台阵地震学方法及对间断面结构的研究进展

地震台阵是为了监测核爆而发展起来的一种地震观测系统。近年来,地震台阵被推广到地球内部速度间断面的研究中并极大地推动了地震学的发展。本文主要介绍处理台阵资料的技术方法,如聚束、倾斜叠加、N次根叠加、频率波数法以及相位加权叠加等,并讨论各种方法的优缺点。在提取微弱但相关信号方面,重点讨论相位加权叠加方法及现有的研究成果。结果表明,这些方法都在不同程度上提高了记录的信噪比,高质量的台阵数据使得地球内部速度结构的成像研究更加精细。     

Remarks on Urban Active Fault Exploration and Assessment of Fault Activity

to the practice of urban active fault exploration and associated fault activity assessment conducted in recent years, this paper summarizes the problems encountered in geological, geomorphological, geochemical and geophysical surveys, and proposes the following means and suggestions to solve these problems. To determine the most recent faults or fault zones, emphasis should be placed on identifying the youngest active faults and offset geomorphology. To understand the history of faulting and to discover the latest offset event, it is suggested that geophysical prospecting, drilling and trenching be conducted on one pro/de. Because of significant uncertainties in late Quaternary dating, we advise systematic sampling and the use of multiple dating methods. Shallow seismic reflection has been proven to be the most useful method in urban active fault exploration. However, there is a pressing need to increase the quality of data acquisition and processing to obtain high resolution images so as to enhance our ability to identify active faults. The combination of seismic P-wave reflection and S-wave reflection methods is proved to be a powerful means to investigate the tectonic environments of the deep crust.     

Crustal-scale prestack depth imaging of the 1994 and 1999 LARSE surveys

While seismic imaging for crustal and mantle structures has traditionally relied on surface wave and refraction data, the use of reflection data for crustal-scale targets has been largely limited to the common midpoint (CMP) stack techniques. The rapid increase in the number of seismograph array deployments in recent years in crustal and mantle seismology has reached a level such that a re-examination of the imaging techniques is becoming necessary. In this paper we show the advantage of prestack depth imaging for crustal reflection studies, based on data from two reflection surveys of the Los Angeles Regional Seismic Experiment (LARSE) to map faults and crustal-scale structures. Our analysis indicates that the quality of the previous images of these surveys is limited by the CMP stack technique. For comparison, we present here depth images of the same LARSE data using wave equation prestack depth imaging and a tomographic velocity model based on first arrivals of the LARSE surveys and local earthquakes. Our new images are considerably improved over previous images in terms of resolution and reflector continuity. The new images show reflectors throughout the crust and suggest truncations in the Moho associated with the San Andreas Fault. A series of bright reflector segments, which are associated with the San Gabriel and San Andreas faults have been identified and might represent reflections from the fault zones. Our results suggest that the presence of high noise level, strong lateral velocity heterogeneity and wide angle geometry argue for, rather than against, the use of prestack depth imaging over the simple CMP stack techniques. As demonstrated in this study, it is now viable to conduct prestack depth imaging of crustal reflection data using a velocity model based on earthquake first arrivals thanks to the dense acquisition deployment.     

高密度空间采样地震数据特点分析

中国陆相沉积盆地的地质结构复杂,储层岩性的多变,需要有高精度的勘探方法。高密度空间采样是提高地震勘探精度的一项新技术。本文简要说明了点激发和点接收技术,分析高密度空间采样的野外工作方法,介绍了Gijs j．o．Vermeer提出的对称采样原理,从波场连续性的角度探讨了高密度空间采样技术。重点分析高密度空间采样数据的特点, 即:高密集的初至波有利于近地表结构的调查,可提高静校正的精度;小偏移距、小点距接收增加了浅层的有效覆盖次数,提高浅层反射的成像精度; 对规则噪声可实现无假频采样,室内的噪声分析和噪声压制的精度随着提高;高密度采集使波场连续性增强,使得各种数学变换的精度提高,有利于不同波场的分离。最后指出高密度空间采样地震勘探技术的难点在于室内数据处理,针对海量数据的分析和处理方法还需要进行深入细致的研究工作。     

