Automatic cross-well tomography by semblance and differential semblance optimization: theory and gradient computation

A technique for automatic cross-well tomography based on semblance and differential semblance optimization is presented. Given a background velocity, the recorded seismic data traces are back-propagated towards the source, i.e. shifted towards time zero using the modelled traveltime between the source and the receiver and corrected for the geometrical spreading. Therefore each back-propagated trace should be a pulse, close to time zero. The mismatches between the back-propagated traces indicate an error in the velocity model. This error can be measured by stacking the back-propagated traces (semblance optimization) or by computing the norm of the difference between adjacent traces (differential semblance optimization).
It is known from surface seismic reflection tomography that both the semblance and differential semblance functional have good convexity properties, although the differential semblance functional is believed to have a larger basin of attraction (region of convergence) around the true velocity model. In the case of the cross-well transmission tomography described in this paper, similar properties are found for these functionals.
The implementation of this automatic method for cross-well tomography is based on the high-frequency approximation to wave propagation. The wavefronts are constructed using a ray-tracing algorithm. The gradient of the cost function is computed by the adjoint-state technique, which has the same complexity as the computation of the functional. This provides an efficient algorithm to invert cross-well data. The method is applied to a synthetic data set to demonstrate its efficacy.     

Inversion of reflection seismograms by differential semblance analysis: algorithm structure and synthetic examples1

Seismograms predicted from acoustic or elastic earth models depend very non-linearly on the long wavelength components of velocity. This sensitive dependence demands the use of special variational principles in waveform-based inversion algorithms. The differential semblance variational principle is well-suited to velocity inversion by gradient methods, since its objective function is smooth and convex over a large range of velocity models. An extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient. Non-linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum, which is near the ordinary least-squares global minimum when coherent data noise is small. Several examples, based on the 2D primaries-only acoustic model, illustrate features of the method and its performance.     

频率域2.5-D井间波形层析成像及其实际应用

从频率域3-D声波波动方程出发,结合井间观测方式的特点,基于Tarantola广义反演理论,提出了一种频率域2.5-D井间波形层析成像方法.数值模型试验结果表明：该方法对薄层厚度的分辨能力能达到约主频波长的1/4,且分辨率显著高于走时层析成像,尤其垂直分辨率有实质改善.模拟资料的抗噪试验表明：在信噪比为0.8的情况下,随机噪声对波形层析成像的影响较小;而相干噪声对全波形层析成像的影响显著,特别是初至波附近的强振幅干扰影响更为严重.井间实际资料的试处理结果表明：波形层析成像能很好地刻画井间介质的分布情况与储层连通性,对于油藏开发阶段的方案实施具有指导意义.     

Attenuation tomography: An application to gas-hydrate and free-gas detection

We estimate the quality factor (Q) from seismic reflections by using a tomographic inversion algorithm based on the frequency‐shift method. The algorithm is verified with a synthetic case and is applied to offshore data, acquired at western Svalbard, to detect the presence of bottom‐simulating reflectors (BSR) and gas hydrates. An array of 20 ocean‐bottom seismographs has been used. The combined use of traveltime and attenuation tomography provides a 3D velocity–Q cube, which can be used to map the spatial distribution of the gas‐hydrate concentration and free‐gas saturation. In general, high P‐wave velocity and quality factor indicate the presence of solid hydrates and low P‐wave velocity and quality factor correspond to free‐gas bearing sediments. The Q‐values vary between 200 and 25, with higher values (150–200) above the BSR and lower values below the BSR (25–40). These results seem to confirm that hydrates cement the grains, and attenuation decreases with increasing hydrate concentration.     

Verifying adequacy of the seismic deformation method by using real examples of earthquake damage

In a seismic design, the dynamic loads are generally dependent on the inertial interaction caused by earthquake. But for the foundations embedded in soil, the dynamic loads are influenced by both the inertial and kinematic interactions among superstructure, foundation and soil. Especially, when a foundation is embedded in soft surface ground, the effects due to the kinematic interaction increase and should be considered in seismic design. For this reason, a method called seismic deformation method (SDM), which is suitable for an intensive earthquake motion (level 2 earthquake motion), has been stipulated recently in a new design code called Seismic Design Code for railway structures (the Railway Code, drawn up by Railway Technical Research Institute, Japan, 1999) [Railway Technical Research Institute. Seismic Design Code for railway structures. Tokyo: Maruzen; 1999]. In order to grasp the suitability of the SDM to actual structures, pile foundations, which experienced the Hyogoken-Nanbu earthquake, were taken as the objects for investigations. Comparison studies between the SDM analysis and reconnaissance were conducted. As a result, the adequacy of the SDM to actual foundations was confirmed to prove good agreement between the two results from the viewpoint of engineering practice.In addition, determination of indices for seismic-performance evaluation and speculation of damage mechanism of the foundations are also discussed in this paper.     

