Ground-Motion Characteristics of Idealized Supershear Ruptures: Do They Matter for Engineering Applications?

We study ground-motion characteristics of idealized supershear earthquake ruptures, where the rupture velocity exceeds the shear-wave speed. Using dynamic rupture simulations, we compare supershear and subshear ruptures to identify similarities and differences in patterns of ground-motion intensity measures. Our findings reveal that in the absence of seismic scattering, prolonged and sustained supershear ruptures consistently produce stronger ground-motion amplitudes than their subshear counterparts across examined metrics. Peak ground velocity values for supershear ruptures remain elevated beyond 20 km from the fault due to the mildly attenuating nature of surface Mach waves and the absence of a scattering medium that could potentially reduce the Mach-wave coherence. We find that in the near-fault regions (<7 km), supershear ruptures generate longer shaking durations than subshear ruptures. Furthermore, we find that supershear ruptures generate larger spectral accelerations, particularly in the high-frequency regime (2–3 Hz). These findings highlight the importance of considering supershear rupture effects in seismic hazard assessment and suggest that current building codes may be insufficient for structures exposed to supershear ruptures in the near field.