Kappa (k) derived from accelerograms recorded in the 2008 Wenchuan mainshock, Sichuan, China

Abstract

High-frequency spectral decay factor, kappa (k), in the accelerograms of the Wenchuan mainshock was measured using strong motion data from 52 stations within 311km of the epicenter. The derived k range from 0.0034s to 0.0468s. The correlation of k versus fault distance was given, which is k=0.01288+5.9068×10–5R for the N-S component, k=0.01881+1.4219×10–5R for the E-W component, and k=0.00855+5.6086×10–5R for the U-D component. The analysis on the spatial variation of k demonstrates that k relates to source effect and propagation effect besides local site effect. Ground motions for the 52 stations were simulated using derived k and compared to actual recordings in terms of waveforms, amplitude spectra and response spectra. The results show agreement at shorter periods (<1s), but a slight overestimation at longer periods (1–7s).