Multiparameter monitoring of electromagnetic earthquake precursors in the frequency range 0.1 Hz-1 MHz

An approach to monitoring of electromagnetic earthquake precursors including variations of the apparent resistivity, electrotelluric fields, electromagnetic emission, and ionospheric disturbances perspective for short-term and mid-term earthquake prediction is considered. Parameters of hardware-software systems for audio- and radiomagnetotelluric soundings used in the monitoring of these precursors in a wide range of frequencies from 0.1 Hz to 1 MHz are described. The technique for the stress-strain sensitive area selection for the creation of monitoring networks based on the analysis of geological and geophysical characteristics of seismo active regions, study of geoelectric structures of preselected sites, and monitoring test sessions with the assessment of the response on tidal media deformations is presented. Recommendations on the recording technique of earthquake electromagnetic precursors are provided.     

强干扰环境下有效数字地震信号的提取

城市扩张和人类活动所带来的环境干扰已经越来越严重地影响到地震监测,给地震参数的确定和其他地球物理研究造成不确定性。本研究以处于高环境噪声的防灾地震台记录的2008年5月12日汶川地震波形资料为例,给出如何采用数字信号处理手段从强干扰环境下提取到地震波有效信号,并按方位角和出射角方向对地震信号各分向信号进行了分解与组合,最后归纳出提取有效信号的一般过程。     

Earthquake precursory research in western Himalaya based on the multi-parametric geophysical observatory data

The opening of cracks and influx of fluids in the dilatancy zone of impending earthquake is expected to induce short-term changes in physical/chemical/hydrological properties during earthquake build-up cycle, which should be reflected in time-varying geophysical fields. With this rationale, eleven geophysical parameters are being recorded in continuous mode at the Multi-Parametric Geophysical Observatory (MPGO), in Ghuttu, Garhwal Himalaya, for earthquake precursory research. The critical analysis of various geophysical time series indicates anomalous behavior at few occasions; however, the data is also influenced by many external forces. These external influences are the major deterrent for the isolation of precursory signals. The recent work is focused on the data adoptive techniques to estimate and eliminate effects of solar-terrestrial and hydrological/environmental factors for delimiting the data to identify short-term precursors. Although any significant earthquake is not reported close to the observatory, some weak precursory signals and coseismic changes have been identified in few parameters related to the occurrence of moderate and strong earthquakes.     

Earthquake prediction in northeast India—A review

A multidimensional geophysical approach is made to study earthquake precursors in northeast India. Resistivity, gravity and seismological precursor anomalies for the two recent damaging earthquakes, one on December 30, 1984, magnitude 5.8, and the other on August 6, 1988, magnitude 7.5, are very encouraging to intensify these studies in the region. Improved methods of magnetic and geohydrological precursor studies are suggested.     

Search for anomalous effects in geophysical fields in relation to earthquakes in the Baikal rift zone

The paper presents data of electrical conductivity monitoring for the upper crust obtained with the use of a controllable electromagnetic source by the dipole, vertical electromagnetic, and transient electromagnetic sounding methods, as well as variations in the geomagnetic field and the Lake Baikal water level. With the help of spectral, spectral time, and multivariate analyses, main spatial and temporal patterns of variations in geophysical parameters are determined. The present study revealed anomalous effects in the behavior of the canonical coherence (parameter K) and aggregated signal (parameter A) and other anomalous variations in geophysical parameters related to earthquakes in the Baikal rift zone.     

Microseismic noise in the low frequency range (Periods of 1–300 min): Properties and possible prognostic features

The paper generalizes the experience accumulated in studies of microseismic noise in the period range from 1 to 300 min observed during time intervals preceding a few strong earthquakes. This frequency range is the least studied and occupies an intermediate position between low frequency seismology and investigations of slow geophysical processes. The range includes oscillations induced by atmospheric and oceanic processes and various modes of the Earth’s free oscillations excited by very strong earthquakes. The main attention in the paper is given to the background behavior of microseisms, which contains continuous present arrivals from near weak and far strong and moderate earthquakes. The paper focuses on the examination of synchronization effects arising in joint multivariate analysis of information from several stations with estimation of multifractal spectra of singularity and multidimensional spectral measures of coherent behavior of singularity spectral parameters. The problem of using the synchronization effects of microseismic background in the search for new precursors of strong earthquakes is discussed.     

