Abstract On 20 November 2019, an Mw 6.3 (ML 6.4) earthquake occurred in Xayaburi Province, Lao People’s Democratic Republic (Lao PDR), about 19 km from the Thai border. Although this earthquake is of a moderate size, it was widely felt across northern Thailand and caused damage to houses and schools on both sides of the border, emphasizing the significance of the seismic hazard from intraplate earthquakes. In this study, we analyzed seismic data recorded by both permanent and temporary seismic networks in Thailand to investigate the earthquake sequence that began with an Mw 5.7 foreshock occurring less than three hours before the mainshock, followed by aftershocks ranging from ML 0.1 to 5.7 between 20 November 2019 and 31 December 2022. Relocated hypocenters of this earthquake sequence define a north-northwest–south-southeast-trending, 35 km long seismicity zone at roughly 10 km depth, indicating rupture along a previously undocumented active fault segment. The fault mechanisms of the largest 16 earthquakes with Mw 3.8–6.3 in this sequence, including the mainshock, indicate right-lateral strike-slip motion, consistent with other intraplate deformation in the region. Aftershock decay follows Omori’s law. Coulomb stress modeling suggests that the foreshock may have stressed the fault patch that occupies the mainshock, and that subsequent stress transfer from the Mw 5.7, 6.3, and 5.6 earthquakes influenced nearby faults, particularly toward the north and south fault extensions and active faults in Thailand. This earthquake sequence provides new seismological evidence of active faulting in northern Lao PDR that had not previously been documented as active in existing geological or seismic hazard map, and highlights the need for regional seismic hazard assessments for both Lao PDR and northern Thailand.
Pholsonda et al. (Wed,) studied this question.