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1.
The computation of static corrections requires information about subsurface velocities. This information can be obtained by different methods: surface wave analysis, short refraction lines, downhole times, uphole times and first arrivals from seismograms. For pure shear waves generated by SH sources the analysis of first arrivals from seismograms combined, if necessary, with short refraction lines has proved to be most accurate and economic. A comparison of first-arrival plots from P- and S-wave surveys of the same line measured in areas of unconsolidated sediments in northern Germany illustrates the characteristic differences between the two velocity models. P-waves show a marked velocity increase at the water table from about 600 to 1800 m/s. S-wave velocities of the same strata increase gradually from about 100 to 400 m/s. As a consequence, S-wave models are vertically and laterally more complex and, in general, show no significant velocity increase at a defined boundary as P-wave models do. Therefore, other suitable correction levels with specific velocities must be chosen. A comparison of “tgd-corrections” (correction time between geophone position and datum level) for P- and S-waves in areas of unconsolidated sediments shows that their ratio is different from the P-/S-velocity ratio for the respective correction level because of the greater depth of the S-wave refractor. Therefore, P- and S-waves are influenced by different near-surface anomalies, and time corrections calculated for both wave types are largely independent. 相似文献
2.
Active Source Seismic Identification and Automatic Picking of the P-wave First Arrival Using a Convolutional Neural Network 总被引：1，自引：1，他引：0
XU Zhen WANG Tao XU Shanhui WANG Baoshan FENG Xuping SHI Jing YANG Minghan 《中国地震研究》2019,33(2):288-304
In seismic data processing, picking of the P-wave first arrivals takes up plenty of time and labor, and its accuracy plays a key role in imaging seismic structures. Based on the convolution neural network (CNN), we propose a new method to pick up the P-wave first arrivals automatically. Emitted from MINI28 vibroseis in the Jingdezhen seismic experiment, the vertical component of seismic waveforms recorded by EPS 32-bit portable seismometers are used for manually picking up the first arrivals (a total of 7242). Based on these arrivals, we establish the training and testing sets, including 25,290 event samples and 710,616 noise samples (length of each sample:2s). After 3,000 steps of training, we obtain a convergent CNN model, which can automatically classify seismic events and noise samples with high accuracy (> 99%). With the trained CNN model, we scan continuous seismic records and take the maximum output (probability of a seismic event) as the P-wave first arrival time. Compared with STA/LTA (short time average/long time average), our method shows higher precision and stronger anti-noise ability, especially with the low SNR seismic data. This CNN method is of great significance for promoting the intellectualization of seismic data processing, improving the resolution of seismic imaging, and promoting the joint inversion of active and passive sources. 相似文献
3.
Seismic phase picking is the preliminary work of earthquake location and body-wave travel time tomography. Manual picking is considered as the most accurate way to access the arrival times but time consuming. Many automatic picking methods were proposed in the past decades, but their precisions are not as high as human experts especially for events with low ratio of signal to noise and later arrivals. As the increasing deployment of large seismic array, the existing methods can not meet the requirements of quick and accurate phase picking. In this study, we applied a phase picking algorithm developed on the base of deep convolutional neuron network (PickNet) to pick seismic phase arrivals in ChinArray-Phase III. The comparison of picking error of PickNet and the traditional method shows that PickNet is capable of picking more precise phases and can be applied in a large dense array. The raw picked travel-time data shows a large variation deviated from the traveltime curves. The absolute location residual is a key criteria for travel-time data selection. Besides, we proposed a flowchart to determine the accurate location of the single-station earthquake via dense seismic array and phase arrival picked by PickNet. This research expands the phase arrival dataset and improves the location accuracy of single-station earthquake. 相似文献
4.
5.
微地震事件初至拾取是井下微地震监测数据处理的关键步骤之一.初至误差的存在会使微地震震源定位结果产生较大偏差,进而影响后续的压裂裂缝解释.通常初至拾取过程对所有的微地震事件选择相同的特征函数并采用一致的拾取参数进行统一处理,然而当事件的能量、震源机制、传播路径以及背景噪声等存在明显差异时,所得初至拾取结果差别显著.为了提高微地震事件初至拾取标准一致性,本文提出基于波形相似特征的初至拾取及全局校正方法.该方法首先利用互相关函数对每个事件内的各道记录进行时差校正,得到初始初至信息并形成叠加道,再对所有事件的叠加道进行全局互相关得到事件间初至相对校正量,最终初至结果可以通过各个事件的初始初至信息与其相对校正量相加得到.方法将所有微地震事件初至结果作为一个整体处理,从而能够克服常规方法初至拾取标准一致性差的缺陷.实际资料处理结果表明,相比于常规方法,该方法可以有效提高事件初至拾取和定位结果的一致性. 相似文献
6.
