山东临沂地区砂土剪切波速与标准贯入击数关系统计分析

剪切波速(V_S)与标贯击数(N)之间存在相关关系,受地区土壤条件影响很大。对临沂地区场地实测得到的砂土的剪切波速和标贯击数之间的关系进行了统计分析,得到了砾砂、粗砂、中砂和细砂相应的关系曲线。结果发现受沉积环境的影响,砂土层粒径与埋深呈正相关,砂土粒径越大其密实段样本点数量越多。为消除不同密实程度段之间的相互影响,以密实度为划分标准进一步进行分区段统计分析,得到了不同密实程度的四类砂土的相关关系方程,通过实际钻孔数据对比了分段与不分段的统计分析结果,分段模拟能更好地反映两者之间的相关关系。将砂土根据密实度进行划分再给出剪切波速和标贯击数的回归关系可以提高分析结果的准确性,同时可以考虑土体特性的影响,更为科学。此研究为临沂地区提供了一种简便预估剪切波速的方法,对相关地区的工程建设和科学研究也具有参考价值。     

Shear wave crustal velocity model of the Western Bohemian Massif from Love wave phase velocity dispersion

We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif, Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles (~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling. An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area of the Eger Rift (Teplá-Barrandian–Saxothuringian unit contact) is significantly different from all other three units. Low upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming.     

Characterization of liquefaction resistance in gravelly soil: large hammer penetration test and shear wave velocity approach

Gravelly soil is generally recognized to have no liquefaction potential. However, liquefaction cases were reported in central Taiwan in the 1999 Chi-Chi Taiwan earthquake and in the 1988 Armenia earthquake. Thus, further studies on the liquefaction potential of gravelly soil are warranted. Because large particles can impede the penetration of both standard penetration test and cone penetration test, shear wave velocity-based correlations and large hammer penetration tests (LPT) are employed to evaluate the liquefaction resistance of gravelly soils. A liquefied gravelly deposit site during the Chi-Chi earthquake was selected for this research. In situ physical properties of soil deposits were collected from exploratory trenches. Instrumented LPT and shear wave velocity (V_s) measurements were performed to evaluate the liquefaction resistance. In addition, large-scale cyclic triaxial tests on remolded gravelly soil samples (15 cm in diameter, 30 cm in height) were conducted to verify and improve LPT-based and V_s-based correlations. The results show that the LPT and shear wave velocity methods are reasonably suitable for liquefaction assessment of gravelly soils.     

Applicability of existing empirical shear wave velocity correlations to seismic cone penetration test data in Christchurch New Zealand

Seismic piezocone (SCPTu) data compiled from 86 sites in the greater Christchurch, New Zealand area are used to evaluate several existing empirical correlations for predicting shear wave velocity from cone penetration test (CPT) data. It is shown that all the considered prediction models are biased towards overestimation of the shear wave velocity of the Christchurch soil deposits, demonstrating the need for a Christchurch-specific shear wave velocity prediction model (McGann et al., 2014) [1]. It is hypothesized that the unique depositional environment of the considered soils and the potential loss of soil ageing effects brought about by the 2010–2011 Canterbury earthquake sequence are the primary source of the observed prediction bias.     

场地剪切波波速测试及其应用

介绍了场地剪切波波速测试、实测波形的分析、解释、计算的方法以及波速测试在地震设防和工程地质中的应用。并对影响波速测试的一些因素做了探讨．对波速测试中存在的问题提出了一些看法。     

Signal processing method for shear wave velocity measurement

Soil shear wave velocity (SWV) is an important parameter in geotechnical engineering. To measure the soil SWV, three methods are generally used in China, including the single-hole method, cross-hole method and the surface-wave technique. An optimized approach based on a correlation function for single-hole SWV measurement is presented in this paper. In this approach, inherent inconsistencies of the artificial methods such as negative velocities, and too-large and too- small velocities, are eliminated from the single-hole method, and the efficiency of data processing is improved. In addition, verification using the cross-hole method of upper measuring points shows that the proposed optimized approach yields high precision in signal processing.     

