Statistical Constraints of b-Value Based Forecasting in Indonesia

The predictive potential of the b-value from the Gutenberg-Richter law remains a key topic in seismology. In this study, we apply a probabilistic b-value estimation method to the BMKG catalog (2008–2024) for the Indonesian region, focusing on background and triggered events. Our findings reveal that the b-value for background and triggered events is statistically indistinguishable for magnitudes greater than the completeness magnitude (Mc = 4.7). While limited indications of differences are observed in small subsets of data, the high Mc prevents detailed analyses of lower magnitudes. This universality of b-values between background and triggered events suggests a shared underlying physical process. Leveraging this insight, we propose combining all events into a single dataset to enhance reliability and statistical power for forecasting.
However, attempts to perform blind forecasting analyses based on b-value variations before and after major (M > 7) earthquakes are hindered by the insufficient number of events in the time windows preceding large earthquakes, preventing an unbiased estimation of the b-value. Even by extending spatial and temporal windows to reasonable limits, the lack of data remains a critical limitation. This emphasizes the need for improved seismic catalog completeness to enable reliable forecasting based on the b-value. While the b-value holds potential as a universal metric for seismic hazard assessment, its use as a forecasting tool requires not only refined methodologies but also significantly enhanced data quality and coverage.

References

¹Godano, C., Petrillo, G., & Lippiello, E. (2024). Evaluating the incompleteness magnitude using an unbiased estimate of the b value. Geophysical Journal International, 236(2), 994-1001.

²Lippiello, E., & Petrillo, G. (2024). b‐more‐incomplete and b‐more‐positive: Insights on a robust estimator of magnitude distribution. Journal of Geophysical Research: Solid Earth, 129(2), e2023JB027849.