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1.
纵、横波的分离是多波多分量地震资料处理中很重要的一步,其分离结果直接影响到后续数据处理的质量.各向同性介质中纵波为无旋场,横波为无散场,因此可以在频率-波数域利用散度和旋度算子对地震记录进行纵、横波分离,但是此处理过程必须知道地表处的纵、横波速度.本文给出了一种估算地表纵、横波速度的方法,可以在纵、横波速度值未知的情况下,将其估算出来.针对弹性波场进行散度和旋度运算时,纵、横波的相位和振幅比发生改变的问题,本文给出了相位和纵、横波振幅比的校正方法. 相似文献
2.
地震波传播过程中,质点的振动不仅包括三个独立的平移部分,还包括三个独立的旋转部分.本文基于一阶速度-应力弹性波方程,采用分裂完全匹配层(SPML)的吸收边界条件,推导了时间导数二阶精度和空间导数高阶精度的交错网格有限差分格式的弹性波速度与应力各分量计算公式,模拟了各向同性介质中均匀模型和层状模型下的六分量波场,并对二维各向同性层状模型下的三个分量地震记录做高分辨率线性拉东变换得到各自的频散能谱.数值模拟分析结果表明:(1)旋转分量的能量要比平动分量弱的多;(2)在平动分量上,面波能量强,频率低,反射P波能量较强,反射S波能量稍弱;在旋转分量上,反射P波能量很弱,S波能量强;(3)与平动分量相比,旋转分量的频散能谱效果更好,能看到基阶和完整的高阶面波,即旋转分量能反映更多的地下介质信息. 相似文献
3.
为了便于研究双相介质固流相混合弹性波场中纵横波波场的传播规律,提出了基于交错网格的Biot双相各向同性介质弹性波动方程高精度波场分离正演数值模拟方法.采用高阶交错网格有限差分法来构建一阶双曲型双相各向同性介质弹性波动方程正演算子实现波场正演,并在每一步递推过程中,分别计算出同相和流相分量相应的散度场(纯纵波场)和旋度场... 相似文献
4.
本文使用炮并行和区域分解(物理上分割模型,使用基于MPI的分布式存储架构的计算集群,节约单个CPU内核的内存使用量,快速进行正演数值模拟)两种并行算法.该方法的每一步迭代都能确保近似海森矩阵的正定,因此,算法稳健.将时间正向传播的炮波场和反向逆时间传播的残差波场(伴随波场)进行零延迟互相关计算,得到误差泛函的梯度,然后对梯度乘以一个预条件算子,从而加快反演的收敛速度.通过抛物线搜索方法而估计步长,使用L-BFGS算法(限定内存的BFGS算法)求解模型的更新量,进行二维时间空间域弹性波全波形反演.将该反演方法应用到Marmousi2弹性波理论模型,分别反演Marmousi2理论模型的纵波速度、横波速度以及密度等三个参数.我们分别使用截止频率为2 Hz、5 Hz、10 Hz和20 Hz四个阶段的低通巴特沃斯滤波器,采用多尺度的策略,从理论模型数据的低频分量开始反演,将低频分量的反演结果作为高频分量反演时的初始模型,然后依次反演数据的高频分量.理论模型数值试验反演所得到的结果证实:二维时间空间域弹性波全波形反演计算灵活,适用于各种观测系统,能够方便地对地震数据进行加时窗;二维时间空间域弹性波全波形反演所得纵波速度模型的分辨率最高,横波速度模型的分辨率次之,密度模型的分辨率稍微差些. 相似文献
5.
波场延拓得到的多分量波场中既包含纵波信息也包含横波信息,能否在全波场中实现纵横波的分离对各向同性和各向异性逆时偏移都有非常重要的意义.传统的散度旋度分离只适应于各向同性介质而对各向异性介质却无效.在非规则、非结构网格的弹性波数值模拟方法的基础上,发展了一种适应于各向异性介质的波场分离方法.该方法通过求解Christoffel方程,得到相角和极化角的关系,再利用群角和相角的关系,直接得到群角和极化角的关系.该方法与现存的各向异性波场分离相比,获得的计算效率改进更显著,而且存储量小.用简单各向异性模型和SEG各向异性Hess模型进行测试,都得到了较好的效果,证明了本文方法的有效性. 相似文献
6.
