龙陵强震群震害分布特点与场地影响

本文根据龙陵地震观场调查的震害资料,讨论了这次强震群震害分布的特点,认为同一地区在多次强震作用下震害的迭加效应是很明显的,震害程度是多次地震作用的总后果。指出,仅用宏观调查的方法只能是粗略地加以区分,若能配合微观手段布设连续多次触发的强震仪台网,观测地震地面运动可能是比较有效的途径。分析了这次地震的震害分布与场地条件的关系,有迹象表明,大面积的震害分布除了受发震构造不明,小尺度多次破裂过程和震中分散的震群特征的影响外,震区特定的地质构造和花岗岩介质物性对震害分布有很大影响。小范围的震害差异是由于地基土质条件和局部孤突地形的影响。因地基土引起的震害差异可达2度左右,局部孤突地形对震害的影响幅度一般为1度以上。     

西藏雄巴地区重力异常特征分析及火山沉积型硼矿成矿预测（英文）

火山沉积型硼矿是一种重要的硼矿床成因类型,主要发育在第三纪湖相蒸发岩沉积层和火山岩互层的二元结构单元中。针对硼矿具有低密度的特点,本文对西藏雄巴地区进行了1:5万高精度重力勘探,获得了研究区布格重力异常和剩余重力异常。根据其异常特征进一步分析了区域构造特征、断裂体系、沉积单元以及火成岩的分布与火山沉积型硼矿的形成关系;通过对所获得重力资料的处理,清楚地揭示了局部异常的变化和研究区的断裂构造特征;通过对重力异常进行优选延拓和小波变换处理,并结合研究区的其他地质资料的综合分析,对火山沉积型硼矿的分布范围进行了预测,为该地区火山沉积型硼矿的钻探工程部署提供了地球物理依据。     

利用强震记录进行场地反应分析研究综述

场地反应对地震动的影响是地震工程学中最重要的课题之一,一些破坏性大地震的震害资料表明局部场地反应可以大大加剧地面运动和建筑结构的破坏。分析比较了几种常用的利用强震记录来分析场地地震反应的方法,并就国内外研究现状做了总结。在此基础上详细介绍了各种方法的原理、适用性及存在的问题,针对其中的某些问题提出了可能的解决方法。对于场地地震动反应问题的进一步研究具有参考价值。     

平面SH波作用下部分充填圆弧形沉积谷的二维土层和地形放大效应

场地效应通常包含土层放大效应和地形放大效应,为了揭示二者的相对贡献,本文构造了平面SH波作用下部分充填沉积谷的解析模型,借助于区域分解策略,在波函数展开法的框架下,提出了超定方程组解法,得到了部分充填圆弧形沉积谷对平面SH波散射的波函数级数解,而且级数解的收敛测试表明了超定方程组解法的必要性.通过与文献结果进行对比,验证了本文方法的正确性.通过调整解析模型中两个子区域内的材料参数,计算了沉积谷引起的场地放大效应和相应的空河谷引起的地形放大效应.对二维土层与地形效应进行对比分析,结果显示,在沉积谷内二维土层放大效应通常强于地形放大效应,而地形放大效应决定了沉积谷外的地面运动放大形态.针对最大地面运动,进行了沉积谷和相应空河谷的参数分析,进一步描述了二维土层放大效应,研究结果表明二维土层放大效应引起的最大地面运动通常远远大于地形放大效应引起的最大地面运动,并且二维土层效应通常随着土层与基岩的阻抗比的增大而增大,但不是一维土层放大效应与二维地形放大效应的简单线性叠加.      

天水市建筑场地地面脉动特征

通过对天水市建筑场地地面脉动的观测与分析,说明地面脉动幅值受多种因素的影响,並随地形地貌的改变而变化。水平向脉动明显地有一个卓越方向,水平振动的卓越方向在整体上受场地周围的地形所约束,局部场地条件只具有次要的影响。地面脉动频谱特性一般是在大区域范围内才能反应出变化来,且受区域地质和新构造运动的情况所控制,地面脉动的特征是局部地形地貌对谱型的影响迭加在区域背景上的结果。地面脉动与强震时地面运动特征的对比及二者的相关性是今后研究场地地面运动的重要问题。按场地地面脉动的卓越周期和谱型将测区场地作了区段划分。     

