陆地地震勘探随机噪声统计特性

在地震勘探随机噪声压制领域,噪声通常被假设为平稳、高斯随机过程的信息.然而,在某些情况下,这样的假设并不准确.本文应用现代统计检验方法对地震勘探随机噪声的平稳性、高斯性和线性进行了研究.结果表明地震勘探随机噪声并不是传统意义上认为的平稳随机过程,其平稳性受到噪声时长和采集环境复杂程度的影响.发现噪声时间越长,采集环境越复杂,随机噪声的平稳性越差,但是对于短时长随机噪声而言,其可以近似认为是平稳的.同时,采集环境的复杂程度也影响着随机噪声的高斯性和线性特性,环境条件越复杂,随机噪声高斯性越好,线性特性越差,但总的来说随机噪声可以归为线性非高斯随机过程.

     

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。     

利用背景噪声进行地震成像的新方法

利用背景地震噪声提取格林函数，即通过一对台站记录的地震噪声进行互相关计算，来近似台站间的格林函数，并进一步通过地震成像获取地下结构的认识，成为最近跨学科研究的热点问题之一.本文首先叙述了其发展背景及过程，然后分别从四个角度，简要介绍了目前对其物理原理的解释.如果该方法能得到进一步的发展，将不再依赖于天然地震以及人工地震，而仅仅利用地震台站记录的地震噪声便可获取高分辨率的地下成像.该方法将会大大促进地震学的发展.     

Monitoring temporal variations in instrument responses in regional broadband seismic network using ambient seismic noise

High‐quality broadband data are required to promote the development of seismology research. Instrument response errors that affect data quality are often difficult to detect from visual waveform inspection alone. Here, we propose a method that uses ambient noise data in the period range of 5?25 s to monitor instrument performance and check data quality in situ. Amplitude information of coda waves and travel time of surface waves extracted from cross‐correlations of ambient noise are used to assess temporal variations in the sensitivity and poles–zeros of instrument responses. The method is based on an analysis of amplitude and phase index parameters calculated from pairwise cross‐correlations of three stations, which provides multiple references for reliable error estimates. Index parameters calculated daily during a two‐year observation period are evaluated to identify stations with instrument response errors in real time. During data processing, initial instrument responses are used in place of available instrument responses to simulate instrument response errors, which are then used to verify our results. The coda waves of noise cross‐correlations help mitigate the effects of a non‐isotropic field and make the amplitude measurements quite stable. Additionally, effects of instrument response errors that experience pole–zero variations on monitoring temporal variations in crustal properties appear statistically significant of velocity perturbation and larger than the standard deviation. Monitoring seismic instrument performance helps eliminate data pollution before analysis begins.     

反射法地震勘探噪声消除技术研究

噪声消除是地震勘探资料处理的基础,地震资料信噪比的高低将直接影响到后续处理的效果.因此,选取正确的噪声消除方法是整个资料处理的前提.本文从反射法地震勘探中噪声的特性出发,将常用的去噪方法分为四类,分析了它们的优点和局限性,并且对不同的处理方法进行了简单的比较,介绍了他们的应用领域.     

Fractal variations of the Transcarpathians,West Ukraine,seismicity and their potential relation to changing phases of local seismic cycles

The evolution of spatial arrangement of the Transcarpathian earthquakes is studied by means of fractal analysis. Spatial correlation dimension is evaluated for a subset of fixed number of catalogue events consecutively shifted in time by one event forward. Distinctive patterns that may be related to different phases of local seismic cycle/cycles have been identified, corresponding to extreme values of the dimension. Their potential relation to evolution of the seismogenic stress field is discussed. The time it takes for the capacity dimension to reach the so-called percolation threshold is estimated for a subset consecutively extended by adding next catalogue events. Temporal and spatial frames of percolation analysis are discussed in relation to parameters of the future earthquake.     

Site response obtained from array techniques applied to the seismic noise: Two examples in Italy

The vertical component of the seismic noise has been recorded in two different sites near the towns of Mercato S. Severino and Benevento in Southern Italy by a small aperture array, in order to investigate the characteristics of the noise propagation and to study the site response. Three different array techniques have been applied in the two investigated sites: Beam Forming, High Resolution and Spatial Correlation methods. We used two simple array geometry for localising possible noise sources and estimating local shallow structure using ambient noise. The cross shaped array results effective for determining the phase velocity of waves in the case when the noise is from a single localised source; the circular array, on the other hand, is successfully used when the noise sources are distributed. The main results are: the analysis of a coherent component of the noise recorded in the two sites, interpreted as Rayleigh waves, results in reasonable velocity models; the noise recorded in the M.S.S. Plain is a space stationary signal, while the noise at the Benevento site is possibly produced by a stable noise source located close to the array. Due to this evidence, the correlation method does not yield satisfactory results when applied to the Benevento site. The 2–6 Hz spectral peaks of the noise recorded in the M.S.S. Plain can be interpreted as due to a site effect, considering the satisfactory agreement of the noise spectrum at those frequencies with the theoretical transfer function computed on the basis of the velocity model deduced from the Rayleigh waves dispersion analysis.     

