2008年青海大柴旦Mw6.3地震地面运动模拟

2008年11月10日在青海柴达木盆地北缘发生了大柴旦M_W6.3地震,为了研究该地震的区域地震波传播与地面运动特征,本文利用地质资料和地壳速度结构研究成果,构建了柴达木盆地及周边区域三维传播介质模型,采用有限差分方法模拟了大柴旦地震波场传播过程以及地面运动分布特征.结果表明,柴达木盆地对波场传播有明显影响,表现为地震波传入盆地后在边界产生次生面波,盆地沉积物对地震波具有围陷作用,地震地面运动在盆地内振幅增大、持时延长.模拟结果给出的地震地面运动峰值速度分布以及理论地震图均和观测结果符合较好,反映数值模拟较好地给出了观测地面运动的主要特征以及传播介质模型的合理性.     

横向非均匀地壳结构中人工地震资料反演的初步探讨

在横向非均匀的复杂地壳结构中,地震波的理论走时和理论地震图的计算一般借助于射线近似法。基于上述理论,本文探讨了由人工地震资料反演横向非均匀的地壳结构的方法和步骤。反演过程中,综合考虑了波的运动学特征和动力学特征。以任县—武清剖面的资料处理为例,说明了该方法的实际应用。     

地震波层析成像方法于孤石探测的应用分析

研究地震波原始记录特征,可为提高地震波层析成像探测地下孤石的精确度提供理论基础与科学依据.论文首先引用一地震波层析成像探测孤石的实例,并对其进行反演分析;然后对原始数据进行频谱分析,得出频谱图中高频能量强弱与地下介质高、低速介质分布有关;再分析单道地震波记录中的初至畸变与地下介质岩性突变异常相关,从而推测地下孤石分布的位置;最后经钻探成果资料的验证,充分说明地震波波场规律准确合理以及层析成像反演结果的精确度.     

苏北测震台网地面和井下地震记录波形频谱分析

根据苏北测震台网地面台站和深井台站记录的地震波形资料,分析2009年10月以来台网附近 ML ≥2．8地震波频谱特性。分析可知：地面记录与井下记录的地震波频谱特性存在一定差异,地面记录地震波拐角频率较井下约大0．28 Hz,地震波峰值频率比井下约小0．22 Hz;对于ML ＞4．5地震,地面记录地震波的优势频率范围小于井下记录;地震矩和矩震级地面台站记录数值较大,差值分别为3．104×10^14 N·m 和0．32级。     

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。     

准各向异性粘弹介质地震波的数字仿真

本文论述准各向异性粘弹波动方程有限元数值解地震波响应的原理与计算方法,并给出地震衰减因子与方程中粘滞系数的计算关系式。列出了所研制的地面记录地震剖面与井中记录垂直地震剖面,以及波场时间切片图、散度与旋度图、应变能与动能的时间切片图。本方法适于任意分层形态且层间物性参数为强间断的实际地震剖面的仿真,旨在研究正问题以实现反问题。     

利用SP''''、P_s测定太原台附近的地壳厚度

确定地震波的走时,实现精确的地震定位,从地震台所在地区入手研究地壳内部结构及地壳厚度是很重要.地壳结构有明显的地区性,因此地震波走时也有地区性差异.地震波穿过地壳和地球内部传播,能够带来与地壳和地球内部结构的一些信息,它可通过在地震图上分析、辩认、处理与地壳结构有关的震相获得.我们利用本台1977—1981年记录的远震资料,分析记录较清的SP′和Ps震相,利用SP′和S的走时差计算本台附近的地壳厚度,并利用Ps震相进行了互比对照.     

