Comparison of Frequency-Selection Strategies for 2D Frequency-Domain Acoustic Waveform Inversion

Several frequency-selection strategies have been used to obtain global minimum solutions in waveform inversion. One strategy, called the discretization method, is to discretize frequencies with a large sampling interval to minimize redundancy in wavenumber information. Another method, the grouping method, groups frequencies with redundancy in wavenumber information. The grouping method can be carried out in two ways. With the first method, the minimum frequency is fixed and the maximum frequency is gradually extended upward (i.e., the overlap-grouping method). Under the second method, frequencies are not overlapped across the groups and waveform inversion proceeds from lower to higher frequency groups (i.e., the individual-grouping method). In this study, we compare these three frequency-selection strategies using both synthetic and real data examples based on logarithmic waveform inversion. Numerical examples for synthetic and real field data demonstrate that the three frequency-selection methods provide solutions closer to the global minimum compared to solutions resulting from simultaneously performed waveform inversion, and that the individual-grouping method yields slightly better resolution for the velocity models than the other methods, particularly for the deeper part. These results may imply that using either too small or too large data sets at every stage slightly deteriorates inversion results, and that grouping data in appropriately sized aggregations improves inversion results.     

基于地震波反演的地震震源深度研究

基于区域数字地震台网记录,利用CAP方法反演得到了2011年2月23日迭部MS4.0级地震的震源机制解和震源深度,然后利用深度震相sPg和参考震相Pg对震源深度进行了详细的分析。结果表明,迭部4.0级地震的最佳双力偶解为节面Ⅰ,走向110°、倾角57°、滑动角23°,表现为带少量逆冲分量的走滑型地震,震源深度为7 km。通过合作台上理论地震图与实际观测记录的比较,确认了震源深度结果的可靠性。     

3D Neural Network Inversion of Field Geoelectric Data with Calculating Posterior Estimates

Izvestiya, Physics of the Solid Earth - Abstract—The approximation neural network (ANN) method for solving the inverse geoelectric problem in the piecewise constant classes of media with the...     

CPU/GPU协同计算在频率域二维全波形反演中的应用

全波形反演利用波场的运动学和动力学信息重建地下物理参数,是建立高精度速度模型的有效手段,巨大的计算量是制约其实用化的瓶颈之一。本文针对全波形反演中频率域正演的复杂计算问题,采用粗细结合的并行策略,将MPI技术应用于多炮间并行计算,同时利用GPU技术加速正演过程中大型稀疏线性代数方程组的求解,以提高频率域全波形反演的计算效率。通过理论模型验证本文方法的正确性和有效性,给出不同数据量与GPU计算效率的相关分析结论,提出频率域全波形反演CPU/GPU协同并行计算的制约瓶颈和发展方向。     

ELRIS2D: A MATLAB Package for the 2D Inversion of DC Resistivity/IP Data

ELRIS2D is an open source code written in MATLAB for the two-dimensional inversion of direct current resistivity (DCR) and time domain induced polarization (IP) data. The user interface of the program is designed for functionality and ease of use. All available settings of the program can be reached from the main window. The subsurface is discre-tized using a hybrid mesh generated by the combination of structured and unstructured meshes, which reduces the computational cost of the whole inversion procedure. The inversion routine is based on the smoothness constrained least squares method. In order to verify the program, responses of two test models and field data sets were inverted. The models inverted from the synthetic data sets are consistent with the original test models in both DC resistivity and IP cases. A field data set acquired in an archaeological site is also used for the verification of outcomes of the program in comparison with the excavation results.     

