2020 Tangshan earthquake

The 2020 Tangshan earthquake (Chinese: 2020年唐山地震; pinyin: 2020 Nián Tángshān Dìzhèn) was a magnitude 4.7-5.1 earthquake that hit Tangshan, Hebei, China on 12 July 2020, at 6:38 in the morning. It was geologically related to the 1976 Tangshan earthquake and caused minor damage in the region.

2020 Tangshan earthquake
Intensity distribution map published by the United States Geological Survey.
UTC time2020-07-12 06:38:25
ISC event
USGS-ANSS
Local dateJuly 12, 2020 (2020-07-12)
Local time06:38:25UTC+8
MagnitudeMw 5.1 (CEA)[1][2]
Mw 4.8 (USGS)[3]
Depth10 km (6 mi)
Epicenter39.78°N 118.44°E / 39.78; 118.44
Areas affectedHebei, Beijing, Tianjin
Max. intensity6（VI)（MMI (USGS)[3]
CasualtiesNone[4]

Background
Further information: 1976 Tangshan earthquake

Tangshan was previously struck by the magnitude 7.8 1976 Tangshan earthquake that caused at least 240,000 deaths in one of the dealiest recorded natural disasters in history.[1][2]

Geology
Tectonic elements surrounding the North China Craton on which Tangshan lies.

Tangshan lies at the northern edge of the Beijing-Tianjin-Tangshan Plain, an alluvial plain that stretches from Beijing to the Sea of Bohai.[5]:77 This plain – the northeastern corner of the great North China Plain – is where sediments eroded from the Yanshan mountains to the north have filled in the ancient Sea of Bohai, with Tangshan near where the shore was about 4,000 years ago.[5]:84–85 To the south these sediments have formed a layer of weak soils as much as three kilometers thick. At Tangshan and northward these sediments are thinner where the underlying strata crops out to form isolated hills.[5]:84[6]:88 This underlying strata is a thick (typically 10 km) layer of mainly sedimentary strata such as limestone and sandstone, with large deposits of coal.[7]:27 Tangshan is located particularly over a northeast oriented syncline, a fold in the sedimentary strata that has brought massive deposits of coal close enough to the surface to be mined. In this area the overlying alluvium varies in thickness from several meters to around 600 m (2,000 ft).[8]:626

Underlying all this is the ancient bedrock of different kinds of metamorphic rock (such as schist, gneiss, quartz, granulite, etc.) that form the Eastern Block of the North China Craton.[7]:27 This craton was formed approximately two billion years ago[lower-alpha 1] by the collision of two major crustal blocks that left a belt of uplifted mountains – the Central (China) Orogenic Belt (COB) – that crosses China approximately southwest to northeast, passing just west and north of Beijing.[10]:3 Just north of Zunhua another orogenic belt, the east–west trending Yanshan mountain fault-fold belt (also known as the Yanshan seismic belt) marks the northern edge of the North China Craton (and of the alluvial plain). It is also the location of over half of the destructive earthquakes in Hebei province,[11]:50 as under the plain several fault zones (oriented parallel to the Central Orogenic Belt) terminate against the Yanshan mountains.

Many of these faults are ancient, but have been reactivated by the force transmitted from the collision of the Indian Plate against the Eurasian Plate, [11]:50 making the Eastern Block unusually active seismically, accounting for six of the ten deadliest earthquakes in recorded history.[10]:20

Earthquake

The earthquake occurred at 6:38:25 a.m. on 12 July 2020 in Guye District of Tangshan city, Hebei province, China.[1][2][4] The epicenter was monitored at 39.78 degrees north latitude and 118.44 degrees east longitude in the Guye District of Tangshan with a focal depth of 10 km (6 mi), roughly 180 km (112 mi) east of Beijing.[1][2][4][12] The magnitude of the earthquake was Mw 5.1 according to the China Earthquake Administration (CEA) and Mw 4.8 according to the United States Geological Survey (USGS).[1][2][3] It was the strongest of the 17 earthquakes in the region over the preceding five years.[1]

Two aftershocks occurred within an hour of the first earthquake: a magnitude 2.2 aftershock at 7:02 a.m. and a magnitude 2.0 aftershock at 7:26 a.m.[1][4][13]

The earthquake was caused by a geological fault in the region and was related to the 1976 Tangshan earthquake.[1]

Damage

According to the USGS, the maximum intensity was "Strong" (VI) on the Modified Mercalli intensity scale.[3] Online footage showed minor damage to buildings and structures throughout the city.[1] The Tangshan Emergency Department said that "only some old buildings" had reported cracks from the earthquake.[1] No deaths or injuries were reported.[4]