中国东部马鞍山-常熟-启东地带地壳与上地幔结构和速度分布的爆炸地震研究

本文根据马鞍山、常熟两地井中组合爆炸激发的地震波,在马鞍山-常熟-启东长约300余公里的测线上,利用相遇和单支观测系统得到的记录,进行了数据处理、走时拟合和反演计算,并通过射线跟踪和理论地震图等,探讨了地壳介质的横向不均匀性,建立了该区成层地壳结构与速度分布的初步模型。 研究结果表明,该区不同界面的首波和反射波具有不同的特征。根据走时的间断、跳跃,视速度变化,频谱形态与主频率分布,Q值变化与振幅特征表明,在江苏省溧阳地震活动地区,地壳内部存在着深断裂和介质疏松破碎地带。 在该测线所辖地区,地壳由成层介质组成,其平均厚度为32-28km,在该地壳中存在着低速层,向东陆缘地带地壳缓慢变薄。 本文最后讨论了剖面所经溧阳地震地区的深部结构特征。     

广角地震波场特征分析

地震宽角反射/折射方法主要是利用壳内与上地幔顶层的广角反射信息重建地壳上地幔结构,是研究地壳上地幔结构构造最有效的方法之一.同时,宽角地震接收到的超临界角的广角反射信息,相对于临界角之内的反射信息必定存在着随偏移距变化的时移现象.本文通过构建地壳模型采用交错网格有限差分方法合成广角地震记录,并从理论地震图上分别用传统射线方法和考虑时移影响的方法标定了震相走时,分析了广角反射的地震波场特征,揭示了地震资料中的广角效应,继而分析了广角信息存在对接收波场的响应影响.     

利用单台波形资料计算大柴旦6．3级地震余震震源机制

以2008年11月10日大柴旦Ms6．3级地震余震数字地震波观测资料为基础,运用矩张量反演方法,利用单台三分量波形资料计算余震的震源机制。收集整理大柴旦Ms6．3级地震公认的震源参数结果和青海区域地震台网数字地震波资料,以大柴旦Ms6．3级地震的震源参数作为约束,计算理论地震波来确定该区域的地壳速度模型。以此模型计算ML≥2．0级余震震源机制解。共收集160个余震资料,最后确定了85个余震震源机制解,其中最大震级为朋。4．7,最小震级为ML2.0。进行单台与多台联合矩张量反演结果对比,两种方法所确定的结果相差不大。实际计算表明,在观测资料信噪比较高的情况下,运用单台数字地震波观测资料可以较好地确定中小地震的震源机制。     

层状介质中内源引起的地震波理论地震图的部分分离变量——有限差分计算方法

文献〔1〕给出了震源在地表时计算理论地震图的部分分离变量——有限差分方法。本文继〔1〕讨论了震源在介质内部时,特别是震源在介质分界面上时理论地震图的计算方法。含贝塞尔函数的数值积分是用FiLon方法完成的,它具有精度高,运算速度快的特点。作为例子,本文最后给出了利用所述计算方法得到的不同内源在含两个高速夹层地壳模型中的理论地震图。     

火山地震的理论地震图计算方法

本文首先分析了不同类型火山地震的波形,提出了相应的震源模型.然后发展了计算层状介质理论地震图的部分分离变量—有限差分方法,其最重要的环节是引用了吸收边界条件,使计算工作得以简化.这种方法特别适用于火山地震的理论地震图计算.最后,本文给出了计算实例.     

由深源远震体波记录反演华北北部地壳上地幔速度结构

重点研究的地区为河北省北部包括京津地区，以及山西、内蒙的部分地区，在此区选取了２９个台站；在向东延伸的背景区，选取了６个台站。利用这些台站的深源远震体波记录资料，通过选取介质结构模型，计算理论地震图，与观测图进行拟合，以确定地震台下介质结构的可接受模型。在拟合时，对每个地震台站都选择若干次深源远震的体波记录作为观测图。对每个地震台站一般都算出６０个不同模型的理论图。实际上做出的结果比地壳深，为大约８０ｋｍ（即大致相当于岩石层或称岩石圈）厚度内的地壳上地幔介质结构，它们大都由１０层左右的介质组成。通过波形拟合共给出了上述３５个台站下的壳幔介质分层结构。并由此给出了Ｍｏｈｏ面的轮廓。     

