Publication Date:
2013-11-22
Description:
A hybrid empirical method is proposed to simulate broadband strong ground motion that combines a kinematic complex source model with both numerical and empirical Green’s functions. The kinematic approach is based on a composite source model description where subevents are generated using a fractal distribution of sizes. The subevents are set up with a size-dependent rise time. Each elementary source is described as a crack-type slip model that starts radiating when the rupture front reaches the nucleation point located randomly inside a size-dependent nucleation region. The synthetic acceleration spectra follow the 2 model, and the spectral amplitudes are scaled by a frequency-dependent directivity coefficient. In this study, the hypothesis of constant stress drop of subevents is released to better model the high-frequency level radiated by the source. Taking advantage of small-magnitude events, synthetic seismograms are computed using hybrid Green’s functions (HGF) to model the impulsive response of the medium. The procedure computes HGF for each subfault combining the numerical low-frequency and the empirical high-frequency Green’s functions with appropriate amplitude and phase correction (geometrical spreading and time delays due to the S -wave travel-time propagation). This methodology is applied to simulate the strong ground motions recorded during the 1997 M w 5.9 Yamaguchi-Ken, Hokubu, Japan, earthquake. Some of the finite-source rupture parameters (e.g., rupture velocity, asperity size, and seismic moment) were chosen according to previously published studies conducted on this event. Only random generation of k –2 composite slip distributions was allowed ( k being the radial wavenumber), to model heterogeneous slip while mimicking the main asperity size and location imaged. Comparisons of predicted and observed strong-motion characteristics show that predictions are largely improved, when both HGF and variable stress drop of subevents are used.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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