迭溪7.5级地震的地质构造背景及其对发震构造条件的认识

1933年迭溪7.5级地震震区位于我国东西两大块体过渡带——“中国南北构造带”的中段。区内构造复杂,几个不同构造体系的构造成分互相牵制、干扰、复合,还有引人注目的较场弧形构造及其西翼的北西向断裂带。新构造运动表现为强烈抬升背景上的断块差异运动和局部褶断特征。根据对航磁、重力资料的分析,划分出五个磁异常区(带),并作了相应的构造解释。从地震地裂缝、建筑物变形特征、地震崩塌滑坡定向性所反映的应力场以及烈度分布、震源机制解,推测迭溪7.5级地震是在北东东或近东西向的区域构造应力场作用下,导致北西向的松坪沟断裂发生反时针水平错动的结果。故认为松坪沟断裂是迭溪地震的发震构造,而刷金寺——迭溪东西向隐伏断裂带也起了一定的阻隔、牵制以至应力加强的作用。     

非一致激励条件下非线性工程场地地震动相干函数研究

将土非线性分析的等效线性化方法与随机工程波动散射问题的求解方法相结合,建立了开放系统中非一致激励条件下考虑岩土介质非线性的工程场地地震动随机场数值模拟方法并研究了介质非线性对场地地震动相干性的影响。分析结果表明：与不考虑非线性相比,在地震过程中,场地土介质的非线性改变了复杂场地的局部特性从而导致场地地震动空间相干性的变化,因此有必要在场地地震动相干函数的分析中考虑场地介质非线性特性对地震动相干性的影响。     

西昌断陷盆地场地地震动差异分析

以汶川地震中的非发震断层安宁河断裂带周边西昌地区所获取的加速度记录为依据,研究了这些记录在峰值、频谱之间的差异,并通过这些地区的局部场地条件差异进行了初步解释。在此基础上通过数值模拟方法,利用基于显式有限元和局部透射人工边界的二维有限元模型对该地区的地面运动进行了模拟。数值试验结果表明：这些简单的理想化模型对这一地区地震动的本质特征进行重现,并对产生地面运动差异的机理进行合理解释。通过分析,初步揭示了由深部断层构造所控制的断陷盆地对地震动影响显著。     

西昌断陷盆地场地地震动差异分析

以汶川地震中的非发震断层安宁河断裂带周边西昌地区所获取的加速度记录为依据,研究了这些记录在峰值、频谱之间的差异,并通过这些地区的局部场地条件差异进行了初步解释。在此基础上通过数值模拟方法,利用基于显式有限元和局部透射人工边界的二维有限元模型对该地区的地面运动进行了模拟。数值试验结果表明：这些简单的理想化模型对这一地区地震动的本质特征进行重现,并对产生地面运动差异的机理进行合理解释。通过分析,初步揭示了由深部断层构造所控制的断陷盆地对地震动影响显著。     

强震动台站周边地面建筑物对观测结果的影响分析

强震动观测是获取地震地面运动最基本的手段,但其观测质量会受到观测台站周边环境的影响。本文针对不同场地条件的观测台站和附近不同高度建筑物,开展建筑物对观测场地地震动影响的模拟分析,探讨其对强震动观测的影响规律。基于ABAQUS有限元分析软件以及粘弹性边界方法,建立了8个场地-建筑物体系计算模型,分别考虑了4种不同剪切波速的场地和4种不同层数的框架结构建筑物,计算分析了建筑物高度、观测点与建筑之间的距离对强震动观测及场地土波速变化的影响。结果表明:强震动台站附近地面建筑物的存在对观测结果将产生明显的影响,近距离建筑物影响的相对误差可高达20%以上;建筑物高度的变化并没有明显改变其影响程度和影响较大的地震动周期范围,但较高建筑物的影响程度会随距离增加衰减速度减慢;场地土越软,周边建筑物对观测带来的影响越大。建议:对于较软弱场地（土层平均剪切波速低至210m/s）,强震动台站避让建筑物的距离应不小于40m,对于较坚硬场地（土层平均剪切波速大于250m/s）,强震动台站避让建筑物的距离应不小于25m。同时还认为,如果强震动观测要求较高精度,需进一步增加避让距离,且应具体考虑建筑物高度等因素的影响。     

四川地区地震前跨断层数据异常分析

概述四川7.0级以上大震前观测场地的异常情况。在核实2个大震震前异常的基础上,将传统异常判别方法进行汇总。总结近年来针对跨断层监测数据进行分析进而识别异常的方法:原始数据反映的断层活动速率异常以及转折异常。在此基础上,引入小波分析的方法对大震前的异常进行判别。对小波分解得到的两个趋势项进行分析,发现了大震与小波分解项异常的对应性。最后,基于对原始数据和小波分解项的分析,提出利用跨断层数据分析大震前兆的参考意见,为以后的震前异常研究工作提供了基础。     