研究了三维弱各向异性近似下,利用伪P波(伪纵波)模拟弹性波场P分量在倾斜对称轴的横向各向同性(TTI)介质中的传播过程,并对比了分别基于弹性Hooke定律、弹性波投影和运动学色散方程所建立的三种二阶差分伪P波方程的正演特点.目前这些伪P波方程数值计算主要采用规则网格差分,但是规则网格在TTI模拟中有低效率、低精度以及不稳定的缺点.为了提高计算的精度,本文构建出相应方程的交错网格有限差分格式.通过对比伪P波方程在三维TTI介质中不同的数值模拟的表达形式,本文认为基于色散方程所建立的伪P波方程在模拟弹性波中P波传播的过程中具有最小的噪声.本文分析不同的各向同性对称轴空间角度的频散特征,并引入适当的横波速度维持计算的稳定.二维模型算例表明,本文提出的交错网格正演算法可以得到稳定光滑的伪P波正演波场.使用本文交错网格算法对二维BP TTI模型的逆时偏移也具有较稳定的偏移结果. 相似文献
7.
以多分量地震观测为基础,联合纵波和转换横波数据能更有效地估计地下介质的弹性和物性参数,提升地质构造成像与油气储层描述的精度.在海底多分量地震数据处理过程中,观测记录的上-下行波分解和P/S波分离可压制水层鸣震以及P与S波之间的串扰,对偏移成像和纵横波速度建模至关重要.但受海底环境、仪器与观测因素共同影响,许多海底多分量地震资料都无法基于现有的海底波场分离方法与流程取得合理的结果.本文以海底声波场与弹性波场分离基本原理为基础,通过对方法流程的修正,摆脱常规流程对中小偏移距直达波信号的依赖性.借助模拟数据实验讨论了波场分离对海底介质参数、噪声的敏感性.结合东海YQ探区海底多分量地震资料上-下行P/S波分离及其叠前深度偏移处理,验证了本文方法流程的可行性. 相似文献
8.
τ-p变换在隧道反射地震超前预报波场分离中应用的数值模拟研究 总被引：1，自引：0，他引：1
本文基于二维有限元数值方法,模拟了复杂条件下隧道内的地震全波波场,分析了隧道地震超前预报中的反射记录中的多方向和多波反射波特征,证实了分离前方有效反射波和其它方向的干扰反射波,以及有效反射波的P波、S波分离在预报准确性中的重要性.基于多个数值模型,研究了τ-p变换进行波场分离的有效性和影响因素.研究结果表明:在隧道前方反射层倾向与隧道轴线交角变化较大范围内(90°～45°),τ-p变换都可以有效的分离多方向和多波反射事件,提取主要来自掌子面前方的有效反射波剖面.来自隧道项、底的缓倾界面的具有双曲时距曲线特征的干扰波和S波的高视速度会对P波的波场分离产生较大干扰;而由于S波的低速和强能量特征,其波场分离受具有双曲时距曲线特征的干扰波的视速度影响较小,且不受P波的影响. 相似文献
9.
《地球物理学进展》2017,(4)
弹性波逆时偏移是当前多分量地震资料相对准确的偏移算法,它能够形成多波模式的成像剖面,从而减少纵波勘探的多解性.本文首先依据各向同性介质中矢量分离纵横波场的速度-应力方程组,利用高阶交错网格有限差分数值方法求解弹性波方程,进而构建矢量的纵波和横波波场,不同于散度和旋度算子分离纵横波场的传统方法,文中提出的矢量分离纵横波场方法保持了原始波场的振幅和相位特征.文中也提出将震源归一化的内积成像条件应用于分离后的纯纵波和横波矢量场,由此得到的转换波成像避免了传统弹性波成像方法中出现的极性反转.水平层状和复杂构造模型测试表明,文中提出的基于矢量分离纵横波场的弹性波逆时偏移方法成像精度高,转换波成像PS和SP极性无反转,所形成的多种模式纯波剖面能够准确地对复杂地下构造成像. 相似文献
10.
