A Robust Time-Domain Approach for Measuring Moment Magnitudes Using Peak Displacement Amplitude

ABSTRACT

The moment magnitude of an earthquake, based on the Brune source model (Brune, 1970), is commonly determined from the S-wave spectrum. Recently, time-domain methods have been proposed that apply multiple narrow band-pass filters and measure the maximum shear displacement amplitudes to determine the seismic moment and corner frequency of earthquakes (Al-Ismail et al., 2023; Knudson et al., 2025). These studies require region-specific empirical attenuation curves of frequency and distance to match normalized peak amplitudes with spectral amplitudes, limiting their applicability. In this study, we modified the time-domain approach by separating the correction terms into four components: two constant factors for spectral-amplitude matching and S-wave partitioning, together with corrections for geometrical spreading, and regional anelastic attenuation. The moment magnitudes of 490 earthquakes (ML≥2.0) in the Korean Peninsula from 2017 to 2022 were determined in the time domain by applying regional attenuation corrections; the results were consistent with the source spectra method, exhibiting a coefficient of determination (R2) of 0.97. To verify the applicability of the method, we determined moment magnitudes of ∼11,000 earthquakes from the two-week-long 2019 Ridgecrest earthquake sequence (Mw 1.0–7.1). The results were in good agreement with the reference moment magnitudes of Trugman (2020), with an R2 of 0.91. These results demonstrate that moment magnitudes can be accurately determined without empirical curves, when regional attenuation models are available. The estimated corner frequencies are also broadly consistent with previous results, with remaining discrepancies likely attributable to methodological differences in their estimation. This time-domain filtering approach can offer an operationally efficient alternative for real-time earthquake monitoring, enabling rapid and reliable estimation of moment magnitudes.