山西地区面波相速度分布图像

本文根据山西数字地震台网31个台站和周边河北、河南、陕西、内蒙数字地震台网6个台站2009年2月-2011年11月记录的面波资料,利用双台法测定了350条路径上周期8～75 s的基阶瑞利波相速度频散曲线.通过Ditmar&Yanovskaya方法反演得到33个周期分辨率为40～50 km的相速度分布图像.分析研究了4个具有代表性周期的相速度分布图像和3条不同方向的相速度剖面,这些图像揭示了山西地区地壳上地慢速度结构的横向非均匀性质和相速度纵向变化特征.10s周期的相速度分布图像显示出断陷带与两侧隆起区相速度存在明显的差异,凡个断陷盆地的最大沉降中心附近呈现低相速度异常;山西6级以上强震大都分布在15s周期高相速度与低相速度急剧变化的过渡带上;20～26 s周期的相速度以38°N为界呈现出南高北低格局,与山西断陷盆地带莫霍界面埋深南浅北深的结果相吻合;36 s～54 s周期相速度图像的低速区域逐渐收缩到大同一带,进一步说明南部区域在该周期反映的深度范围已进入上地慢,而大同盆地的低速可能与该区域的新生代火山群有关.沿113°E的南北相速度纵剖面显示周期25～75 s以38°N为界,南部相速度高、北部相速度低,证实了38°N线附近是晋北地块、晋南地块的“软”、“硬”块体的结合部位,可能是由于软流圈上涌幅度不同造成了深部速度的南北差异;其他两个横切裂谷的剖面显示出与人工地震测深剖面相似的特征.     

中国大陆及邻区Rayleigh面波相速度分布特征

本文根据102个数字化台站记录的长周期垂直向面波资料,利用双台互相关方法测量了538条独立路径的基阶Rayleigh面波相速度频散资料,反演获得了中国大陆及边邻地区（70°E～140°E,18°N～55°N）20～120 s（周期间隔为5 s） 共21个周期的Rayleigh波相速度空间分布图像. 检测板测试结果显示中国大陆中东部地区横向分辨率可达3°,而西部及边邻地区大约5°. 研究表明,中国大陆地区的Rayleigh波相速度分布横向差异显著,大致以104°E为界,可分成具有不同速度结构特征的东、西两部分. 一般较短周期（20～35 s）的相速度分布受地形和地壳厚度的影响较大,总体表现为东部速度高,西部速度低;塔里木盆地、青藏地块及其东缘的松潘-甘孜地块形成整个研究区内最为突出的低速异常体,蒙古西部低速特征也较清晰;东部的四川盆地、扬子地块、华南地块、松辽盆地、日本海及蒙古东部高速特征明显. 随着周期的增大,青藏地块中部的低速异常体横向尺度逐渐缩小,而喜马拉雅冲断带、塔里木盆地相速度不断升高,意味着青藏低速区受到南、西北、东三个方向的高速区夹击,可能导致高原中部软弱的低速物质向东南方向迁移;同时,东部地区由高速逐渐转变为大面积的低速分布,反映东部地区岩石圈较薄而软流圈发育. 随着青藏地块低速特征的减弱,印支地块北部及相邻海域、东海、东北吉林深震区、日本海、中-朝地块至蒙古东部成为120 s周期上突出的低速异常体,而上扬子地块包括四川盆地高速特征依然明显,显示出稳定的古板块特征. 南北地震带始终呈现出相对较低的速度特征,并成为划分中国大陆具有不同岩石圈相速度特征的东部与西部的天然分界.     

利用多重滤波方法提取面波频散曲线

多重滤波方法已被证明在分析面波的频散特性时是一种有效而快速的方法。本文用单个台站的单次地震事件记录,应用MFT(Multiple Filter Technique)方法提取了内华达地区的面波频散曲线并分析了其特征,认为其具有大陆基振型瑞利波频散曲线的典型特征。还利用广义反透射系数法快速计算了瑞利面波频散曲线,尤其是基阶瑞利波相速度及群速度频散曲线;并且在由振型叠加方法合成的理论地震图的基础上,通过比较理论频散曲线和MFT方法得到的频散曲线,研究了多重滤波的可靠性。     

3-D surface wave group velocity distribution in Central-Southern Africa

Group velocities estimated from fundamental mode Love and Rayleigh waves are used in a tomography process in central-southern Africa. The waves were generated by eighteen earthquakes, which occurred along the East African Rift and recorded at BOSA, LBTB and SLR seismic stations in southern Africa. The group velocities from Love and Rayleigh waves were isolated using the Multiple Filter Technique (MFT) at the period range of 10 to 50 seconds. The tomography method developed by Ditmar and Yanovskaya (1987) and Yanovskaya and Ditmar (1990), was applied to calculate the lateral distribution of surface wave group velocities in central-southern Africa. The results of the tomographic inversion were plotted as distribution maps. In addition to the maps, I also produced two velocity cross-sections across the area of study. The velocity distribution maps show the regional tectonic units, though with poor resolution. The azimuthal bias of the surface wave paths is reflected in the distribution of the group velocities. The Moho depth appears to correlate with velocities at a period of about 30 s. A low velocity feature observed beneath the Zimbabwe craton implies a thickening upper asthenosphere and lithospheric thinning beneath the Zimbabwe craton. Also estimated was a shear wave velocity model beneath the Zimbabwe craton.     

