【作者】 刘必灯；

【导师】 李小军；

【作者基本信息】 中国地震局工程力学研究所 ， 桥梁与隧道工程， 2011， 博士

【摘要】 地震动场的确定一直是工程地震的主要研究内容之一,发震断层的震源效应和地震动衰减规律影响地震动场的确定,同时局部场地条件也是一个非常重要的影响因素,其包括局部土层、局部地形和局部构造,而局部断层构造对地震动场的影响研究国内外不同学者的认识还不统一“十五”期间在中国西南的重点监视防御区的鲜水河断裂带、安宁河断裂带周边布设了大量强震动观测台站,这些台站自正式投入运营后的两个月恰逢汶川地震发生,获取了此次地震主、余震的大量强震动记录,其中很多记录为研究非发震断层对场地地震动的影响提供了重要资料。本文以汶川地震中的非发震断层鲜水河断裂带、安宁河断裂带、渭河断裂带周边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这几个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了重现,并对产生地面运动差异的机理进行了合理解释。通过对西昌地区地震动记录差异性进行分析,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：宝鸡地区地震动记录差异性结果表明由断层控制的断陷盆地及断层陡坎地形对地震动影响显著；通过对石棉地区地震动记录差异性结果的分析,揭示了非发震断层近震源侧地震动强度更大、高频更丰富的特点,并指出了非发震断层的隔震效应。本文就断层参数对场地地震动影响方面进行了大量研究,得到了若干结论。通过数值模型计算揭示了以断层破碎带为表征的各种断层参数对场地地震动的影响。研究结果表明：断层低速度破碎带的存在产生了大量的转换波；介质波速差异较大时(3倍以上)断层破碎带中产生明显的断层陷波；断层低速度破碎带的存在使输入场地的能量向低速度带中集聚,且随着破碎带宽度增大,这种集聚效应增大；竖向断层破碎带能阻隔斜入射地震波,在入射波动所指向的一侧地面运动更小,且随着入射角度增加,这种阻隔效应更明显。针对宽度和介质波速对地震动影响研究表明,断层场地对地震动的放大效应与频率相关,模型放大效应对不同卓越频率的输入地震动具有选择性,宽度较窄和介质波速较高的断层破碎带对地震动中较高的频率成份放大显著,而宽度较宽和介质波速较低的断层破碎带对地震动中较低的频率成份放大显著。其原因是放大效应与场地卓越频率有关,破碎带宽度越宽或波速越低,其卓越频率越低。对隐伏断层场地的地面运动分析表明,隐伏断层的上覆岩体对垂直入射地震动的传播有阻隔作用,随着上覆岩体厚度的增加,阻隔效应越来越强。另外,断层破碎带对地表地震动的影响随着埋深的增加而变小,当埋深达到一定深度后断层破碎带对地表地震动的影响可以忽略。随着覆盖层厚度的增大,整个场地及破碎带地表投影区的地震动反应幅值和高频成份都逐渐减小,在自由地表影响范围也逐渐减小,且地震动强度沿深度衰减加快：覆盖层波速越低,场地自由地表地震动越强,而断层破碎带对地表地震动的影响越弱；倾滑隐伏断层场地地震动分析结果表明,总体上,断层破碎带上侧区域的地震动反应小于下侧,表明倾斜破碎带对垂直入射地震动具有一定的隔震效应。更多还原

