1946 Sagaing earthquakes

The 1946 Sagaing earthquakes (also known as the Wuntho earthquakes) struck central Burma at 15:17 local time on 12 September.[3] The first earthquake measured a magnitude of 7.3 Mw  and was followed by a 7.7 Mw  earthquake. Both events remain some of the largest in the country since the 1762 Arakan earthquake.[3][4]

1946 Sagaing earthquakes
1946 M8.0 epicenter.
1946 M8.0 epicenter.
1946 Sagaing earthquakes (Asia)
UTC time1946-09-12 15:17:23
 1946-09-12 15:20:28
ISC event898579
 898580
USGS-ANSSComCat
 ComCat
Local dateSeptember 12, 1946
Magnitude7.3 Mw, 7.9 Ms[1]
 7.7 Mw ,[1] 7.8 Ms [2]
Depth15.0 km
Epicenter22.35°N 96.24°E / 22.35; 96.24
FaultSagaing Fault
TypeStrike-slip

Tectonic setting

Both the mainshock and aftershock occurred along the Sagaing Fault; a continental transform fault boundary that links the Andaman Spreading Center to the south and the Main Himalayan Thrust to the north.[5] It defines the boundary between the Burma Plate and Sunda Plate. The Sagaing Fault is the most active geological structure in the country and poses significant risks to major cities such as Yangon, Mandalay, and Naypyidaw. Another major tectonic feature in Myanmar is the Sunda Megathrust that runs off the coast of Western Myanmar and the Kabaw Fault that traces the foothills of the Arakan Mountains and Indo-Burman Range.

Earthquakes
A pressure ridge along the Sagaing Fault, obstructed by vegetation, outside Mandalay. This section of the fault likely ruptured in the 1956 event.

The Mw  7.3 earthquake ruptured along the Sagaing Fault. It had a rupture length of approximately 80 kilometres (50 mi), and possibly as long as 155 kilometres (96 mi) along the Indaw segment.[6] A second shock of magnitude Mw  7.7 came three minutes later and ruptured south of the first event for a length of 185 kilometres (115 mi).[1] The latter earthquake ruptured along the Sagaing segment, through the villages of Tagaung and Thabeikkyin.[6]

From observing the historical records of earthquakes, the years 1906 and 1908 saw two major events in the northernmost end of the Sagaing Fault.[7] The 1906 Putao earthquake on August 31 had an estimated moment magnitude Mw  of 7.0, and the 1908 earthquake measured Mw  7.5.[8][9] Coulomb stress transfer to the south from the 1906 quake triggered rupture of the fault in the stressed area in 1908.

The 1908 earthquake resulted in the accumulation of stress towards the south, where the future 1931 Ms  7.7 earthquake would take place. Similarly, the 1946 earthquake rupture segments were directly south of the 1931 rupture. The first mainshock in the 1946 doublet sequence then triggered the second mainshock due to the sudden increase in stress levels on the fault.[7]

Ten years later, an Mw  7.1 earthquake near Mandalay killed at least 40 people. That earthquake broke a 60-kilometre (37 mi) segment south of the 1946 rupture. In 1991, a seismic gap between the two 1946 ruptures generated an Mw  7.0 earthquake, partially re-rupturing a 49-kilometre (30 mi) section of the 1946 ruptures. Another Mw  6.8 earthquake in 2012 partially ruptured the Sagaing segment.[6]

See also

References
  1. ISC (2016), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2012), Version 3.0, International Seismological Centre
  2. "Event Index 1904 to 1959". International Seismological Centre. Retrieved 15 February 2022.
  3. United States Geological Survey. "M8.0 - Myanmar". United States Geological Survey. Archived from the original on 2021-07-11. Retrieved August 30, 2020.
  4. ISC: On-Line Bulletin. "Event 898580 Myanmar". International Seismological Centre. Archived from the original on 2020-10-17. Retrieved 31 August 2020.
  5. Aung, Hla Hla (August 2017). "Sagaing Fault" (PDF). Myanmar Earthquake History: 14 – via University of Yangon.
  6. Tun, Soe Thura; Watkinson, Ian M. (2017). "Myanmar: Geology, Resources and Tectonics". Geological Society, London, Memoirs. 48: 413–441. doi:10.1144/M48.19. S2CID 134291037.
  7. Xiong, X.; Shan, B.; Zhou, Y. M.; Wei, S. J.; Li, Y. D.; Wang, R. J.; Zheng, Y. (2017). "Coulomb stress transfer and accumulation on the Sagaing Fault, Myanmar, over the past 110 years and its implications for seismic hazard". Geophysical Research Letters. 44 (10): 4781–4789. doi:10.1002/2017GL072770. hdl:10220/46403. S2CID 55509712.
  8. "Event 914281 Myanmar-India border region". ISC: On-Line Bulletin. International Seismological Center. Retrieved 3 March 2021.
  9. "Event 16958007 Myanmar". ISC: On-Line Bulletin. International Seismological Centre. Retrieved 3 March 2021.
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