Temporal evolution of local seismicity along the Sagaing fault with reference to the March 2025 M7.7 Myanmar earthquake sequence

Shankho Niyogi, & Abhijit Ghosh

Submitted September 7, 2025, SCEC Contribution #14956, 2025 SCEC Annual Meeting Poster #TBD

We analyze continuous waveforms from the sparse set of permanent stations in Myanmar spanning 2016-2025 to investigate temporal changes in local event rates with reference to the 2025 March Mw 7.7 mainshock on the Sagaing Fault. We detected local earthquakes with an EQTransformer model trained on local waveforms , producing probabilistic P and S picks on continuous data from 2016–2025. We filtered high confidence events from the detections and then by small SP travel-time differences (≤ 10 s). Since determining hypocenters of the small earthquakes is challenging, given the sparsity of the seismic stations, the counts of these local events form our basis for understanding local seismic activity around each station. We determine and analyze such seismic activities before and after the M7.7 event starting a few years before the mainshock to 2 months in the aftershock activities. Daily detection curves show a clear increase of activity around the station nearest to the Sagaing fault weeks before the mainshock, followed by heightened activity through the M7.7 aftershock sequence and a gradual decay that remains above background for weeks.

We also attempt to discover and investigate repeating earthquakes by cross correlating the filtered local events. Events with consistently high correlation across components are clustered into repeating sets. We observe that multiple pairs of repeating earthquakes. The recurrence interval of different repeating earthquakes varies with several pairs exhibiting intervals of weeks to months preceding the mainshock. Many pairs are present in the aftershock period with high waveform similarity, consistent with re-rupture of the same patches. Together, these observations point to the Sagaing and nearby faults being characterized with patches of locked asperities embedded within zones of aseismic slip where stressing and slip evolve unevenly over time.

Our results highlight the challenges of working with a sparse network as station spacing limits locations and completeness estimates. Nevertheless, these results are consistent with patterns exhibiting an earlier onset of foreshocks and possibly an elevated stressing rate on the Sagaing and nearby faults. Our observations can also guide future geodetic investigations and provide a basis for deploying denser seismic deployments to better understand the Sagaing Fault system.

Key Words
Sagaing fault, Myanmar earthquake, foreshock activity, repeating earthquakes

Citation
Niyogi, S., & Ghosh, A. (2025, 09). Temporal evolution of local seismicity along the Sagaing fault with reference to the March 2025 M7.7 Myanmar earthquake sequence. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology