1988 Lancang earthquake

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1988 Lancang-Gengma earthquakes (澜沧江－耿马地震)
epicenter.
epicenter.
1988 Lancang earthquake (Myanmar)
UTC time1988-11-06 13:03:19
ISC event419867
 419869
USGS-ANSSComCat
 ComCat
Local date6 November 1988
Duration19 seconds
Magnitude7.7 Mw (USGS), 7.6 Ms (CEA), 7.3 Ms (USGS)[1]
 7.2 Ms (CEA), 6.4 mb (USGS), 6.4 Ms (USGS)[1]
Depth17.8 km
 15.9 km
EpicenterChina-Myanmar border region
22°47′20″N 99°36′40″E / 22.789°N 99.611°E / 22.789; 99.611Coordinates: 22°47′20″N 99°36′40″E / 22.789°N 99.611°E / 22.789; 99.611
TypeStrike-slip
Areas affectedChina, Myanmar and Thailand
Total damage$270 million USD in 1988
Max. intensityMMI -- X (Extreme) (1st shock)

MMI -- IX (Violent) (2nd shock)
LandslidesYes
ForeshocksYes
Aftershocks600 +, largest was an Mw  6.1[2]
Casualties730-939 fatalities, 7,700 injured[3]

The 1988 Lancang–Gengma earthquakes (simplified Chinese: 澜沧江－耿马地震; traditional Chinese: 瀾滄江－耿馬地震; pinyin: Láncāngjiāng-gěng mǎ dìzhèn), also known as the 11.6 earthquake by the Chinese media were a pair of devastating seismic events which struck Lancang and Gengma counties, Yunnan, near the border with Shan State, Burma in the Shan Plateau.[4] The pair of earthquakes occurred thirteen minutes apart with the first registering 7.7 on the moment magnitude scale and second measuring 7.2 on the surface wave magnitude scale. The two earthquakes were assigned their maximum Mercalli intensities of X (Extreme) and IX (Violent) respectively. At least 939 people were killed and more than 7,700 were injured in 20 counties across five prefectures in Yunnan, making it the worst in the country since the 1976 Tangshan earthquake.[5] Both earthquakes resulted in US $270 million (in 1988 dollars) in damages and economical losses. Moderately large aftershocks continued to rock the region, causing additional casualties and damages. Much information about the earthquake and its devastation were hidden by the Chinese government as the country was going through major political and cultural revolutions at the time.[6]

It is the largest earthquake to affect both Yunnan Province and Shan State since 1970 and 1912, respectively. In January 1970, a Mw  7.1 struck Tonghai County, resulting in over 15,000 deaths, and in May 1912, Shan State was hit with a Mw  7.8 that caused serious damage in the region. Earthquakes in this part of Southeast Asia (the Shan Plateau) usually have focal mechanisms corresponding to both shallow left-lateral (sinistral) and right-lateral (dextral) strike-slip faulting.[7][8] Sinistral systems follow an east-north-east or east-west trend for hundreds of kilometers, sometimes causing massive offsets in the Mekong and Salween rivers. On the other hand, dextral structures run along a more north-west or north-southernly strike. The earthquakes of November 6, 1988 were a result of slip along one of these dextral fault zones.[8]

Tectonic setting[]

The Shan Plateau is crisscrossed with numerous strike-slip structures to accommodate crustal rotation of the Sunda Block and deformation as a result of the India-Asia collision where the Indian Plate is underthrusted beneath the Eurasian Plate. The Shan Plateau was formed by uplift along the Shan Scarp Fault Zone, an inactive shear zone and reverse or thrust fault along its western base.[9][10] Located east of the Shan Scarp Fault is the active Sagaing Fault, a dextral transform fault that separates the Burma Plate from the Sunda Plate. At the northern boundary of the Shan Plateau lies the Red River Fault, an active 1,000 km-long dextral fault.[11] Bookshelf-style faulting as a result of shear deformation between the Red River and Sagaing faults have resulted in predominantly right-lateral strike-slip faulting within the Shan Plateau.[12] Seven years later, the 1995 Myanmar–China earthquake with a moment magnitude of 6.8 struck the same area that was affected by the Lancang earthquake.[13] That event left some 11 people dead, destroyed over 100,000 homes and damaged an additional 42,000 in the same area.[14] It is believed to have been triggered by the transfer of stress from the 1988 doublet event.[12]

Earthquake[]