Emil Blias 《Geophysical Prospecting》2009,57(3):323-341
Lateral velocity changes (velocity anomalies) in the overburden may cause significant oscillations in normal moveout velocities. Explicit analytical moveout formulas are presented and provide a direct explanation of these lateral fluctuations and other phenomena for a subsurface with gentle deep structures and shallow overburden anomalies. The analytical conditions for this have been derived for a depth-velocity model with gentle structures with dips not exceeding 12°. The influence of lateral interval velocity changes and curvilinear overburden velocity boundaries can be estimated and analysed using these formulas. An analytical approach to normal moveout velocity analysis in a laterally inhomogeneous medium provides an understanding of the connection between lateral interval velocity changes and normal moveout velocities. In the presence of uncorrected shallow velocity anomalies, the difference between root-mean-square and stacking velocity can be arbitrarily large to the extent of reversing the normal moveout function around normal incidence traveltimes. The main reason for anomalous stacking velocity behaviour is non-linear lateral variations in the shallow overburden interval velocities or the velocity boundaries.
A special technique has been developed to determine and remove shallow velocity anomaly effects. This technique includes automatic continuous velocity picking, an inversion method for the determination of shallow velocity anomalies, improving the depth-velocity model by an optimization approach to traveltime inversion (layered reflection tomography) and shallow velocity anomaly replacement. Model and field data examples are used to illustrate this technique. 相似文献
A special technique has been developed to determine and remove shallow velocity anomaly effects. This technique includes automatic continuous velocity picking, an inversion method for the determination of shallow velocity anomalies, improving the depth-velocity model by an optimization approach to traveltime inversion (layered reflection tomography) and shallow velocity anomaly replacement. Model and field data examples are used to illustrate this technique. 相似文献
7.
For years, severe rockburst problems at the Lucky Friday mine in northern Idaho have been a persistent safety hazard and an impediment to production. An MP250 based microseismic monitoring system, which uses simple voltage threshold picking of first arrivals, has been used in this mine since 1973 to provide source locations and energy estimates of seismic events. Recently, interest has been expressed in developing a whole waveform microseismic monitoring system for the mine to provide more accurate source locations and information about source characteristics. For this study, we have developed a prototype whole-waveform microseismic monitoring system based on a 80386 computer equipped with a 50 kHz analog-digital convertor board. The software developed includes a data collection program, a data analysis program, and an event detection program. Whole-waveform data collected and analyzed using this system during a three-day test have been employed to investigate sources of error in the hypocenter location process and to develop an automatic phase picker appropriate for microseismic events.Comparison of hypocenter estimates produced by the MP250 system to those produced by the whole-waveform system shows that significant timing errors are common in the MP250 system and that these errors caused a large part of the scatter evident in the daily activity plots produced at the mine. Simulations and analysis of blast data show that analytical control over the solutions is strongly influenced by the array geometry. Within the geophone array, large errors in the velocity model or moderate timing errors may result in small changes in the solution, but outside the array, the solution is very sensitive to small changes in the data.Our whole-waveform detection program picks event onset times and determines event durations by analysis of a segmented envelope function (SEF) derived from the microseismic signal. The detection program has been tested by comparing its arrival time picks to those generated by human analysis of the data set. The program picked 87% of the channels that were picked by hand with a standard error of 0.75 milliseconds. Source locations calculated using times provided by our entire waveform detection program were similar to those calculated using hand-picked arrival times. In particular, they show far less scatter than source locations calculated using arrival times based on simple voltage threshold picking of first arrivals. 相似文献
8.
微地震（MS）波初始到时的自动拾取是MS监测数据处理的关键技术之一,也是实现MS震源自动定位的技术难点.本文在MS震源定位结果反演与推断的研究基础上,对不同类型MS波的到时点特征进行了分析与描述,并对不同时窗长度下能量特征值的变化规律进行了研究,提出了控制时窗移动范围和确定时窗长度自适应参数的具体方法,利用建立的MS波初始到时点特征的模式识别库,对拾取的到时进行模式归类、定量评价和匹配,提高了自动拾取结果的可靠性.研究结果表明,对典型的信噪比高的MS波,到时自动拾取的结果与手工拾取的结果基本一致;对无量纲大振幅的MS波,到时自动拾取结果的可靠性要高于手工拾取,对信噪比低和到时点不清晰的MS波自动拾取的可靠性较低. 相似文献
9.
