The effectiveness of a pseudo-inverse extended Born operator to handle lateral heterogeneity for imaging and velocity analysis applications     

Abdullah Alali  Bingbing Sun  Tariq Alkhalifah 《Geophysical Prospecting》2020,68(4):1154-1166

Wave equation–based migration velocity analysis techniques aim to construct a kinematically accurate velocity model for imaging or as an initial model for full waveform inversion applications. The most popular wave equation–based migration velocity analysis method is differential semblance optimization, where the velocity model is iteratively updated by minimizing the unfocused energy in an extended image volume. However, differential semblance optimization suffers from artefacts, courtesy of the adjoint operator used in imaging, leading to poor convergence. Recent findings show that true amplitude imaging plays a significant role in enhancing the differential semblance optimization's gradient and reducing the artefacts. Here, we focus on a pseudo-inverse operator to the horizontally extended Born as a true amplitude imaging operator. For laterally inhomogeneous models, the operator required a derivative with respect to a vertical shift. Extending the image vertically to evaluate such a derivative is costly and impractical. The inverse operator can be simplified in laterally homogeneous models. We derive an extension of the approach to apply the full inverse formula and evaluate the derivative efficiently. We simplified the implementation by applying the derivative to the imaging condition and utilize the relationship between the source and receiver wavefields and the vertical shift. Specifically, we verify the effectiveness of the approach using the Marmousi model and show that the term required for the lateral inhomogeneity treatment has a relatively small impact on the results for many cases. We then apply the operator in differential semblance optimization and invert for an accurate macro-velocity model, which can serve as an initial velocity model for full waveform inversion.  相似文献   

Analysis of Anomalous Characteristics of Regional Crustal Deformation before the September 16th, 2019 Zhangye MS5.0 Earthquake, Gansu, China     

MA Haiping  WANG Qian  ZHANG Bo  WU Shanyi  WANG Pengtao  DOU Xiying  LI Minjuan 《中国地震研究》2020,34(2):210-218

To study the crustal movement in the vicinity of the epicenter before the Zhangye M_S5.0 earthquake in 2019, the characteristics of crustal deformation before the earthquake are discussed through the GPS velocity field analysis based on the CMONOC data observed from GPS. The baseline time series between two continuous GPS stations and the strain time series of an area among several stations are analyzed in the epicenter area. The resulting time series of baseline azimuth around the epicenter reflects that the energy of the fault in the northern margin of Qilian Mountain is accumulated continuously before 2017. Besides, the movement trend of azimuth slows down after 2017, indicating the stress accumulation on both sides of the seismogenic fault zone has reached a certain degree. The first shear strain and EW-direction linear strain in the epicentral area of the Zhangye M_S5.0 earthquake remain steady after 2017, and the surface strain rate decreases gradually after 2016. It is illustrated that there is an obvious deformation loss at the epicentral region three years before the earthquake, indicating that a certain degree of strain energy is accumulated in this area before the earthquake.  相似文献   

青藏高原东南缘Moho面速度密度跃变研究   总被引：1，自引：0，他引：1       下载免费PDF全文

董蕾  沈旭章  钱银苹 《地球物理学报》2020,63(3):915-927

青藏高原东南缘地下深部结构的研究对了解青藏高原的变形机制和动力学过程具有重要意义.本文利用四川、云南固定台站记录到的远震波形资料,首先采用接收函数H-k叠加方法获得青藏高原东南缘台站下方的地壳厚度和波速比.进而利用接收函数一次转换波和多次波幅度信息确定了青藏高原东南缘Moho面上的S波速度和密度跃变.研究结果表明:研究区由南到北地壳厚度逐渐增加,从永德、沧源、孟连地区的33 km左右增至巴塘地区的69.7 km左右,厚度变化了近乎37 km.四川盆地和松潘甘孜块体南部的姑咱地区具有高泊松比、速度密度跃变较小特征,表明这两个地区含有较多铁镁物质.腾冲地区、龙门山西侧的汶川地区、四川盆地西南缘的沐川地区以及则木河断裂的石门坎至东川地区同属于高泊松比、速度密度跃变较大,显示这些地区壳内存在部分熔融.  相似文献   

USE OF SEISMIC WAVEFORMS AND INSAR DATA FOR DETERMINATION OF THE SEISMOTECTONICS OF THE MAINLING M_S6.9 EARTHQUAKE ON NOV.18, 2017     

LIU Yun-hua  SHAN Xin-jian  ZHANG Ying-feng  ZHAO De-zheng  QU Chun-yan 《地震地质》2018,40(6):1254-1275

