Present-day inter-seismic velocities and fault slip rate of Ketahun segment, Sumatran Fault System (SFS) inferred from Global Positioning System (GPS) observations

The Ketahun segment of the Sumatran Fault System (SFS) is distinctive and tectonically active segment, yet the slip rate of the segment is not widely known. The Ketahun segment underwent two major earthquakes of M_s 7.6 in 1946 and M_s 6.8 in 1952, respectively. Using Global Positioning System (GPS) data, we aim to better estimate the slip rates using a dislocation elastic model following a Bayesian approach with Metropolis Markov chain Monte Carlo (MCMC) samplers to estimate optimum fault parameters. Then we determined the potential amount of cumulative energy stored at the segment. We processed raw GPS data from 35 GPS stations, combining from GIA, SuGAr, and UNIB networks during 2018–2024 using GAMIT/GLOBK software. The daily GPS solutions were constrained into the ITRF-2014 frame, and the GPS velocities were translated into Sunda block. Before we model the trench parallel GPS velocities, we attempted to correct the viscoelastic velocities due to the 2007 Mw 8.4 Bengkulu earthquake incorporating the effect of megathrust coupling on the trench parallel GPS velocities. We find the importance of viscoelastic response and megathrust coupling effect in our analysis, providing better slip rate and locking depth estimation. Our result inferred that the estimated fault slip rate is 14.5 [−1.2, +1.3] mm/yr with a locking depth of 14.4 [−4.9, +4.8] km across in the Ketahun segment. The segment is capable of generating a magnitude ∼6 to 7+ if a single earthquake occurs every 50 to 200 years.