Modeling Coastal Salinity in Quasi 2D and 3D Using a DUALEM‐421 and Inversion Software

Rising sea levels, owing to climate change, are a threat to fresh water coastal aquifers. This is because saline intrusions are caused by increases and intensification of medium‐large scale influences including sea level rise, wave climate, tidal cycles, and shifts in beach morphology. Methods are therefore required to understand the dynamics of these interactions. While traditional borehole and galvanic contact resistivity (GCR) techniques have been successful they are time‐consuming. Alternatively, frequency‐domain electromagnetic (FEM) induction is potentially useful as physical contact with the ground is not required. A DUALEM‐421 and EM4Soil inversion software package are used to develop a quasi two‐ (2D) and quasi three‐dimensional (3D) electromagnetic conductivity images (EMCI) across Long Reef Beach located north of Sydney Harbour, New South Wales, Australia. The quasi 2D models discern: the dry sand (<10 mS/m) associated with the incipient dune; sand with fresh water (10 to 20 mS/m); mixing of fresh and saline water (20 to 500 mS/m), and; saline sand of varying moisture (more than 500 mS/m). The quasi 3D EMCIs generated for low and high tides suggest that daily tidal cycles do not have a significant effect on local groundwater salinity. Instead, the saline intrusion is most likely influenced by medium‐large scale drivers including local wave climate and morphology along this wave‐dominated beach. Further research is required to elucidate the influence of spring‐neap tidal cycles, contrasting beach morphological states and sea level rise.     

井间电磁波CT中的非块体分段反演算法

本文给出了用网格节点表示的介质中直射线追踪的算法。在实际工作中,我们常发现当井间CT 应用于强不均匀体存在的区域时,反演结果往往会严重失真,为了解决这一问题,我们采用对测量数据分段反演的新算法。首先利用强信号(即弱衰减)确定衰减量较小的背景介质的衰减系数,固定背景介质的衰减系数(或对其加入强约束),然后逐渐用较弱的信号确定衰减系数较大的介质在井间的分布,直至反演出整个井间的吸收系数分布。实践表明,当强不均匀体存在时,运用这一方法得到的结果明显优于不作分段时得到的结果。     

2-D Frequency-domain Waveform Inversion of Coupled Acoustic-Elastic Media with an Irregular Interface

In order to correctly interpret marine exploration data, which contain many elastic signals such as S waves, surface waves and converted waves, we have developed both a frequency-domain modeling algorithm for acoustic-elastic coupled media with an irregular interface, and the corresponding waveform inversion algorithm. By applying the continuity condition between acoustic (fluid) and elastic (solid) media, wave propagation can be properly simulated throughout the coupled domain. The arbitrary interface is represented by tessellating square and triangular finite elements. Although the resulting complex impedance matrix generated by finite element methods for the acoustic-elastic coupled wave equation is asymmetric, we can exploit the usual back-propagation algorithm used in the frequency domain through modern sparse matrix technology. By running numerical experiments on a synthetic model, we demonstrate that our inversion algorithm can successfully recover P- and S-wave velocity and density models from marine exploration data (pressure data only).     

Best Practice in Earthquake Location Using Broadband Three-component Seismic Waveform Data

—?We present an earthquake location algorithm, the Broadband Waveform Regional Earthquake Location Program (BW_RELP), which utilizes phase onset times and wave azimuths recorded by three-component broadband seismic stations and an adaptive migrating grid search algorithm to find the global minimum in an arbitrary normed misfit parameter. The performance of BW_RELP is demonstrated using regional (300–800?km distant) broadband recordings to locate events in the 1995 Ridgecrest, California earthquake sequence. The purpose of this study is to introduce the BW_RELP algorithm in detail and to expand on the previous paper by Deger et?al. (BSSA, 88, 1353–1362, 1998), using one Berkeley Digital Seismic Network (BDSN) station (YBH) and two USNSN stations (ELK and MNV) which span 300–800?km in distance and 55 degrees in azimuth, to further investigate the capability of a sparse broadband network of three-component stations at monitoring a region located outside of the network, as will be the case in the monitoring of the Comprehensive Test-Ban-Treaty (CTBT) for low magnitude seismic events. We assess the capability of this sparse three-station broadband network and we compare locations estimated from phase onset time and wave azimuth measurements to a ground-truth catalog of high-quality earthquake locations derived from data recorded by the Southern California Seismic Network (SCSN). The results indicate that in the regional distance range it is possible, when an appropriate calibration event is available, to obtain absolute event locations to within 18?km as is prescribed by the CTBT.     