Seismic tomography of Yunnan region using short-period surface wave phase velocity

Introduction The Yunnan region is located on the east margin of the collision zone between the Indian and Eurasian plates; it belongs to the south section of the N-S Seismic Belt of China and is the junc-ture of the Yangtze metaplatform, Songpan-Garz?fold system, Sanjiang fold system and South China fold system. This region has complex tectonic movements, crisscross faults and frequently occurring strong earthquakes, and hence it is one of the regions with the strongest earthquake ac-tivi…     

Contribution to phase velocity investigations of Rayleigh-waves in middle Europe

Summary The phase velocity curve of Rayleigh-waves is determined for a profile crossing the area of GDR from south to north. Two different methods of seismogram processing are used which are discussed in detail. The phase velocities found are checked for compatibility. An inversion of a common phase velocity curve is done by using hedgehog procedure.Akademie der Wissenschaften der DDR, Zentralinstitut für Physik der Erde, Mitteilung Nr. 579.     

Effect of soil stiffness in the attenuation of Rayleigh-wave motions from field measurements

The amplitude of vertical ground surface vibrations generated by impact tests on the ground surface was measured at various radial distances from the point of impact at locations of Greece. The results of measurements were analyzed in the frequency domain (in the range from 0–100 Hz) and the attenuation characteristics of soil materials were studied in terms of a frequency-independent attenuation coefficient, a₀, of the empirical Bornitz equation. The aim of the study was to investigate the effect of soil stiffness (expressed by the value of low-amplitude shear wave velocity of soil, V_SO) on the value of attenuation coefficient, a₀. Values of V_SO for the tested soils were estimated by applying the methodology of Spectral Analysis of Surface Waves (SASW) technique and utilizing the surface vibration data. An empirical relationship between a₀ and V_SO1 (V_SO1 is the representative value of V_SO for the soil profile up to a depth of one wavelength) was established for values of V_SO1 ranging from 140 to 1000 m/s. A similar relationship in terms of the low-amplitude shear modulus of soil, G_O1, was also established by converting the V_SO1 values to G_O1 values. The experimental results were compared to values reported in the literature for comparable soil types and frequencies of vibration and a reasonable agreement was found to exist. The proposed empirical relationship can be utilized in many practical applications of soil dynamics requiring the knowledge of the attenuation rate of Rayleigh waves with distance in various types of soils.     

华北地区基于噪声的瑞利面波群速度层析成像

本文利用华北地震科学台阵2007年1~4月份、190个宽频带和10个甚宽带垂直分量的地震噪声数据,通过互相关方法提取了瑞利面波的经验格林函数,用多重滤波方法测量了瑞利面波的群速度频散曲线.我们将研究区域划分为0.5°×0.5°的网格,利用噪声层析成像方法得到了研究区域7 s、12 s、16 s、23 s的瑞利面波群速度分布图像,所得结果较好地揭示了地壳内部、尤其是浅部地壳的横向速度变化.研究表明,短周期的群速度分布同地表地质结构、地形密切相关;华北地区的地壳结构具有明显的横向不均匀性,华北盆地及山间的沉积盆地显示出低速异常,而基岩广泛出露的太行山和燕山隆起区,呈现高速异常;多数强震(M≥6.0级)都发生在高群速度与低群速度的过渡地带.     

Transmission and reflection of Rayleigh waves at a thin low velocity vertical layer: A laboratory and theoretical study

A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling.     

欧亚大陆及西太平洋边缘海地区瑞雷波群速度结构与各向异性分布

根据欧亚大陆及西太平洋地区102个数字化台站记录的近万次地震事件的长周期垂直向瑞雷波资料,利用时频分析方法测量并筛选后共得到11213条质量较高的基阶瑞雷波群速度频散资料.纯路径频散的反演中同时计算方位各向异性,反演获得了欧亚大陆及西太平洋边缘海地区(10°E—150°E,10°S—80°N)8—200s共28个周期的瑞雷波群速度及各向异性空间分布图象.瑞雷波高分辨率层析成像表明,30—60s周期,以青藏高原为中心呈极低速分布;100—120s周期,速度差异幅度较大,在东亚东部及西太平洋边缘海,自北向南显示出一条宽2500—4000km,长约8000km的巨型低速异常带.相对海洋来说,欧亚大陆各向异性强度较弱且快波方向较复杂.由于受到印度板块与欧亚板块的碰撞,中国大陆西部的各向异性强度明显大于东部.     

