4:00 PM - 4:15 PM
[SCG69-03] Inter-seismic behavior and Indian Ocean Dipole records along the western Myanmar subduction zone recorded by coral microatolls
Keywords:Myanmar, inter-seismic deformation, coral microatolls, seismic hazard
For some coral genus such as Porites, the highest level of survival (HLS) is constrained within a few centimeters of the lowest tide level. Therefore, once the relationship between HLS and the sea level is established, the morphology of the microatolls can provide us the relative sea-level history based on the patterns of their annual growth bands under x-radiographs. U-Th dating technique can constrain the age of the coral, and we can also identify sea level anomalies caused by climatic events through oxygen isotope analysis.
We collected several slabs of coral microatolls from the intertidal zone near Leik-Ka-Maw, a small village in northwestern Ramree Island, approximately 80 km away from the trench. The microatolls were uplifted and killed during a local earthquake event in 1848, and preserved HLS records of about 80 years between the 1762 Arakan earthquake and the 1848 event. Our results show that the coral recorded a HLS rise at a rate about 6 mm/yr, which represents land-level subsidence during the inter-seismic period. Several temporary HLS die-down events are also present, likely produced by Indian Ocean Dipole (IOD) events based on the microatoll morphology and results of oxygen isotope analysis. We hope our results would provide additional constraints for improving the earthquake recurrence interval calculations for hazard assessments in this populous area.