A partial visualization of an active fault trace that aligns with the present-day Sagaing Fault trace was recorded by Fritz Noetling, a geologist, in the book The Miocene of Burma published in 1900. In 1913, Thomas Henry Digges La Touche of the Geological Survey of India[3] acknowledged the existence of a plate boundary feature along the Shan Plateau's western margin in Mandalay, including the one dividing metamorphic stratas of the Sagaing Hills from the Central Tertiary Basin. While analysing historical earthquakes in Myanmar, Harbans Lal Chhibber (1934) discovered a linear trace when joining their epicenters which he inferred to be along the same fault.[4] In 1970, Aung Khin and others confirmed the fault's existence using geophysical techniques and a Bouguer gravity investigation from Taungoo to Thabeikkyin. That same year, Win Swe nomenclated it the "Sagaing Fault". He also made the first description of the fault in Rift features at the Sagaing Tagaung Ridge at the Fifth Burma Research Congress. He determined the fault running nearly the entire length of Myanmar from south to north had a strike-slip mechanism, and linked it to historical earthquakes. A 1991 study of the fault determined a total displacement of 203km (126mi) and slip rate of 22mm (0.87in) per year by analyzing two metamorphic units and assuming the fault's origins in the end Oligocene or early Miocene.[5]
Geology
Sagaing Fault represents a boundary of the Burma Microplate (bottom)
The Sagaing Fault begins offshore in the Andaman Sea at a divergent boundary before passing through the central Myanmar basin. The fault has a relatively low topographical relief for most of its length compared to the Shan Scarp Fault to the west.[6] Its total length from the Eastern Himalayan Syntaxis to the Andaman Sea is 1,400km (870mi).[7] While the fault runs uninterrupted by large stepovers for most of its length, the northern 400km (250mi) branches outwards in a "horsetail" fashion into individual segments 100km (62mi) in width.
The total slip rate across the Indian–Sunda plate boundary is about 35mm/yr, of which 18mm/yr is accommodated by the Sagaing Fault, according to GPS data.[8] The measured maximum displacement along the fault is about 100km, although several authors have proposed between 360km to 400km.[9][10]
Southern section
A simplified version of the regional geological features in Myanmar
The southern section comprises, from south to north, the Bago, Pyu, Naypyidaw, Meiktila and Sagaing segments. The 170km (110mi) Bago segment runs from Myanmar's coast, southeast of Yangon, to 18°N, where the fault experiences a sharp bend. The southern termination and offshore section remains uncertain, however, several tens of kilometers offshore, it connects to normal faults striking east–west. Approximately 100km (62mi) of the Bago segment ruptured during a Mw7.4 earthquake in May 1930 with offsets of at least 3m (9.8ft).[9]
The Pyu segment begins where the Bago segment terminated and continues 130km (81mi) to 19.1°N. It runs along the base of the Bago-Yoma range. There lies a terrace along the central part of the segment east of the fault trace which represents the hanging wall of a reverse fault expressed on the feature's eastern side. This feature is due to a small transpressional component where the segment experiences crustal compression. A majority of the segment ruptured during a Mw7.3 earthquake in December 1930 which originated at its southern limit.[9]
The Naypyidaw segment consists of two parallel strands that branches out at 19.1°N for its entire 70km (43mi). Both strands cut through channels and alluvial fans. The western strand runs east of Naypyidaw. A damaging but moderate earthquake in close proximity to the segment in August 1929 damaged railroads and bridges 40km (25mi) south of Naypyidaw.[9] The International Seismological Centre assigned the earthquake Mw 6.5.[11]
The Meiktila segment runs 220km (140mi) through a wide valley from Naypyidaw to Mandalay. This segment does not produce any dip-slip movement, evident from the absence of elevation differences across the fault. At 20°N, the fault offsets a stream by 2.4km (1.5mi); the largest observable offset along the segment. Although no major historical earthquake has been clearly associated with the segment, a possible contender is the 1839 Ava earthquake which destroyed the city of Inwa and caused severe damage to areas east and south of the Irrawaddy River.[9]
