Spectral Decomposition Using the CEEMD Method: a Case Study from the Carpathian Foredeep

The purpose of this work is to select the optimal spectral decomposition (SD) method for channel detection in the Miocene strata of the Carpathian Fordeep, SE Poland. For analysis, two spectral decomposition algorithms were tested on 3D seismic data: the first, based on Fast Fourier Transform (FFT), and second, on Complete Ensemble Empirical Mode Decomposition (CEEMD). Additionally the results of instantaneous frequency (IF) were compared with the results of peak frequency (PF) computed after the CEEMD. Both algorithms of SD enabled us to interpret channels, but the results are marginally different, i.e. the FFT shows more coarse, linear structures, that are desirable for channel interpretation, whereas the CEEMD does not highlight these structures as clearly and shows more, what the authors believe to be, noise.     

垂直和倾斜断层围陷波的谱元法数值模拟及其波场特征对比

低速断层破碎带内传播的断层围陷波是断层内部信息的重要载体,研究其波场特征是反,演断层内部结构的关键。前人对围陷波的模拟主要针对垂直断层,但实际断层大部分是倾斜的。本文利用谱元法数值模拟地震波在垂直和倾斜断层区域的传播,并分别单独改变断层破碎带或断层两盘速度差异等参数,对比分析地震动在时域和频域发生的变化,研究这些参数对波场特征的影响。对比研究表明,当存在一定宽度的低速破碎带时,倾斜断层对近断层区域波场的影响和垂直断层相比在幅值分布上有比较显著的差异,尤其是当断层两盘同时还存在速度差异时;在倾斜和垂直断层破碎带上方,均能产生断层围陷波,其幅值特征差异不大,但在跨断层平面上的质点极化方式可能会存在差异:垂直断层围陷波质点极化方向表现为单一,而倾斜断层可能会出现多个方向。这些模拟结果有助于反演真实断层破碎带结构,也能够加深对近断层的强地面运动特征的认识。     

基于谱修正方法的非高斯风场模拟

为克服基于H erm ite谱修正方法的缺点,减少该方法中计算H erm ite多项式系数所需耗费的大量机时,提出了一种模拟非高斯风压场的新方法,采用非高斯累积分布函数（CDF）映射技术来代替基于H erm ite的概率密度函数（PDF）修正。选择任意边缘PDF模型作为概率目标模型,采用目标功率谱密度（PSD）作为样本函数,通过迭代修正该样本函数,使其收敛于目标概率密度函数和目标功率谱密度。将该方法应用于实际结构的非高斯风场模拟,模拟结果与目标谱符合良好,表明本文方法模拟非高斯风场具有较高的精确度和计算效率。     

Control Volume Method for the Dynamo Problem in the Sphere with the Free Rotating Inner Core

A model of thermally driven dynamo in the Boussinesq approximation in the spherical shell with the free rotating inner core is considered. To solve equations we use a new in dynamo modeling control volume technique (for details of this method for hydrodynamics see Patankar, 1980). The main advantage of this method over previous attempts to solve magnetohydrodynamics equations in the spherical grids is that no filtering of high harmonics in the pole regions is needed. We present the results of simulations for the self-consistent dynamo system evolution over the diffusion time and longer periods. Different ways of stabilizations of magnetohydrodynamics equations, when convective terms are of the same order (or larger) as conductive ones, are considered.     

基于一种新智能优化算法与谱相关方法对重力固体潮的分析

根据月球与太阳相对于地球位置的关系,建立一个三维正交分解模型来揭示重力固体潮中包含的谐波成分。在此基础上,提出一种基于单形邻域与多角色进化策略智能优化算法的独立分量分析方法,用以提高算法效率和全局寻优能力;并结合谱相关方法,对重力固体潮观测数据进行处理和分析,观察其频域和时域的变化。最后引入理论信号和理论计算值作为参考背景,以凸显其异常变化特征。研究表明,利用该方法可以有效地反映出重力固体潮潮汐的日波、半日波、长周期波等特征。同时,发现重力固体潮潮汐的异常变化中隐含有地震前兆信息,通过对云南地区观测数据的分析,在排除测量误差和环境影响外,发现在地震前2~5个月内,重力固体潮的长周期波均呈现出规律性的异常变化。这反映出地震的前兆异常信息,可能对地震时间和地点的预测提供依据。     

不考虑磁层顶磁重联的全球三维MHD模型

本文介绍了一个新的磁层全球三维MHD模型,该模型可通过把IMF和地球磁场分开处理的方法“关闭”磁层顶的磁重联,从而可直观地显示不同IMF条件下磁层顶的IMF与地磁场的反平行区域,即磁重联最可能发生的地方,结果表示,IMFBx分量对磁层顶磁重联有重要影响。由于可关闭磁重联,该模型还可有效地研究有无磁重联时,太阳风对磁层位形（如晨-昏不对称性）、粒子输运等重要问题的影响,有助于揭示磁层物理现象的基本特性。     