岩石超声检测中最重要的一个环节是初至的拾取,然而该项工作往往费时费力,拾取精度受人为因素影响较大。为提高声波速度检测、声发射定位、以及超声层析成像的应用效率和精度,本研究将地震学中应用比较广泛的AIC初至自动提取技术引入到岩石超声检测中,并进行了适当改进。利用改进前后的AIC方法,自动拾取仿真信号和实际信号的初至,并利用长短时窗比方法(STA/LTA)和手动方法拾取了初至,同时分别与设定的实际初至进行对比。根据实验结果,对于信噪比较低的信号AIC方法要优于STA/LTA方法;改进前的AIC方法适用于起跳干脆、幅度变化大的信号,而改进后的AIC方法则适用于起跳较平缓的信号,且拾取到的初至与手动拾取的初至更加接近。 相似文献
10.
利用地震走时数据,采用联合反演方法获取了江苏地区的一维P波速度模型。与仅采用初至波走时的传统天然地震走时获取方法相比,该方法充分利用了大量存在的续至波参与反演,能有效改进中下地壳的反演能力。针对地震震相目录中常存在震相标识错误的问题,采用的自动判别筛选震相方法能最大限度提高数据走时的精度,可以对不同震相进行有效区分。与其他常用一维速度模型相比,本文反演的模型对Pg、Pn震相走时拟合效果最佳,残差最小。当所用走时数据拥有较高定位精度时,该反演方法能为研究区三维速度结构成像和地震定位提供较可靠的一维速度模型。 相似文献
11.
Accurate Location of Synthetic Acoustic Emissions and Location Sensitivity to Relocation Methods, Velocity Perturbations, and Seismic Anisotropy 总被引：1，自引：0，他引：1
G. A. Jones S. E. J. Nippress A. Rietbrock J. M. Reyes-Montes 《Pure and Applied Geophysics》2008,165(2):235-254
Acoustic emission (AE) monitoring is a non-invasive method of monitoring fracturing both in situ, and in experimental rock deformation studies. Until recently, the major impediment for imaging brittle failure within a
rock mass is the accuracy at which the hypocenters may be located. However, recent advances in the location of regional scale
earthquakes have successfully reduced hypocentral uncertainties by an order of magnitude. The least-squares Geiger, master
event relocation, and double difference methods have been considered in a series of synthetic experiments which investigate
their ability to resolve AE hypocentral locations. The effect of AE hypocenter location accuracy due to seismic velocity perturbations,
uncertainty in the first arrival pick, array geometry and the inversion of a seismically anisotropic structure with an isotropic
velocity model were tested. Hypocenters determined using the Geiger procedure for a homogeneous, isotropic sample with a known
velocity model gave a RMS error for the hypocenter locations of 2.6 mm; in contrast the double difference method is capable
of reducing the location error of these hypocenters by an order of magnitude. We test uncertainties in velocity model of up
to ±10% and show that the double difference method can attain the same RMS error as using the standard Geiger procedure with
a known velocity model. The double difference method is also capable of precise locations even in a 40% anisotropic velocity
structure using an isotropic model for location and attains a RMS mislocation error of 2.6 mm that is comparable to a RMS
mislocation error produced with an isotropic known velocity model using the Geiger approach. We test the effect of sensor
geometry on location accuracy and find that, even when sensors are missing, the double difference method is capable of a 1.43
mm total RMS mislocation compared to 4.58 mm for the Geiger method. The accuracy of automatic picking algorithms used for
AE studies is ±0.5 μs (1 time sample when the sampling rate is 0.2 μs). We investigate how AE locations are effected by the
accuracy of first arrival picking by randomly delaying the actual first arrival by up to 5 time samples. We find that even
when noise levels are set to 5 time samples the double difference method successfully relocates the synthetic AE. 相似文献
12.