Rail services in the region were immediately suspended for safety checks.[1][2][4]

The tremors were felt in Hebei, Beijing, Tianjin and other places.[14][2]

Aftermath

Passenger rail services began to gradually resume regular service on the afternoon of 12 July 2020.[1] According to Xinhua in August 2020, Hebei's provincial-level rural home reconstruction program involving earthquake-proofing was expanded in earthquake-prone areas following the July 2020 earthquake.[15]

Notes
  1. Some say 1.8 Ga, others 2.5 Ga.[9][10]:20

References
  1. Liu, Zhen (12 July 2020). "Chinese city of Tangshan hit by magnitude 5.1 quake, stirring memories of 1976 tragedy". South China Morning Post. Retrieved 11 October 2020.
  2. "Quake rattles Chinese city hit by massive 1976 disaster". CNA. Agence France Presse. 12 July 2020. Retrieved 11 October 2020.
  3. USGS. "M 4.8 - 5 km NE of Zhaogezhuang, China". USGS. Retrieved 11 October 2020.
  4. "Quake Shakes Northeast Chinese City; No Injuries Reported". Associated Press. 11 July 2020. Retrieved 11 October 2020.
  5. Jennings, Paul C. (1980). "Chapter 4: Report on the Tangshan Earthquake". Earthquake Engineering and Hazards Reduction in China: A Trip Report of the American Earthquake Engineering and Hazards Reduction Delegation (Report). National Academy of Sciences. pp. 69–133. ISBN 978-0-309-02937-7.
  6. Xing, Jiaming; Zou, Baoshan (2002). "Geomorphologic Characteristics in the Beijing–Tianjin–Tangshan Area and Their Relation with Tectonic Activity" (PDF). In Housner, George W.; He, Duxin (eds.). The Great Tangshan Earthquake of 1976 (Report). Volume 1. Pasadena, California: Earthquake Engineering Research Laboratory, California Institute of Technology. pp. 85–98.
  7. Guo, Shunmin (2002). "Occurrence of the Tangshan Earthquake from the View of Fault Block Movement". In Housner, George W.; He, Duxin (eds.). The Great Tangshan Earthquake of 1976 (Report). Volume 1. Pasadena, California: Earthquake Engineering Research Laboratory, California Institute of Technology. pp. 24–47.
  8. Zhao, Yucheng (2002). "Earthquake Damage to Shafts and Roadways in Kailuan" (PDF). In Housner, George W.; He, Duxin (eds.). The Great Tangshan Earthquake of 1976 (Report). Volume 2. Pasadena, California: Earthquake Engineering Research Laboratory, California Institute of Technology. pp. 625–645.
  9. Kusky, Timothy M.; Li, Jianhai (December 2003). "Paleoproterozoic tectonic evolution of the North China Craton". Journal of Asian Earth Sciences. 22 (4): 383–397. Bibcode:2003JAESc..22..383K. doi:10.1016/S1367-9120(03)00071-3.
  10. Kusky, Timothy M.; Windley, B. F.; Zhai, M.-G. (2007). Zhai, M.-G.; Windley, B. F.; Kusky, T. M.; Meng, Q. R. (eds.). "Tectonic evolution of the North China Block: from orogen to craton to orogen" (PDF). Mesozoic Sub-Continental Lithospheric Thinning Under Eastern Asia. Special Publications 280. Geological Society. 280 (1): 1–34. Bibcode:2007GSLSP.280....1K. doi:10.1144/SP280.1. S2CID 129902429.
  11. Yang, Lihua (2002b). "Distribution and Ground Failure Intensity Distribution of the Tangshan Earthquake" (PDF). In Housner, George W.; He, Duxin (eds.). The Great Tangshan Earthquake of 1976. Volume 1. Pasadena, California: Earthquake Engineering Research Laboratory, California Institute of Technology. pp. 171–183.
  12. "5.1 magnitude earthquake jolts China's Hebei province". Hindustan Times. Asian News International. 12 July 2020. Retrieved 11 October 2020.
  13. "河北唐山市古冶区2.0级地震" (in Chinese). China Earthquake Networks Center. Retrieved 11 October 2020.
  14. 河北唐山附近地震 网友：天津北京河北有震感. sina (in Chinese). 2020-07-11. Retrieved 2020-07-12.
  15. "China's Hebei speeds up quakeproofing of houses". Xinhua. 2 August 2020. Retrieved 11 October 2020.
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