The geomorphologic features of the Sagaing segment led to its discovery in 1970. This segment runs relatively linear; it runs west of the Irrawaddy River from 21.9°N to 22.6°N, where it offsets alluvial fans of the post-Pliocene. It cuts through the Singu Plateau and splits into two segments running east and west of the river. Its western strand to the north is the Tawma segment. In 1946, a Mw7.7 earthquake was likely associated with the segment's northern two-thirds. This segment also ruptured during a smaller Mw6.8 earthquake in 2012. The remaining portion to the south likely ruptured during the destructive Mw7.1 earthquake in 1956.[9]
Northern section
The Sagaing Fault begins to fan outwards in a "horsetail" fashion into four separate fault zones from 23.5°N. The Tawma segment runs along an east-facing scarp and streams display dextral offsets. The western strand of the Sagaing segment extends north and is represented by the Tawma segment. The trace is no longer visible at 24°N where a left stepover leads to the Ban Mauk segment 10km (6.2mi) west. Between the stepover is a series of northeast–southwest striking faults that cuts through a transpressional ridge. Many are shorter than 20km (12mi) long and some show normal-component in their slip; however their weak expression suggest small slip rates compared to the Sagaing Fault's main branches.[9]
The Ban Mauk segment runs from 23.8°N and continues for 150km (93mi). Due to the rarity of clear geomorphic offsets associated with this segment, its slip rate is inferred to be low. The segment marks the boundary between the Neogene volcanics of the west and Miocene sedimentary strata of the east. At 25°N, the fault trace disappears, buried by clastic deposits of the Taungthonton Volcano to the east. At 23.7°N, the in Daw segment branches away from the Tawma segment at the Irrawaddy River's northern bank; continuing its north–northeasternly trace. A 3km (1.9mi) wide pull-apart basin at 24.25°N separates it from the Mawlu segment where it continues north–northwest for 90km (56mi). The combined length of both segments is estimated at 170km (110mi). Geodetic analysis of these segments revealed an annual strain accumulation of about 2cm (0.79in). A Mw 7.3 foreshock occurred along the in Daw segment three minutes before the Mw 7.7 earthquake in 1946.[9]
The fault branches into three segments where the Mawlu segment terminates: the Shaduzup, Kamaing, and Mogang segments. The Shaduzup segment, the westernmost of the three, is not believe to exceed 120km (75mi). The lack of clear geomorphic features suggest less activity occurs on this segment. The Kamaing segment continues further north into the Naga Hills, beyond 26.7°N. Right-lateral displacements are also well-expressed in drainage channels on the eastern flank of the Naga Hills at its northern termination. The fault continues north and joins a thrust fault system associated with the Assam Valley. the Mogang segment, the most active of the three, though less seismically active than the Kamaing segment, runs in a broad arc from 24.8°N. It ends at 26.8°N where it transforms into a northwest–southeast striking thrust fault. One of these segments produced a Mw7.6 earthquake in January 1931, though due to the lack of seismic data and isoseismal map its origin segment remains tentative. However, shaking was more intense along the Kamaing segment.[9]
Damaging earthquakes have been associated with the fault for centuries. The great 1839 Ava earthquake killed hundreds and damaged many cities, including the then imperial capital Inwa.[12] That earthquake is thought to have a moment magnitude of 8.0 or greater. The large magnitude would imply a rupture length of at least 300km along the fault.
In the early 20th century, from 1929 to 1931, more than half the length of the Sagaing Fault was involved in significant earthquakes. The first earthquake—which was followed-up by subsequent larger events—struck southwest of Nay Pyi Daw, and east of Thayetmyo in the Pegu Range in August 1929.[13] There are insufficient reports of damage caused by this earthquake, although it was said that buildings were swaying and objects were displaced at Yamethin, roughly 133.6km north of the quake epicenter.[14] The magnitude of this earthquake was no greater than 7.0.
On the night of May 5, a large shock registering Mw 7.5 struck north of the city of Pegu resulting in widespread deaths and destruction.[15] There were no foreshocks that preceded. The earthquake had a maximum intensity of IX to X on the Rossi–Forel scale.[9] The city of Pegu, Rangoon and several other towns were destroyed. In Pegu, fires erupted, and severe liquefaction caused further damage. Approximately 500 people died in Pegu while 58 were killed in Rangoon. More deaths were recorded in other villages.[14] It triggered a small tsunami which inundated villages along the coast.[12] This is the deadliest earthquake in the 1929–1931 sequence.