地震波数值模拟的褶积微分算子法与伪谱法的对比分析

将基于Forsyte广义正交多项式的褶积微分算子法运用于复杂非均匀介质地震波场模拟中,并将计算结果与伪谱法计算结果进行分析比较。通过二者的计算时间对比发现:在同样的计算条件下,褶积微分算子法的采样时间始终小于伪谱法,这是其进行地震波数值模拟的一个明显优势。通过波场快照的对比,褶积微分算子法的模拟结果与伪谱法数值模拟结果的频散效应相当,可为地震波场的值计算提供一种新的选择。     

随机方法模拟地震动的应用研究

对随机方法模拟地震动的实际应用进行了研究。通过实际模拟验证,此方法简单有效,可为结构抗震设计提供验算依据,同时为设计反应谱的拟合提供参照数据,有一定的实用性,但仍存在一定的不足。     

人工源宽角地震实验的谱元法模拟和逆时偏移成像方法研究

人工源宽角反射(折射)地震资料具有偏移距较大、信噪比较低等特点,通常用于地震波走时反演重建地壳速度结构。逆时偏移成像方法作为勘探地震学领域获取地下构造形态的有效手段之一,可以有效弥补走时反演方法的不足。本文针对大偏移距宽角反射(折射)地震实验,利用四边形网格谱元法进行波场模拟,结合了有限元法的灵活性和谱方法的指数收敛性,高效且高精度获取模型合成地震记录,后采用逆时偏移成像方法将合成地震记录偏移归位,获取地壳几何结构,验证了逆时偏移成像方法在宽角地震资料处理及结果解释中的适用性,为后期实际地震资料的偏移成像提供了理论依据和支持。     

用HV谱比法推测银川市区沉积层基底分布特征

在缺乏其他资料的情况下,地脉动常常用做确定地震动对地表介质产生影响效应的简便手段。本文以银川市区为研究对象,根据地震勘探资料有目的的选取5条测线在银川市区进行地脉动观测,观测点共141个。用Nakamura提出的HV谱比法解析观测数据,在给定地下构造剪切波速度(VS)的基础上,由H/V比值曲线中的基本频率推测盆地深层地下构造。通过理论计算进一步验证了解析结果。结合前人地震勘探资料推测了银川市区脉动基本频率分布特征,并给出2D和3D银川市基底构造变化情况,对比分析表明,HV谱比法得到的脉动基本频率值可以反映银川盆地基底变化情况。     

Groundwater Depth Forecasting Using Configurational Entropy Spectral Analyses with the Optimal Input

Accurate groundwater depth forecasting is particularly important for human life and sustainable groundwater management in arid and semi-arid areas. To improve the groundwater forecasting accuracy, in this paper, a hybrid groundwater depth forecasting model using configurational entropy spectral analyses (CESA) with the optimal input is constructed. An original groundwater depth series is decomposed into subseries of different frequencies using the variational mode decomposition (VMD) method. Cross-correlation analysis and Shannon entropy methods are applied to select the optimal input series for the model. The ultimate forecasted values of the groundwater depth can be obtained from the various forecasted values of the selected series with the CESA model. The applicability of the hybrid model is verified using the groundwater depth data from four monitoring wells in the Xi'an of Northwest China. The forecasting accuracy of the models was evaluated based on the average relative error (RE), root mean square error (RMSE), correlation coefficient (R) and Nash-Sutcliffe coefficient (NSE). The results indicated that comparing with the CESA and autoregressive model, the hybrid model has higher prediction performance.     

Source Scaling of Inland Crustal Earthquake Sequences in Japan Using the S-Wave Coda Spectral Ratio Method

We estimate corner frequencies and stress drops for 298 events ranging from M _w 3.2–7.0 in 17 inland crustal earthquake sequences in Japan to investigate the source scaling and variation in stress drops. We obtain the source spectral ratio from observed records by the S-wave coda spectral ratio method. The advantage of using the S-wave coda is in obtaining much more stable source spectral ratios than using direct S-waves. We carefully examine the common shape of the decay of coda envelopes between event pair records. The corner frequency and stress drop are estimated by modeling the observed source spectral ratio with the omega-square source spectral model. We investigate the dependences of stress drops on some tectonic effects such as regionality, focal mechanism, and source depth. The principal findings are as follows: (1) a break in self-similar source scaling is found in our dataset. Events larger than M _w 4.5 show larger stress drops than those of smaller events. (2) Stress drops of aftershocks are mostly smaller than those of mainshocks in each sequence. (3) There are no systematic differences between stress drops of events occurring inside and outside the Niigata-Kobe Tectonic Zone in Japan. (4) Clear dependence of the faulting type on stress drops cannot be seen. (5) Stress drops of aftershocks depend on their source depth. (6) The crack size obtained from the corner frequency corresponds to the total rupture area of heterogeneous slip models for large events.     