Revisiting the Phasor-Walkout method for detailed investigation of harmonic signals in time series

A well-known but rarely used powerful method to investigate the presence of harmonic signals in time series is the Phasor Walkout method (other names are: Graphical Fourier Transform, Summation Dial, Complex Demodulation). At a given test frequency the complex contributions (phasors) to the Fourier Transform of each sample in an equidistantly sampled series are added vectorially in the complex plane. The resulting pattern, the walkout, reveals information about the properties of the signal which is not easy to obtain by other methods. Synthetic examples are used to demonstrate the resolving power of the method. The following geophysical examples for the application of this method are shown: determination of the frequency of the breathing mode₀ S ₀ of the earth after a large earthquake; the study of superconducting gravimeter records after a large deep earthquake used in the core mode interpretation of a spectral peak, the study of the residualS ₃ (8 h period) signal in a tidal record and the bichromatic Rayleigh-waves from Mount Pinatubo on June 15, 1991.     

Synchronization signals in the variations of groundwater chemical composition in Kamchatka in relation to the strong (M W ≥ 6.6) earthquakes

We consider the results of the statistical analysis using the methods of the principal components and canonical coherences applied to the processing of long (1986–2005) time series of hydrogeochemical observations at the flowing wells and springs in Kamchatka. The time-frequency diagrams of the evolution of informative statistics characterizing the collective behavior of multidimensional hydrogeochemical time series are constructed, and the time intervals and frequency bands where the synchronization signals (Lyubushin, 2007) appear are identified. The features of their occurrence are analyzed in comparison to the strong (M _w = 6.6?7.8) local earthquakes. It is found that such signals in the measurements of some multidimensional time series can arise both before and after earthquakes, i.e. these signals have a precursory (P2) and postseismic (P3) character.     

2021年11月17日江苏大丰海域MS 5.0地震总结

2021年11月17日江苏大丰海域M_S 5.0地震发生在中强地震活动较为集中的黄海南部凹陷区,位于苏北—滨海断裂带附近,震源机制结果显示为走滑型破裂。截至2022年1月31日,发生M_L≥2.0余震14次,最大余震为2021年12月8日M_S 3.8地震,主震释放能量占比约98.89%,判断地震序列应为主余型序列。主震发生3天后地震序列迅速衰减,因余震数量偏少,无法得到合理的序列参数。本次地震视应力值约1.3 MPa,基本处于研究区域正常背景水平。鉴于鲁东—黄海地块历史地震期幕活动特征,认为江苏及近海区域近期发生6级以上地震的可能性不大。系统梳理此次大丰海域M_S 5.0地震前出现的地震活动和地球物理观测异常,可知：①地震活动：震前存在地震平静、霍山地震窗、长岛地震窗和地震空区等趋势异常;②地球物理观测：震前存在兴化水温异常。综合分析认为,此次地震发生前,地震活动异常相对较少,并以趋势异常为主,地球物理观测异常相对偏少,震前出现的流体短期异常现象可作为短期判定的参考依据。     

利用独立成分分析检测2004年和2012年印度洋地震的重力变化

2004年12月苏门答腊发生M_W9.3地震,造成巨大的质量重新分布.利用GRACE卫星月重力场数据计算了研究区域地面1°×1°网格点上的重力变化时间序列,采用主成分分析和独立成分分析两种方法,提取了重力变化的空间与时间特征,结果显示震中两侧区域的重力变化呈两极分布,其中东侧重力下降,西侧重力增加.相较于传统的主成分分析方法,独立成分分析能更好地从原始信号中提取地震的信息,能分解出具有显著阶跃变化的独立成分.除了2004年的苏门答腊大地震外,独立成分分析还分解得到了2012年Andaman地震的特征,与该次地震的空间特征与时间序列基本一致.相较于适合定量分析的多项式拟合方法,独立成分分析更适合大范围区域的定性分析,建议将两种方法相结合,取长补短,从而为GRACE地震监测提供一种更为客观、有效的方法.     

