Strong Ground Motion Simulation of Illapel Earthquake Using Empirical Green's Functions

Abstract eng:
The September 16th 2015 Illapel, Chile, earthquake (M w 8.4) generated a good set of aftershock data that enabled us to develop and to validate a model for synthetic ground motion generation. This study presents a methodology to generate strong ground motions based on site amplification and phase characteristics of seismic waves, and also based on a source model that was newly developed for the earthquake. The methodology includes the superposition of corrected empirical Green’s functions that consider the three effects: source, path and site. The path effects incorporate the attenuation of seismic waves between the source and the recording stations, and include both geometric spreading and inelastic attenuation. Weak motion data obtained at the strong-motion stations was used to evaluate empirical site amplification factors. For this purpose, aftershocks recorded during the first three months after the main shock were used. Furthermore, the phase characteristics of the Green’s functions were determined based on the weak motion data recorded at the stations. The source model involves two SPGAs (strong-motion pulse generation areas). The locations of the SPGAs were basically determined based on the arrival times of the velocity pulses. The SPGA sizes were chosen according to the pulse duration. The methodology was validated using observed records in terms of velocity waveforms and Fourier spectra. According to the results, the velocity waveforms including pulses were well reproduced in a frequency range of interest to structural engineering (0.2 to 1 Hz). The agreement between the simulated and measured waveforms makes this model a strong platform to assess hazard at specific sites where detailed hazard assessment is required.

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