消防射水对火灾后高性能混凝土剩余抗压强度的影响

对火灾后消防射水对高性能混凝土（HPC）剩余抗压强度的影响进行了研究。分析了在不同温度、不同冷却方式条件下,C40HPC剩余抗压强度的变化规律,并利用ORIGIN 7.5软件,拟合了高温作用后HPC剩余抗压强度与温度之间的关系。研究表明：消防射水对高温作用后的HPC的剩余抗压强度的影响很大,射水冷却后的HPC剩余抗压强度明显低于自然冷却后的剩余抗压强度;随着破坏温度的升高,经消防射水冷却的HPC剩余抗压强度呈衰减状态。最后,建立了自然冷却及消防射水冷却条件下,C40HPC剩余强度与火场温度之间的二元回归曲线公式。     

振幅衰减特性在地震与爆破识别中的应用

基于小震级地震与爆破事件,从快速识别要求出发,分析了P波初动振幅AI和P波最大振幅AP分别与S波最大振幅AS的幅值比判据及其对事件的识别能力．考虑到传播路径对地震与爆破各振幅的影响,选用合理的振幅随距离衰减公式,分别研究了P波、 S波各振幅随震中距的衰减特征,结果显示爆破振幅衰减比地震快; 在100 km处进行衰减校正后重新计算P波与S波幅值比,得到经过衰减校正后的幅值比AI/AS正确识别率从84%提高到98%,AP/AS正确识别率从92%提高到100%,表明经衰减校正后的幅值比判据可以更好地应用于小震级地震与爆破的识别中．      

等效线性场地响应程序对比研究

为了评价4种等效线性场地响应软件的适用性,选取深厚场地作为研究对象,将基岩地震波作为地震输入,根据土层剪切波波速和容重确定初始剪切模量并设置对应的模量衰减和阻尼比曲线,分别用SHAKE 2000、 DEEPSOIL、EERA和Strata 4种等效线性场地响应程序计算得到地表的加速度时程及相应的加速度反应谱和傅里叶幅值谱\,场地的最大剪应变和峰值加速度随深度的变化曲线。计算结果表明,由4种场地响应软件得到的地表加速度时程对应的加速度反应谱和傅里叶幅值谱一致,由于土层划分方式不同,Strata软件得到的峰值加速度和最大剪应变深度曲线不同。总结4种软件的不同,DEEPSOIL可以较全面考虑土的动力特性,Strata提供随机振动理论进行场地响应分析并可以考虑土层参数的变异性。     

Biot理论的唯象修正对S波特性的影响

将复模量引入Biot方程后，在一维条件下通过S波的波动方程研究了S波的传播特性，S波的数值分析显示在频率域或温度域上都能获得热弛豫衰减峰和Biot衰减峰. 在频率域上由于温度的变化引起两峰相向位移,在温度域上,因频率的变化也发生相对移动. 随着温度和频率的不断提高，两峰发生叠加，叠加后两峰互换位置. 低频或低温段的热弛豫峰移到了高频或高温段，高频或高温段的Biot峰移到了低频或低温段.由于两峰的衰减机制不同，导致S波波速随频率或温度变化规律的复杂性. 这些规律已部分被共振实验所证实，证实该理论模型具有实验基础.     

传染型余震序列模型震后早期参数特征及其地震学意义

研究中国大陆地区中强地震序列震后早期阶段（震后15天）ETAS模型参数的平均统计特征，据此讨论不同统计条件下的序列衰减及余震激发问题.宏观而言，模型参数b、p、α数值分布较为离散，不同统计条件下模型参数平均值的差异显著性不十分突出.详细对比不同统计条件下模型参数平均值的微小差异，b值随主震震级增大而增大，但b值随不同区域、不同主震断层类型或不同序列类型的变化不明显.p、α具有一定的区域特征，西南、西北p值略低于新疆及华北，表明西南、西北序列衰减相对较慢而新疆、华北序列衰减相对较快，华北α较低而西北α相对最高，意味着尽管华北序列衰减相对较快，但其激发高阶余震的能力却相对强，西北尽管序列衰减较慢，但序列结构单一，激发高阶余震的能力弱.p与主震断层类型关系不明显，即主震破裂性质不是决定序列衰减快慢的主要因素；α与主震断层类型有一定关系，走滑-近走滑型破裂所导致序列的α值最小、斜滑型次之、倾滑-近倾滑型最大，表明走滑-近走滑型序列激发高阶余震的能力最强、逆冲型最弱、斜滑型居中.p、α随主震震级增大而减小，意味着主震震级越高则序列衰减越慢、激发高阶余震的能力越强.不同类型序列p、α有一定差异，主余型序列p最小、孤立型p最大，表明相对而言主余型序列衰减最慢、孤立型序列衰减最快、多震型序列衰减速率居中.孤立型序列与主余型序列α大体一致、大于多震型序列的α值，即多震型序列激发高阶余震的能力相对最强，孤立型及主余型序列则相对较弱.     