Gabor变换参数对信号时频分辨率的影响

窗函数的衰减系数和采样间隔究竟对地球物理信号时频分辨率造成多大的影响,如何才能更好地消除这种影响,是该文的主要出发点。提高分辨率是信号时频分析处理的关键,在地球物理数据处理和属性参数提取等方面具有重要作用和广泛应用。该文研究了Gabor变换窗函数衰减系数选择正确与否和采样间隔对信号分辨率的影响。参数选择不当,不仅降低信号时频谱的分辨率,甚至要丢失信号。在用Gabor变换作时频分析时,通过模拟计算预先给出最佳窗函数和最佳参数范围是十分必要的。文中还给出了常规地震信号最佳采样间隔的范围和选择、处理方法。     

Effects of Gabor transform parameters on signa time-frequency resolution

In this paper, it is described that the time-frequency resolution of geophysical signals is affected by the time window function attenuation coefficient and sampling interval and how such effects are eliminated effectively. Improving the signal resolution is the key to signal time-frequency analysis processing and has wide use in geophysical data processing and extraction of attribute parameters. In this paper, authors research the effects of the attenuation coefficient choice of the Gabor transform window function and sampling interval on signal resolution. Unsuitable parameters not only decrease the signal resolution on the frequency spectrum but also miss the signals. It is essential to first give the optimum window and range of parameters through time-frequency analysis simulation using the Gabor transform. In the paper, the suggestions about the range and choice of the optimum sampling interval and processing methods of general seismic signals are given.     

Measurements of translation, rotation and strain: new approaches to seismic processing and inversion

We propose a novel approach to seismic tomography based on the joint processing of translation, strain and rotation measurements. Our concept is based on the apparent S and P velocities, defined as the ratios of displacement velocity and rotation amplitude, and displacement velocity and divergence amplitude, respectively. To assess the capability of these new observables to constrain various aspects of 3D Earth structure, we study their corresponding finite-frequency kernels, computed with a combination of spectral-element simulations and adjoint techniques. The principal conclusion is that both the apparent S and P velocities are generally sensitive only to small-scale near-receiver structure, irrespective of the type of seismic wave considered. It follows that knowledge of deeper Earth structure would not be required in tomographic inversions for local structure based on the new observables. In a synthetic finite-perturbation test, we confirm the ability of the apparent S and P velocities to directly detect both the location and the sign of shallow lateral velocity variations.     

Wavenumber response of Shanghai Seismic array

Seismic array can be traced back to 1950s when it mainly aimed at detecting and distinguishing the signals of nuclear explosion and seismic signals. The research on seismic array includes seismic array techniques and applications of array in geophysics. Array techniques involve array design and data processing methods (Anne, 1990). Nowadays, the continuous development of seismic array￠s theory could relate to many scientific issues in geophysical field (Tormod, 1989; Mykkeltveit, Bungum, 1984). Seismic array is mainly applied to detect weak events. The response characteristic of array is an important indication of array￠s detection ability. Therefore, when we study an array or construct an array, one of the neces-sary works is to calculate the response characteristics of the array (Harjes, 1990). The aperture and layout of array are two dominating geometrical features. The typical aperture of interna-tional array is generally from several to tens kilometers. For instance, arrays with aperture of dozens kilometers aperture are KSA, WRA, YKA, etc, while arrays with several kilometer aperture are ARC, FIN, GEE, etc. Moreo-ver, in the view of array￠s layout, NOR, GER, etc have circle layout, while WRA, YKA, etc have decussating layout. This paper mainly discusses the relation between deployment of array and wavenumber response. With the example of constructing Shanghai Seismic Array, this paper provides one practical solution to search the proper array deployment. In this paper, the simple delay beam technique is adopted to calculate the response characteris-tics of array. Certainly, the different processing methods have different result, but the result from the simple delay beam processing could be enough to reflect the feature of an array.     