A Numerical Experiment on the Horizontal to Vertical Spectral Ratio in Flat Sedimentary Basins

—?In this paper we study the seismic response of flat sedimentary basins and carry out numerical experiments to determine the extent to which we could go using the Horizontal to Vertical Spectral Ratio (HVSR) for a given site. The HVSR has been used by many researchers to characterize local conditions in terms of the dynamic response of the soil, and one of its variants, that proposed by NAKAMURA (1989) in which records of microtremors are used, is one of the most applied in recent years. We study the response of different configurations under incident waves coming from an explosive source using the Indirect Boundary Element Method (IBEM), and we investigate two cases: low- and high-velocity contrast. We compute the seismic response using the HVSR technique at various locations in the free surface of the basins, and compare it with the response calculated with the horizontal Sediment to Bedrock Spectral Ratio (SBSR) and with the Horizontal Component (HC) of the transfer function for the displacement at the same locations. The comparison shows that, in general, HVSR cannot provide the predominant period of a site due to the fact that this technique cannot predict accurately the Spectral amplification levels. On the other hand, the HVSR provides an erroneous response in the sedimentary basins which have a low-impedance contrast, with respect to bedrock, and with shape ratios like the one studied here, whereas it can reasonably well predict the fundamental local frequency when there is a high-impedance contrast, except in the center of the basin.     

关于盆地分析思想的发展

中国海陆地区内,沉积岩的分布面积达550万平方公里.这些沉积岩所存在的盆地保留着各种地质作用的记录,赋存着石油天然气和煤炭等矿产资源,是探索地质历史的窗口,也是国民经济建设的重要能源基地.因此,盆地的分析研究显得格外重要,其分析理论思想经历了直观阶段、发展阶段和深化阶段.目前比较完善的是运用综合地球物理方法研究盆地的一套系统工程理论,并将刘光鼎教授提出的综合地球物理解释方法学进一步深化.本文还讨论了盆地分析的有关理论基础.     

基于背景噪声成像方法的新疆呼图壁储气库地区近地表速度结构研究

近年来,背景噪声成像方法在恢复高频面波信号及获取近地表速度结构方面得到了广泛的应用,本文将该方法应用于准噶尔盆地南缘的呼图壁背斜地区的呼图壁储气库.采用储气库及其周边区域22个台站记录的连续背景噪声数据的垂直分量,通过噪声互相关方法获得了台站对之间的瑞利面波经验格林函数,并进一步提取了0.5~1.5 s的基阶瑞利面波群速度频散曲线.首先根据区域平均频散曲线得到了该地区地下数百米的平均一维横波速度结构,然后利用基于面波射线路径追踪的面波频散直接成像方法得到该地区深度为500 m以上的三维横波速度结构.反演结果显示该地区沉积层较厚,整体横波速度值较小（0.4~0.9 km·s^-1）.储气库在地表投影区域的横波速度值较小,这可能是由于抽注水、气引起的沉积岩石裂隙所导致.储气库东北和东南方向均有明显的相对高速区,推测是区域地下水位和地形起伏综合作用的结果.本研究获得的近地表三维速度结构为呼图壁储气库地区的上覆地层物性研究、区域微震精定位、场地效应的评估和去除浅层影响的深部介质成像等研究提供了重要基础.     

3D configuration of Mygdonian basin and preliminary estimate of its site response

Euroseistest is currently the longest running test site in the world. It was originally defined as the 2D cross-section of the Mygdonian basin going from Profitis to Stivos villages. In this paper, we present the first results of the effort to extend the idea of test site to a larger portion of the whole sedimentary structure, i.e. the extension of the idea of Euroseistest from a 2D to a 3D structure. To this end we have compiled available geological and geotechnical information. We have analyzed microtremor and earthquake data recorded seven years ago, that had not been thoroughly exploited. We present the results of the analysis of H/V spectral ratios from microtremors recorded at 195 sites, and from earthquake records at 14 stations. The results are validated through comparison with the well studied 2D cross-section. In addition to this, the geometry of the edges of the basin has been deduced from electrical tomographies. The synthesis of all these data allowed us to propose reliable map of dominant frequencies throughout the basin, a good constrain on the geometry of the basin at the edges, and shear-wave velocity profiles at some points. Our results indicate that average shear-wave velocity is not constant throughout, and thus the dominant frequency map is not a faithful image of the geometry of the basin. We have also obtained a reliable estimate of the site response throughout the basin. The results have been used to plan an additional measurement campaign, and are currently used to compute site response using a 3D seismic modelling code. We expect that the usefulness of Euroseistest to understand site effects in 3D geological structures will be as large as it has been in its 2D phase.     

