The 2022 M_w6.2 Pasaman, Indonesia, earthquake sequence and its implication of seismic hazard in central-west Sumatra

The 2022 M_w6.2 Pasaman earthquake took place in central-west Sumatra in association with activity in the Sumatran Fault system. This study clarifies the spatial and temporal distribution of the Pasaman earthquake sequence and forecasts the earthquake sequence’s impact on the seismicity in the vicinity and in the Sumatran Fault system. We first examined the seismicity before the mainshock and observed temporal low b-value anomalies, shedding light on the earthquake’s precursor by monitoring b-values prior to the event. Based on the aftershocks in the first 18 days, we modeled the temporal distribution of the aftershocks according to the modified Omori’s law, which suggested this sequence could last 49–473 days. By further considering Båth’s law and the Gutenberg–Richter law, we estimated the temporal distribution of the maximum magnitudes in the aftershock sequence. To understand the spatial pattern of the aftershocks, we calculated the coseismic Coulomb stress change imparted by the Pasaman mainshock. Considering uncertainties of the Coulomb stress calculations from rupture geometry, mainshock parameters, friction coefficients, and strike angles of the receiver plane, the patterns of the Coulomb stress changes are similar that the stress increases extended northwest and southeast, consistent with aftershock distribution. We further evaluated rupture probability for each segment of the Sumatran Fault. Considering the stress perturbation imparted by the Pasaman earthquake, we expected a seismicity rate increase of ca. 40% at the Sumpur and Sianok segments in the short term. To quantify long-term rupture probability, the recurrence interval and the time elapsed since the previous earthquake were incorporated based on the time-dependent Brownian passage-time model. The earthquake probability at the Sumani segment in the coming 50 years was determined to be 72%. The results of this study have significant implications for subsequent probabilistic seismic hazard assessments, not only for Sumatra but also for certain metropolitan areas in Malaysia and Singapore.