井间地震与常规地震相比具有较高的分辨率,同时波场也更加复杂.利用视速度特征的差异很容易地分离井间上下行波场,根据纵横波偏振特征的不同可将纵横波完全分离,但是针对井间地震侧面波的研究并不多.本文构建高速透镜体和断层模型进行波场数值模拟,通过对三维地震波场的传播特征进行分析可知,井间地震接收的波场既有岩性分界面的响应,还会有侧向地质不均匀体产生的干扰,严重影响成像的质量和精度.经偏振旋转后的T分量记录对物性横向变化较为敏感,综合分析X、Y、Z分量和T分量上不同连井剖面的波场传播特征,可对侧向传播的干扰波进行有效识别,利用线性Radon变换可以在一定程度上将侧面波进行压制,为后续井间地震资料处理提供高信噪比的数据.本文通过理论模型进行试算研究,验证了该方法的有效性,并对理论记录取得了较好的分离效果. 相似文献
11.
12.
M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
14.
《地震工程与工程振动(英文版)》2014,(4)
正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and 相似文献
15.
O. Martins 《水文研究》1988,2(1):19-29
Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO3 > SO4 > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals. 相似文献
16.
Historical earthquakes noted in the written records of the South China region, including Hong Kong, are not well delineated along identified prominent fault sources. Despite the lack of any definitive, localised trend in the spatial distribution of seismic activity in the region, there does appear to be some major disparity in the seismic activity rates (especially for large magnitude earthquakes) between the near-field and the far-field regions of Hong Kong. Despite this observation, previous studies of the regional seismic activity and seismic ground motion hazard (the latter using a probabilistic seismic hazard assessment, PSHA) have considered very broad source zone regions, in which uniform levels of seismic activity have been assumed. The present paper further scrutinises this broad source zone (BSZ) approach by adopting a novel expanding circular disc (ECD) method to determine the rates of earthquake recurrence. Such a method is intended to counter-check previously developed models by determining earthquake scenario events in terms of magnitude–distance (M–R) pairs or combinations, having defined values of average return period. Unlike the BSZ approach, the ECD method specifically accounts for the supposed variations in the seismic activity rates between events in the near-field and the far-field of Hong Kong.The form of the developed method is particularly suited to the determination of design-level earthquake ground motions for bedrock sites, since it assumes a directionally-independent attenuation model as described in the companion paper. It is found that, whilst the BSZ approach may indicate the overall average levels of hazard that are representative of the South China region as a whole, it does not capture the large disparity in seismic activity rates between near-field and far-field events. This important feature is expected to have a significant impact upon engineering assessments of the seismic safety of structures in Hong Kong and elsewhere in the South China region. For example, it is found that for events with M≥6, the seismic activity rate (normalised by time and area) in the very far-field is around 3.5 times larger than in the near-field and medium-field of Hong Kong. The resulting design M-R combinations, covering a range of return periods from 70 to 2500 years, are limited, for very long return periods and for distant events, by the maximum credible earthquake (MCE) magnitude. Intensive research to determine this seismic hazard parameter is recommended, in order to refine further the results of the ECD analysis, which presently conservatively assumes the MCE to range between M=6 in the near-field of Hong Kong to M=8 in the very far-field, at distances greater than 280 km from Hong Kong. 相似文献
17.
Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia 
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下载免费PDF全文 Hitoshi Hasegawa Hisao Ando Noriko Hasebe Niiden Ichinnorov Tohru Ohta Takashi Hasegawa Masanobu Yamamoto Gang Li Bat‐Orshikh Erdenetsogt Ulrich Heimhofer Takayuki Murata Hironori Shinya G. Enerel G. Oyunjargal O. Munkhtsetseg Noriyuki Suzuki Tomohisa Irino Koshi Yamamoto 《Island Arc》2018,27(3)
Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia. 相似文献
18.
A. C. LIAKOPOULOS Dr. Eng. 《水文科学杂志》2013,58(1):69-110
ABSTRACT The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content. Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data. Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme. Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate. 相似文献
19.
Church repair swarms and earthquakes in Rhodes Island, Greece 总被引：1，自引：0，他引：1
20.
GHODRAT TORABI 《Island Arc》2012,21(3):215-229
Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO 2 (67.8–71.0 wt%), Al 2 O 3 (14.9–17.1 wt%) and Na 2 O (5.3–8.6 wt%), low K 2 O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area. 相似文献