Power spectral characteristics of drought indices in the Ebro river basin at different temporal scales

A deep spectral investigation of the monthly time series of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) in 45 meteorological stations in the Ebro basin (Spain) from 1950 to 2006 for timescales ranging from 1 to 48 months was performed. In order to summarize the results for the whole basin, the spectral analysis was also carried out on the four principal components of SPI and SPEI. Results confirm that SPI and SPEI presents very similar spectral characteristics. At the shorter time scales, the signal of SPI and SPEI is characterized by purely random temporal fluctuations. The longer time scales tend to feature the signal as a smoothly varying time series or persistent, mostly due to the aggregated nature of the indices calculation. The comparative analysis of the spectral properties of the drought indices for all the 45 sites in the Ebro basin lead to the identification of global or regional effects discriminated by local effects. It was found that some periodical signals are common to almost all the sites, while others where only identified in specific meteorological stations.     

求解反应谱的小波方法及汶川地震反应谱分析

采用四阶基数B-样条小波模拟地震动加速度时程,进而建立一种求地震反应的通用方法,解的误差仅来自于对地震动加速度时程的模拟。并用小波分解,将地震波分解为不同周期成分之和,以各分量最大加速度值的大小来衡量其在原波中的比重,可以清楚看到距震中不同远近地震波的性态,并做定量分析和观察各分量卓越周期的变化。求地震波及各分量的反应谱,从各分量的标准加速度反应谱中,可以看到地震波不同周期分量对体系固有周期的影响,这是以往做不到的。将上述方法应用于汶川8.0级地震加速度记录,研究不同地震记录的性态。     

地球物理信号处理的进展和今后方向

本文简要叙述了近年来我国地球物理信号处理的进展和国际动态.其中包括:强干扰背景下微弱地球物理信号的提取;非稳态地震前兆信息的处理;现代谱估计的进展;瞬态谱理论在地球物理资料处理中的应用;畸变信号恢复的研究以及其它有关信号处理的研究.     

福建省数字化形变资料的异常分析

为了提取中短期地震前兆信息,对福建省2006～2008年数字化形变观测整点值资料进行了二进小波多分辨率分析,结果表明：小波分析结果的细节部分dn主要包含周期为2n-2a＋1小时的信号,而近似部分‰包含所有周期大于2n＋1小时的信号;在此期间,福建省及其邻近地区的中强地震发生前,多数形变观测台站或测项同步接收到了周期大约为21～43d幅度较大的异常信号,这些信号可能是地震前兆。     

利用EMD和子波振幅谱与相位谱关系的时变子波提取方法

本文首先分析了地震波在黏弹介质的传播规律,基于黏弹介质地震波动方程总结了时变子波振幅谱和相位谱的关系,从而得出结论,准确估计子波相位谱初值和不同时刻的子波振幅谱是实现时变子波准确提取的必要条件.在此基础上,针对传统方法限制子波振幅谱形态且受限于分段平稳假设的问题,提出了一种利用EMD(Empirical Mode Decomposition)和子波振幅谱与相位谱关系的时变子波提取方法,根据子波对数振幅谱光滑连续而反射系数对数振幅谱振荡剧烈的特点,采用EMD方法将不同时刻地震记录的对数振幅谱分解为一组具有不同振荡尺度的模态分量,通过滤除振荡剧烈分量、重构光滑连续分量提取时变子波振幅谱;再应用子波振幅谱和相位谱的关系提取时变子波相位谱,将分别提取的振幅谱和相位谱逐点进行合成,最终实现时变子波的准确提取.本文方法不需要求取Q值,适用于变Q值的情况,具有良好的抗噪性能.数值仿真和叠后实际资料处理结果表明,相比传统的分段提取方法,利用本文方法提取的时变子波准确度更高,研究成果对提高地震资料分辨率具有重要意义.     