华北地区瑞雷面波相速度层析成像

利用华北科学探测台阵190个宽频带台站和8个甚宽带台站2006年10月至2009年5月记录的远震垂直向资料,用小波变换频时分析方法测定了1587条独立路径的基阶瑞雷波相速度频散曲线,并使用Ditmar & Yanovskaya 方法反演得到111°~120°E,37°~42°N区域内、周期10~60 s的高分辨率相速度分布图像.本文的研究结果表明,华北地区的地壳上地幔横波速度结构存在横向非均匀性.短周期(如10 s)的相速度分布与地表地质构造具有明显的相关性,随着周期的增大(如15 s),地形的控制作用相对减弱.中周期(如30 s)的相速度分布差异暗示华北克拉通中、东部地区下地壳具有不同的物质组成,图中相速度梯度带与太行山重力梯度带位置十分相近,说明该重力梯度带两侧的地壳速度结构差异较大.与短周期相比,研究区内长周期(如60 s)相速度分布的横向非均匀性明显减弱,表明研究区上地幔顶部速度结构差异较地壳的小.与全球典型大陆克拉通相比,华北克拉通10~60 s的相速度频散明显偏低,其频散特征与全球典型裂谷地区相类似,这暗示华北克拉通已经遭受了明显的侵蚀与破坏.     

Generation of earth stratified models compatible with both ellipticity and phase velocity observations of Rayleigh waves

In the eigenvalue eigenvector decomposition used in inversion techniques, we can sometimes obtain eigenvalues close to zero. Related to these eigenvalues close to zero, a set of stratified earth models is generated. These are compatible with the theoretical observations according to a given model. The method is applied to ellipticities and phase velocities of Rayleigh waves, and supply proof of the advantage of working with both sets of data together.     

Group velocity distribution of Rayleigh waves and crustal and upper mantle velocity structure of the Chinese mainland and its vicinity

Introduction A lot of results have been achieved on the study of crust and upper mantle structure in Chinese mainland by the surface wave dispersion. The seismometer can be classified into three types based on the development from the analog to digital instrument. FENG, et al (1981) measured the dispersion curves of group and phase velocity along 28 paths, with 19 earthquakes recorded by 15 base analog seismic stations, subdivided the Chinese mainland into 5 blocks and obtained the average c…     

华北东北部的面波相速度层析成像研究

本文用华北临时地震台阵197个宽频带台站2006年12月～2007年6月记录的面波资料,用双台法测定了435条路径上周期8～75 s的基阶瑞利波相速度频散曲线.通过Ditmar & Yanovskaya 方法反演得到33个周期分辨率为30～50 km的相速度分布图像.分析研究了4个具有代表性周期的相速度分布图像,这些图像揭示了华北东北部地壳上地幔速度结构的横向非均匀性质.10 s周期的相速度分布图像清晰地勾绘出了华北东北部盆地与山区及其内部次级构造单元的边界,平原与山区的相速度存在明显的差异;华北东北部6级以上的强震大都分布在16 s周期高相速度与低相速度急剧变化的过渡带上,规模较大的断裂也大部分位于过渡带的边界附近;在研究区域中部,26 s周期的相速度出现一个明显的呈北东向展布的相速度梯度带,该梯度带与重力梯度带位置相近,说明该重力梯度带两侧的地壳速度结构差异较大.     

层状黏弹性介质中Rayleigh波频散曲线“交叉”现象分析

Rayleigh波勘探方法在探测近地表横波速度、动力学特征等环境与工程地球物理领域获得了广泛应用.这种方法以弹性层状介质理论为基础,然而实际介质具有黏弹性,研究面波在层状黏弹性介质中的传播特征,将为近地表面波勘探提供有益帮助.在某些弹性层状介质模型中,例如存在低速夹层和强波阻抗差异地层模型,Rayleigh波相邻两条频散曲线彼此会非常靠近,产生看似彼此"交叉"的现象,即"osculation"现象,但对于黏弹性介质中的这种现象并没有进行相关的研究.本文利用Muller法计算层状黏弹性介质Rayleigh波频散方程,基于层状介质模型中Rayleigh波频散和衰减曲线连续的性质,结合本征位移曲线特征,分析二层黏弹性介质模型中Rayleigh波频散曲线"交叉"现象以及"交叉"点附近的波动特性.结果表明:与弹性介质相比,黏弹性介质中Rayleigh波的波动特性存在明显差异,随着介质对地震波的损耗越来越强,将导致Rayleigh波频散曲线发生"交叉"现象.     