A review of numerical experiments on seismic wave scattering

This paper reviews applications of the finite-difference and finite-element methods to the study of seismic wave scattering in both simple and complex velocity models. These numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity, such as the crust. The methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases (e.g.,P toSV, SV toP, body wave to surface wave). The numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important. Progress has been made with numerical methods in understanding how near-surface, low-velocity basin structures scatter surface waves and vertically-incident body waves. The numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth. Numerical studies have demonstrated the importance of conversions from body waves to surface waves (andvice versa) when lateral heterogeneities and topographic relief are present in the uppermost crust. Recently, several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space. This stochastic approach seeks to understand the effects of small-scale complexity in the earth which cannot be resolved deterministically. These experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high-frequency (1 Hz) seismograms. These simulations have been applied to the study of many features observed in actual high-frequency seismic waves, including: the amplitude and time decay of seismic coda, the apparent attenuation from scattering, the dispersion of waveforms, and the travel time and waveform variations across arrays of receivers.     

不同模型下爆炸源和层裂源的 Lg波特性研究

地下核爆炸区域及远区地震波信号中,有二次源即层裂源的贡献,其对区域震相Lg波具有调制作用.本文利用理论地震图数值模拟方法,分析爆炸源和层裂源在3种典型介质速度模型下的区域震相特征,得到了爆炸源和层裂源所激发的Lg波与介质速度模型的关系,并结合CLVD源所激发的S波随震中距的演化过程,对Lg波的形成机制进行了阐述.结果表明,CLVD源是激发地下核爆炸低频Lg波的主要因素.      

地震波在垂向不均匀介质中传播问题的某些探讨

本文计算了含有高速夹层介质中首波的理论地震图。通过分析得到,当高速夹层薄到一定程度时,就会产生干涉型首波,从而从一个侧面证明了射线理论的局限性。通过对地震波反射—折射系数能量守恒关系的分析,探讨了反射—折射系数大于1的可能性。最后,介绍了一种计算垂向不均匀介质中拉梅问题理论地震图的数值方法——有限差分法。     

Synthetic Seismograms and Wide-angle Seismic Attributes from the Gaussian Beam and Reflectivity Methods for Models with Interfaces and Velocity Gradients

— The effects of interfaces and velocity gradients on wide-angle seismic attributes are investigated using synthetic seismograms. The seismic attributes considered include envelope amplitude, pulse instantaneous frequency, and arrival time of selected phases. For models with interfaces and homogeneous layers, head waves can propagate which have lower amplitudes, as well as frequency content, compared to the direct arrivals. For media with interfaces and velocity gradients, higher amplitude diving waves and interference waves can also occur. The Gaussian beam and reflectivity methods are used to compute synthetic seismograms for simple models with interfaces and gradients. From the results of these methods, seismic attributes are obtained and compared. It was found that both methods were able to simulate wide-angle seismic attributes for the simple models considered. The advantage of using the Gaussian beam method for seismic modeling and inversion is that it is fast and also asymptotically valid for laterally varying media.     

理论地震图计算方法

近二十多年来,随着理论地震学和计算技术的发展,理论地震图的计算技术有了飞速发展.目前已能对不同的介质模型和震源计算各种体波、面波、地球自由震荡和静态位移场.它们在研究天然地震震源过程、地球内部结构、近场强地面运动、核爆作监测以及地震勘探等领域中发挥了越来越大的作用. 目前常用的理论地震图计算方法主要包括积分变换法、离散数值方法和射线方法几大类.本文对这些方法分类进行了简单介绍,并评论了各种方法的特点和各自的适用范围.     

