Rapid estimation of seismic intensities by analyzing early aftershock sequences using the robust locally weighted regression program (LOWESS)

Abstract. Accurate and rapid assessment of seismic intensity after a destructive earthquake is essential for efficient early emergency response. We proposed an improved method, AL-SM99, to assess seismic intensity by analyzing aftershock sequences that occur within 2 h of mainshocks. The implementation effect and application conditions of this method were illustrated using 27 earthquakes with Mw 6.5–8.3 that occurred globally between 2000 and 2023. When the fault system in the seismic region is clear and simple, the robust LOWESS-fitted (locally weighted regression program) curves could be used to estimate the location and length of the fault rupture. LOWESS results can indicate the overall rupture trend and make reliable rupture-scale judgments even when the fault system is complex. When Mw ≥ 7.0 and the number of aftershocks exceeds 40, the AL-SM99 intensity evaluation results may be more reliable. Using aftershock catalogues obtained by conventional means allows for a stable assessment of seismic intensities within 1.5 h of the mainshock. When the number of aftershocks is sufficiently large, the intensity assessment time can be greatly reduced. With early accessible aftershocks, we can quickly determine the rupture fault planes and have a better estimate of the seismic intensities. The results of the intensity assessment provide a useful guide for determining the extent of the hardest-hit areas. By expanding the data sources for seismic intensity assessment, the early accessible data are utilized adequately. This study provides a valuable reference point for investigating the relationship between early aftershock events and fault rupture.