Two moderate foreshocks occurred on the night of December 3. The first lasted 5 seconds, generated some panic, and it was felt in Pyinmana and Rangoon. The other foreshock was described as being stronger than the first, but was not felt as widespread as the first.[16][17][18]
Violent shaking from an Mw7.3 earthquakedisrupted the early morning of December 4 in Pyu, Taungoo District.[19] The December 4 event occurred further north of the epicenter of the May earthquake, about 6.4 to 9.7km west southwest of Pyu. Damage was severe, with a railroad being shifted off and twisted, while many buildings in the city collapsed. About 30 people were killed. The maximum intensity was assigned X on the Rossi–Forel scale.[16] This event is not an aftershock of the May quake because it ruptured a different segment of the Sagaing Fault.[9]
Although the May and December 1930 earthquakes occurred during this active period, they were separate events, unrelated to the activity in the northern part. The December 1930 earthquake, however, was triggered due to stress transfer from the previous event in May.[20]
A lesser-known earthquake on July 18, 1930, in the Ayeyarwady Region killed about 50 people.[21] According to the National Centers for Environmental Information database, there is no magnitude assigned to this event.[12] The book Southeast Asia Association of Seismology is the only published work mentioning this event.[22]
Another violent earthquake of unknown magnitude occurred 146.5km north of Pyu. It was felt in Mandalay and Thanatpin.[14] Six brick buildings sustained damage. On August 19, another tremor caused cracks to appear in buildings in Mandalay and lightly affected Kalaw.[16] The city was rocked another time, resulting in the collapse of the Shwe Sandaw Pagoda in Taungoo.[14]
Two powerful earthquakes north of Mandalay measuring Mw 7.3 and 7.7 occurred on September 12, 1946.[11] The doublet earthquake sequence would remain as one of the largest in the country. Not much about this event is known due to sparse records.
Looking back at the historical records of earthquakes, the years 1906 and 1908 saw two major events in the northernmost end of the Sagaing Fault.[20] The 1906 Putao earthquake on August 31 had an estimated moment magnitude of 7.0, and the 1908 earthquake measured Mw 7.5.[24][25]
The 1908 earthquake resulted in the accumulation of stress towards the south, where the future 1931 quake 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 Mw7.1 earthquake near Mandalay killed at least 40 people.[12] That earthquake broke a segment south of the 1946 rupture. In 1991, a small seismic gap between the two 1946 ruptures generated an Mw 7.0 earthquake, partially re-rupturing a small section of the 1946 quakes, killing two.[26]
The 2012 Shwebo earthquake was the most recent major event on the Sagaing Fault. It had a moment magnitude of 6.8 and ruptured the fault north of Mandalay. A detailed and thorough evaluation of the event suggested the rupture was estimated at 45-km-long. The centroid moment tensor solution suggested the earthquake ruptured a north–south trending and sub-vertical fault that steeply dipped to the east.[6]
Hazard
The Sagaing Fault was dubbed an "earthquake fault superhighway" for to its potential to promote supershear earthquakes. Such events occur when an earthquake's rupture velocity exceeds its S wave velocity and potentially reaching that of the P wave. Fast-propagating ruptures can inflict trememdous damage. The Sagaing Fault's relatively straight geometry, the longest continuous observed worldwide, could sustain supershear ruptures. Due to the fault's proximity to populated areas, supershear earthquakes can have devastating effects.[27]
The length of fault running 260km (160mi) from 19.2°N to 21.5°N, on the Meiktila segment, is designated a seismic gap due to the absence of major earthquake ruptures since at least 1897. At least 2m (6ft 7in) of slip has accumulated along the fault corresponding to a magnitude 7.9 earthquake. Another seismic gap running 180km (110mi) lies in the Andaman Sea south of Yangon, potentially generating a magnitude 7.7 earthquake.[28]
The Queen Charlotte Fault is an active transform fault that marks the boundary of the North American plate and the Pacific plate. It is Canada's right-lateral strike-slip equivalent to the San Andreas Fault to the south in California. The Queen Charlotte Fault forms a triple junction south with the Cascadia subduction zone and the Explorer Ridge. The Queen Charlotte Fault (QCF) forms a transpressional plate boundary, and is as active as other major transform fault systems in terms of slip rates and seismogenic potential. It sustains the highest known deformation rates among continental or continent-ocean transform systems globally, accommodating greater than 50mm/yr dextral offset. The entire approximately 900 km offshore length has ruptured in seven greater than magnitude 7 events during the last century, making the cumulative historical seismic moment release higher than any other modern transform plate boundary system.
The 1931 Myitkyina earthquake, or also known as the 1931 Kamaing earthquake, occurred on January 28 at 02:35 local time. It was located in northern Burma, then part of British India. The magnitude of this earthquake was put at Mw 7.6. According to some sources the depth was 35 km, and according to a study of Phyo M. M. the depth was 5 to 30 km.
The 1930 Pyu earthquake occurred on December 4 at 01:21 local time. The epicenter was located north to Bago, Burma, then part of British India. The magnitude of the earthquake was estimated at Mw 7.3, or Ms 7.3.