利用1-HzGPS波形数据反演2011年日本北大地震震源破裂过程

利用1-Hz GPS数据反演2011年3月日本东北大地震的时空破裂过程,通过理论波形图与观测波形图的拟合,以及ABIC准则的判定,反演得到滑移分布的稳定估计.结果表明:破裂集中在震源附近,并在震中以下30 km处达到最大位错量,约72 m,在岩手和福岛靠近海岸线处有两个较小的破裂区,断层的南半段破裂很小,同时也是余震最为密集的地方.整个破裂过程由3个破裂阶段组成,发震后断层从震源向周围缓慢破裂,在50～60 s破裂延伸至地表(海沟);60～90 s在震中下方迅速发生强烈破裂,形成了最大位错区,这一阶段主要是倾向上的双边破裂;90～120 s在断层最北西处和断层南半段发生较小破裂,整个破裂过程持续大约120 s.反演得到的地震矩为3.8×1022 Nm,相应的矩震级为MW 9.0.     

A Stochastic Inversion Method for Potential Field Data: Ant Colony Optimization

Simulating natural ants’ foraging behavior, the ant colony optimization (ACO) algorithm performs excellently in combinational optimization problems, for example the traveling salesman problem and the quadratic assignment problem. However, the ACO is seldom used to inverted for gravitational and magnetic data. On the basis of the continuous and multi-dimensional objective function for potential field data optimization inversion, we present the node partition strategy ACO (NP-ACO) algorithm for inversion of model variables of fixed shape and recovery of physical property distributions of complicated shape models. We divide the continuous variables into discrete nodes and ants directionally tour the nodes by use of transition probabilities. We update the pheromone trails by use of Gaussian mapping between the objective function value and the quantity of pheromone. It can analyze the search results in real time and promote the rate of convergence and precision of inversion. Traditional mapping, including the ant-cycle system, weaken the differences between ant individuals and lead to premature convergence. We tested our method by use of synthetic data and real data from scenarios involving gravity and magnetic anomalies. The inverted model variables and recovered physical property distributions were in good agreement with the true values. The ACO algorithm for binary representation imaging and full imaging can recover sharper physical property distributions than traditional linear inversion methods. The ACO has good optimization capability and some excellent characteristics, for example robustness, parallel implementation, and portability, compared with other stochastic metaheuristics.     

Inversion of 2D spectral induced polarization imaging data

Laboratory measurements of various materials suggest that more information can be obtained by measuring the in‐phase and out‐of‐phase potentials at a number of frequencies. One common model used to describe the variation of the electrical properties with frequency is the Cole‐Cole model. Apart from the DC resistivity (ρ) and chargeability (m) parameters used in conventional induced‐polarization (IP) surveys, the Cole‐Cole model has two additional parameters, i.e. the time (τ) and relaxation (c) constants. Much research has been conducted on the use of the additional Cole‐Cole parameters to distinguish between different IP sources. Here, we propose a modified inversion method to recover the Cole‐Cole parameters from a 2D spectral IP (SIP) survey. In this method, an approximate inversion method is initially used to construct a non‐homogeneous starting model for the resistivity and chargeability values. The 2D model consists of a number of rectangular cells with constant resistivity (ρ), chargeability (m), time (τ) and relaxation (c) constant values in each cell. A regularized least‐squares optimization method is then used to recover the time and relaxation constant parameters as well as to refine the chargeability values in the 2D model. We present results from tests carried out with the proposed method for a synthetic data set as well as from a laboratory tank experiment.     

DEMETER卫星磁场波形数据分析方法初探

为充分利用法国DEMETER地震电磁卫星中心提供的磁场波形数据对地震事件进行分析研究,详细介绍了峰度演化方法,并对峰度演化方法的有效性进行了检验.最后将峰度演化方法应用于汶川地震前后DEMETER卫星所记录到的实际数据.分析研究发现.所采用的方法能够较好的处理DEMETER卫星记录到的磁场波形数据:汶川地震发生之前较长...     

