Seismic Swarms Occurrence Rate and b-value Mapping at Taupo Volcanic Zone
DOI:
https://doi.org/10.26443/seismica.v5i1.1893Keywords:
ETAS model, b-value tomography, swarm-informed ETAS, Taupo Volcanic ZoneAbstract
We analyze the seismicity of the Taupō Volcanic Zone (TVZ) over a 17-year period (2007-2024) using a swarm-informed ETAS model and high-resolution b-value mapping. To better describe swarm dynamics, marked by rapid, clustered activity without a mainshock, we introduce a modified Epidemic Type Aftershock Sequence (ETAS) kernel with finite memory and exponential tapering, which explicitly accounts for the finite duration of seismic swarm activity. This new model outperforms the classical ETAS, capturing the full temporal evolution of swarm sequences. The inferred rate highlights recurrent swarm episodes and captures known unrest periods in the TVZ (e.g., the 2019 Taupō unrest), illustrating how the proposed kernel can represent multi-swarm, non-Omori temporal clustering. Moreover, using the unstruCtUred B mappIng Tool CUBIT algorithm and the b-more-positive estimator, we map spatial and temporal variations in the b-value. Higher b-values are observed in younger, hotter volcanic centers, while older systems show lower values. A subtle positive skewness in the b-value distribution is linked to local magnitude range effects, underscoring the interplay between catalog completeness and stress heterogeneity. Our results highlight the importance of combining physically informed models with robust statistical tools to understand and monitor volcanic swarm activity.
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