不同制样方法对木质素改良黄土力学特性影响

利用加水湿拌和泥浆搅拌2种方法对木质素改良黄土试样先进行均匀混合,后利用静压法在50mm×100mm圆柱形模具中两端压实制备试样,基于三轴仪对不同制样方法下改良土试样进行无侧限抗压强度试验和固结不排水三轴试验。试验结果表明:泥浆制样法获得改良土试样无侧限抗压强度值和固结不排水剪切强度值均高于加水湿拌法获得改良土试样强度值。结合扫描电镜试验对不同制样方法下改良土试样细观结构进行分析,发现对于木质素改良土,泥浆搅拌法获得的试样中木质素与黄土颗粒形成了新的胶结物和团聚物;而加水湿拌法获得试样中,木质素在土颗粒中仅起到加筋作用,未出现新的胶结物。该结果从微结构角度揭示了2种制样法制备试样的本质差异。     

地震数据采集器非线性指标测试方法及其影响分析

为了分析总谐波失真度和互调失真度这两个非线性指标的测试方法、输入信号幅值等变化对其测试结果的影响,本文从总谐波失真信号、互调失真信号的产生原理出发,详细地给出了两种指标的测试方法、数据处理方法及相关影响分析,并通过实际应用中不同类型的输入信号进行了总谐波失真度和互调失真度试验。测试结果表明:信号模式和信号幅值对总谐波失真度的影响显著;输入信号幅值对互调失真度的影响较大;输入信号的频率变化对两指标的测试结果无影响。本研究进一步细化了地震数据采集器性能指标的标准化测试方法,该方法可广泛应用于地震数据采集器的非线性指标测试。      

强地震动幅值谱随机涨落特征的研究

本文从工程应用的观点，将强地面运动幅值谱?Ａ（ｆ）│表示为强度受到调制的随机过程即│Ａ（ｆ）│＝│Ａ（ｆ）│〔１＋ｎ（ｆ）〕其中，│Ａ（ｆ）│为随频率变化的确定性函数亦是│Ａ（ｆ）│的均值，ｎ（ｆ）为均值为零的随机过程。在随机过程ｎ（ｆ）为各态历经的假定下，研究了ｎ（ｆ）的功率谱密度函数的特征及其衰减形式。根据地震学的有关理论，提出了用四个参数控制幅值谱的均值随频率变化的函数形式并对拟合这些参数的     

单向玄武岩布增强高分子湿法浸渍片材的高温性能研究

与碳纤维与玻璃纤维相同,单向玄武岩纤维布可以通过外粘结工艺用于土木结构的加固。由于用于粘结纤维布的高分子胶粘剂易燃烧,高温软化,本文系统研究了单向玄武岩纤维布增强环氧树脂基湿法浸渍片材的高温中及高温处理后的力学性能。BFRP片材经100、150、200°C处理720小时,冷却后,其拉伸模量保持不变,而拉伸强度在200°C下处理720小时后下降约20%。电子显微镜照片及玻璃化温度变化分析表明,在高温处理过程中,树脂的降解与界面脱粘是导致BFRP拉伸性能下降的主要因素。BFRP的拉伸模量随着试样温度的升高,逐步下降,当达到最大试验温度300°C时,模量下降约35%。BFRP的拉伸强度对试样温度更为敏感。当测试温度超过树脂的玻璃化温度(约82°C)后,BFRP的拉伸强度急剧下降,并趋于稳定,约为室温初始值的45%。当温度超过树脂基体的玻璃化温度后,树脂开始从玻璃态转变为高弹态,不能有效地传递应力,导致BFRP片材的拉伸性能下降。     