利用远震接收函数反演黔江地震台下方的速度结构

本文选取黔江地震台2007年至2011年记录到的60个远震宽频带数字地震记录,采用频率域反褶积法获得台站的接收函数,并用H-Kappa叠加法来反演台站下方的地壳厚度和泊松比,最终得到了黔江地震台下方的地壳速度结构。同时,通过H-Kappa法反演得到的台站下方的地壳厚度作为波速反演的约束条件,以减少反演的非唯一性。计算结果显示,黔江地震台下方的地壳厚度为44km,这与广泛认同的中国大陆中西部地区莫霍深度在38—45km基本一致。本文对增强该地区深部地质构造特征研究和孕震机制分析具有积极的意义。     

用地质雷达数据资料反演二维地下介质的方法

从二维麦克斯韦方程组出发推导出反演介电常数和电导率等二维介质物性参数的反演公式.反演的步骤是: 建立初始猜测模型,利用电磁波时间域有限差分法模拟正演数据,用正演数据与观测数据之间的数据残差建立目标函数,通过引入一个由麦克斯韦方程计算的伴随场,将目标函数对介质参数的导数表示成显式形式,应用最优化理论得出对初始猜测模型的修改,用共轭梯度法迭代,最终得到反演结果.用合成数据反演具有粗糙地表的非导电介质的介电常数,用实验数据同时反演介电常数和电导率,并比较了麦克斯韦方程反演结果与声波方程反演结果、波动方程偏移剖面的差异.     

Geoelectric Characterization of Thermal Water Aquifers Using 2.5D Inversion of VES Measurements

This paper presents a short theoretical summary of the series expansion-based 2.5D combined geoelectric weighted inversion (CGWI) method and highlights the advantageous way with which the number of unknowns can be decreased due to the simultaneous characteristic of this inversion. 2.5D CGWI is an approximate inversion method for the determination of 3D structures, which uses the joint 2D forward modeling of dip and strike direction data. In the inversion procedure, the Steiner’s most frequent value method is applied to the automatic separation of dip and strike direction data and outliers. The workflow of inversion and its practical application are presented in the study. For conventional vertical electrical sounding (VES) measurements, this method can determine the parameters of complex structures more accurately than the single inversion method. Field data show that the 2.5D CGWI which was developed can determine the optimal location for drilling an exploratory thermal water prospecting well. The novelty of this research is that the measured VES data in dip and strike direction are jointly inverted by the 2.5D CGWI method.     

利用水位资料反演华北地区构造应力场变化

本文选取华北地区观测条件较好的63口水位观测井资料, 运用小波分析法去除各井水位资料中的短期高频信息, 提取出能反映水位多年动态变化的趋势信息, 并利用各井水位趋势变化数据反演出华北地区多年构造应力场变化图像, 结合其它水文资料, 探讨了华北地区近年来的构造应力场变化特征。     

用数字化地震波形资料分析云南及邻区环境剪应力场

利用昆明数字化地震台网记录的数字化地震波形资料．测算了云南及邻区2002年到2004年8月2513个中小地震的剪应力值T0和矩震级值Mw,分析了它们之间的相关关系。研究表明,地震剪应力值与地震大小存在线性依赖关系,地震越大,环境剪应力场越强,强震的发生需要较强的剪应力场环境。小地震在较弱的环境剪应力场状态下也可以发生,随机性较强。在环境剪应力场较强的地方,会发生强震,也会发生数量众多的中小地震。而在环境剪应力场较弱的地方,往往只会发生中小震。统计分析表明,通常,中小地震的T0〈10MPa,将T0≥10MPa的地震视为高剪应力值地震,高剪应力值地震集中分布的区域,或应力等值线大于10MPa的分布区即为高应力值区,高剪应力值分布区是环境剪应力场的异常分布区,它的形成和分布往往与强震的发生有关。据此,对云南省环境剪应力场动态变化及其与地震活动的关系作了分析研究。