基于LLNL-G3Dv3全球P波三维速度模型,应用FMM软件包计算并建立了中国地震台网990个台站的初至P波区域三维走时表．该走时表覆盖了以台站为中心的水平向20°×20°、 垂直向-5.1—80 km （向下为正）的三维空间. 其水平向间隔为0.2°,垂直向间隔为5 km．这样对于任一深度小于80 km的震源,均可以应用此三维走时表计算其到周围10°范围内台站的走时．中国地震台网初至P波区域三维走时表的建立,对于改善区域初至P波走时预测,提高地震定位精度有一定现实意义． 相似文献
13.
Miroslav Novotný 《Surveys in Geophysics》2011,32(6):827-855
The refraction CEL09 profile from the CELEBRATION 2000 project intersects the main terranes of the Bohemian Massif in the
NW–SE direction: the Saxothuringian, the Teplá-Barrandian, the Moldanubian and the Moravo-Silesian. In its easternmost part,
it crosses the Western Outer Carpathians overthrust westward onto the Bohemian Massif. Only the first 450 km were surveyed
with the densest deployment of shot points providing data suitable for a reliable geological interpretation. The first-arrival
depth-recursive tomography was applied here to derive a P-wave velocity image of the upper and middle crust (Part A). The
proper interpretation of the obtained velocity features is the subject of the accompanying paper (Part B). The attained resolution
in the velocity image is shown to be superior as compared with the previous CEL09 models based also on the more uncertain
later arrivals of reflection waves. The applied DRTG (depth-recursive tomography on grid) method is based on a regular network
of refraction grid rays generated for iteratively updated starting models. Only the distinct first arrivals with minimum uncertainty
are used for the DRTG inversions to yield the maximum resolution. Thanks to the full control of the data fit by the grid rays
used, the statistical lateral resolution could be determined at single grid depths for the chosen confidence levels. Thus,
the lateral sizes of the anomalies that can be yet resolved are determined in dependence on their depths and their velocity
excesses. The defocusing of the imaged features is studied on the basis of the spatial responses to spike excitation. The
calculated spatial responses also allowed the edge smearing of the velocity anomalies to be assessed. Special attention is
paid to the imaging of low-velocity zones that are usually suppressed by the smoothing measures used in standard tomographic
methods. An improvement was achieved if the smoothing was suggested with regard to the occurrence of the low-velocity zones
repeatedly appearing in higher iterations. The gained deblurring effect concerns both the negative and positive anomalies
as documented on the velocity features interpreted in the accompanying paper. 相似文献
14.
The estimation of velocity and depth is an important stage in seismic data processing and interpretation. We present a method for velocity-depth model estimation from unstacked data. This method is formulated as an iterative algorithm producing a model which maximizes some measure of coherency computed along traveltimes generated by tracing rays through the model. In the model the interfaces are represented as cubic splines and it is assumed that the velocity in each layer is constant. The inversion includes the determination of the velocities in all the layers and the location of the spline knots. The process input consists of unstacked seismic data and an initial velocity-depth model. This model is often based on nearby well information and an interpretation of the stacked section. Inversion is performed iteratively layer after layer; during each iteration synthetic travel-time curves are calculated for the interface under consideration. A functional characterizing the main correlation properties of the wavefield is then formed along the synthetic arrival times. It is assumed that the functional reaches a maximum value when the synthetic arrival time curves match the arrival times of the events on the field gathers. The maximum value of the functional is obtained by an effective algorithm of non-linear programming. The present inversion algorithm has the advantages that event picking on the unstacked data is not required and is not based on curve fitting of hyperbolic approximations of the arrival times. The method has been successfully applied to both synthetic and field data. 相似文献
15.
利用环渤海地区的天然地震P波到时资料，采用纬度和经度方向分别为05°×06°的网格划分，反演了该地区地壳上地幔的三维P波速度结构.初步结果表明，环渤海地区地壳上地幔的速度结构具有明显的横向不均匀性：京津唐地区地壳中上部的速度异常反映了浅表层的地质构造特征，造山带和隆起区对应于高速异常，坳陷区和沉积盆地对应于低速异常；地壳下部出现大规模的低速异常与华北地区广泛存在的高导层相对应，估计与壳内的滑脱层和局部熔融、岩浆活动有关；莫霍面附近的速度异常反映了地壳厚度的变化及壳幔边界附近热状态的差异；上地幔顶部大范围的低速异常可能是上地幔软流层热物质大规模上涌所致. 相似文献
16.
