1930 Bago earthquake
The 1930 Bago earthquake (Burmese: ၁၉၃၀ ပဲခူးတိုင်းငလျင်), also known as the Swa earthquake and Pegu earthquake struck Burma on May 5 with a surface wave magnitude between 7.2 and 7.5 . This earthquake was one of the most destructive to hit the country, and one of many earthquakes to affect the country between 1929 and 1931. Extensive damage was reported in the southern part of the country. More than 550 people were reportedly killed, although the death toll may be as high as 5,000–7,000. A moderate tsunami was generated along the Burmese coast, causing minor damage. Earthquake. This  earthquake ruptured along the Bago segment of the Sagaing Fault for a length of , extending from the southern coast of Burma (Gulf of Martaban) to roughly north of the city of Bago. The entire Bago segment is approximately 170 km in length, hence this event was a partial rupture of the segment. Its epicenter is located north of Bago, near the Pegu range. The mainshock was followed-up with the 1930 Pyu earthquake seven months later. A maximum offset of was measured on the surface during a field survey of the rupture site in 2009. Earthquakes on the Sagaing Fault  have been very destructive in the past. The maximum magnitudes of these events vary across the 1,200-km-long fault zone, from 7.0–8.0. The recurrence interval of earthquakes on the fault also vary depending on which location on the fault. The southern segments which ruptured in 1930 have short periods of 100–150 years based on paleoseismology studies. Tectonic setting. Burma is wedged between four tectonic plates; the Indian, Eurasian, Sunda and Burma plates that interact due to 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 north of Burma where it ends at the eastern Himalayas. The Sagaing Fault is a mostly continental transform fault that runs through Burma and connects the Andaman spreading center to the collision zone in the north. It accommodates motion between the Burma and Sunda Plates as they slide past each other at a rate of 18 to 49 mm/yr . The fault runs the entire length of the country for over 1,200 km and continues its trace into the Andaman Sea. The Sagaing Fault is Burma's largest and most active source of seismic threat, running through or close to major cities like Yangon, Nay Pyi Daw and Mandalay. Several large and damaging earthquakes have occurred on this fault in historical times. Destructive earthquakes have rocked this area for centuries, but very little academic research has been invested to understand their seismological characteristics. Most earthquakes in Burma, including large, surface rupturing events are not well understood. A large 8.5–8.8 earthquake  in 1762 ruptured a section of the Sunda megathrust off the Rakhine coast. That earthquake is thought to be the result of the Indian Plate subducting beneath the Burma Plate along the megathrust. The subduction of the Indian Plate also causes intraslab earthquakes beneath Central Burma. The 1975 7.0 earthquake in Bagan was caused by reverse faulting at an intermediate depth of 120 km. Intensity. In the meizoseismal area, shaking intensity peaked at IX–X on the Rossi–Forel scale within a pear-shaped area of along the fault. Within this area, buildings were either partially or totally destroyed. Bago  was located at the northern end of this isoseismal area. Large fissures and thrusted alluvium was observed during surveys of the land. Intensity VIII covered the townships of Kyauktan, Thongwa, Kayan, and Kawa. Many houses suffered significant damage while a few collapsed partially. Many household items reportedly fell towards the north or south, and large almirahs in a hospital and police station were thrown to the floor. Massive cracks appeared in the ground and sections of land fell into a nearby river. The regions of Toungoo and Rangoon were within the intensity VII–VI zone. Poorly constructed buildings collapsed in  this area. Brick chimneys and walls were thrown down due to the force of the earthquake. A number of buildings were so badly compromised that they were not safe for anyone to enter. Impact. Shaking was violent enough to destroy much of Bago. An eyewitness observed surface waves propagating through a tennis court as the earthquake occurred. People on the ground were thrown upwards due to the rapid ground acceleration. Fires erupted, causing further destruction in the city. There were also reports of severe liquefaction taking place shortly after, in the form of fissures erupting sand and water. Loud rumbling  noises were heard by people in the city. The Shwemawdaw Pagoda, a religious monument in the city, was seriously weakened, and half of the structure collapsed, killing some at the base. The death toll is estimated at 500 in Pegu. Survivors described feeling two distinct jolts, separated by a short pause. The second shock was reportedly the most violent. The duration of the earthquake only lasted some 30 seconds. In Tawa, seven people were killed, two buildings totally collapsed, pagodas and roads destroyed and subsidence occurred. At Khayan, there was a partial collapse of a hospital, various buildings, and a  mosque. Fissures and vents spewed enough water and to bury parts of the town and cause floods. Between 12 and 16 deaths were from here. In Thongwa, which sits atop the Sagaing Fault, the town suffered major destruction during the quake. A railway station platform fissured, and abutments of the railway bridge sank and were shifted from their original positions. Like in many other affected other towns, most masonry buildings collapsed or were badly damaged. In Rangoon, the shock toppled the Shwedagon Pagoda, an important religious landmark in the city. Like Pegu, the earthquake threw people off the ground. More  than 50 buildings had to be replaced. The confirmed death toll was reported at 50 or 58, while press agencies reported 200. Another 204 were injured by collapsed masonry. The most severe damage was situated in the southern part of the city which sits on a river delta where alluvium is deposited by the Irrawaddy River. The British Geological Survey building along Dalhousie Road cracked in many areas. The interior of the building which housed a laboratory and museum was wrecked. Along China Street, pucca houses caved inwards and numerous buildings withstood shaking but were uninhabitable. The shock was powerful  enough to be felt in Shan state and the Kingdom of Siam. It was felt over an estimated area size greater than . Survivors of the earthquakes were interviewed in 2008, with many saying the ground fissured and erupted water. One surviving eyewitness said he saw a monastery shift laterally by a foot ot two. Several ground cracks were up to 10 meters long. There were reports that people could not stand due to the extreme ground motions. Surface waves were observed propagating through the ground. At a village in Thanatpin Township, its elevation was raised and construction was offset. Railroads  were shifted and some tilted, but there were not twisted. Tsunami. A local tsunami with a run-up height of was recorded along the coast. The tsunami travelled up the Sittaung River and flooded several villages along the way. Some ships docked at the Rangoon Harbour were uplifted up to 4 feet while others began to rock back and forth. The waves also caused ships to slam into the wharf resulting in damage to the port. Related events. The Bago earthquake was one of several destructive earthquakes to occur in Burma from 1929 to 1932. Aftershocks. Countless aftershocks were reported  months after the earthquake. An aftershock on September 16, at 5:30 pm, resulted in the cracking of a brick wall on a police station in Pado. December 4 earthquake. Seven months after the earthquake at Bago, another earthquake of magnitude 7.3 struck about 48.2 km north, along the Sagaing Fault killing a further 36 people. Slippage along the fault twisted a crossing railroad. Major damage in Pyu, similar to the severity of the May shock was seen. Future threat. Seismologists have identified a ~-long seismic gap on the Sagaing Fault which did not rupture in both the May and December  1930 earthquakes. This gap is located between the rupture zones of both events and is capable of producing an earthquake up to a magnitude of 7.0. North of the December 1930 rupture and Nay Pyi Daw, a ~260 km-long segment of the Sagaing Fault was also identified as a seismic gap capable of producing a magnitude 7.9 event. The last known earthquake in that area was the 1912 Maymyo earthquake with a magnitude of 7.7 to 7.9 however, that involved a rupture along the nearby Kyaukkyan Fault. It is believed that the segment last ruptured in the 1839 Ava  earthquake. To the south, the offshore segment with a length of 180 km has also never been involved in any major earthquake in recent historical records thus it is expected that a magnitude 7.7 quake could occur there.