Shear wave velocity modelling in crustal rock for seismic hazard analysis

P-wave velocity data along with the thickness of sedimentary and crystalline layers within bedrock were collected from all global regions and presented in the Global Crustal Model CRUST2.0, published in 2001. This well-organised database provides invaluable potential contributions towards future seismic hazard modelling, particularly for stable continental regions (SCRs), where there is a scarcity of representative strong motion records for conventional modelling purposes. The P-wave velocity information presented in CRUST2.0 has been converted herein to S-wave velocity information. The latter is especially important for purposes of seismic hazard modelling. The value of the CRUST2.0 model has therefore been greatly enhanced by the important findings presented and further developed in this paper. By making the best use of available information on crustal conditions, the amplification behaviour of seismic waves affecting a region, an area or a site for any given earthquake scenario may be predicted. The developed methodology, which is intended for worldwide applications, has been illustrated by case studies in which model S-wave velocity profiles were developed for different geological regions within North America. The model profiles were found to be in excellent agreement with field measurements reported for each respective region.     

土层平均剪切波速确定及其可靠性验证——基于钻井台阵强震动记录

震害资料显示,场地条件对地震动特性以及工程结构破坏程度影响显著。为减少因场地效应而造成的经济损失和社会影响,在进行场地地震反应分析时,需最大限度地减小因场地土层模型参数的不确定性引起的地震动评估偏差,为工程结构地震反应分析选取并生成适当的地震动输入。随着强震动观测技术的逐渐发展,大量可靠的钻井台阵记录为地震过程中场地观测点的动力反应提供了直接数据。以美国加州地区La Cienega钻井台阵强震动观测数据为基础,利用互相关函数,对不同强度地震作用下场地土层的平均剪切波速进行分析,并在此基础上,以Cyclic 1D为模拟平台,建立一维自由场地地震反应有限元分析模型。分析结果表明：通过钻井台阵地震动观测数据识别,得到场地平均剪切波速,能够反映该场地的动力特性,数值模拟计算结果和台阵地震动记录基本吻合,可为数值模型参数选取提供依据。     

Shear wave velocity prediction using seismic attributes and well log data

Formation’s properties can be estimated indirectly using joint analysis of compressional and shear wave velocities. Shear wave data is not usually acquired during well logging, which is most likely for cost saving purposes. Even if shear data is available, the logging programs provide only sparsely sampled one-dimensional measurements: this information is inadequate to estimate reservoir rock properties. Thus, if the shear wave data can be obtained using seismic methods, the results can be used across the field to estimate reservoir properties. The aim of this paper is to use seismic attributes for prediction of shear wave velocity in a field located in southern part of Iran. Independent component analysis (ICA) was used to select the most relevant attributes to shear velocity data. Considering the nonlinear relationship between seismic attributes and shear wave velocity, multi-layer feed forward neural network was used for prediction of shear wave velocity and promising results were presented.     

Shear wave velocity structure of the upper mantle under the NW Indian Ocean

Shear wave velocity structure of the NW Indian ocean is analysed by using fundamental mode Rayleigh wave dispersion data of 67 events occurred during 1990–98 at the central Indian Ridge and Carlsberg Ridge and recorded at Hyderabad Geoscope station (HYB). These events provide a dense coverage of the NW Indian ocean and Chagos-Laccadive Ridge (CLR) in the back-azimuthal range of 192–253° with respect to HYB. The dispersion curves, corrected for continental and young ocean paths, indicate large variations in the shear wave velocity structure of the region. The group velocities along the CLR path support a typical aseismic ridge-type structure. However, the central region bounded between the Central Indian Ridge and India in the back-azimuth of 206–234° indicates a decrease in the group velocity by 0.1 km/s. Inversion of these data sets indicates presence of aseismic-ridge type lithospheric structure for CLR, a thin lithosphere and high velocity block in the depth range of 125–200 km for the central region, and a continental-type lithospheric structure for the northern-most part of the Indian ocean. It is inferred that the dynamic state of the upper mantle in this region has been significantly perturbed during the recent geological past.     

Empirical criteria for liquefaction in sands via standard penetration tests and seismic wave energy

Five empirical equations are presented, describing initiation of liquefaction in fully saturated sands, in terms of standard penetration values and initial overburden stress on level ground. These equations are based on 90 case histories of liquefaction, and relate empirically the pore pressure increase to earthquake magnitude, epicentral distance, energy of strong motion at the site, peak ground velocity, Fourier amplitude of velocity and duration of strong motion. The results are given in terms of raw standard penetration values corrected for overburden pressure. For all the models presented, the standard deviation of the residuals, representing the differences between the observed and predicted penetration values is less than six blow counts.     

