Focal mechanism of the November 9, 2023, Mw 4.1 earthquake in northern Thailand determined by full-waveform inversion

• Date: 2025
• Main Authors: Saetang, K., Srisawat, W.
• Format: Article
• Language: English
• Published: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2025
• Subjects: focal mechanism; full-waveform inversion; minimal 1D velocity model; northern Thailand; seismotectonics
• Online Access: https://journals.uran.ua/geofizicheskiy/article/view/333550
• Journal Title: Geofizicheskiy Zhurnal

A Mw 4.1 earthquake occurred in northern Thailand (19.498°N, 98.518°E) on 09 November 2023 (centroid time: 07:30:19.86 UTC), within the seismically active Shan-Thai terrane. Source parameter determination employed full-waveform inversion utilizing three-component seismic data from ten regional stations at distances of 73—108 km, operated by the Thai Meteorological Department’s seismic monitoring network, the Department of Mineral Resources network of Thailand, and the Myanmar National Seismic Network. The inversion methodology utilized the ISOLA software package, implementing iterative deconvolution based on the six-element moment tensor framework, and incorporated a minimal 1D velocity model with station corrections specifically calibrated for northern Thailand. Data preprocessing included instrumental response removal, baseline corrections, and band-pass filtering. Green’s functions were computed using the frequency-wave number integration technique within a 0.03—0.10 Hz frequency band. Moment tensor inversion yielded a predominantly strike-slip mechanism with two nodal planes: plane 1 (strike=1°, dip=59°, rake=–148°) and plane 2 (strike=253°, dip=63°, rake=–35°) with 75  % double-couple and –1.2  % CLVD components. Grid search analysis systematically explored source depths from 0—35 km and determined an optimal centroid depth of 2.5 km, with maximum correlation coefficients exceeding 0.4 within the 2—4 km depth range. Waveform analysis demonstrates variance reduction values ranging from 0.40 to 0.80 at near-regional stations (Δ<250 km), indicating robust source parameter determination. The focal mechanism and seismicity distribution indicate strain release along an NE-SW trending structure, located 17 km west of the N-S trending Wiang Haeng fault system.