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Zusammenfassung:
This study presents the coupling of the spectral decomposition results for anelastic attenuation,
stress drop, and site effects with the Graves-Pitarka (GP) hybrid ground-motion simulation
methodology, as implemented on the Southern California Earthquake Center
(SCEC) broadband platform (BBP). It is targeted to applications in the Upper Rhine graben
(URG), which is among the seismically active areas in western Europe, yet a moderate seismicity
area. Our development consists of three main steps: (1) calibration of regional highfrequency
(HF) attenuation properties; (2) modification of the hybrid approach to add compressional
waves in the HF computation and examine various strategies to evaluate site
amplification factors in the Fourier domain (e.g., VS30-based or site-specific factors); (3) testing
of the simulations using earthquake records from the URG (3:7 < Mw < 5). The validation
process of the simulated time histories is performed first on rock sites, and, then
subsequently at all stations, whatever their site conditions. The performance of the simulations
for rock sites is assessed through the standard validation technique in the BBP
(comparison of the waveforms, intensity measures, and estimation of the response spectra
model bias). We additionally compare the Fourier amplitude spectrum of the simulations
and observations, and compute their corresponding bias. The results show that the simulated
ground motions match the general characteristics of the recorded motions, and that
the model bias generally fluctuates around zero across the broadband frequency range.
Hence, the hybrid ground-motion methodology implemented in the SCEC BBP can be successfully
applied outside high-seismicity areas and outside those areas for which it had
been generally calibrated. Our results also show that HF modification and calibration were
necessary to improve the fits with the observation, and demonstrate the potential benefits
of using site-specific amplification factors compared to VS30-based amplification factors.