【Abstract】 Analysis and Simulation of ground motion field is one of the main aspects in engineering seismology. Besides source effect of causative fault and attenuation effect of ground motion, local site conditions are the important influencing factors of ground motion, which contains local site soil, local topography, and local tectonics. There is no common understanding about the effect of the local tectonics on ground motion.In the key region of earthquake monitoring and defending in southwestern China, such as the surrounding areas of the Xianshuihe fault zone and Anninghe fault zone, many strong motion observation stations were arranged in the ’tenth five-year plan’. Just two months later after these stations entered formal operation, numerous records were obtained from Wenchuan earthquake and its aftershocks, some of which are very useful to study the effect of the non-causative fault ion ground motion.In this study, by analyzing the peak ground acceleration (PGA) and spectral characteristics of the earthquake acceleration records from the main shock and aftershocks of Wenchuan Earthquake, the difference of the ground motion at both sides of the non-causative faults such as Xianshuihe fault zone, Anninghe fault zone and Weihe fault zone are discussed. By analyzing the difference of the local site conditions at the observation stations, such as local site soil, local topography, and local tectonics, pilot explaining of the discrepancy is attained, and numerical solution of 2-D model of those sites derived by the explicit finite element combining with local multi-transmitting artificial boundary method is used for interpreting the mechanism of difference of the ground motion. Results of numerical calculation indicate that, in spite of its simplicity, such an idealized model is also successful in reproducing many of the essential characters of ground motion and the mechanism of the difference of ground motion within the fault zones of Xianshuihe, Anninghe and Weihe.The character of dislocation basin under control of the Anninghe fault zone may be used for the interpretation of observed seismic data obtained in Wenchuan main shock and theoretical calculations of near fault responses in Xichang City. And the character of dislocation basin and fault scarp under control of the fault may be used for the interpretation of observed seismic data obtained in Wenchuan mainshock and theoretical calculations of near fault responses in Baoji City. By comparing the difference between the acceleration records in Shimian region obtained in Wenchuan main shock and its aftershocks and Shimian shock, and theoretical calculations of near fault responses in this area, anomalously large amplitude and extremely rich high frenquency in the ground motion are found near source side (right side of the fault in this case). The results indicate that the non-causative fault can obstruct the spread of seismic wave. And the isolation effect of the non-causative fault is found.Abundant research on the fault parameter influencing the site ground motion was done, and some valuable results are achieved. Numerous numerical simulation indicates that the parameters of low velocity fault zone (LVFZ), such as the width and wave velocity, influence the site ground motion prominently. The numerical simulation shows that transform waves can develop inside LVFZ when struck by external, vertically incident seismic radiation. And trapped waves can develop obviously inside the LVFZ while the wall rock’s wave velocity is 3 times larger than LVFZ’s. This result implies that the invariance of energy, struck by external incident seismic radiation, is congregated at the low velocity zone, and the convergence effect increases with the increase of the width of the LVFZ. The study of 2-D vertical LVFZ model struck by external oblique incidence seismic radiation shows that, vertical LVFZ can obstruct the spread of oblique incidence seismic wave, and the isolation effect decreases with the increscing incidence angle.The study about the seismic response of a variety of LVFZ models with different width and velocity struck by external vertically incident seismic radiation implies that, the amplification characteristics of ground motion in near fault zone site are frequency dependent. The site amplification characteristics are different under the earthquake input with different predominant frequency. The higher frequency components of earthquake input are amplified obviously by the fault fracture zone with narrow width and low medium velocity, rather than vice versa. It is because that the site amplification coefficient is frequency dependent, and the narrower width and lower velocity of fault fracture zone, the lower predominant frequency.The analysis of ground motion at the hidden fault site shows that the vertical incidence of earthquake input is obstructed by the overlying rock mass, and with the increase of thickness of the rock mass, the obstruction effect becomes stronger. Besides that, the effect of fault fracture zone on the ground motion becomes smaller with the depth increasing, and the effect can be neglected at some depth. The amplitude and high frequency components of ground motion at the whole site and the projection area of the fault fracture zone decrease with the increase of the depth of overburden, meanwhile, the influence scope of the surface becomes smaller and the intensity of ground motion decreases with the increase of the depth. With the decrease of overburden velocity, the ground motion becomes stronger; however, the effect of fault fracture zone on the ground motion becomes weaker. The analysis of ground motion at the dip-slip fault site shows that the ground motion at the upside area of the fault fracture zone is smaller than that at the underside, and the isolation effect exists when the vertical incidence of earthquake input spreads through the fault fracture zone.更多还原