参数对地震动随机模拟结果的影响分析

Effects Analysis of Parameters on Stochastically Simulated Ground Motions

随机有限断层法是模拟近场高频地震动常用的方法,且被国内外研究者证实是成功的且有效的模拟高频地震动的工具。由于随机有限断层模拟方法输入参数较多,造成对模拟结果的不确定因素也相应较多,因此在使用随机有限断层法时如何合理地确定输入参数则成为研究者需要考虑的首要问题,也是成功重建场点加速度纪录的关键环节。简要地介绍了地震动模拟的基本理论、流程和主要参数的意义,在国内外研究者的研究成果基础上以芦山Mw6.6地震为例重点分析了地震动持时对峰值加速度(PGA)、5%阻尼比加速度反应谱(PSA)和加速度傅里叶谱(FAS)模拟结果的影响。主要得出以下结论:(1)在特定震级下,持时模型对峰值加速度影响较大,特别是断层距越小时,这种影响作用越明显;(2)通过四种持时模型得到的傅里叶谱和反应谱以及模型偏差分析可知,根据记录90%有效持时拟合其与震中距得到的持时模型表现较好。最后分析了脉冲百分比和断层上缘埋深等参数对模拟反应谱的影响,结果显示:(1)在相同震级下,反应谱幅值随脉冲百分比的变化差异不大;(2)在断层方位尺寸给定的前提下,反应谱幅值随上缘埋深的增加而减小。这些结论可以为随机有限断层模拟方法的工程实际应用时更合理地挑选参数提供理论依据,也可以相应的提高模拟精度。

Stochastic finite-fault method is commonly utilized to simulate near-field high-frequency ground motion,and is proved to be a successful and effective tool by researchers at home and abroad.Due to a large number of input parameters,there are many uncertainties in the simulation results.Therefore,how to reasonably determine the input parameters has become a most important problem for researchers,and is also the key to successfully reconstructing the acceleration record of the field site. By introducing the basic principle,procedure and parameters meaning of ground motion simulation,taking the Lushan Mw6.6 earthquake as an example,this paper focuses on the influence of ground motion duration on peak ground acceleration(PGA),5%-damped spectral acceleration(PSA)and Fourier acceleration spectrum(FAS)based on the research results of domestic and foreign researchers. The main conclusions are as follows:(1)The duration model has a great influence on the PGA at a specific magnitude;(2)According to the analysis on the Fourier spectrum,response spectra and model bias of the four duration models,the duration model obtained by fitting the 90% effective duration with the epicenter distance is better. At the same time,the influence of the pulse area percentage and the buried depth of the fault on response spectra is analyzed. The results show that:(1)Under the same magnitude,the amplitude of response spectra has little change with the pulse area percentage;(2)When the orientation of the fault is given,the amplitude of response spectra decreases with the increase of buried depth of the fault. These conclusions can provide a theoretical basis for the more reasonable selection of parameters in the practical application of the stochastic finite-fault simulation method,and can also improve the simulation accuracy accordingly.