[O-12] 2025 Myanmar Earthquake and its disaster

[O12-02] The 2025 Myanmar earthquake considering the tectonic geomorphology and paleoseismology of the Sagaing fault

★Invited Papers

*Hiroyuki Tsutsumi¹ (1.Department of Environmental Systems Science, Faculty of Science and Engineering, Doshisha University)

Keywords:Sagaing fault, 2025 Myanmar earthquake, tectonic geomorphology, paleoseismology, recurrence intervals of earthquakes, fault geometry

The Sagaing fault is a ~1,500-km-long continental transform fault and is one of the longest and fastest-moving right-lateral strike-slip faults globally. It results from the oblique subduction and collision of the Indo-Australia plate with the Sunda plate. The fault is accompanied by well-defined tectonic geomorphic features and has produced several surface-rupturing earthquakes since the mid-19th century. In collaboration with geoscientists from the Myanmar Earthquake Committee, we have mapped the Sagaing fault in detail based on the interpretation of CORONA satellite images and 1:24,000-scale aerial photographs. We also conducted three trenching campaigns across the surface rupture of the December 1930 Ryu earthquake. The 2025 earthquake ruptured the Meiktila and Naypyidaw segments and part of the Sagaing segment, which appear to have last ruptured during the 1839 Ava earthquake. The surface rupture occurred almost exactly along the previously mapped fault trace, highlighting the importance of precise active fault maps for seismic hazard mitigation. The rupture may have initiated at an 800-m-wide releasing step west of Mandalay, one of the most pronounced geometric discontinuities of the Sagaing fault. The northern end of the rupture coincides with the area where volcanic rocks are exposed at the surface, while the southern end roughly aligns with the northern tip of the December 1930 Pyu earthquake rupture. Paleoseismic trenching across the December 1930 rupture suggests a recurrence interval of surface-rupturing earthquakes of ~100 years. The average slip of the 2025 earthquake and geodetic slip rates suggest a recurrence interval of 100-200 years for earthquakes similar to that of 2025. Detailed mapping of the surface ruptures and paleoseismic trenching across the neighboring segments is essential to mitigate seismic hazards from future earthquakes on the Sagaing fault.