陷落柱地震波场特征分析

以典型的圆锥形陷落柱构建模型,采用声波方程对其地震波场响应进行模拟.分别从炮点位于陷落柱顶以及位于陷落柱顶一侧较近的两种情况对陷落柱地震波场特征进行细致分析.我们认识到了陷落柱柱壁绕射是陷落柱地震响应的重要特征.陷落柱的"反射--透射波"以及"透射--反射波"可成为识别陷落柱的重要标志.     

连云港地震台台基噪声与干扰源分析

通过对连云港地震台台基背景噪声进行计算和分析,得出该台台基背景噪声属于Ⅰ类噪声水平。分析该台6—7月观测数据,得出日夜噪声差值约3 dB。分析发现,该台人为干扰为基础建设的工程车干扰、景区人员聚集和车辆干扰;自然环境干扰主要来自大风干扰。     

Statistical analysis of background noise in seismic prospecting

From a conventional viewpoint, seismic‐prospecting background noise is usually regarded as the product of a stationary and Gaussian stochastic process. In this paper, we use statistical methods to investigate the properties of the land‐seismic‐prospecting background noise on stationarity, Gaussianity, power spectral density, and spatial correlation. We use and analyse the passive noise records collected by receiver arrays at different typical geological environments (desert, steppe, and mountainous regions). Differences exist in the statistical properties of the background noise from different geological environments, but we still find some common characteristics. It is shown that the background noise is not strictly stationary and has different stationary properties over different timescales. Most of the noise records appear to be a Gaussian process when examined over a period of about 20 s but are found to be non‐Gaussian when examined over shorter periods of about 1 s. The background noise is a kind of colored noise, and its energy mainly concentrates in the low‐frequency bands. We also find that the spatial correlation of the background noise is weak. The results of this paper provide a scientific understanding about the properties of seismic‐prospecting background noise.     

东南沿海地震带的地震丛集窗及震级结构特征分析

基于东南沿海地震带的地震活动特点和构造背景, 确定了若干个地震活动特别集中的区域, 并引入地震丛集窗和震级结构的概念分析这些区域的局部特点。结果表明, 这些地震丛集窗的地震活动水平变化反映了所属大区的应力状态, 当某个地震丛集窗发生震级结构异常, 具备前兆震群特征的地震密集事件时, 该地震丛集窗内或其相关部位的介质性状可能发生了变化, 这对以后可能对应发生中强地震或强震具有一定的中期预测效能。     

1996～2003年全世界灾害地震统计分析

讨论了1996～2003年8年期间全世界灾害地震的空间分布特征和地震灾情与全球地震活动性、地震震级和地震发震时刻的关系。结果表明：这8年期间地震灾情与全球地震活动性及地震震级无明显的统计相关关系,似乎与发震的国度、地震的发震时刻有一定的关系。     

福建数字地震台网对泉州地震的监测能力

1604年泉州海外大地震区的地震活动多，且震级大，破坏性强，为了完整记录地震波形资料、提供完备的地震活动目录，本文根据不同的仪器设备和台站的背景噪声值计算了福建省数字地震台网各个台站对该区地震记录的上限与下限。通过计算，发现16位数据采集器的台站震级上限偏小，而24位数据采集器的台站基本满足需要，并对此提出了对16位台站进行24位升级改造，进一步提高台网地震监测能力的建议。     

Periodic features of seismic activity in Albania

By statistica means, the temporal variation of the seismic activity in Albania is discussed in this study. We have investigated the seismic energy release for this century also using the periodogram technique to study the time series of the seismic energy release.A sequentially stationary model to evaluate the seismic rates for Albanian earthquakes with magnitudeM _s 6.0, is constructed, by using the least square method.The study of seismic energy release for Albanian earthquakes of this century and the time distribution of major earthquakes for the last two centuries supports the cyclicity of the seismic activity in a regional scale.     