The earthquake originated along the Longlin-Lancang Fault Zone, a northwest striking, 210 kilometres (130 mi) long fault structure. Its northern section is a single strand, unlike the northern section consisting of a set of clustered faults. It formed in the early to middle Miocene. The fault has a dextral sense of slip with a maximum displacement of 17 kilometres (11 mi). The estimated slip rate is 3.4 mm/yr.[15]

Right-lateral (dextral) offset of 1.4 to 2 metres (4 ft 7 in to 6 ft 7 in) was measured along the surface rupture for the 7.7 mainshock. Very small dip-slip (reverse) component was also measured. Ground ruptures followed a north-northwest strike for about 24 kilometres (15 mi). Seismologists estimated the first mainshock ruptured a 52 to 70 km long, 26 km wide fault zone extending northwest and southeast, in the process, creating new fault zones.[15] Maximum dextral surface offset was 1.4 meters and the vertical offset was 0.5 metres (1 ft 8 in).[16][17] Fault rupture velocity was estimated to be at 2 km/s.[15]

Thirteen minutes later, the second mainshock with a surface wave magnitude of 7.2 struck 63 km north northwest of the initial shock.[1] The rupture area was nearly twice that of the 7.7 mainshock. The event has been considered a doublet earthquake.[18][15]

Right before the 7.7 mainshock, a 2.6 foreshock preceded the disaster, it was the only recorded foreshock activity in the event sequence.

Intensity distribution[]

Lancang earthquake[]

USGS shake map for the earthquake.

The first mainshock struck a remote and mountainous location near the Myanmar–China border with a moment magnitude of 7.7, and surface wave magnitude measuring 7.6 or 7.3. Shaking from this event earned X (Extreme) on the Mercalli intensity scale, and IX on the China seismic intensity scale (Liedu).[19] This intensity zone had an axis length of 27 km, with the widest width measuring 8 km, covering an area of 170 km². It extends northwest to southeast from Mujia to Zhutang Township. Its northeast border lies along the eastern bank of the Heihe River, west of Fubang Township. Landslides, surface ruptures, liquefaction and ground failure was observed throughout.[18]

Zhongke Township in Ximeng County, close to the epicenter of the first mainshock. Photo taken in 2013.

Intensity VIII encompassed Xuelin Wa Ethnic Township in Mujia Township to the north, and Zhutang Township in the southeast. Also within this zone was Ximeng County to the west. This zone had an axis length of 52 km and a width of 20 km, covering an area of 820 km². Nearly every house in the region collapsed, with very few left intact. The earthquake also caused landslides and ground failures throughout this zone.[18]

For intensity VII, Cangyuan Va Autonomous County to the north to Shangyun, Lancang County in the south was included in the area. The western boundary also extended into Ximeng County, well past the Myanmar–China border, into Shan State, Myanmar. Here, damage was less extreme although some houses did collapse.[18] Light homes remained intact, and much of the damage to ordinary homes reported include cracking of walls. Landslides also occurred, together with ground cracks and sand boils. This zone covered a large area of 3,680 km².[18]

Weaker shaking was felt in Thailand, Laos, Vietnam and Bangladesh as well.[18]

Gengma earthquake[]

The second shock measured 7.2 or 6.4 on the surface wave magnitude and 6.4 on the body wave magnitude.[1] It had a maximum Liedu intensity of X.[19][18] The zone included Gengma County to the north, and Yanshuai towards the south, Tuanjie Township, Cangyuan County to the east, and Mengsheng Township, Cangyuan County in the west. Many houses totally collapsed or were severely compromised in this zone. Most of the buildings were also seriously damaged. Lightly constructed homes also collapsed or tilted due to damage resulting from fault rupture. Liquefaction and fissures erupting water were seen everywhere. The zone is a north-west ellipse with a major axis of 25 km and a minor axis of 8 km, covering an area of 160 km².[18]

The zone of intensity VIII extended from Gengma in the north to Yanshuai and Nuoliang Township in the south. Here, very few homes remained standing and lightweight houses tilted. Damage to the ground was the same as seen in the zone of IX. This zone followed a north-west ellipse area of 940 km².[18]

Aiguo New Village, Gengxuan Town, Gengma County in the north, to south of the Shuangjiang River in the east, to south of Lancang Shangyun in the south, and west to Minliang of Menglai Township, Cangyuan County in the west fell within intensity VII. Adobe houses here totally collapsed as a result. Intensity VII was felt for an area of 3,020 km².[18]