Shear wave velocity structure of the crust and upper mantle underneath the Tianshan orogenic belt

From April, 2003 to September, 2004, a passive broadband seismic array consisting of 60 stations was deployed over the Tianshan orogenic belt by State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration. Among them, 51 stations make up an about 500-km-long profile across the Tianshan Mountains from Kuytun to Kuqa. The receiver function profile and S-wave velocity structure of the crust and upper mantle down to 100 km deep are obtained by using the re-ceiver function method (Liu et al. 1996, 2000). The main results can be summarized as follows: (1) A clear mountain root does not exist beneath the Tianshan Mountains, and the crust-mantle boundaries underneath the stations mostly have transitional structures. This implies that the material differentia-tion between the crust and mantle is not yet accomplished and the orogenic process is still going on. (2) The crust beneath the Tianshan Mountains has laterally blocked structures in direction perpendicular to the mountain strike, and the crust-mantle boundary has a clear dislocation structure. Both of them correspond to each other. (3) The offsets of the Moho discontinuity are highly correlated to the tectonic borders on the surface and that corresponding to the frontal southern Tianshan fault reaches to 14 km. This manifests that large vertical divergent movement took place between different blocks. This sup-ports the discontinuous model of the Tianshan orogeny, and the Tarim block subduction is restricted only to the southern side of the South Tianshan. (4) Inside the upper and middle crust of the Tianshan Mountains exist several low-velocity bodies correlated with high seismicity located on the moun-tain-basin jointures on both sides of the mountain and between different blocks, and the low-velocity bodies on the mountain-basin jointures are inclined obviously to the mountain. This implies that the low-velocity bodies may be correlated closely to the thrust and subduction of the basins on both sides of the mountain, the splicing of adjacent blocks and the fast uplift of the Tianshan Mountains.     

Shear wave velocity structure of the crust and upper mantle underneath the Tianshan orosenic belt

From April,2003 to September,2004,a passive broadband seismic array consisting of 60 stations was deployed over the Tianshan orogenic belt by State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration.Among them,51 stations make up an about 500-km-long profile across the Tianshan Mountains from Kuytun to Kuqa.The receiver function profile and S-wave velocity structure of the crust and upper mantle down to 100 km deep are obtained by using the receiver function method (Liu et al.1996,2000).The main results can be summarized as follows:(1) A clear mountain root does not exist beneath the Tianshan Mountains,and the crust-mantle boundaries underneath the stations mostly have transitional structures.This implies that the material differentiation between the crust and mantle is not yet accomplished and the orogenic process is still going on.(2)The crust beneath the Tianshan Mountains has laterally blocked structures in direction perpendicular to the mountain strike,and the crust-mantle boundary has a clear dislocation structure.Both of them correspond to each other.(3)The offsets of the Moho discontinuity are highly correlated to the tectonic borders on the surface and that corresponding to the frontal southern Tianshan fault reaches to 14 km.This manifests that large vertical divergent movement took place between different blocks.This supports the discontinuous model of the Tianshan orogeny,and the Tarim block subduction is restricted only to the southern side of the South Tianshan.(4)Inside the upper and middle crust of the Tianshan Mountains exist several low-velocity bodies correlated with high seismicity located on the mountain-basin jointures on both sides of the mountain and between different blocks,and the low-velocity bodies on the mountain-basin jointures are inclined obviously to the mountain.This implies that the low-velocity bodies may be correlated closely to the thrust and subduction of the basins on both sides of the mountain,the splicing of adjacent blocks and the fast uplift of the Tianshan Mountains.     

Shear wave velocity structure in western Thessaloniki (Greece) using mainly alternative SPAC method

The aim of the paper is the definition of the material parameters of sediments in the western part of Thessaloniki useful in the prediction of strong ground motion. The region of interest is elongated in the E–W direction and is confined between the Kalochori suburb and the harbor of Thessaloniki, while in the N–S direction it is extended between the coastline and the region of sediments and outcrop rock boundary. Many geological and seismotectonic studies, as well as geophysical surveys with electrical soundings and geotechnical boreholes, contribute to our understanding of the general sedimentary structure. Nonetheless, these studies could not provide any information regarding the material stiffness in terms of shear wave velocity; the most useful parameter in site response studies.     