黑龙江省地震科学台阵背景噪声特征分析

2019年黑龙江省完成"一带一路"地震科学台阵项目中台址勘选工作,基于科学台阵中136个台址的地面运动噪声数据,通过计算不同频段范围内背景噪声记录的加速度功率谱密度,研究不同环境噪声下科学台阵记录数据的地噪声特征及其台基响应。结果表明：黑龙江西北和东南部地区地面运动噪声水平低,观测环境较好;中部和东北部地区噪声水平较高,大庆地区尤为严重。勘选结果真实反映了黑龙江区域内的背景噪声分布,使我们对本区域地噪声水平和干扰因素有了新的认识。     

福建数字地震台网台址背景噪声分析

在使用福建区数字地震台网选台过程中,用１２个台址得到的背景噪声数字记录,计算分析了其背景噪声地动速度均方根值（ＲＭＳ）,有效测量动态范围、噪声功率谱及功率谱密度。所得结果可作为供评价仪器性能,台址安静程度的参考。对利用仪器所提供的动态范围,根据区域台网周围地震环境和台网记录地震的目的及任务设置适当的增益量程是也是有用的 。     

浙江临安地震台阵勘选测试与背景噪声水平分析

在大中城市周边建设地震台阵,可解决城市内地震监测台站建设不便和背景噪声高等问题,增强人口密集区的地震监测能力。杭州湾地区沉积层较厚,建设基岩地震台站不够现实,为适应长三角区域的一体化发展,增强该区地震和非天然地震的监测能力,在浙江临安建设地震台阵。使用GL-PS60一体化宽频带地震计进行测点勘选工作,利用Welch平均周期法,对9个子台进行背景噪声功率谱估计。结果发现,背景噪声功率谱相关性较好,且与全球噪声模型一致性较好。在台阵勘选过程中,于2017年4月12日和13日分别记录到临安4.2级地震及菲律宾远震事件,波形清晰,表明初选台址效果较好,符合地震台阵建设要求。     

脉冲编码震源的匹配冲击技术

常规Vibroseis可控震源Chirp扫描的地震响应存在明显的旁瓣效应,二元m-序列伪随机扫描的解码地震剖面中存在严重的相关噪声,而基于伪随机编码的匹配扫描方法可有效压制解码地震剖面中的相关噪声,提高了地震记录的信噪比.为了将匹配伪随机编码方法应用到冲击式震源中,提出了基于脉冲编码震源的匹配冲击技术.以匹配扫描方法为理论基础给出了匹配冲击信号的编码与解码过程,以有限元差分法对匹配冲击技术和常规线性扫描冲击技术进行了地震数值模拟.结果表明,匹配冲击的综合解码地震剖面中,不存在线性扫描冲击解码地震剖面中能量较强的相关噪声干扰,剖面具有很高的信噪比和分辨率.地震波激发采集对比实验验证了匹配冲击技术在压制相关噪声及远偏移距地震道随机噪声方面相比线性扫描冲击技术所具有的优势.     

西北太平洋海岛地区地震背景噪声特征及海洋学解释

台风是全球最具破坏力的气象灾害之一,由于台风过境时现场海洋观测资料相对匮乏,与目前对台风的监测、预报和防灾减灾的迫切需求尚不相匹配。近年来,利用地震学观测资料与技术手段,通过台风激发的地震背景噪声,对台风进行监测的新方法逐渐兴起。本文对近年来有关台风激发地震背景噪声机理、源区分布以及基于地震背景噪声的台风定位追踪、海浪参数反演等研究进展进行综述,分析已取得的研究成果及可能存在的问题,讨论并展望基于地震学的台风监测研究思路与热点。基于地震学的台风监测有望为传统台风观测与研究提供跨学科的观测资料与技术支持。     

基于浅层反射地震勘探技术的大庆地区近地表构造特征研究

目前,对于大庆地区的地质构造研究成果仅局限在深部构造上,该地区从未开展过针对近地表隐伏断裂的探查工作.本文采用浅层反射地震勘探方法,查明了克山—大安断裂嫩江组以上地层的详细地层信息以及断裂的展布形态;同时,在主干断裂上覆的背斜构造中,发现了许多次级断裂,这些次级断裂在前人的成果中并未提出过,并且在本区的断裂-褶皱构造体系中,次级断裂的活动特性同样受主干断裂活动的影响;然后通过钻孔验证,证实了浅层反射地震勘探结果的可靠性,并且确定了次级断裂的最新活动时代;最后综合编制了松辽盆地长垣隆起地区浅层地质模型,并讨论了本地区的构造体系受晚白垩纪以来太平洋板块俯冲方向变化的影响而形成的构造特征.本次研究中的方法和成果可为大庆市城市发展规划、重大工程建设选址和大庆油田安全高效生产等提供科学依据,可为其他地区开展近地表断裂探查提供借鉴和参考,为本地区浅层地质构造后续研究提供了基础资料,填补该地区近地表地球物理勘探构造研究的空白.