section_path: Tectonic setting
section_name: Tectonic setting
paragraph_text: Tectonic setting
  
  Myanmar is wedged between four tectonic plates (the Indian, Eurasian, Sunda, and Burma plates) that interact in active geological processes. Along the west coast of the Coco Islands, off the Rakhine coast, and into Bangladesh, is a highly oblique convergent boundary known as the Sunda megathrust. This large fault marks the boundary between the Indian and Burma plates. The megathrust emerges from the seafloor in Bangladesh, where it runs parallel and east of the Chin Hills. This boundary continues to the north of Myanmar where it ends at the eastern Himalayas.
  
  A 1,400-kilometre (870 mi) transform fault runs through Myanmar and connects the Andaman spreading center to a collision zone in the north. Called the Sagaing Fault, it is a boundary between the Burma and Sunda plates as they slide past each other at 18–49 mm (0.71–1.93 in) per year. It is Myanmar's largest and most active source of earthquakes, running through or close to major cities including Yangon, Naypyidaw, and Mandalay. Large and damaging earthquakes occurred along the fault in May and December 1930 (M 7.3 & 7.5), 1931 (M 7.5), 1946 (M 7.3 & 7.7), 1956 (M 7.1), 1991 (M 6.8) and 2012 (M 6.9). The magnitudes of earthquakes on the Sagaing Fault vary across the fault zone from M 7.0 to 8.0. The recurrence interval also varies depending on the location along the fault; its southern segments, which ruptured in 1930, have return periods of 100–150 years based on paleoseismological studies.
  
  Destructive earthquakes have affected the area for centuries, but academic research has been limited. Most earthquakes in Myanmar, including large surface rupturing events, are thus not well understood. A large M 8.5–8.8 earthquake in 1762 ruptured a section of the Sunda megathrust off the Rakhine coast. That earthquake may have been caused by the Indian plate subducting beneath the Burma plate along the megathrust. Remnants of the subducted Indian plate beneath central Myanmar also cause intraslab earthquakes; one example is the 1975 Bagan earthquake (M 7.0) which occurred at a depth of 120 km (75 mi).
  
  According to a study published in Journal of Geophysical Research: Solid Earth, the Sagaing Fault can be divided into two regions; the northern and southern sections. The Sagaing Fault between 16.5 and 23.5 degrees north latitude is defined as the southern section. It is further divided into five segments from south to north; the Bago, Pyu, Naypyidaw, Meiktila, and Sagaing segments. The Naypyidaw segment is characterised by two parallel faults running for 70 km (43 mi) with parts of them located beneath the capital city, Naypyidaw. The last recorded earthquake was in 1929 with a magnitude smaller than 7.0. The 220 km (140 mi) long Meiktila segment extends between Mandalay and Naypyidaw and is characterised as a linear feature. The nearly flat topography across this segment suggest the slip component is entirely horizontal. This segment has not experienced any major earthquakes, although it possibly ruptured during the 1839 Ava earthquake. The Sagaing segment is also another linear segment that runs parallel to the Irrawaddy River. The northern part of this segment ruptured during one of the mainshocks in the 1946 Sagaing earthquakes, while the 1956 Sagaing earthquake ruptured the southern strand.
  
  This earthquake also affected Thailand, with damage primarily concentrated in the Bangkok region, about 1,000 km (620 mi) away from the epicenter. Bangkok's geology, characterised by a top layer of soft marine clay, renders its emerging high-rises vulnerable to distant, powerful earthquakes, as the ubiquitous clay layer contributes to local site effects amplifying long-period ground motion which in turn can match the resonant frequency of tall buildings. Occupants in Bangkok have often felt effects from earthquakes centered many hundreds or even thousands of kilometres away. Research headed by Pennung Warnitchai of the Asian Institute of Technology had previously identified the Sagaing Fault as a potential risk, if a magnitude-8.0 earthquake were to occur in the Andaman Sea, 400 km (250 mi) from the city, resulting in future disaster. For preventing catastrophic effects in skyscrapers, elementary seismic considerations were only added to the building code in 2007, with older structures being particularly dangerous.