特征和有效动态范围等,初步获得了井下地震计在六安的运行情况。研究表明,井下地震计观测效果明显优于地面地震计,这对于未来地震台站选址、仪器选型等具有参考意义。     

Application of the optical angular rate sensors for rotational measurements in seismology

The development of large ring lasers made it possible for accurate detection of rotational seismic waves over a wide range of amplitudes and frequencies. Due to their insensitivity to translational motion the optical angular rate sensors are very attractive for application in seismology, geodesy, and even fundamental physics. However, the operation of the large ring lasers in the near-field is difficult due to their mass, size and, environmental requirements. Hence, the fiber-optic gyros may be used for seismic applications, where the mobility is more important and where the high rotation rates are expected. This kind of sensors also can be used for correction of standard seismometers subjected to tilt. In this paper we present the current state of experimental research dedicated to application of fiber-optic gyros for seismology. The test results demonstrate that the tactical grade optical sensors are capable of successfully measuring small rotation fluctuations down to 10^?5 rad/s. However, the seismometer correction seems only feasible in the range of rotation rates about 10^?3 rad/s and higher. This limitation is caused by the excessive noise in the output of the fiber-optic gyro. The possible measures to overcome this problem are discussed as well as advantages of optical gyros for strong motion seismology.     

宽频带流动地震台站中地震计浅井式安装研究

在井下地震观测中,各种地表背景噪声具有显著衰减作用,针对中国地震科学台阵现有大量非专用浅井式设计的Guralp CMG系列地震计,以及目前多个新获批项目在高背景噪声区域的观测需求,设计一种野外实用浅井观测方式,在北京国家地球观象台进行不同深度、不同井壁材质的观测对比实验,分析研究观测数据的背景噪声功率谱密度,结果表明,随着浅井深度的增加,地震背景噪声在垂直、水平向得到改善,改善程度随频率变化有所不同。分析认为,在华北现有地质环境下,6 m浅井是较为经济的观测方式,性价比高、占地小、施工简便,可用于后续多个项目的宽频带流动地震台阵观测。     

地震计自噪声的研究

仪器的固有噪声水平是地震计的关键技术指标。 如何降低仪器的自噪声是地震计设计中需要解决的重要问题。 本文分析了产生地震计自噪声的两个主要噪声源: 布朗热噪声和电子噪声(1/f噪声), 以及它们对地震计传递函数的影响。 分析了三种地震计所记录的地震台台基噪声, 并且通过试验来检验仪器噪声对地震计观测数据的影响。     

Integral equations in MHD: theory and application

The induction equation of magnetohydrodynamics (MHD) is mathematically equivalent to a system of integral equations for the magnetic field in the bulk of the fluid and for the electric potential at its boundary. We summarize the recent developments concerning the numerical implementation of this scheme and its applications to various forward and inverse problems in dynamo theory and applied MHD.     

Investigation of array-derived rotation in TAIPEI 101

We investigate rotational motions derived from measurements by arrays of translational seismometers??hereafter called array-derived rotations (ADRs)??and compare these to measurements made by a commercially available point rotation sensor (eentec? R-1?). We focus on two aspects of the array problem: (1) the requisite conditions for calculating an ADR well and (2) the effect of array configuration on the result. Our data set consists of translational accelerations and rotation rates recorded by an array of Kinemetrics? EpiSensor? accelerometers and two R-1? rotational sensors in the TAIPEI 101 building in Taipei, Taiwan. Our results indicate that (1) array configuration affects the accuracy of ADRs about orthogonal components in horizontal plane, (2) coherence between two point rotation measurements (two R-1?) can determine the maximum frequency of translations viably used for the calculating ADRs, and (3) the performance of the R-1? is adequate, at least above a frequency of 0.12?Hz (periods shorter than 8?s). We also discuss deriving strain from the same array.     

江苏省测震台网井下地震计方位角检测

为获取江苏省测震台网井下地震计精确方位角,架设地面参考地震计,将其精确指北,并与井下地震计检测结果进行对比,利用相关分析法计算22个深井台站精度较高的方位角。研究结果表明,受多因素制约,井下地震计检测结果普遍偏差较大,部分台站水平向分量几乎反向,如提井,需重新进行方位角检测;地面与井下地震计同频带有利于提高相关性,从而获取高精度检测结果;利用不同频带地震计进行井下地震计方位角检测时,对较宽频带地震计进行仿真处理尤为重要;溧阳2台站新建井下地震计检测结果表明相关分析法可应用于井下地震计方位角检测;尽可能选择台基噪声功率谱密度曲线具有明显波峰频段作为滤波频段,有利于提高地面与井下地震计观测数据相关性,提高方位角检测精度。     

Comparative analysis of the characteristics of domestic and foreign broadband seismometers with capacitive transducers

A family of seismometers has been developed with capacitive transducers that convert the relative displacement between the inertial mass and the base of the device into an electric signal. The seismometers have high sensitivity and a unified electronic circuit, and they can be rather easily manufactured, installed, and calibrated. Mass production of these instruments looks promising. To assess the possibility of using these seismometers as substitutes for imported counterparts, a comparative analysis was carried out to study the performance of an SM-3E broadband sensor with a capacitive transducer and imported STS-2 and CMG-6T seismometers. Seismic recordings of these three instruments mounted on the same pedestal were statically analyzed in the time and frequency domains.     

The digital seismometer, a modern instrument

On the basis of an analysis of the development history of seismometers, the conclusion is made that a new generation of instruments—digital seismometers—should be created. The functions of a digital seismometer and its advantages over other existing instruments are described in brief.     

用相关分析法检测两种地震计性能及记录数据差异

阐明利用同点记录数据相关性检测两种地震计性能及记录数据差异的方法,并用两台经过测试且性能相同的FBS - 3B型地震计进行验证,最后用该方法检测了STS -2、KS - 2000型地震计的高频段性能及记录数据差异.     

连云港地震台BBVS-120、CTS-1E型地震计系统性能对比

通过对连云港地震台BBVS-120、CTS-1E型地震计台基噪声功率谱分析,正弦标定和脉冲标定计算分析,近震和远震震级对比分析,研究在实际工作中2种地震计性能差异,对比观测数据质量,检验稳定性,以期为地震监测及相关研究工作提供依据。