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Abstract

While classic double-couple earthquake models explain seismic wavefields accurately at low frequencies, at higher frequencies, seismic radiation exhibits significantly more complex and stochastic characteristics. Various on-fault and off-fault mechanisms have been proposed to explain high-frequency radiation, yet their relative contributions and trade-offs remain debated. In this study, we analyze near-fault high-frequency characteristics of the 2023 Mw 7.8 Kahramanmaraş earthquake with 19 strong-motion stations within approximately 10 km of its southern rupture. Above Hz, we observe a loss of horizontal polarity and reduced coherence between the two horizontal components, which cannot be explained by heterogeneous rupture on a planar fault. Additionally, the Hz transition frequency is lower than the commonly accepted rule-of-thumb value of 1 Hz. The near-fault high-frequency energy arrives concurrently with low-frequency signals, suggesting that high-frequency radiation originates near the fault rather than from medium scattering. Comparison with regional stations and back-projection analysis suggests that high-frequency signatures from the source persist even at greater distances. These findings indicate that the small-scale radiation processes near the rupture front are more complex than those described in conventional earthquake source representations. Our results highlight the need for improved earthquake source parameterization to assess high-frequency ground motion hazards and may provide valuable constraints for theoretical studies on high-frequency radiation mechanisms.