On November 18, 2017, a M_S6.9 earthquake struck Mainling County, Tibet, with a depth of 10km. The earthquake occurred at the eastern Himalaya syntaxis. The Namche Barwan moved northward relative to the Himalayan terrane and was subducted deeply beneath the Lhasa terrane, forming the eastern syntaxis after the collision of the Indian plate and Asian plates. Firstly, this paper uses the far and near field broadband seismic waveform for joint inversion (CAPJoint method)of the earthquake focal mechanism. Two groups of nodal planes are obtained after 1000 times Bootstrap test. The strike, dip and rake of the best solution are calculated to be 302°, 76° and 84° (the nodal plane Ⅰ)and 138°, 27° and 104° (the nodal plane Ⅱ), respectively. This event was captured by interferometric synthetic aperture radar (InSAR)measurements from the Sentinel-1A radar satellite, which provide the opportunity to determine the fault plane, as well as the co-seismic slip distribution, and assess the seismic hazards. The overall trend of the deformation field revealed by InSAR is consistent with the GPS displacement field released by the Gan Wei-Jun's team. Geodesy (InSAR and GPS)observation of the earthquake deformation field shows the northeastern side of the epicenter uplifting and the southwestern side sinking. According to geodetic measurements and the thrust characteristics of fault deformation field, we speculate that the nodal plane Ⅰ is the true rupture plane. Secondly, based on the focal mechanism, we use InSAR data as the constraint to invert for the fine slip distribution on the fault plane. Our best model suggests that the seismogenic fault is a NW-SE striking thrust fault with a high angle. Combined with the slip distribution and aftershocks, we suggest that the earthquake is a high-angle thrust event, which is caused by the NE-dipping thrust beneath the Namche Barwa syntaxis subducted deeply beneath the Lhasa terrane.  相似文献   

瑞雷波多阶模式频散曲线稀疏正则化反演方法研究     

崔岩  王彦飞 《地球物理学报》2022,65(3):1086-1095

目前瑞雷波多阶模式频散曲线反演中仅考虑数据的拟合,缺乏对模型的约束,不能很好地刻画地层间断面的问题,针对此问题,研究了瑞雷波多阶模式频散曲线稀疏正则化反演方法.正演模拟基于广义反射-透射系数法,数值计算上采用一种快速求根方法,与二等分方法相比,能够在很短的时间内达到最优的收敛效果;反演建模时采用L₁范数正则化方法对模型进行稀疏性刻画,使反演结果更加符合地质实际;在反问题的数值实现上,针对稀疏正则化模型提出一种隐式迭代正则化算法,其迭代算子具有非膨胀特性,可以收敛到极小化问题的解.数值实验结果表明,新的反演方案具有计算效率高,模型"逐块"光滑的特性刻画好,对非高斯噪声鲁棒性强的特点.  相似文献   

Attenuation Characteristics of Earthquake Ground Motion for Large Volume Airgun     

CAI Huiteng  CHEN Yong  JIN Xing  XU Yihe  LI Wen 《中国地震研究》2019,33(4):544-556

In order to further deepen the understanding of seismic wave propagation characteristics induced by the large volume airgun source, experimental data from multiple fixed excitation points in Fujian Province were used to obtain the equivalent single excitation high signal-to-noise ratio velocity and displacement records through linear stacking and simulation techniques. Then the peak displacements of different epicentral distances were used to calculate the equivalent magnitude of the airgun source excitation at different fixed excitation points so as to establish the attenuation relationship between equivalent magnitude,epicenter distance and velocity peak. Our results show that:① Within 270 km of epicentral distance,for the large-volume airgun's single shot,the peak velocity range is about 700-4 nm/s,and the peak displacement range is about 200. 0-0. 2 nm;② The equivalent magnitude of the P-wave from the airgun source with a total capacity of 8,000 in 3 is 0. 181-0. 760,and the equivalent magnitude of the S-wave is 0. 294-0. 832. By contrast,the equivalent magnitude of the P-wave from the airgun source with a total capacity of 12,000 in 3 is 0. 533-0. 896,and the equivalent magnitude of the S-wave is 0. 611-0. 946. The S-wave energy is greater than the P-wave energy, and the excitation efficiency varies greatly with different excitation environment;③ The peak velocity increases with the equivalent magnitude,and decreases with the epicentral distance. The vertical component of the P-wave peak velocity is the largest among those three components,while the S-wave has the smallest vertical component and similar horizontal components. Hence,our research can provide an important basis for the quantitative judgment of the seismic wave propagation distance using the airgun and the design of the observation system in deep exploration or monitoring with airgun.  相似文献   