深内部地球结构对内核平动振荡本征周期的影响

地球固态内核的平动振荡是地球的基本简正模之一,又称Slichter模,其本征周期大约为几个小时,与地球内部结构密切相关.为了研究影响内核平动振荡的本征周期与内部结构的依赖关系,本文利用球对称、非自转、弹性和各向同性地球模型（SNREI）,通过自由振荡运动方程的数值积分,以地球模型PREM为基础,理论上系统研究了地球内部介质（包括密度、地震波速等）分布异常对Slichter模本征周期的影响.数值结果表明,Slichter模周期随着内外核边界（ICB）密度差的增加以类似于双曲线的特征显著减小,当ICB密度差从597 kg·m^-3减小到200 kg·m^-3时,周期增大66.44%,当ICB密度差从597 kg·m^-3增大到1000 kg·m^-3时,周期减小21.48%;Slichter模周期随着核幔边界（CMB）密度差的增大而缓慢增大;相对于PREM,地球模型1066A在ICB和CMB的密度差分别相差45.321%和1.132%,内部地震波速度和密度梯度也存在差异,但是,当密度差减小到1066A模型提供的数值时,得到的Slichter模周期与基于1066A获得的结果（4.599 h）非常接近,差异分别只有3.762%和0.037%;表明Slichter模本征周期与地球内部介质的精细结构关系不大,而对ICB的密度差非常敏感.内、外核P波波速分布异常对Slichter模周期的影响基本相当,当内核和外核P波波速均增加5%时,Slichter周期分别减小1.02%和1.69%,P波波速分别减小5%时,Slichter模周期分别增加1.27%和1.847%,内核S波波速分布异常比P波波速分布异常对Slichter模周期的影响小1个量级;与地核相比,地幔中的地震波速异常对Slichter模本征周期的影响小1~2个量级;表明地核中地震波速异常对Slichter模周期的影响很小,目前有关Slichter模周期理论计算的差异主要来自于所采用的地球模型中内核边界的密度差的差异,本文结果可以为Slichter模的研究、探测及其对地球深内部结构的约束提供理论依据.     

上月壳中的散射引起月震尾波的数值模拟研究

在阿波罗月震记录中普遍存在着强烈持久的尾波信号,这样的波形特征无法用均匀分层月球模型解释.一个普遍被接受的解释是月震尾波由月球浅层结构对月震波的散射引起.我们采用基于交错网格的伪谱和有限差分混合方法模拟研究非均匀上月壳对月震波的散射效应,在此基础上解释月震尾波的形成机制,并估计出上月壳速度扰动的强度.我们发现,在均匀分层模型基础上,进一步考虑上月壳中的非均匀结构对月震波的散射效应,能有效地解释月震信号中强烈持久的尾波.我们认为月震尾波可能是由上月壳中的低波速、低衰减和散射这三个因素的共同作用所引起.采用不同的扰动标准差模拟上月壳的非均匀性,并比较模拟波形与真实月震图的相似程度,我们发现上月壳中速度扰动的标准差应该在3%到5%之间,很可能接近于3%.     

EXPERIMENTAL STUDY ON THE CHANGES OF ULTRASONIC CODA WAVE AND ACOUSTIC EMISSION DURING ROCK LOADING AND DEFORMATION

The coda wave propagation path has received extensive attention as it is more sensitive to small changes in the medium than the direct wave. During the process of loading, the wave velocity, medium or source changes may cause the coda wave to change. The physical mechanism of change in the ultrasonic coda wave varies during different deformation stages. Meanwhile, there exist local damages in the rock sample during the deformation, and it will be accompanied by acoustic emission. Combining the ultrasonic coda wave and acoustic emission is beneficial to characterize the coda wave characteristics and damage degree of the sample at different deformation stages. In this paper, three kinds of rocks, including granodiorite, marble and sandstone with the sizes of 50mm×50mm×150mm, are used to carry out observations of ultrasonic coda wave and acoustic emission during the whole process of loading so as to study characteristics of the coda wave at different deformation stages. The major results are given below: 1)There is a good correspondence between the coda wave variation and the acoustic emission evolution process. When the acoustic emission frequency increases, the coda wave changes accordingly. In particular, the coda wave changes in the early stages of increased acoustic emission frequency, which indicates that the early damage information of rock can be obtained by analysis of the coda wave. 2)The physical mechanism of the coda wave change is different in different deformation stages. At the initial stage of loading, there are obvious scatterer changes in the coda wave change; then, in the linear elastic deformation stage, the wave velocity change is dominating; in the late-stage of loading, the scatterer change increases and coexists with the wave velocity change, the scatterer change effect is related with the rock micro-fracture degree, the rock will locally be damaged before rupturing, and the role of the scatterer will be enhanced. 3)With the increase of loading, the amplitude of increase of the wave velocity generally decreases gradually, which is basically consistent with the understanding obtained through the direct wave. The interference of acoustic emission can be eliminated because of the Kaiser effect when analyzing the coda wave. The consistency of the wave velocity change and stress loading and unloading is further verified. 4)The micro-fracture generated during rock deformation will change the physical mechanism of the coda wave change, and the scatterer effect will be significantly enhanced. At the same time, the acoustic emission waveform will cause interference to the ultrasonic coda wave. This means that attention needs to be paid when analyzing rock damage using only coda wave data. In short, the ultrasonic coda wave and acoustic emission can reflect the damage inside the rock, and the change mechanism of the coda wave in different deformation stages is different. The joint observation of the two can play a mutual verification role, which is conducive to improving the reliability of the observation results.     