Estimation of Elastic Moduli in a Compressible Gibson Half-space by Inverting Rayleigh-wave Phase Velocity

A Gibson half-space model (a non-layered Earth model) has the shear modulus varying linearly with depth in an inhomogeneous elastic half-space. In a half-space of sedimentary granular soil under a geostatic state of initial stress, the density and the Poisson’s ratio do not vary considerably with depth. In such an Earth body, the dynamic shear modulus is the parameter that mainly affects the dispersion of propagating waves. We have estimated shear-wave velocities in the compressible Gibson half-space by inverting Rayleigh-wave phase velocities. An analytical dispersion law of Rayleigh-type waves in a compressible Gibson half-space is given in an algebraic form, which makes our inversion process extremely simple and fast. The convergence of the weighted damping solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Calculation efficiency is achieved by reconstructing a weighted damping solution using singular value decomposition techniques. The main advantage of this algorithm is that only three parameters define the compressible Gibson half-space model. Theoretically, to determine the model by the inversion, only three Rayleigh-wave phase velocities at different frequencies are required. This is useful in practice where Rayleigh-wave energy is only developed in a limited frequency range or at certain frequencies as data acquired at manmade structures such as dams and levees. Two real examples are presented and verified by borehole S-wave velocity measurements. The results of these real examples are also compared with the results of the layered-Earth model.     

利用双台脉动记录的相关系数估计福建地区瑞利面波的群速度

本文利用福建省数字地震监测台网中8个宽频带台站的速度型脉动记录,计算两两台站之间垂直分量的脉动在相同时间窗(窗长为5分钟)的相关系数,按照移动窗技术得到各个不重叠窗口的相关系数,并对其进行相干叠加,依此计算出两个台站之间瑞利面波的群速度及其在福建地区的空间分布。结果表明,叠加结果的信噪比随叠加次数的增加而增加,不同时间段叠加结果波形相似;峰值到时稳定,台风不会对结果产生明显影响;利用这个方法得到的福建地区周期约为3～5秒的瑞利面波群速度在2.9～3.1km/s之间,这和传统方法得到的瑞利面波的传播速度很接近。     

利用地震背景噪声成像技术反演三峡库区及邻近地区地壳剪切波速度结构

本文利用三峡库区重庆遥测台网及邻近地区台网2012年1月至12月期间的连续波形记录,通过噪声互相关,提取了这些台站间的经验格林函数.并通过获取的经验格林函数瑞利面波频散信息,反演出该区域5~40 s瑞利面波相速度分布.周期5 s及10 s的相速度分布结果显示：四川盆地具有较厚的沉积盖层,其中盆地中部沉积层相对偏浅.而周期20 s及35 s的相速度分布结果显示：中下地壳的扬子克拉通整体呈现较高的相速度分布,具有相对坚硬的中下地壳结构.这其中吉首—常德的武陵山区附近出现明显高速异常,可能与江南古陆古火山岛链（雪峰—九岭弧形古火山群）活动有关,火山活动导致大量的基性-超基性幔源物质侵入地壳,造成了武陵山重力异常,并一定程度上阻挡了云贵高原和湘鄂西部的物质向南逃逸;在地形上,此处恰好对应我国地形第二阶梯向第三阶梯的过渡带,并将华南地块分隔为东西两大部分.最后我们在瑞利面波相速度成像的基础上,反演出该区域三维剪切波速度分布,结果显示四川盆地周边的龙门山、米仓山、大巴山、七曜山和大娄山等地质构造与地壳剪切波速度结构具有明显对应关系.研究结果有助于深入研究该区的深部地质构造特征与地震发生机理.     

Crustal and uppermost mantle structure of SE Tibetan plateau from Rayleigh-wave group-velocity measurements

A shear-wave velocity model of the crust and uppermost mantle beneath the SE Tibetan plateau was derived by inverting Rayleigh-wave group-velocity measurements of periods between 10 and 70 s. Rayleigh-wave group-velocity dispersions along more than 3,000 interstation paths were measured based on analysis of teleseismic waveform data recorded by temporary seismic stations. These observations were then utilized to construct 2D group-velocity maps in the period range of 10–70 s. The new group-velocity maps have an enhanced resolution compared with previous global and regional group-velocity models in this region because of the denser and more uniform data coverage. The lateral resolution across the region is about 0.5° for the periods used in this study. Local dispersion curves were then inverted for a 3D shear-wave velocity model of the region by applying a linear inversion scheme. Our 3D shear-wave model confirms the presence of low-velocity zones (LVZs) in the crust beneath the northern part of this region. Our imaging shows that the upper-middle crustal LVZ beneath the Tengchong region is isolated from these LVZs beneath the eastern and northern part of this region. The upper–middle crustal LVZ may be regarded as evidence of a magma chamber in the crust beneath the Tengchong Volcanoes. Our model also reveals a slow lithospheric structure beneath Tengchong and a fast shield-like mantle beneath the stable Yangtze block.