Estimates of site seismicity rates using ill-defined macroseismic data

A new approach to the problem of site seismic hazard analysis is proposed, based on intensity data affected by uncertainties. This approach takes into account the ordinal and discrete character of intensities, trying to avoid misleading results due to the assumption that intensity can be treated as a real number (continuous distribution estimators, attenuation relationships, etc.). The proposed formulation is based on the use of a distribution function describing, for each earthquake, the probability that site seismic effects can be described by each possible intensity value. In order to obtain site hazard estimates where local data are lacking, the dependence of this distribution function with the distance from the macroseismic epicenter and with epicentral intensity is examined. A methodology has been developed for the purpose of combining such probabilities and estimating site seismicity rates which takes into account the effect of uncertainties involved in this kind of analysis. An application of this approach is described and discussed.     

Spatial correlation of shear-wave velocity in the San Francisco Bay Area sediments

Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for predicting site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average shear-wave velocity of the upper 30 m, V_s(30). We model the horizontal variability of near-surface soil shear-wave velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze shear-wave velocity data over regional distances and find that surface shear-wave velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface waves. We propose a method to map site effects by using geostatistical methods based on the shear-wave velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced shear-wave velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects.     

基于快速推进迎风双线性插值法的三维地震波走时计算

三维地震波走时计算技术是三维地震反演、层析成像、偏移成像等诸多地震数据处理技术中非常重要的正演计算工具.为了获得精度高且兼顾效率的三维走时计算方法:首先,在常规双线性插值公式推导过程中,充分利用平面波双线性假设的结论,获得了二元极小值超越方程的解析解,进而推导出了准确的局部走时计算公式,同时构造性地证明了该计算公式满足地震波的传播规律和Eikonal方程;其次,引入迎风差分的基本思想,提出迎风双线性插值的局部走时计算策略,该计算策略能简化算法、提高效率且保证无条件稳定性;然后,将上述计算公式和迎风双线性插值策略与常规快速推进法中的窄带技术结合,获得了一种新的基于快速推进迎风双线性插值法的三维地震波走时计算方法;最后,通过精度和效率分析检验了新算法的精度、效率和正确性,并通过计算实例验证了算法在面对复杂介质时的稳定性和有效性.     

Soil characteristics in Doon Valley (north west Himalaya,India) by inversion of H/V spectral ratios from ambient noise measurements

Past and recent observations have shown that the local site conditions significantly affect the behavior of seismic waves and its potential to cause destructive earthquakes. Thus, seismic microzonation studies have become crucial for seismic hazard assessment, providing local soil characteristics that can help to evaluate the possible seismic effects. Among the different methods used for estimating the soil characteristics, the ones based on ambient noise measurements, such as the H/V technique, become a cheap, non-invasive and successful way for evaluating the soil properties along a studied area.In this work, ambient noise measurements were taken at 240 sites around the Doon Valley, India, in order to characterize the sediment deposits. First, the H/V analysis has been carried out to estimate the resonant frequencies along the valley. Subsequently, some of this H/V results have been inverted, using the neighborhood algorithm and the available geotechnical information, in order to provide an estimation of the S-wave velocity profiles at the studied sites.Using all these information, we have characterized the sedimentary deposits in different areas of the Doon Valley, providing the resonant frequency, the soil thickness, the mean S-wave velocity of the sediments, and the mean S-wave velocity in the uppermost 30 m.     

Shallow geology characterization using Rayleigh and Love wave dispersion curves derived from seismic noise array measurements

The local geology and shallow S-wave velocity structure of a site are recognized to be key factors for the increase in the damaging potential of seismic waves. Indeed, seismic amplitudes may be amplified in frequency ranges unfavorable for building stock by the presence of soft sedimentary covers over lying hard bedrock. Hence, microzonation activities, which aim at assessing the site response as accurately as possible, have become a fundamental task for the seismic risk reduction of urbanized areas. Methods based on the measurement of seismic noise, which typically are fast, non-invasive, and low cost, have become a very attractive option in microzonation studies.Using observations derived from seismic noise recordings collected by two-dimensional arrays of seismic stations, we present a novel joint inversion scheme for surface wave curves. In particular, the Love wave, the Rayleigh wave dispersion and the HVSR curves are innovatively combined in a joint inversion procedure carried out following a global search approach (i.e., the Genetic Algorithm).The procedure is tested using a data set of seismic noise recordings collected at the Bevagna (Italy) test-site. The results of the novel inversion scheme are compared with the inversion scheme proposed by Parolai et al. (2005), where only Rayleigh wave dispersion and HVSR curves are used, and with a cross-hole survey.