Multi-Scale Analysis of Gutenberg–Richter b-Value Variability in a Complex Oblique Convergent System: The Indo-Burmese Arc Region

Abstract:

The Indo-Burmese Arc is a tectonically complex region formed by the oblique convergence of the Indian Plate with the overriding Burma microplate, within the broader influence of the Sunda Plate. This oblique convergence leads to a mix of subduction, strike–slip movement and crustal deformation, creating a varied stress pattern and complex seismic activity. This study explores how the Gutenberg–Richter b-value changes over time as an indicator of stress variation along the Indo-Burmese Arc. Earthquake catalogue data spanning 1900-2016 are analysed using multiple moving event windows (500, 200 and 100 events) to resolve both long-term trends and short-term fluctuations. To ensure methodological robustness, b-values are estimated using both maximum likelihood estimation (MLE) and b-positive approaches. The results reveal a long-term increase in b-values throughout much of the 20th century, followed by a systematic decline up to December 2015. Higher-resolution analyses capture pronounced short-term variability, with a consistent decrease in b-values preceding the 13th April 2016 Mw 6.9 Myanmar earthquake, indicating progressive stress accumulation. This behaviour is observed across different depth intervals (≤60 km and ≤200 km), suggesting coherent stress evolution within the lithosphere. The observed temporal patterns suggest alternating phases of stress release and subsequent accumulation, reflecting the dynamic and evolving behaviour of this obliquely convergent system. These results highlight the importance of combining various b-value estimation methods to better identify potential seismic precursors and deepen understanding of stress dynamics in complex plate boundary environments. This work marks an initial step towards incorporating additional seismotectonic and geodetic constraints, laying a foundation for future research. Future efforts will extend the analysis to recent seismicity, including the 28^th March 2025 Mw 7.7 Myanmar earthquake, and integrate GNSS-derived deformation to better constrain geodynamic processes and assess evolving seismic hazard across the Indo-Burmese Arc region.