Reliability Analysis on Non-Parametric Spectral Inversion of Seismic Ground Motion
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摘要:
非参数化谱反演是研究地震动震源、传播路径及场地效应的关键技术,反演的可靠性对地震震源物理的准确认识及地震危险性的有效预测具有重要影响. 为分析震源和场地项权衡的约束条件、单步法/两步法的选择、震源参数估计等关键环节对反演可靠性的影响,以2016—2017年意大利中部地震序列的地震动谱反演为例,给出确保反演可靠性的合理建议. 研究结果表明:参考场地的选择显著影响反演可靠性,在综合考虑场地地质资料、观测记录水平/垂直(H/V)谱比等初选基础上,根据震源谱、震源参数等的试算结果最终确定合适的参考场地;非参数化谱反演的单步法和两步法的选取显著影响远场高频路径衰减的反演结果,一定程度上影响高频震源谱,对震源参数估计结果的影响较小,由于两步法的路径衰减项易被场地项干扰,单步法是最佳选择;利用网格搜索方法估计反演震源谱的矩震级、拐角频率和高频衰减参数时,为尽可能避免拐角频率和高频衰减参数之间的权衡,应利用中低频震源谱估计矩震级和拐角频率,当拐角频率大于0.5 Hz时,可不考虑矩震级和拐角频率的权衡对其估计的影响,对于拐角频率较小且震级较大地震可直接利用地震矩计算结果,以提高震源参数估计的可靠性.
Abstract:Non-parametric spectral inversion is the key technology to study the seismic source, propagation path and site effects. The reliability of spectral inversion was responsible for exactly understanding seismic source physics and effectively predicting seismic hazards. In this work, the non-parametric spectral inversion of ground motions during the 2016—2017 central Italy seismic sequence was used to systematically evaluate how the reliability of spectral inversion was dominantly controlled by several decisive factors, i.e., constraints for trade-offs between source and site terms, selection of one- or two-step non-parametric inversion methods, and potential effects of trade-offs among the parameters describing source spectra on their estimations. Results show the crucial effects of reference site on the inversion reliability. Multiple trials for the source spectra and source parameters were necessary for selecting the appropriate reference sites, which were preliminarily regarded as rock sites based on the surface geological information, the horizontal-to-vertical spectral ratios, etc. The usage of either one- or two-step method has obvious effects on high-frequency propagation path attenuation at far fields. However, negligible effects occurred on source parameter estimates. The one-step method was preferred because the path attenuation given by two-step method could be interfered by the site term. In order to eliminate the effects of trade-offs between corner frequency (
f c) and high-frequency decay parameter, low- and intermediate-frequency source spectra were suggested to estimate the moment magnitude and corner frequency. It was found that trade-offs between the moment magnitude and corner frequency have weak effects on their estimations for the cases off c > 0.5Hz. Predefined the moment magnitude can be included for the reliable corner frequency estimates for those large events with small corner frequency.-
Key words:
- seismic ground motion /
- spectral inversion /
- reliability /
- reference site /
- source parameters
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