Digital Processing Of Earth Observation Images

Earth observation techniques provide digital images of the Earth's surface. In the field of environmental applications, image processing techniques can be used to manipulate the data, in particular to display satellite images in gray level or in a color composition, to radiometrically and geometrically preprocess the data, and to extract thematic information, by visual interpretation or by semi-automatic techniques.This paper presents some basic concepts in digital image processing and givesa general overview of the main processing methods that can be applied to derivegeographical information from Earth observation images.     

地震台阵及其数据处理方法

介绍了地震台阵的基础知识和地震台阵的发展状况，同时阐述了地震台阵数据处理方法及国内外研究概况。     

卷积神经网络在远-近地震震相拾取中的应用及模型解释

利用北京国家观象台的测震记录,探索了样本构建、训练过程、模型结构等因素对远震震相P-S和近震震相Pg-Sg拾取模型性能的影响。结果表明：适中的卷积层深度、正则化和数据清洗能够有效地改善模型性能,而残差块的影响却相对有限。与此同时,基于类模型可视化和平滑GradCAM++的模型解释显示：卷积神经网络复现了震相的关键特征,其决策敏感区域也与震相识别的经验准则一致。最后,连续波形的扫描结果展示了卷积神经网络在远-近地震震相识别的应用前景与提升空间。此外,本文针对模型搭建与训练中存在的问题提出了样本选择、模型架构、标签标注和集成学习等改进方案,以供后续研究参考。     

Optimal filtering high-resolution seismic reflection data using a weighted-mode empirical mode decomposition operator

Gas-hydrate related processes in deep-water marine settings exist on spatial scales that challenge conventional seismic reflection profiling to successfully image them. The conventional approach to acoustic identification of buried hydrates is to use advanced, cost-prohibitive survey techniques and highly customized software to define subsurface structure wherein compositional changes may be modeled and/or interpreted. This study adopts a different approach derived from recent theoretical advancements in signal processing. The method consists in optimal filtering high resolution, single-channel seismic reflection data using the Empirical Mode Decomposition (EMD). The time series is decomposed in sub-components and the noisy portions are suppressed adopting the technique that we referred as Weighted Mode(s) EMD. The optimal filtering greatly improves the resolution and fidelity of the seismic data set.High Resolution single channel seismic profiles, acquired over a carbonate\hydrates site in the northern Gulf of Mexico, manipulated in such way, show a complex, shallow subsurface, and suggest potential evidence for buried gas hydrates.     

Tutorial review of seismic surface waves’ phenomenology

In recent years, surface wave seismology has become one of the leading directions in seismological investigations of the Earth’s structure and seismic sources. Various applications cover a wide spectrum of goals, dealing with differences in sources of seismic excitation, penetration depths, frequency ranges, and interpretation techniques. Observed seismic data demonstrates the great variability of phenomenology which can produce difficulties in interpretation for beginners. This tutorial review is based on the many years’ experience of authors in processing and interpretation of seismic surface wave observations and the lectures of one of the authors (ALL) at Workshops on Seismic Wave Excitation, Propagation and Interpretation held at the Abdus Salam International Center for Theoretical Physics (Trieste, Italy) in 1990–2012. We present some typical examples of wave patterns which could be encountered in different applications and which can serve as a guide to analysis of observed seismograms.     

小波变换应用于日长变化的研究进展

随着空间测地技术的发展,日长变化的观测资料已经达到了空前高的程度,迫切需要合适的数学工具和方法从这些高精度的观测资料中提取有价值的信息.近些年,小波变换被应用于天文学和地球科学的资料分析中,它通过伸缩和平移等运算对时间信号进行多尺度的细化分析,从中提取有效的信息.本文主要介绍了小波变换应用于日长变化的研究进展,并初步探讨该领域以后的研究方向.     

