1976 Longling earthquake

The 1976 Longling earthquake in Yunnan Province, People's Republic of China, was a doublet earthquake, with two main shocks striking just east of Longling at 12:23:20 and 14:00:22 UTC (20:23 and 22:00 local time). The magnitudes were estimated at 6.7 and 6.6, respectively, on the Mw(GCMT)  scale, and 6.9 and 7.0 on the Ms scale;[5] Chinese sources put these at 7.4 and 7.3 on the Ms7 scale.[6] The region is noted for the quantity and intensity of its earthquakes, and the complexity of its tectonics, which are closely related to the collision between the Indian and Eurasian tectonic plates.[7]

1976 Longling earthquake
UTC timeDoublet earthquake:    
 A: 1976-05-29 12:23:20
 B: 1976-05-29 14:00:22
ISC event 
 A: 714808
 B: 714811
USGS-ANSS 
 A: ComCat
 B: ComCat
Local date
Local time
Magnitude 
 A: 6.7 Mw, 7.0 Ms[1]
 B: 6.6 Mw , 6.9 Ms [2]
Epicenter24.49°N 98.96°E / 24.49; 98.96[3]
24.54°N 98.72°E / 24.54; 98.72[4]
Areas affectedLongling County, Yunnan
Landslidesyes

No one died in the Longling county town[8] Loss in the 9 counties in Baoshan, Lincang and Dehong were 98 deaths, 451 severe injuries and 1991 light injuries. 420,000 buildings collapsed in an area of 1883 square kilometers.[9]

Geology

Yunnan is a mountainous region lying east of Tibet, and north of the Red River Fault that strikes southeast along the Red River into North Vietnam and the South China Sea. The Red River fault is deep – some believe it may reach the lithosphere[10] – and forms a major tectonic boundary that separates Indochina from the South China block.[11]

The seismotectonics of Yunnan and the adjacent areas is driven by the collision of the Indian Plate with the Eurasian Plate.[12] This has uplifted the Tibetan Plateau (and the Himalaya Mountains) and forced it eastwards, pushing the South China Block and Indochina towards the westward subducting Philippine Sea Plate and creating various extensional structures.[13] All of this has created a complicated geological structure with many faults, which in western Yunnan has allowed heat and fluids from the subducting Indian Plate to rise into the upper crust, creating the Tengchong volcanic field to the north of Longling and the Longling fault (location of the first event), and west of the Nu River and Nu River fault (location of the second event).[14] It appears that igneous intrusions have weakened the bedrock in this area, which has led to uneven accumulations of stress, which caused the earthquake.[15]

See also

Notes
  1. ISC-EHB Event 714808 [IRIS].
  2. ISC-EHB Event 714811 [IRIS].
  3. ISC-EHB Event 709781 [IRIS].
  4. ISC-EHB Event 714811 [IRIS].
  5. ISC-EHB Event 714808 [IRIS]. ISC-EHB Event 714811 [IRIS].
  6. Xu et al. 2012, p. 90.
  7. Wang, Chan & Mooney 2003, ¶23.
  8. Shen Zongpei 2010.
  9. Annals of Yunnan, Volume 3. 1999, p. 111.
  10. Lei, Zhao & Su 2009, ¶5.
  11. Lei, Zhao & Su 2009, ¶20.
  12. Wang, Chan & Mooney 2003, ¶1.
  13. Lei, Zhao & Su 2009, ¶20. See also figure 11 in Kusky, Windley & Zhai 2007, p. 18.
  14. Xu et al. 2012, p. 83.
  15. Xu et al. 2012, p. 90.

Sources
  • ANSS, "Yunnan 1976a: M 6.9 - Myanmar-China border region", Comprehensive Catalog, U.S. Geological Survey
  • ANSS, "Yunnan 1976b: M 7.0 - Myanmar-China border region", Comprehensive Catalog, U.S. Geological Survey
  • International Seismological Centre, ISC-EHB Bulletin, Thatcham, United Kingdom, http://www.isc.ac.uk/
  • Chorography Codification Committee of Yunnan; Yunnan Earthquake Administration (1999). 云南省志·卷三 地震志 [Annals of Yunnan, Volume 3, Earthquake] (in Chinese). Kunming: Yunnan People's Publishing House. ISBN 7-222-02829-3.


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