Intensity VI from the second shock covered an area of 32,700 km².[18] The same intensity felt during the first mainshock was significantly constrained due to the overlapping effects caused by the second mainshock.[18]

Earthquake sequence[]

Previous seismicity
Date Time (UTC) Magnitude Depth (km) Ref.
1987-11-25 13:09:47 mb 4.6 33.0 [20]
1988-08-14 17:50:52 mb 4.7 [21]
Mainshocks
Date Time (UTC) Magnitude Depth (km) Ref.
1988-11-06 13:03:19 Mw 7.7
7.6 Ms  		17.8 [22][1]
13:15:43 Ms 7.2
6.4 mb  		10.0 [23][1]

Aftershocks[]

A large aftershock measuring Mw  6.1 occurred 24 days after the two mainshocks.[1] It caused additional injuries and further damaged the already crippled region. By December 20, over 600 aftershocks had been recorded.

Aftershocks magnitude 5.0 or greater hide
Date Time (UTC) Magnitude Depth (km) Notes Ref.
1988-11-06 13:21:04 mb 5.8 10.0 [24]
13:39:48 mb 5.0 [25]
14:13:24 mb 5.1 [26]
16:00:32 mb 5.1 [27]
20:24:24 mb 5.4 [28]
1988-11-07 02:39:56 Mw 5.2 [29]
1988-11-15 10:28:14 Mw 5.3 17.7 [30]
1988-11-18 18:21:44 mb 5.0 10.0 [31]
1988-11-19 01:37:14 mb 5.0 33.0 [32]
1988-11-27 04:17:56 Mw 5.5 15.7 One person injured and some damage was inflicted.[33] [33]
1988-11-30 08:13:29 Mw 6.1 14.5 This aftershock caused further damage to the already affected region. Several people sustained injuries. It was felt in Kumming.[34][35] [34]
1988-12-19 11:06:57 mb 5.0 33.0 [36]
1988-12-22 03:49:46 mb 5.0 10.0 [37]
1989-05-07 00:38:18 Mw 5.6 33.0 One person died, and 91 more injured. At least 5,300 homes were damaged in Gengma County. Damaged totaled USD 54 million.[38] [39]
1989-06-04 15:07:46 mb 5.0 10.0 [40]

Impact[]

The earthquake damaged more than 4,000 schools and medical care facilities in Yunnan. A further 1.308 million homes were destroyed as a result. Over 1,000,000 m³ of rockslide caused damaged highways and choked-up rivers, halting river transportation. Many buildings generally fared well during the earthquake because of better construction practices and retrofitting works conducted before the earthquake. The buildings which had collapsed were mostly built with the consideration of the local seismic hazard. Some buildings including a cinema which was designed to withstand seismic intensity VIII and a residential block made to resist intensity IX were virtually undamaged when the earthquake struck.[41] These buildings were strengthened just before the earthquake.

Casualties[]

Initial reports from the international media claimed that at least 600 inhabitants had been killed, mainly from the village of Shanmato which was obliterated. Telecommunication services were cut and severely disrupted around the Yunnan and Shan State border region. This meant provincial government officials could not provide any updated figures on the dead.[42] Much earlier figures of fatalities were 18 and 37, which could not revised due to the communication disruptions. The majority of homes constructed of wood and mud, resided by farmers did not survive the extreme ground motions which led to the demise of many inhabitants.[42]

On November 9, the death toll totaled 938, at least 7,700 people were seriously injured, more than 3 million people had been affected with 267,000 left homeless.[3][43] Heavy damage was reported in Lancang County and 16 other surrounding counties. Many homes, roads and communication lines in Lancang and Mengliang were destroyed.[35] An estimated 200,000 including 144,000 houses had collapsed, 500,000 buildings including 253,000 homes were badly damaged.[35] About 1,000 schools, 98 clinics and 29 reservoirs were destroyed. Landslides in the area also damaged highways. Kunming, the capital of Yunnan Province did not report any damage, although the earthquake was felt strongly. More damage was reported in Chiang Rai, Thailand. The total damage cost is estimated to be US$269 million (1988 dollars).

Rescue[]

Due to its remote location and the lack of communication and damaged roads, rescue and aid transportation efforts faced difficulties getting to the affected areas.[44] The Yunnan government ordered an airlift of medical and relief supplies to help those affected. The governor of Yunnan Province, He Zhiqiang, along with several medical doctors were also brought to the disaster scene.[42] Several thousand troops and many military vehicles also visited the affected areas, according to the Ministry of Civil Affairs.[45]

See also[]

References[]

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