Study on Empirical Green's Function Method for Broadband Waveform Synthesis Including Long-Period Subsequent Waves

Abstract

In recent years, Japan has accumulated a vast amount of earthquake observation records due to the strong-motion network, and the Empirical Green's Function Method (EGF method) is expected to be more effectively utilized. The EGF method has been used mainly for short-period body waves, but has not been used for broadband seismic motions including subsequent surface waves. It should be noted that the amplitude characteristics of short-period entity waves with random characteristics and long-period surface waves with coherent characteristics differ greatly due to the superposition of element waveforms. In this study, we reproduced broadband seismic motions including surface waves for the 2000 Tottori-ken Seibu Earthquake, for which aftershock records are abundantly observed, and investigated points to be considered when synthesizing waveforms. Two elemental earthquakes of different sizes were selected, and four source models were used for simulation, with different assignments to the two Strong Motion Generation Areas (SMGA) and different rupture propagation types. In order to synthesize long-period subsequent waves at distant stations, it is necessary to use elemental earthquakes with large scale and good signal-to-noise ratio, and Case with a small number of SMGA divisions was also considered. As a result, it was confirmed that different types of ruptures on the fault plane and different propagation directions cause different time differences in waveform synthesis, especially large differences in the amplitude of long-period subsequent waves.