High-Frequency Seismic Wave Simulations in Qs-Constrained von Kármán Random Media for the 2016 Gyeongju Earthquake, South Korea

Characterizing high-frequency (~10 Hz) seismic wave propagation is essential for understanding strong ground motions and improving seismic hazard assessment. High-frequency components are strongly influenced not only by source processes but also by small-scale heterogeneity along the propagation path. In the crust, vertical layering coexists with lateral heterogeneity, which plays a key role in controlling the propagation and attenuation of seismic waves. During propagation, seismic energy is reduced by intrinsic attenuation, in which energy is dissipated into heat and acoustic energy, and by scattering due to heterogeneity, which can produce apparent attenuation or amplification. In this study, we analyze S-wave coda from the 2016 Gyeongju earthquake using Multiple Lapse Time Window Analysis (MLTWA) to estimate the intrinsic (Qi), scattering (Qs), and total (Qt) quality factors in discrete frequency bands. Over the central frequency range of 1.5–22 Hz, the inferred Qs values range from approximately 398 to 4399, Qi from 185 to 1390, and Qt from 120 to 1041, revealing a pronounced frequency dependence of attenuation. The observed Qs–frequency relationship is then interpreted using a von Kármán autocorrelation model, yielding crustal heterogeneity parameters ε = 0.048, κ = 0.32, and a = 8.0 km. These parameters reproduce the empirical Qs curve and are used to generate random heterogeneous media for numerical simulations of high-frequency wave propagation. By integrating observation-based heterogenous crustal modeling, this study quantitatively constrains the influence of crustal heterogeneity on high-frequency seismic wave propagation and provides a physical basis for refining strong ground motion prediction models and improving the reliability of seismic hazard assessments.