Badland Morphology and Evolution: Interpretation Using a Simulation Model

A drainage basin simulation model is used to interpret the morphometry and historical evolution of Mancos Shale badlands in Utah. High relief slopes in these badlands feature narrow divides and linear profiles due to threshold mass-wasting. Threshold slopes become longer in proportion to erosion rate, implying lower drainage density and higher relief. By contrast, in slowly eroding areas of low relief, both model results and observations indicate that drainage density increases with relief, suggesting control by critical shear stress. Field relationships and simulation modelling indicate that the badlands have resulted from rapid downcutting of the master drainage below an Early Wisconsin terrace to the present river level, followed by base level stability. As a result, Early Wisconsin alluvial surfaces on the shale have been dissected up to 62 m into steep badlands, and a Holocene alluvial surface is gradually replacing the badland slopes which are erocing by parallel retreat. © 1997 by John Wiley & Sons, Ltd.     

A New Technique to Synthesize Seismography with More Flexibility: the Legendre Spectral Element Method with Overlapped Elements

The classic spectral element method (SEM) is important for seismographical simulation. However, waves subjected to irregular interfaces or surfaces are difficult to simulate accurately using SEM with quadrangular/hexahedral elements. In this paper we propose a new technique to solve this problem. The technique reconstructs some new elements near the surface/interface to substitute for any element crossing the interface, thus making the boundary of some new elements an accurate fit to the interface/surface. Numerical comparisons with the classic SEM show that the technique has improved flexibility when dealing with interface problems without losing accuracy and efficiency. The technique also enables us to vary the size and shape of an element smoothly as the velocity in a medium varies so that this removes the inaccuracy resulting from the high local variation of the grid in the classic SEM. Therefore, the technique widens the application of the classic SEM in seismographic simulation.     

自适应时间步长法及三维堤坝地震液化数值模拟

三维大模型数值计算因巨大的单元和结点数目而非常耗时,在地震响应分析中受计算时间步长的限值则更加耗时。在饱和砂土动力液化计算平台上开发时域离散误差评估方法和时间步长自适应调整的计算程序,并成功应用于三维堤坝地震液化响应分析。时域离散误差包括土骨架的位移误差和单元孔压误差,通过定义孔压误差影响系数计算出混合误差,根据混合误差和设定的误差允许值进行计算步长的自适应调整。在三维堤坝地震液化数值模拟中,采用自适应时间步长法有效避免小步长精确但耗时、大步长省时而不精确的缺点。在大模型和超大模型计算中,最优调整每一步的计算时间步长,完美实现既节省时间又不失精度的时域离散策略。     

基于谱比法的江苏强震动台站场地特征分析

选取江苏省强震动台网近年来获得的强震动记录,基于水平竖向谱比法(HVSR),计算了22个强震动台站的速度反应谱平均谱比曲线,采用谱比形状一致法进行场地分类,并结合典型台站场地的工程地质资料进行对比分析。研究结果表明,平均谱比曲线的卓越周期、场地放大等特征与台站场地地质资料相吻合,与传统场地分类方法相比,基于谱比法的场地特征分类方法能够突出不同场地的地震动反应特征,较好地体现了台站的场地反应特征。     

Simulation of airflow around rain gauges: Comparison of LES with RANS models

Wind is responsible for systematic errors that affect rain gauge measurements. The authors investigate the use of computational fluid dynamics (CFD) to calculate airflow around rain gauges by applying a high-resolution large eddy simulation (LES) model to determine the flow fields around a measuring system of two rain gauges. The simulated air flow field is characterized by the presence of massive separation which induces the formation and shedding of highly unsteady eddies in the detached shear layers and wakes. Parts of these detached structures occur over the orifice of the rain gauges and may substantially affect the dynamics of the raindrops in this critical region. Non-dissipative LES methods used with fine enough meshes can successfully predict these eddies and their associated fluctuations. The authors compare statistics from LES with steady-state Reynolds averaged Navier–Stokes (RANS) simulations using the k–ε and shear stress transport k–ω turbulence models. They find that both RANS and LES models predict similar mean velocity distributions around the rain gauges. However, they determine the distribution of the resolved turbulent kinetic energy (TKE) to be strongly dependent on the RANS model used. Neither RANS model predictions of TKE are close to those of LES. The authors conclude that the failure of RANS to predict TKE is an important limitation, as TKE is needed to scale the local velocity fluctuations in stochastic models used to calculate the motion of raindrops in the flow field.