The application of resistivity tomography to hydrogeological exploration

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腾冲火山及周边地区双差层析成像

利用云南腾冲火山地区15个固定台站记录到的7923次地震的P波到时资料,采用双差层析成像方法,反演得到腾冲火山及周边地区地壳及上地幔顶部三维P波速度结构和地震重定位结果.研究发现,腾冲火山区域地壳内存在明显的地震波低速区,P波速度低于整个区域地壳速度平均值超过15%,上地幔顶部存在规模较大的低速异常区.推测腾冲火山地区存在较大规模的地幔热物质上涌以及向地壳的侵入,热物质在地壳内以岩浆囊形式存储,并且壳内岩浆囊之间可能存在岩浆通道.通过联合反演获得的地震重定位结果显示,丛集地震位置更加集中,其展布特征与断裂构造具有显著的对应关系,表明研究区域断裂构造比较活跃.获得的高分辨率三维P波层析成像结果,为进一步认识火山地区岩浆存储特征以及地震分布与区域构造之间的关系提供了新的地震学依据.

     

Uncertainty assessment and optimization of hydrological model with the Shuffled Complex Evolution Metropolis algorithm: an application to artificial neural network rainfall-runoff model

Assessment of parameter and predictive uncertainty of hydrologic models is an essential part in the field of hydrology. However, during the past decades, research related to hydrologic model uncertainty is mostly done with conceptual models. As is accepted that uncertainty in model predictions arises from measurement errors associated with the system input and output, from model structural errors and from problems with parameter estimation. Unfortunately, non-conceptual models, such as black-box models, also suffer from these problems. In this paper, we take the artificial neural network (ANN) rainfall-runoff model as an example, and the Shuffled Complex Evolution Metropolis algorithm (SCEM-UA) is employed to analysis the parameter and predictive uncertainty of this model. Furthermore, based on the results of uncertainty assessment, we finally arrive at a simpler incomplete-connection artificial neural network (ICANN) model as well as with better performance compared to original ANN rainfall-runoff model. These results not only indicate that SCEM-UA can be a useful tool for uncertainty analysis of ANN model, but also prove that uncertainty does exist in ANN rainfall-runoff model. Additionally, in some way, it presents that the ICANN model is with smaller uncertainty than the original ANN model.     

约束优化的微分进化算法在波动方程反问题中的应用

本文提出了一种约束优化的微分进化算法,该算法使得种群在演化过程中能保持较好的多样性,且参数设置简单,不容易陷入局部最优,并能在较短时间内找到约束优化问题的最优解.结合有限元法对波动方程反问题进行研究,在对一维及二维波动方程反问题的数值模拟中都得到了较好的结果,表明了该算法具有较好的稳定性和较强的抗噪能力.     

卫星地震台站的电源设计与应用

从设备功耗、气象条件、太阳能板、蓄电池规格等方面设计卫星传输方式所需电源方案,并用于实际传输。由3个月考核运行期的运行率表明：卫星传输方式的电源设计是成功的、合理的,保证卫星地震台站稳定可靠的运行。     

Evaporation process modelling over northern Iran: application of an integrative data-intelligence model with the krill herd optimization algorithm

ABSTRACT

An integrated data-intelligence model based on multilayer perceptron (MLP) and krill herd optimization – the MLP-KH model – is presented for the estimation of daily pan evaporation. Daily climatological information collected from two meteorological stations in the northern region of Iran is used to compare the potential of the proposed model against classical MLP and support vector machine models. The integrated and the classical models were assessed based on different error and goodness-of-fit metrics. The quantitative results evidenced the capacity of the proposed MLP-KH model to estimate daily pan evaporation compared to the classical ones. For both weather stations, the lowest root mean square error (RMSE) of 0.725 and 0.855 mm/d, respectively, was obtained from the integrated model, while the RMSE for MLP was 1.088 and 1.197, and for SVM it was 1.096 and 1.290, respectively.     

Automatic real time parameter determination of tsunami earthquakes in the Far East of Russia: Algorithms and software

A system of algorithms and software modules is described for automatic real time determination of epicenters and magnitudes of potential tsunami earthquakes. Modules are compiled into a single software system called Tsunami Source Quick Location (SS TSQL). The TSQL complex was successfully tested on dozens of real digital recordings. Currently, the TSQL complex is continuously operated in a test mode within the first phase of the seismic subsystem of the Tsunami Warning System (SS TWS) in the Far East of Russia.     