The 2013 Balochistan earthquakes were the deadliest to affect Pakistan since 2005. The mainshock, occurring on 24 September, had a moment magnitude of 7.8 and maximum Mercalli intensity of IX (Violent). It had an epicenter located in Awaran District, 113 km (70 mi) northwest of Bela. The mainshock killed over 820 people, injured hundreds of others, and left 100,000 people homeless. The Awaran District was among the worst affected with 80 percent of its housing stock damaged or destroyed. On 28 September, the region was affected by a Mw 6.8 aftershock, killing an additional 15 people. Rescue and recovery efforts were severely hampered by insurgents who attacked military troops sent to distribute aid. These attacks also prompted the Pakistan government to close its doors to international aid.
An earthquake occurred in southern Mongolia on December 4, 1957, measuring Mw 7.8–8.1 and assigned XII (Extreme) on the Modified Mercalli intensity scale. Surface faulting was observed in the aftermath with peak vertical and horizontal scarp reaching 9 m (30 ft). Because of the extremely sparse population in the area, this event, despite its magnitude, was not catastrophic. However, 30 people died and the towns of Dzun Bogd, Bayan-leg and Baruin Bogd were completely destroyed.
The 1946 Sagaing earthquakes struck central Burma at 15:17 local time on 12 September. 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.
The 1912 Maymyo earthquake or Burma earthquake struck Burma on the morning of May 23, with an epicentre near Taunggyi and Pyin Oo Lwin in Shan State. The earthquake was initially calculated at 8.0 on the surface wave magnitude scale (Ms ) by Beno Gutenberg and Charles Francis Richter, and described by them as being one of the most remarkable seismic events in the early 1900s. Recent re-evaluation of the earthquake, however, have revised the magnitude to 7.6–7.9. It was preceded by two foreshocks on May 18 and 21 with respective intensities V and VII on the Rossi–Forel scale, while the mainshock was assigned IX. Shaking was felt throughout most of Burma, parts of Siam and Yunnan; an area covering approximately 375,000 square miles. It was one of the largest earthquakes in the country.
The 1930 Bago (Pegu) earthquake, also known as the Swa earthquake struck Myanmar on 5 May. The moment magnitude (Mw ) 7.4 earthquake had a focal depth of 35 km (22 mi) and maximum Rossi–Forel intensity of IX. The earthquake was the result of rupture along a 131 km (81 mi) segment of the Sagaing Fault—a major strike-slip fault that runs through the country. Extensive damage was reported in the southern part of the country, particularly in Bago and Yangon, where buildings collapsed and fires erupted. At least 550, and possibly up to 7,000 people were killed. A moderate tsunami was generated along the Burmese coast which caused minor damage to ships and a port. It was felt for over 570,000 km2 (220,000 sq mi) and as far as Shan State and Thailand. The mainshock was followed by many aftershocks; several were damaging; additional earthquakes occurred in July and December, killing dozens. The December earthquake was similarly sized which also occurred along the Sagaing Fault.
The Kyaukkyan Fault Zone is a large complex strike-slip fault that extends for about 510 km from Shan state, Myanmar to Thailand. It was the source of the 1912 Shan state earthquake when it ruptured for a length of 160 km along the northernmost segment. The fault is not very well studied, unlike the Sagaing Fault. The fault runs through the Shan hills nearly parallel to the Sagaing Fault. It is highly segmented, characterized by a broad array of splaying segments and basins, dominated by releasing bends and associated extensional fault systems. The slip rate for this fault is about 1 mm/yr.
The 1839 Ava earthquake, also known as the Amarapura earthquake or Inwa earthquake, was a disastrous seismic event that struck present-day central Myanmar on March 23. This earthquake with an estimated moment magnitude as high as 8.3, was one of the largest in the country, since 1762. It was assigned a maximum of XI (Extreme) on the Modified Mercalli intensity scale, and was felt in Rangoon and Bhamo. Damage was enormous in Ava, resulting in the death of hundreds.
The 2003 Taungdwingyi earthquake struck central Myanmar at midnight, on 21 September with a magnitude of Mwb 6.6.
The Haiyuan Fault is a major active intracontinental strike-slip (sinistral) fault in Central Asia.
