Seismicity-rate estimation based on geodetic strain rates from continuous GNSS observations in Kalimantan, Indonesia

Abstract This study presents a geodetically derived seismicity-rate model for Kalimantan, Indonesia—a tectonically stable yet geologically diverse region with limited earthquake and fault data. Horizontal GNSS (Global Navigation Satellite System) velocity fields from 25 continuously operating stations were interpolated into strain-rate tensors, which were then converted to geodetic moment rates and seismicity rates using a truncated Gutenberg–Richter formulation. Sensitivity testing reveals that seismogenic thickness and seismic coupling are the primary controls on seismicity rates, increasing modeled rates from approximately 2 to 33 earthquakes per year across tested parameter ranges. Poisson’s ratio, in contrast, had a negligible impact (< 1% variation in total moment rate). Seven candidate models were retrospectively evaluated using the Collaboratory for the Study of Earthquake Predictability (CSEP) framework. A configuration characterized by shallow seismogenic thickness (5 km) and a seismic coupling factor of 0.1 exhibited the most stable long-term behavior, yielding a median estimated rate of about 2 earthquakes per year (range: 1–3) for the M w 4.5–6.5 range. A complementary 46-station configuration enhanced spatial resolution and reduced relative uncertainty, albeit with increased residual velocities, underscoring the trade-off between improved coverage and signal complexity. These results demonstrate that geodetic strain provides a physically grounded basis for estimating seismicity rates in low-seismicity regions. The derived model can complement catalog- and fault-based approaches, supporting future probabilistic seismic hazard assessments in Kalimantan. Graphical Abstract