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 moment magnitude of 7.4 Mw . 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.[3] A moderate tsunami was generated along the Burmese coast, causing minor damage.

1930 Bago earthquake
epicenter.
epicenter.
1930 Bago earthquake (Myanmar)
UTC time1930-05-05 13:46:01
ISC event907352
USGS-ANSSComCat
Local dateMay 5, 1930
Local time20:18:01 MST
Magnitude7.4 Mw[1]
Depth35 km (22 mi)[1]
Epicenter17°51′36″N 96°25′48″E / 17.860°N 96.430°E / 17.860; 96.430Coordinates: 17°51′36″N 96°25′48″E / 17.860°N 96.430°E / 17.860; 96.430
FaultSagaing Fault
TypeStrike-slip
Areas affectedBurma
Max. intensityIX (Devastating tremor)[2]
Tsunami1.06 m (Local)
Casualties550–7,000 fatalities,[3] 58 fatalities confirmed in Yangon

EarthquakeEdit

This earthquake ruptured along the Bago segment of the Sagaing Fault for a length of 131 kilometres (81 mi),[2] extending from the southern coast of Burma (Gulf of Martaban) to roughly 20 kilometres (12 mi) north of the city of Bago.[4] The entire Bago segment is approximately 170 kilometres (110 mi) in length, hence this event was a partial rupture of the segment.[5]

Buildings and pagodas near the fault collapsed in a southeast (in Bago), east and east-southeast (Tawa), and west-northwest (Tongyi) direction. These collapse patterns indicate shaking occurred in an east–west to northwest–southeast direction. At locations far from the fault (Insein, Yangon, Syriam, and Kyauktan), shaking was in a north–south direction. These shaking reports supported a right-lateral rupture.[6]

Widespread ground deformation was reported. Surface ruptures, fault scarps and fissures appeared. A 2009 field study of the Sagaing Fault found vertical displacements up to 20 cm (7.9 in) high which were the product of surface ruptures. Along traces of the Sagaing Fault, right-lateral offsets up to 15 m (49 ft) were measured, caused by the accumulation of displacements during previous earthquakes.[6] The 1930 Bago earthquake likely produced at least 3 m (9.8 ft) of right-lateral offset.[7] By estimating the rupture length and width to be 120 km (75 mi) and 15 km (9.3 mi), respectively, and averaging the slip to 3 m (9.8 ft), a magnitude of 7.4 Mw  was computed.[6]

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 Mw  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.[5] The mainshock was followed-up by the 1930 Pyu earthquake seven months later. The Pyu earthquake ruptured north of the May event. The May earthquake likely triggered this event due to coulomb stress transfer, increasing strain on the Sagaing Fault.[6]

Tectonic settingEdit

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.[5]

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.[5]

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 Mw  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 Mw7.0 earthquake in Bagan was caused by reverse faulting at an intermediate depth of 120 km.[5]

IntensityEdit

In the meizoseismal area, shaking intensity peaked at IX–X on the Rossi–Forel scale within a pear-shaped area of 375 square miles (970 km2) along the fault.[8][2] 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.[8]

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.[8]

ImpactEdit

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.[9] 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.[8]

In Rangoon, the shock toppled the Shwedagon Pagoda, an important religious landmark in the city.[10] 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.[11] 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.[12] 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.[8]

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 220,000 square miles (570,000 km2).[11]

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 or 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.[5]

TsunamiEdit

A local tsunami with a run-up height of 1.06 metres (3 ft 6 in) was recorded along the coast.[13] 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.[8]

Related eventsEdit

The Bago earthquake was one of several destructive earthquakes to occur in Burma from 1929 to 1932.

AftershocksEdit

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.[8]

December 4 earthquakeEdit

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 threatEdit

Seismologists have identified a ~50 kilometres (31 mi)-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.[2]

GalleryEdit

See alsoEdit

ReferencesEdit

  1. ^ a b ISC (2022), ISC-GEM Global Instrumental Earthquake Catalogue (1904–2018), Version 9.1, International Seismological Centre
  2. ^ a b c d Nobuo Hurukawa; Phyo Maung Maung (2011). "Two seismic gaps on the Sagaing Fault, Myanmar, derived from relocation of historical earthquakes since 1918". Geophysical Research Letters. 38 (1): n/a. Bibcode:2011GeoRL..38.1310H. doi:10.1029/2010GL046099. S2CID 129866068.
  3. ^ a b "5,000 to 7,000 Killed in Burmese Quake; Tidal Wave Wrecks Port; Rangoon Hard Hit". New York Times. 7 May 1930. p. 1.
  4. ^ Yu, Wang (2014). "Active tectonics and earthquake potential of the Myanmar region". Journal of Geophysical Research: Solid Earth. 119 (4): 3767. Bibcode:2014JGRB..119.3767W. doi:10.1002/2013JB010762.
  5. ^ a b c d e f Wang, Yu (2013). Earthquake Geology of Myanmar (Ph.D.). California Institute of Technology. doi:10.7907/XWW2-9P26.
  6. ^ a b c d Tsutsumi, Hiroyuki; Sato, Tsutsumi (2009). "Tectonic Geomorphology of the Southernmost Sagaing Fault and Surface Rupture Associated with the May 1930 Pegu (Bago) Earthquake, Myanmar". Bulletin of the Seismological Society of America. 99 (4): 2155–2168. doi:10.1785/0120080113.
  7. ^ Yu, Wang (2011). "Earthquakes and slip rate of the southern Sagaing fault: insights from an offset ancient fort wall, lower Burma (Myanmar)" (PDF). Geophysical Journal International. 185 (1): 49–64. Bibcode:2011GeoJI.185...49W. doi:10.1111/j.1365-246X.2010.04918.x.
  8. ^ a b c d e f g Brown, Coggin. "A preliminary note on the Pegu earthquake of May 5th 1930". Geological Survey of India. LXV.
  9. ^ "On This Day The 1930 Earthquake Which Flattened Bago". The Irrawaddy. 2019-05-05. Retrieved 2020-10-14.
  10. ^ "May 5, 1930 – the last time Yangon rocked". The Myanmar Times. 2016-12-09. Retrieved 2020-10-14.
  11. ^ a b National Geophysical Data Center / World Data Service (NGDC/WDS) (1972), Significant Earthquake Database (Data Set), National Geophysical Data Center, NOAA, doi:10.7289/V5TD9V7K
  12. ^ Aung, Hla Hla (2012). "Reinterpretation of historical earthquakes during 1929 to 1931, Myanmar". Solid Earth Science. 31: 43. Bibcode:2012aogs...31...43A. doi:10.1142/9789814405775_0005. ISBN 978-981-4405-76-8.
  13. ^ National Geophysical Data Center / World Data Service (NGDC/WDS) (1972), Global Historical Tsunami Database (Data Set), National Geophysical Data Center, NOAA, doi:10.7289/V5PN93H7