On 6 November 1988, two earthquakes struck Lancang and Gengma counties, Yunnan, near the China–Myanmar border. These earthquakes measured moment magnitude (Mw ) 7.0 and 6.9, respectively, spaced 12 minutes apart. These earthquakes were assigned a maximum China seismic intensity of IX and X, respectively. Between 748 and 939 people were killed; more than 7,700 were injured. Both earthquakes caused damage and economic losses estimated at CN¥ 2.05 billion. Moderately large aftershocks continued to rock the region, causing additional casualties and damage.
In 1954, the state of Nevada was struck by a series of earthquakes that began with three magnitude 6.0+ events in July and August that preceded the Mw 7.1–7.3 mainshock and M 6.9 aftershock, both on December 12. All five earthquakes are among the largest in the state, and the largest since the Cedar Mountain earthquake of 1932 and Pleasant Valley event in 1915. The earthquake was felt throughout much of the western United States.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST in the geologically active Salton Trough of Southern California. The Salton Trough represents a pull-apart basin formed by movements along major faults. This region is dominated by major strike-slip faults one of them being the San Jacinto Fault which produced the 1968 earthquake. The mainshock's epicenter was near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). The zone of surface rupture was assigned a maximum Modified Mercalli intensity (MMI) of VII.
The 1995 Menglian earthquake or 1995 Myanmar–China earthquake occurred on 12 July at 05:46:43 local time in the Myanmar–China border region. The earthquake had an epicenter on the Myanmar side of the border, located in the mountainous region of Shan State. It registered 7.3 on the Chinese surface wave magnitude scale (Ms ) and 6.8 on the moment magnitude scale (Mw ). With a maximum Mercalli intensity assigned at VIII, it killed 11 people and left another 136 injured. Over 100,000 homes in both countries were destroyed and 42,000 seriously damaged. Some damage to structures were also reported in Chiang Mai and Chiang Rai, Thailand. The low death toll from this earthquake was attributed to an early warning issued prior to it happening. Precursor events including foreshocks and some seismic anomalies led to an evacuation of the area before the mainshock struck. It is thought to be one of the few successfully predicted earthquakes in history.
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.
The 1933 Sumatra earthquake or Liwa earthquake occurred in West Lampung Regency, Lampung Province, Indonesia on June 25. The earthquake had an estimated surface-wave magnitude (Ms ) of 7.7 occurring at a shallow depth of 20 km. It had an epicenter onshore, devastating the city of Liwa. At least 788 people were reported killed, although the death toll may have been in the thousands. Aftershocks followed, including one which was strong enough to cause additional fatalities. The mainshock also triggered a nearby volcanic eruption two weeks later, killing some people.
The 1858 Prome earthquake occurred on August 24 at 15:38 local time in British Burma. The earthquake occurred with a magnitude of 7.6–8.3 on the moment magnitude scale. It had an epicenter in near the city of Pyay (Prome), Bago. The shock was felt with a maximum Modified Mercalli intensity of XI (Extreme) for about one minute. Severe damage was reported in Bago, and off the coast of Rakhine, an island sunk.
The 1766 Marmara earthquake occurred on 5 August; the second major earthquake to strike the Sea of Marmara region of present-day Turkey that same year. Estimates of the earthquake's moment magnitude (Mw ) range between 7.4 and 7.6. The earthquake was caused by strike-slip movement along a segment of the North Anatolian Fault. There was further damage and casualties in the Sea of Marmara area which had been affected by another major earthquake in May 1766. The worst affected areas were Tekirdağ and Gelibolu.
1 2 Soe Thura Tun; Ian M. Watkinson (2017). "Myanmar: Geology, Resources and Tectonics". Geological Society, London, Memoirs. 48: 413–441. doi:10.1144/M48.19. S2CID134291037.
↑ Chit Thet Mon, Xuan Gong, Yun Wen, Mingming Jiang, Qi-Fu Chen, Miao Zhang, Guangbing Hou, Myo Thant, Kyaing Sein, Yumei He (2020). "Insight into Major Active Faults in Central Myanmar and the Related Geodynamic Sources". Geophysical Research Letters. 47 (8). Bibcode:2020GeoRL..4786236M. doi:10.1029/2019GL086236.{{cite journal}}: CS1 maint: multiple names: authors list (link)
↑ Tsutsumi, H.; Sato, T. (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. Bibcode:2009BuSSA..99.2155T. doi:10.1785/0120080113.
↑ Hurukawa, Nobuo; Maung, Phyo Maung (2011). "Two seismic gaps on the Sagaing Fault, Myanmar, derived from relocation of historical earthquakes since 1918". Geophysical Research Letters. 38 (L01310). Bibcode:2011GeoRL..38.1310H. doi:10.1029/2010GL046099.
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