Hypocenter distribution of volcanic earthquakes beneath Mount Sinabung (Oct 2023–Apr 2024) using an adaptive damping Geiger relocation

Relevance. Mount Sinabung has remained one of the most active volcanoes in Indonesia during the past decade, producing recurrent seismic swarms that reflect dynamic subsurface processes. Understanding the spatial distribution of hypocenters is critical for constraining magma transport pathways and assessing volcanic hazards in densely populated regions. The aim of this study is to refine the earthquake catalogue for Sinabung by relocating events with improved accuracy, thereby distinguishing shallow brittle-failure processes from deeper magmatic activity. We analyzed 61 volcanic earthquakes recorded between October 2023 and April 2024. Hypocenter relocation was performed using a Geiger least-squares algorithm with adaptive damping, designed to minimize instability in heterogeneous velocity structures. Methods. To evaluate robustness, we applied ±10 % P-wave velocity sensitivity tests and jackknife resampling of seismic stations. These procedures allowed us to identify well-constrained events and flag model-sensitive cases requiring cautious interpretation. The results reveal two distinct hypocenter populations. Shallow VTB events (0.3–2.0 km depth) occur as semi-continuous swarms beneath the summit and upper flanks, consistent with near-surface brittle failure or hydrothermal cracking. In contrast, deeper VTA events (2.5–14 km depth) form several aligned clusters rather than a single source, delineating vertically segmented pathways coherent with conduit structures or mid-crustal magma transport. Epicenters are concentrated within 0–5 km of the summit, highlighting a vertically continuous but segmented plumbing system. These findings provide new constraints on the geometry of magma pathways beneath Sinabung and contribute to improved models of volcanic hazard assessment in northern Sumatra.