Constituents of Vertical-component Coda Waves at Long Periods

Aki (1969) first modeled coda waves of a local earthquake as a superposition of scattered surface waves. This paper attempts to clarify the constituents of surface-wave coda at long periods at very long lapse times. For a large earthquake of magnitude 7 or larger, vertical component oscillation in periods from 90 to 180 s persists for more than 20 hours from the earthquake origin time. Although the early portion of the coda envelope is successfully modeled by assuming incoherent scattered Rayleigh waves by heterogeneities distributed all over the Earth, the later potion of the observed coda envelope (roughly later than 35,000 s) has systematically larger amplitude than theoretical prediction. To clarify the cause of this discrepancy, we studied the constituents of vertical-component seismograms of three large earthquakes recorded by the F-net in Japan using the f-k power spectral analysis. We found that the direct and scattered fundamental-mode Rayleigh waves of velocity about 3.7 km/s are dominant in the earlier part of each envelope. It justifies the use of a scattering model of the fundamental Rayleigh waves for synthesizing the envelope. At lapse times later than 20,000 s–35,000 s, higher modes with phase velocities around 20 km/s become dominant. The transition time to the dominance of higher modes is found to become earlier for a deeper focus earthquake. The small coda attenuation factor from (1.90±0.23) × 10⁻³ to (2.38±0.32) × 10⁻³ estimated from later coda envelopes recorded at IRIS stations distributed worldwide also agrees with the attenuation factor of spheroidal modes according to PREM. We may interpret that higher mode waves are uniformly distributed at large lapse time due to large velocity dispersion and/or scattering and they dominate over the fundamental mode waves because of smaller attenuation in the lower mantle. The coda attenuation measurement proposed by Aki is found to be useful even for long periods and at very large lapse times.     

Effect of anelastic and scattering structures of the lithosphere on the shape of local earthquake coda

A simple model of single acoustic scattering is used to study the dependence of the shape of local earthquake coda on the anelastic and scattering structures of the lithosphere. The model is applied to the coda of earthquakes located near Stone Canyon, central California, and provides an explanation for the features observed in the data, which include an interesting temporal variation in the coda shape. A surficial layer with aQ of 50 and thickness of 10 or 25 km underlain by a zone with aQ of 1000 extending to the bottom of the lithosphere, together with a scattering scale length,a, that varies with depthz according to the relationa=0.3 exp[-(z/45)²] are found to constitute the simplest structure of the medium compatible with the coda data and with body and surface wave attenuation data. The profile of heterogeneity sizes implies that the scattering strength increases strongly with depth, a constraint required by the necessity to boost the energy of the later coda without forcing the intrinsicQ to be excessively high in the uppermost mantle. This constraint is viewed as an artifact of the single scattering model which overstimates the scattering coefficient due to the neglect of multiple scattering. The observed temporal variation of the signal is difficult to explain by a simple change of the intrinsicQ at some depth. Rather, it is suggested that the scattering properties at depth changed with time through a variation of the fractional rms velocity fluctuation on the order of one percent.     

Regional features of coda attenuation of aftershocks of Wuding, Yunnan earthquake in near field

IntroductionSeismic wave is an important information source to analyze and study seismic source and internal structure of the earth. Studies of wave on different frequency ranges can provide many features of seismic source and internal structure of the earth. In recent years in quantitative study of seismic wave seismologists at home and abroad have developed a wide study field on the coda. Especially seismologists have done a lot of work in coda geneses, mechanism and its attenuation to explo…     

利用超声尾波观测1.5 m长岩石断层黏滑实验的波速变化

在实验室内利用超声尾波观测大尺度(1.5 m)岩石断层的黏滑过程.利用基于尾波干涉的观测方法,我们获得了高达10~(-6)的相对波速变化的观测精度,这相当于~10 kPa的应力变化.利用高精度的测量,我们获取两种不同加载速率下(1μm·s~(-1),10μm·s~(-1))黏滑过程三个阶段(恢复、加载和滑动)基于波速变化的特征量.我们更进一步获取了断层失稳阶段波速变化的时空演化过程.最后讨论了该观测方法需要改进的地方.以上研究结果表明作为一种对现有实验观测手段的有益补充,利用超声尾波观测实验室大尺度岩石断层的动力学过程是可行的.     