利用小波包分析进行地震相关热红外辐射异常信息检测

研究表明很多地震前后存在明显的热红外辐射异常.影响地物热红外辐射信息的因素很多,而地震相关的热红外辐射异常是强干扰背景下的弱信息,难以简单地将其提取出来.本文将地震相关的热红外辐射异常作为一种事件性的信号分析,通过小波包分析将热红外辐射信息的时间序列分解成不同频带的信号,通过分析各频带信号能量的变化规律进行事件性信号检测.2005年11月26日九江地震、2006年4月21日堪察加地震和1998年8月27日伽师地震的研究结果表明,小波包分析能有效检测这种事件性信号,同时显示这种事件性信号与地震活动之间关系的机理和时空演化特征是进一步研究的重点.     

地磁前兆异常的动态从属函数

地震前兆涉及到多种地球物理观测方法,且计量单位各不相同,因此,各类前兆异常之间无法进行直接的定量对比,这给地震预报研究带来了困难.应用异常从属函数值（无量纲量）可统一规划不同性质、不同计量单位的地震前兆异常.本文通过研究地磁资料从属函数,发现1995年9月20日山东苍山Ms5.2级地震前有明显的前兆异常.增强了对地震前兆异常的识别能力,文中提出该方法在地磁场研究中应注意的问题.     

储层流体识别的新方法

利用小波变换方法可以把原始信号分解为一系列载有不同信息的子信号,每种子信号载有储层的特定信息,包括流体、岩性和孔隙结构等。我们开发出了基于小波变换的谱分析方法,利用该方法可以从这些子信号中提取出反映地层流体特性的子信号,通过对该子信号的处理识别出地层所含流体的特性。本文利用该流体识别新方法对某油田的实际测井资料进行了处理,处理结果与试油结果符合得很好,进一步证明了本方法的可靠性和实用性。     

Geophysical Applications of Multidimensional Filtering with Wavelets

--We present imaging results in geophysics based on using multidimensional Gaussian wavelets as a filter in a 2-D Cartesian domain. Besides decomposing the field into various distinct lengthscales, we have also constructed the 2-D maps describing the spatial distributions of the maximum of the wavelet-transformed L₂-norm E_max (x,y) and its corresponding local wavenumber k_max (x,y), where x and y are the Cartesian coordinates. For geoid anomalies, using a wavelet filter extending to 90 degrees, we have discerned the distinct outlines of convergent and divergent tectonic zones and have conducted a quantitative comparison of the short-wavelength gravitational anomalies at those wavelengths between two different geographical locations. We have also compared the wavelet results with a nonlinear bandpass filter in the spectral domain where a Gaussian filter with the logarithm of the degree l acting as the argument has been employed. A wavelet solution, with a length-scale corresponding to 256 degrees, would need a filter with over 400 spherical harmonics centering around l=157 for an optimal spatial fit. The computational effort with the bandpass filter technique greatly exceeds those associated with wavelets. We have also shown the ability of the wavelets to analyze the vastly different scales present in high Rayleigh number convection and the mixing of passive heterogeneities driven by thermal convection. Wavelets will be a useful tool for rapid analyzing of the large multidimensional fields to be captured in many other geophysical endeavors, such as the upcoming gravity satellite missions and satellite radar interferometry images.     

MT时间序列的小波去噪分析

从本质上说 ,MT时间序列中噪声的强度与类型是能否取得MT响应参数无偏估计的决定性因素。当MT时间序列中磁场和电场中都含有相关噪声时 ,传统的去噪方法已无能为力。结合小波分析与MT时间序列的特征 ,提出了一种基于小波分析的MT时间序列去噪方法 ,讨论了基于小波分析的噪声识别 ,分析了理论数据通过小波分解与重构实现的去噪处理 ,探讨了对实测时间序列的固定源和随机干扰的去噪处理