经验格林函数方法的理论探讨

Discussion about theory of empirical Green's function

通过比较经验格林函数和理论格林函数模拟地震动方法,认为经验格林函数方法能比理论格林函数更好地模拟地震动。同时亦指出用经验格林函数方法模拟地震动时出现两个问题:(1)模拟的结果高频不稳定。(2)模拟的结果有一个"人造周期"。地震工作者提出选择适当的频响函数,比较有效地解决了模拟结果高频不稳定的问题;还提出了完备经验格林函数集的概念,以提高模拟结果与记录的符合程度。但完备经验格林函数集提出了每个大震子断层上都有小震记录的过于苛刻的要求,使得完备经验格林函数集的获得只能靠理论和经验关系结合的办法。本文通过对大震断层滑动速度函数的理论分析认为:可以用多个不同滑动速度和不同上升时间的小震合成经验格林函数,用这种经验格林函数合成的地震动不会产生"人造周期"。但需要加强对小震记录的反演工作并获得丰富的小震参数。

On the basis of the comparison between empirical Green＇s function and theoretic Green＇s function,we draw a conclusion that the empirical Green＇s function can simulate ground motion better than the other one.By analyzing the empirical Green＇s function,there are two problems when we use this method：（1）The results of the simulation are not stable in the high-frequentcy parts;（2） The results of the simulation have a ＂artificial period＂.Seismic operators have solved the problem of unstability in high frequency by choosing proper function of frequency response.Then,the seismic operators put forward the conception of self-contained concourse of empirical Green＇s function to ensure the consistency between the record and simulation.But a strict requirement that every subfault on the big earthquake fault must have small earthquake record is put forward.For getting the self-contained concourse of empirical Green＇s function,the method of combination between theory and empirical relations must be adopted.In this paper we analyse the slip velocity function of big earthquake theoretically.We think that we can get empirical Green＇s function by using more small earthquake with different slip velocities and different rise time.The ground motion that simulates this empirical Green＇s function will not produce ＂artificial period＂,but the inversion of small earthquakes must be strengthened to get more parameters of them.