THE APPLICATION OF PML BOUNDARY CODITIONS IN THE SIMULATION OF SEISMIC WAVE BY THE HIGH-ORDER STAGGERED-GRID FINITE DIFFERENCES AT THE TRANSVERSELY ISOTROPIC MEDIA

In the realm of the numerical simulation, finite difference method and finite element method are more intuitive and effective than other simulation methods. In the process of simulating seismic wave propagation, the finite differences method is widely used because of its high computational efficiency and the advantage of the algorithm is more efficient. With the demand of precision, more and more researchers have proposed more effective methods of finite differences, such as the high-order staggered-grid finite differences method, which can restore the actual process of wave propagation on the premise of ensuring accuracy and improving the efficiency of operation. In the past numerical simulation of seismic wave field, different models of isotropic medium are mostly used, but it is difficult to reflect the true layer situation. With the research demand of natural seismology and seismic exploration, the research on anisotropic media is more and more extensive. Transversely isotropic(TI)media can well simulate the seismic wave propagation in the formation medium, such as gas-bearing sandstone, mudstone, shale et al., the character of TI media is reflected by introducing the Thomsen parameters to reflect its weak anisotropy of vertical direction by using Thomson parameter. Therefore, studying the process of seismic wave propagation in TI media can restore the true information of the formation to the greatest extent, and provide a more reliable simulation basis for the numerical simulation of seismic wave propagation. In the geodynamic simulation and the numerical simulation of the seismic wave field, under the limited influence of the calculation area, if no boundary conditions are added, a strong artificial boundary reflection will be generated, which greatly reduces the validity of the simulation. In order to minimize the influence of model boundaries on the reflection of seismic waves, it is often necessary to introduce absorbing boundary conditions. At present, there are three types of absorption boundary conditions: one-way wave absorption boundary, attenuation absorption boundary, and perfectly matched layer(PML)absorption boundary. In terms of numerical simulation of seismic waves, the boundary absorption effect of PML is stronger than the first two, which is currently the most commonly used method, and it also represents the cutting-edge development direction of absorption boundary technology. The perfectly matched layer absorbing boundary is effectively applied to eliminating the reflective waves from model boundaries, but for transversely isotropic medium, the effect of the absorbing is not very well. For this reason, the elastic dynamic wave equations in transversely isotropic media are derived, and we describe a second-order accurate time, tenth-order accurate space, formulation of the Madariaga-Virieux staggered-grid finite difference methods with the perfectly matched layer(PML)are given. In addition, we have established vertical transversely isotropic(VTI)media and arbitrary inclined tilted transversely isotropic(TTI)media models, using a uniform half-space velocity model and a two-layer velocity model, respectively. By combining the actual geoscience background, we set the corresponding parameters and simulation conditions in order to make our model more research-oriented. When setting model parameters, different PML thickness, incident angle, source frequency and velocity layer models were transformed to verify the inhibition of boundary reflection effect by PML absorption boundary layer. The implementations of this simulation show that the formula is correct and for the transversely isotropic(TI)media of any angular symmetry axis, when the thickness of the PML layer reaches a certain value, the seismic wave reflection effect generated by the artificial boundary can be well suppressed, and the absorption effect of PML is not subject to changes in incident angle and wave frequency. Therefore, the results of our study indicate that our research method can be used to simulate the propagation process of seismic waves in the transversely isotropic(TI)media without being affected by the reflected waves at the model boundary to restore the actual formation information and more valuable geological research.     

弹性介质各向异性研究沿革、现状与问题

各向异性介质中地震波的传播研究是当今地震学研究领域中的前沿课题之一,同时也是地震学中难题之一.由于地下岩石的各向异性主要表现在:地震波速度随传播方向发生变化;不同类型体波间相互耦合;横渡发生分裂:面波速度频散依赖于传播方向等.薄互层与裂隙定向分布等产生视各向异性,放在石油地震勘探、地震预测和岩石层物理与动力学研究中有极大潜力和应用前景,并受到广泛重视.为此,本文较为详尽地讨论了弹性介质中地震波各向异性研究的沿革,简述了国内外现今取得的主要研究成果以及目前尚存在的和有待解决的一些主要问题.最后对我国在各向异性介质中地震波动、检测和应用等研究提出了一些看法.