From the wealth of information which can be deduced from VSP, the information most directly comparable to well logs is considered: P-wave and S-wave interval velocity, acoustic impedance, and the velocity ratio γ=Vs/Vp. This information not only allows better interpretation of surface seismic sections but also improves processing. For these results to be usable a number of precautions must be taken during acquisition and processing; the sampling in depth should be chosen in such a way that aliasing phenomena do not unnecessarily limit the spectra during the separation of upwards and downwards travelling waves. True amplitudes should be respected and checked by recording of signatures, and the interference of upwards and downwards travelling waves should be taken into account for the picking of first arrivals. The different steps in processing and the combination of results in the interpretation of surface seismic results are described with actual records. 相似文献
17.
Orhan Gureli 《Pure and Applied Geophysics》2014,171(8):1805-1827
The refracted arrivals on seismic shot records have long been recognized as an efficient tool for the computation of detailed near-surface information. In this paper, a new concept of refraction static, which is based on the Radon transform and avoids the tedious process of picking first arrival times, is proposed. This method is particularly suitable when a rough near-surface problem necessitates the utilization of numerous shallow refraction data for the one reflector case. Quasi-linearity of refractors and a constant velocity medium are assumed within the shooting range. Synthetic and real cases have been tested to evaluate the performance of the method. The result is revealed to be satisfactory. Comparison of the synthetic model with the results obtained through the Radon transform reveals a very good accuracy for the proposed method. 相似文献
18.
地震层析成像技术在岩体完整性测试中的应用 总被引：3，自引：0，他引：3
地震波层析成像借鉴了医学上X射线断面扫描的基本原理,利用地震波穿过地质体后走时及能量的改变等物理信息,通过数学处理重建地质体内部图像,从而得到所研究地质体的岩性及构造分布。本文利用这种方法,在一个钻孔中利用电火花震源激了弹性波,在另一个钻孔布设多个检波点同时接收,拾取弹性波初至时间,将接收到的数据利用SIRT方法进行反演迭代计算,最终形成一个弹性波速度谱图,然后利用岩土体的弹性波速度差异推断岩体完整性分布。与其它测试方法比较,该方法分辨率高,空间位置准确,在工程物探、岩土工程勘察中具有较好的应用前景。 相似文献
19.
声波测井中的相速度与群速度讨论(英文) 总被引：3，自引：2，他引：1
声波测井过程中获取的速度到底是相速度还是群速度,目前仍存在一些争议,本文从理论分析和数值模拟的角度,使用三种模型对这一问题进行了研究。首先,构造一个相速度与群速度可调的稳态声波传播模型——不同声速的两个平面波叠加模型,利用慢度时间相关(STC)方法提取声波波速,数值模拟结果表明,无论相速度较大或是群速度较大,STC方法提取出来的波速都是相速度;其次,通过频散分析和割线积分得到刚性壁圆柱流体模型中的频散曲线与分波波形,使用STC方法得到的速度与相速度的频散曲线吻合较好,而直接读取波至获得的速度与群速度的频散曲线趋势一致;最后,利用频散分析和实轴积分方法,获得偶极子在慢地层中激发的模式及全波波形,得到的结果再次验证了刚性壁圆柱流体模型中的结论。 相似文献
20.
《Journal of Applied Geophysics》2007,61(2):83-91
The seismic refraction method is commonly used to determine the lithology and stratigraphic geometry of geological sites. Beyond this application there is also the potential to extract additional velocity-related information such as mechanical properties of soils and rocks. However, this requires a reliable model of the subsurface velocity variations. Refraction data, P- and SH-wave first arrivals, and surface waves were analyzed using three different techniques: delay-time in combination with ray-tracing, tomography and multichannel analysis of surface waves (MASW). Results from the first two techniques were compared, which showed that sharp high-contrasting layering is best imaged by the traditional method, delay-time followed by ray-tracing. The tomographic method was unable to detect the water table in the P-wave survey but resolved near-surface gradational velocity changes. On the other hand, in the SH-wave survey the traditional method was not useful because of gradually increasing velocities, which were better suited to the tomographic method. Furthermore, to produce spatially detailed velocity-variation models the tomographic or the MASW methods are applicable. The MASW model showed somewhat lower velocities compared to the SH-refraction tomographic model and, in contrast, showed inverted velocity gradients. This study also presents a comparison between the shear moduli measured in situ, i.e. calculated from shear wave velocities, and determined using empirical relationships. The empirical relationship for sand gives higher values for shear moduli than those measured in situ. 相似文献