Stress Transfer and Seismicity Along the Southern Great Sumatran Fault: Insights from the 1994 Liwa Earthquake

Abstract

The February 15, 1994 Mw 6.8 Liwa earthquake ruptured the southern Great Sumatran Fault (GSF), yet its static stress legacy and relation to subsequent seismicity remain weakly quantified. We integrate high-precision double-difference relocation with Coulomb failure stress (ΔCFS) modelling to evaluate post-1994 stress transfer along the Semangko sector. Using ~16,000 P/S picks and identical inversion settings, we test two 1-D velocity models; CRUST1.0 yields near-zero, narrow differential-time residuals (± 0.3–0.4 s) compared with broader heavy tails for AK135 (± 0.7–0.8 s) and are adopted for the final catalogue. Since phase archives are sparse before 2010, events from 1994 – 2009 are treated as background, whereas 2010–2024 earthquakes are relocated; quality control retains 416 events. Relocation suppresses the artificial ~10 km depth band and collapses epicenters into coherent clusters that delineate the West/East Semangko Faults and Semangko Bay. ΔCFS was computed for depths of 5–20 km and μ′ = 0.2–0.8. All scenarios produce the expected four-lobed right-lateral pattern with maxima >0.10 MPa around WSF-B, ESF-A, and the Kumering Fault. Relocated events preferentially occupy positively loaded regions: ~74% fall at ΔCFS > 0 and ~73% at ΔCFS ≥ 0.01 MPa (10 kPa), robust to μ′ and depth. The results indicate unresolved post-1994 loading on multiple Semangko branches and adjacent segments, highlighting the potential for cross-segment triggering. We advocate expanding seismic and geodetic monitoring and targeted paleoseismic surveys in the Semangko–Kumering corridor to refine recurrence estimates and update physics-based hazard models for southern Sumatra.