Depth and morphology of reflectors from the non-linear inversion of arrival times and waveform semblance data. Part II: modelling and interpretation of real data acquired in Southern Apennines, Italy

In order to retrieve a 2D background velocity model and to retrieve the geometry and depth of shallow crustal reflectors in the Southern Apennines thrust belt a separate inversion of first arrival traveltimes and reflected waveforms was performed. Data were collected during an active seismic experiment in 1999 by Enterprise Oil Italiana and Eni-Agip using a global offset acquisition geometry. A total of 284 on-land shots were recorded by 201 receivers deployed on an 18 km line oriented SW–NE in the Val D'Agri region (Southern Apennines, Italy).
The two-step procedure allows for the retrieval of a reliable velocity model by using a non-linear tomographic inversion and reflected waveform semblance data inversion. The tomographic model shows that the P wave velocity field varies vertically from approximately 3 km/s to 6 km/s within 4 km from the Earth's surface. Moreover, at a distance of approximately 11 km along the profile, there is an abrupt increase in the velocity field. In this zone indeed, an ascent from 2 km depth to 0 km above sea level of the 5.2 km/s iso-velocity contour can be noted. The retrieved velocity can be associated with Plio-Pleistocene clastic deposits outcropping in the basin zone and with Mesozoic limestone deposits. The inversion of waveform semblance data shows that a P-to-P reflector is retrieved at a depth of approximately 2 km. This interface is deeper in the north-eastern part of the profile, where it reaches 3 km depth and can be associated with a limestone horizon.     

Comparative application of two erosion models to a basin

Abstract

Two mathematical models were used to estimate the annual sediment yield resulting from rainfall and runoff at the outlet of the Nestos River basin (Toxotes, Thrace, Greece). The models were applied to that part of the Nestos River basin (838 km²) which lies downstream of three dams. Both models consist of three submodels: a simplified rainfall-runoff submodel, a physically-based surface erosion submodel and a sediment transport submodel for streams. The two models differ only in the surface erosion submodel: that of the first model is based on the relationships of Poesen (1985) for splash detachment and splash transport, while the corresponding submodel of the second model is based on the relationships of Schmidt (1992) for the momentum flux exerted by the droplets and the momentum flux exerted by the overland flow. The degree of conformity between the annual values of sediment yield at the basin outlet according to both models is satisfactory.     

Depth and morphology of reflectors from the non-linear inversion of arrival-time and waveform semblance data. Part I: method and applications to synthetic data

We propose a two-dimensional, non-linear method for the inversion of reflected/converted traveltimes and waveform semblance designed to obtain the location and morphology of seismic reflectors in a lateral heterogeneous medium and in any source-to-receiver acquisition lay-out. This method uses a scheme of non-linear optimization for the determination of the interface parameters where the calculation of the traveltimes is carried out using a finite-difference solver of the Eikonal equation, assuming an a priori known background velocity model. For the search for the optimal interface model, we used a multiscale approach and the genetic algorithm global optimization technique. During the initial stages of inversion, we used the arrival times of the reflection phase to retrieve the interface model that is defined by a small number of parameters. In the successive steps, the inversion is based on the optimization of the semblance value determined along the calculated traveltime curves. Errors in the final model parameters and the criteria for the choice of the best-fit model are also estimated from the shape of the semblance function in the model parameter space. The method is tested and validated on a synthetic dataset that simulates the acquisition of reflection data in a complex volcanic structure. This study shows that the proposed inversion approach is a valid tool for geophysical investigations in complex geological environments, in order to obtain the morphology and positions of embedded discontinuities.     

Spatial pattern analysis using hybrid models: an application to the Hellenic seismicity

Earthquakes are one of the most destructive natural disasters and the spatial distribution of their epicentres generally shows diverse interaction structures at different spatial scales. In this paper, we use a multi-scale point pattern model to describe the main seismicity in the Hellenic area over the last 10 years. We analyze the interaction between events and the relationship with geological information of the study area, using hybrid models as proposed by Baddeley et al. (2013). In our analysis, we find two competing suitable hybrid models, one with a full parametric structure and the other one based on nonparametric kernel estimators for the spatial inhomogeneity.     

A Bayesian analysis of the Gumbel distribution: an application to extreme rainfall data

With the objective of modelling annual rainfall maximum intensities in different geographical zones of Chile, we have created a Bayesian inference method for the generalized extreme value type I distribution (Gumbel distribution). We considered an uninformative prior distribution for the location parameter, μ, and three different prior distributions for the scale parameter, σ. Under these conditions we obtained the posterior distribution of (μ, σ) and associated summary statistics such as modes, expected values, quantiles and credibility intervals. In order to predict and estimate return periods, we obtained the posterior distribution of future observations, its expected value, quantiles and credibility intervals. To obtain several of these posterior summary measures it was necessary to utilize both numerical and Laplace approximations. Furthermore we estimate return period curves and intensity–duration–frequency curves.     

Comparison between two approaches to the implementation of the optimization method for reconstructing a nonlinear force-free field

A comparative testing of two methods for reconstructing a nonlinear force-free field in a bounded spatial domain has mainly been studied based on the optimization method, using (1) fixed boundary values and weighting function and (2) purposefully varied boundary values. The quantitative and qualitative characteristics, reflecting the degree of correspondence between the calculated and known model fields, are presented. It is indicated that the second approach to the implementation of the optimization method gives the best approximation to the required solution, corresponding to the finite solution in an unbounded domain, and the quality of this solution remains unchanged up to the reconstruction domain boundaries.