Broadband strong motion simulation in layered half-space using stochastic Green’s function technique |
| |
Authors: | Y Hisada |
| |
Institution: | (1) Department of Architecture, Kogakuin University, Nishi-Shinjuku 1-24-2, Shinjuku, Tokyo 163-8677, Japan |
| |
Abstract: | The stochastic Green’s function method, which simulates one component of the far-field S-waves from an extended fault plane
at high frequencies (Kamae et al., J Struct Constr Eng Trans AIJ, 430:1–9, 1991), is extended to simulate the three components of the full waveform in layered half-spaces for broadband frequency
range. The method firstly computes ground motions from small earthquakes, which correspond to the ruptures of sub-faults on
a fault plane of a large earthquake, and secondly constructs the strong motions of the large earthquake by superposing the
small ground motions using the empirical Green’s function technique (e.g., Irikura, Proc 7th Japan Earthq Eng Symp, 151–156, 1986). The broadband stochastic omega-square model is proposed as the moment rate functions of the small earthquakes,
in which random and zero phases are used at higher and lower frequencies, respectively. The zero phases are introduced to
simulate a smooth ramp function of the moment function with the duration of 1/fc s (fc: the corner frequency) and to reproduce
coherent strong motions at low frequencies (i.e., the directivity pulse). As for the radiation coefficients, the theoretical
values of double couple sources for lower frequencies and the theoretical isotropic values for the P-, SV-, and SH-waves (Onishi
and Horike, J Struct Constr Eng Trans AIJ, 586:37–44, 2004) for high frequencies are used. The proposed method uses the theoretical Green’s functions of layered half-spaces
instead of the far-field S-waves, which reproduce the complete waves including the direct and reflected P- and S-waves and
surface waves at broadband frequencies. Finally, the proposed method is applied to the 1994 Northridge earthquake, and results
show excellent agreement with the observation records at broadband frequencies. At the same time, the method still needs improvements
especially because it underestimates the high-frequency vertical components in the near fault range. Nonetheless, the method
will be useful for modeling high frequency contributions in the hybrid methods, which use stochastic and deterministic methods
for high and low frequencies, respectively (e.g., the stochastic Green’s function method + finite difference methods; Kamae
et al., Bull Seism Soc Am, 88:357–367, 1998; Pitarka et al., Bull Seism Soc Am 90:566–586, 2000), because it reproduces the full waveforms in layered media including not only random characteristics at
higher frequencies but also theoretical and deterministic coherencies at lower frequencies. |
| |
Keywords: | Broadband strong motion simulation Omega-squared model Green’ s function of layered half-spaces Stochastic Green’ s function method Empirical Green’ s function method The scaling law 1994 Northridge earthquake |
本文献已被 SpringerLink 等数据库收录! |
|