基于误差分布的震源区波速比反演及其应用:乳山震群源区介质性质变化研究          下载免费PDF全文

郑建常  李冬梅 《地球物理学报》2019,62(5):1693-1703

本文利用误差分布和概率统计分析改进了波速比计算方法.对于震源位置相对集中的震群活动,对台站震相到时进行两次差分,通过对差分后的震相数据对进行二维高斯分布拟合,可以稳健地估计震群活动震源区波速比.该方法充分利用了不同台站Pg、Sg到时差的所有信息,其优势是不需要地震事件的震源位置,并且不依赖震源区以外的速度变化,有效消除了震源区到台站的传播路径效应的影响;相对于传统的平均波速比,本文方法得到的震源区波速比,更能真实地反映震源区介质的性质.我们将该方法应用到2013—2016年的乳山震群,结果显示:震源区波速比的变化与震群活动过程密切相关,波速比的变化反映了序列活动的阶段性特征.  相似文献   

利用断裂带首波分析甘孜—玉树断裂带拉张盆地结构特征   总被引：1，自引：0，他引：1       下载免费PDF全文

杨微  王宝善  彭志刚  田晓峰  袁松湧 《地球物理学报》2020,63(3):1197-1213

对断裂带及附近区域地层精细结构的描述是理解地震孕育和发生过程的基础.不同板块或块体边界在构造或区域应力作用下,常常会形成速度间断面和低速的断裂带,间断面和低速带的存在会产生特殊的断裂带地震波,比如断裂带首波和围陷波,并会影响地震的物理过程、破裂速度和破裂方向等.本文主要利用2010年4月14日M_W6.9玉树地震后布设的流动地震台站,对沿着甘孜—玉树断裂带传播的断裂带首波进行识别和分析.分析结果表明,在甘孜—玉树断裂带的不同区域均观测到了断裂带首波,在西段的结隆拉张盆地附近的3个台站沿断裂带界面的平均纵波速度差异值在5%～8%,而其他区域的平均速度差异为1%～3%.通过台站位置分布和断裂带首波特征关系,初步分析了断裂带拉张盆地的结构,结果显示结隆盆地的长度为～40km,宽度为5.35～5.97km,深度不超过5km,在地表浅层形成了一个低速区,分别与巴颜喀拉块体(NE)和羌塘块体(SW)产生了两个物性差异界面,但没有延伸到主震和余震区震源深度.我们的结果表明结合密集台阵资料,通过断裂带首波特征分析可以为断裂带精细结构及几何特征提供一种新的技术方法和途径.  相似文献   

Impact of user parameters in inversion velocity analysis     

T. Zhou  H. Chauris  F. Audebert 《Geophysical Prospecting》2020,68(5):1492-1508

Migration velocity analysis is a method devoted to the evaluation of both reflectivity and background velocity models, associated with the high and low wavenumber components of the model, respectively. Inversion velocity analysis is one of its improved versions, leading to more stable background velocity updates. Still, the impact of the user parameters should be understood for an optimal update of the background velocity. We show that a sign reversal of the background velocity gradient could occur when the selected surface offset range or the space lag range is too small. We derive the theoretical limits and check their consistency through simulations in a simple model with a single interface. These guidelines determine the necessary ranges of surface offsets and space lags for a proper update of the background velocity model. We discuss their applicability on the Marmousi model. Artefacts in the retrieved background velocity model are observed when the guidelines are not satisfied.  相似文献   

鄂尔多斯西缘北段的地壳结构和块体间变形关系          下载免费PDF全文

陈一方  陈九辉  郭飚  李顺成  齐少华  赵盼盼  李晓姝 《地球物理学报》2020,63(3):886-896

本文对喜马拉雅计划二期部分台站的远震波形数据进行接收函数提取,利用接收函数共转换点叠加方法获得阿拉善地块、鄂尔多斯地块以及银川—河套盆地下方0~80 km深度的速度间断面结构.结果表明:鄂尔多斯地块成层性好,地壳厚度为38~42 km,康拉德界面为18~22 km,阿拉善地区的Moho面深度为38~45 km.河套盆地地壳厚度约52 km,银川断陷盆地和贺兰山下方的Moho面最深为~55 km.鄂尔多斯西缘构造边界下方Moho面变化明显,且黄河断裂为深大断裂直接切割莫霍界面.根据本文的间断面成像结果我们进一步确定阿拉善地块与鄂尔多斯地块分属不同的大地构造单元.与此同时,我们推测贺兰山以西70~80 km范围内和鄂尔多斯地块西缘北段存在地壳增厚变形的可能.  相似文献