The 1946 Sagaing earthquakes (also known as the Wuntho earthquakes) struck central

Burma Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...

at 15:17 local time on 12 September. The first earthquake measured a magnitude of 7.3 and was followed by a 7.7 earthquake. Both events remain some of the largest in the country since the

1762 Arakan earthquake The 1762 Arakan earthquake occurred at about 17:00 local time on 2 April, with an epicentre somewhere on the coast from Chittagong (modern Bangladesh) to Arakan in modern Burma. It had an estimated magnitude of as high as 8.8 on the moment magnitu ...

Tectonic setting

Both the mainshock and aftershock occurred along the

Sagaing Fault The Sagaing Fault is a major fault in Burma, a mainly continental right-lateral transform fault between the Indian Plate and Sunda Plate. It links the divergent boundary in the Andaman Sea with the zone of active continental collision along the ...

; a continental

transform Transform may refer to: Arts and entertainment * Transform (scratch), a type of scratch used by turntablists * ''Transform'' (Alva Noto album), 2001 * ''Transform'' (Howard Jones album) or the title song, 2019 * ''Transform'' (Powerman 5000 album ...

fault boundary that links the

Andaman Andaman may refer to: * Andaman Islands * Andaman Sea * ''Andaman'' (1998 film), a Kannada-language film * ''Andaman'' (2016 film), a Tamil-language film * ''Andaman'' (2021 film), a Hindi-language film See also * Andaman and Nicobar Islands ...

Spreading Center A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...

to the south and the

Main Himalayan Thrust The Main Himalayan Thrust (MHT) is a décollement under the Himalaya Range. This thrust fault follows a NW-SE strike, reminiscent of an arc, and gently dip towards the north, beneath the region. It is the largest active continental megathrust f ...

to the north. It defines the boundary between the

Burma Plate The Burma Plate is a minor tectonic plate or microplate located in Southeast Asia, sometimes considered a part of the larger Eurasian Plate. The Andaman Islands, Nicobar Islands, and northwestern Sumatra are located on the plate. This island arc ...

and

Sunda Plate The Sunda Plate is a minor tectonic plate straddling the Equator in the Eastern Hemisphere on which the majority of Southeast Asia is located. The Sunda Plate was formerly considered a part of the Eurasian Plate, but the GPS measurements have ...

. The Sagaing Fault is the most active geological structure in the country and poses significant risks to major cities such as

Yangon Yangon ( my, ရန်ကုန်; ; ), formerly spelled as Rangoon, is the capital of the Yangon Region and the largest city of Myanmar (also known as Burma). Yangon served as the capital of Myanmar until 2006, when the military government ...

Mandalay Mandalay ( or ; ) is the second-largest city in Myanmar, after Yangon. Located on the east bank of the Irrawaddy River, 631km (392 miles) (Road Distance) north of Yangon, the city has a population of 1,225,553 (2014 census). Mandalay was fo ...

, and

Naypyidaw Naypyidaw, officially spelled Nay Pyi Taw (; ), is the capital and third-largest city of Myanmar. The city is located at the centre of the Naypyidaw Union Territory. It is unusual among Myanmar's cities, as it is an entirely planned city outs ...

. Another major tectonic feature in Myanmar is the

Sunda Megathrust The Sunda megathrust is a fault (geology), fault that extends approximately 5,500 km (3300 mi) from Burma, Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating ne ...

that runs off the coast of Western Myanmar and the

Kabaw Fault Kabaw Fault is a fault in Myanmar. It was among those that ruptured during the 1762 Arakan earthquake. Location Kabaw Fault lies roughly parallel with the Indo-Burmese border near Mizoram Mizoram () is a state in Northeast India, with Aiza ...

that traces the foothills of the

Arakan Mountains The Arakan Mountains ( my, ရခိုင်ရိုးမ), also known as the Rakhine Yoma, are a mountain range in western Myanmar, between the coast of Rakhine State and the Central Myanmar Basin, in which flows the Irrawaddy River. It is th ...

and Indo-Burman Range.

Earthquakes

The 7.3 earthquake ruptured along the

. It had a rupture length of approximately , and possibly as long as along the Indaw segment. A second shock of magnitude 7.7 came three minutes later and ruptured south of the first event for a length of . The latter earthquake ruptured along the Sagaing segment, through the villages of Tagaung and Thabeikkyin. From observing the historical records of earthquakes, the years 1906 and 1908 saw two major events in the northernmost end of the

. The 1906 Putao earthquake on August 31 had an estimated moment magnitude of 7.0, and the 1908 earthquake measured 7.5.

Coulomb stress transfer Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events. Using mapped displacements of the Earth's surface during earthquakes, the computed Coulomb stress ...

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 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. Ten years later, an 7.1 earthquake near Mandalay killed at least 40 people. That earthquake broke a segment south of the 1946 rupture. In 1991, a

seismic gap A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long ...

between the two 1946 ruptures generated an 7.0 earthquake, partially re-rupturing a section of the 1946 ruptures. Another 6.8 earthquake in 2012 partially ruptured the Sagaing segment.

References

{{Earthquakes in Myanmar, state=expanded Earthquakes in Myanmar 1946 earthquakes Doublet earthquakes Strike-slip earthquakes 1946 in Burma