低幅度构造识别技术在Carmen油田三维工区的应用

近年来,随着油田勘探开发的深入,规模小,构造幅度低的油气藏所占比例逐年上升,低幅度构造也逐渐受到重视.本文分析了低幅度构造的特点及地震反射特征,结合工区实际情况,提出了在地震资料解释阶段研究低幅度构造的流程和思路,总结了针对低幅度构造的主要识别方法:地震正演模拟、井控提高分辨率处理、层位精细解释、三维速度场分析、构造图倾角校正等.通过以上技术在Carmen油田三维工区识别了12个低幅度构造,结合地质、测井资料综合分析优选了两个钻探目标,取得了较好的勘探效果.     

城市活动断层探测和断层活动性评价问题

根据近年来城市活动断层探测与地震危险性评价的实际工作,归纳了探测工作中在地质地貌、地球化学和地球物理探测中存在的问题,针对性提出了相应的建议,以进一步推进这一工作     

地震数据采集系统计时精度测试方法研究

计时精度是地震数据采集系统的重要性能指标,直接影响到地震勘探对地层分辨的准确度.地震数据采集系统中计时精度主要由采集站的采样率精度决定.本文首先给出了计时精度的定义,基于模拟信号数字处理技术,分别研究了采用单方波脉冲法和双单位脉冲法测量计时精度的两种方法并比较了它们的测试精度,给出了采用本文所述方法的测试结果.最后对测试误差进行了讨论.     

P and S reflection and P refraction: An integration for characterising shallow subsurface

Characterization of shallow structures was performed by using different approaches analysing both P- and S-wave seismic data with different resolution. The refraction tomography provided P and S velocity models of the first 80 m, while the reflection seismic processing gives a reasonable stacking velocity field until 300 m depth for both P- and S-wave data. So, we estimated the V_p/V_s ratio and an empirical relationship between the two velocities. We characterised the shallow layers using tomographic velocity models and the deeper layers using seismic images with different resolution. The seismic images were obtained by conventional CMP reflection seismic processing and by a novel multi-refractor imaging technique.     

THE RESOLUTION POSSIBLE IN IMAGING WITH DIFFRACTED SEISMIC WAVES1

The determination of the vertical and lateral extent of discontinuities is an important aspect of interpreting seismic reflection data. The Common Fault Point (CFP) stacking method appears to be promising in imaging discontinuities in acoustic impedance by making use of diffracted energy from a spatial array of receivers. The problems of vertical and lateral resolution in the method are most important when carrying out an interpretation. Source signature, subsurface velocities and the depth of the discontinuity are the most important parameters affecting the resolution. We use, for a perfectly coherent source, the first derivative of the Gaussian function which is an antisymmetric band-limited wavelet. Rayleigh's, Ricker's and Widess' criteria are also applicable to this wavelet. The limits of vertical and lateral resolution are illustrated by using a step fault and a dike model respectively. The vertical resolution of the CFP method is found to be of the order of λ/16 which is half the theoretically predicted value for a single receiver. The lateral resolution is still limited by the size of the Fresnel zone which depends upon the velocity, two-way time and the dominant frequency of the wavelet. The resolution limits of the CFP method are compared with that of the CDP method, prestack migration and post-stack migration. Obtaining high resolution with real data is limited by the extent to which it is possible to generate a coherent source or to simulate one during computer processing with before stack seismic data. The CFP method is an artificial intelligence approach to imaging diffracting points as it localizes parts of the structure that scatter acoustic waves.     

接收函数方法应用的现状及其发展

利用远震PS转换波波形提取出的接收函数来研究地震台站下方地壳、上地幔速度间断面结构是有效的方法之一\[1\].最近几年，利用SP转换波波形的接收函数为进一步研究地壳、上地幔间断面提高了精度；并出现了利用SKS的Receiver Function及利用切向分量来研究地壳、上地幔的各向异性的研究.随着流动台阵和固定台阵地震数据资料的增加，台阵技术与接收函数的结合，为提高间断面精度提供了有利的技术保障.