云南武定地震余震近场尾波衰减的区域特征

根据地方震尾波散射理论，利用云南武定MS6.5主震后近场田心和云龙两个流动数字化台站记录的余震序列地震资料，以不同中心频率（1.5～20Ｈｚ）取样分频研究了近场尾波振幅衰减率（f ）的空间分布特征．结果表明，两个台站给出的尾波振幅衰减率（f ）存在明显的小区域范围非均匀性变化．位于主发震断层两侧的云龙台（东侧）和田心台（西侧）测得的尾波振幅衰减率（f ）值，当 f ＜6.0Ｈｚ时基本一致．相应的Qc（f ）值为66～120的低值；但在高频范围（f 6.0Ｈｚ），由于穿过主断层的近场尾波遭到断层破碎带强烈的吸收，因而云龙台测得的尾波振幅衰减率（f ）值，比不穿过主断层的田心台给出的（f ）降低30％，并讨论了产生近场尾波振幅衰减空间分布差异的原因．本文的研究结果还表明，波源因子A0（f）不仅与震源强度相关，也与频率犳相关，用1.5～20Ｈｚ求出的Ｓ波平均自由程犔在主断层东侧为30ｋｍ、西侧为40ｋｍ ，由此证实了地震波穿过主断层破碎带时有更强的散射．      

腾冲火山区剪切波和尾波衰减初步研究

用云南腾冲火山地区观测的地震数字化记录进行了尾波和剪切波的衰减测量。用AkiandChouet和Sato单次散射模型获得 5 2秒和 18秒流逝时间尾波的品质因子分别为Qc (f) =5 7×f- 0 94和Qc (f) =2 6×f- 0 95 ,表明地壳上部和地壳上地幔的地震波衰减频率变化率一致。两者均未显示出活火山地区尾波衰减的异常特征。尾波掠过空间椭球的平均半轴 ,前者约为 80km ,大大超出了腾冲火山分布的地理范围 ,后者约为 30km ,在腾冲火山分布的地理范围之内。用尾波规一双台S波振幅比法进一步缩小所用地震波掠过的空间 ,最后获得了S波随频率的衰减有类似于前人报导的活火山地区尾波频率衰减的特征 :相对于低频 (1 5～ 6Hz) ,高频 (6～2 0Hz)的Q- 1s 变化很小。从地表位置看 ,腾冲最年青的全新世的马鞍山和老龟坡火山就在S波掠过范围内 ,打鹰山火山也在近旁。这一结果表明在这三座火山体之下存在低速高衰减体。火山或处于休眠状态 ,或在消亡过程之中。     

Coda waves: A review

The analysis and interpretation of coda waves have received increasing attention since the early seventies. In the past few years interest in this subject has spread worldwide, and the study of high-frequency seismic coda waves has become a very important seismological topic. As a conclusion of the studies accomplished in this time, coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves.P andS waves play a particularly important role in this interaction. The process introduces an attenuation which, added to the intrinsic absorption, gives the observed apparent attenuation. Therefore, coda waves constitute a thumbprint left by the heterogeneities on the seismograms. Coda waves offer decisive information about the mechanism of how scattering and attenuation take place. This review describes coda waves in detail, and summarizes the work done in this subject to 1986. The relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed. Particular attention has been given to the application of coda waves to estimate source and medium parameters. The state-of-the-art of the temporal variations of coda wave shape, and the possible use of these variations as an earthquake precursor also are presented. Care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering.     

Regionalization and dependence of coda Q on frequency and lapse time in the seismically active Peloritani region (northeastern Sicily,Italy)

The Peloritani region is one of the most seismically active regions in Italy and, consequently, the quantification of attenuation of the medium plays an important role for seismic risk evaluation. Moreover, it is necessary for the prediction of earth ground motion and future seismic source studies. An in depth analysis has been made here to understand the frequency and lapse time dependence of attenuation characteristics of the region by using the coda of local earthquakes. A regionalization is likewise performed in order to investigate the spatial variation of coda Q across the whole region. Finally, our results are jointly interpreted with those obtained from recently published 3D velocity tomographies for further insights.