Shear wave velocity models retrieved using Rg wave dispersion data in shallow crust in some regions of southern Ontario, Canada

Many crucial tasks in seismology, such as locating seismic events and estimating focal mechanisms, need crustal velocity models. The velocity models of shallow structures are particularly important in the simulation of ground motions. In southern Ontario, Canada, many small shallow earthquakes occur, generating high-frequency Rayleigh (Rg) waves that are sensitive to shallow structures. In this research, the dispersion of Rg waves was used to obtain shear-wave velocities in the top few kilometers of the crust in the Georgian Bay, Sudbury, and Thunder Bay areas of southern Ontario. Several shallow velocity models were obtained based on the dispersion of recorded Rg waves. The Rg waves generated by an m _N 3.0 natural earthquake on the northern shore of Georgian Bay were used to obtain velocity models for the area of an earthquake swarm in 2007. The Rg waves generated by a mining induced event in the Sudbury area in 2005 were used to retrieve velocity models between Georgian Bay and the Ottawa River. The Rg waves generated by the largest event in a natural earthquake swarm near Thunder Bay in 2008 were used to obtain a velocity model in that swarm area. The basic feature of all the investigated models is that there is a top low-velocity layer with a thickness of about 0.5 km. The seismic velocities changed mainly within the top 2 km, where small earthquakes often occur.     

Estimation of shear wave velocity of earth dam materials using artificial blasting test

The objective of this study is to estimate the shear wave velocity of earth dam materials using the vibration generated from artificial blasting events, and to verify its applicability. In this study, near-field artificial blast testing and monitoring were carried out at the Seongdeok dam, Korea, as the first blasting tests to be carried out on an existing dam in Korea. Vibrations were induced by four different types of blasting, using various explosive charge weights and depths of blasting bore-holes. During the tests, acceleration time histories were measured at the rock outcrop adjacent to the point of the explosion, and at the crest of the dam. The fundamental frequency of the target dam was computed from the frequency analysis of measured acceleration histories. Numerical analyses were carried out, varying the shear modulus of the earth fill zone and using the acceleration histories measured at the rock outcrop as input ground motions. From a comparison between the fundamental frequencies calculated by numerical analyses and those of measured records, the shear wave velocities with depth, which are closely related to shear moduli, could be estimated. It is found that the effect of different blasting types on shear wave velocity estimation for the target dam materials is negligible, and that shear wave velocity can be consistently evaluated. Furthermore, by comparing the evaluated shear wave velocity with empirical formulae from previous research, the applicability of the method was verified. Therefore, in cases of mid-to-small earth dams, where the earthquake record is not available, the shear wave velocity of earth fill materials can be reasonably evaluated using blasting vibration records obtained at the site adjacent to the dam.     

喜马拉雅地区S波分裂研究

利用最小特征值法,分析了喜马拉雅地区56个台站的地震记录,其中有39个台站能观察到S波分裂,其平均分裂时间在0.8 s左右.沿台站GAIG-T0040 连线的东西两侧各向异性参数呈现明显的差别：其以西地区,约有一半的台站没有观测到S波分裂,快波方向主要为NW和NWW方向;以东地区台站的快波方向在MBT（主边界断裂）以南为NNE向,平均分裂时间为1.05 s;低喜马拉雅地区为NE和NEE向,平均分裂时间为0.72 s;而在特提斯喜马拉雅地区为N-S和NE向,平均分裂时间为0.68 s.综合其他研究结果,认为东西向各向异性参数的差异是由于印度块体向北推进时的横向不均匀性造成的,而南北向的变化与该地区构造单元的分布一致.     

安徽及邻区平均波速比的测定及研究

将安徽及邻区(29°~36°N,114°~124°E),按1°×1°分成70个区,依据中国地震局分析预报中心编制的1998年1月1日至2003年12月31日全国地震月报目录,采用单事件多台观测资料,在所分区域里进行平均波速比值的计算,结果在其空间分布图像中显示了一定的特征。这些特征可能与地质构造环境即地质构造所形成的断裂带两侧的介质特性差异有关。计算所得的各区平均波速比对以后波速比值的变化分析有一定的参考作用。