The 1969 Yangjiang earthquake occurred on 26 July, at 6:49 am, Beijing local time (25 July 22:49 UTC). It had a magnitude of 6.4 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

and a maximum perceived intensity of VIII (''Severe'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

. It struck the city of

Yangjiang Yangjiang (, ), alternately romanized as Yeungkong, is a prefecture-level city in southwestern Guangdong Province in the People's Republic of China. It borders Maoming to the west, Yunfu to the north, Jiangmen to the east, and looks out to the ...

, causing over 10,700 houses to collapse and severely damaging a further 36,000. The earthquake also caused landslides and sandblows observed along the coast and along some rivers in the area of Yangjiang. The earthquake was also felt in Hong Kong. There were an unconfirmed total of 3,000 deaths.

Tectonic setting

Guangdong Province Guangdong (, ), alternatively romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020) ...

lies in a tectonically stable part of China, which has relatively low seismicity. The area forms part of the

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting creat ...

between the continental crust of China and the oceanic crust of the northern part of the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Phil ...

. Within the stable South China Block, there are three zones of higher earthquake activity, one of which is the Southeast China Coast seismic zone running through Guangdong and

Fujian Fujian (; alternately romanized as Fukien or Hokkien) is a province on the southeastern coast of China. Fujian is bordered by Zhejiang to the north, Jiangxi to the west, Guangdong to the south, and the Taiwan Strait to the east. Its capi ...

Provinces. This zone follows the South China Maritime Fold Belt, which was formed by a

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

event during the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

epochs. The area is currently in a compressive stress regime with the maximum horizontal stress orientated northwest-southeast. This results from a combination of the continuing

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

between the

Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...

and

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

s, and the subduction of the

Philippine Sea Plate The Philippine Sea Plate or the Philippine Plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

Earthquake

The earthquake occurred on a steeply-dipping fault striking nearly east-west. The

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

shows mainly dextral (right lateral)

strike-slip faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

. The magnitude and number of recorded

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

s and

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

s were unusually small, considering the size of the mainshock. This earthquake is the only damaging event in the epicentral area in historical records.

Damage

The epicentral area lay mostly in Yangjiang County, affecting an area measuring 19 km by 10 km, elongated west to east. In the whole county, a total of 10,762 houses were completely destroyed, a further 35,965 were severely damaged and another 90,840 suffered some damage. In Xinyi about 1,200 houses suffered some damage and several were destroyed. The earthquake was also strongly felt in Fengkai, Huaiji, Xinzhong, Deqing,

Zhaoqing Zhaoqing (), alternately romanized as Shiuhing, is a prefecture-level city in Guangdong Province, China. As of the 2020 census, its population was 4,113,594, with 1,553,109 living in the built-up (or metro) area made of Duanzhou, Dinghu a ...

, Yunan,

Zengcheng Zengcheng District ( alternately romanized as Tsengshing) is one of 11 urban districts of the prefecture-level city of Guangzhou, the capital of Guangdong Province, China. History was established under the Qin following their conquest of ...

, Gaohe and

Panyu Panyu, alternately romanized as Punyu, is one of 11 urban districts of the prefecture-level city of Guangzhou, the capital of Guangdong Province, China. It was a separate county-level city before its incorporation into modern Guangzhou in 200 ...

, although there was no serious damage in these areas. Minor damage was also reported in Hong Kong. A report of 3,000 casualties caused by this earthquake is described as "unconfirmed".

References

External links

* {{Earthquakes in China Yangjiang Earthquake, 1969 Earthquakes in China 1969 in China Yangjiang History of Guangzhou

Tectonic setting

Earthquake

Damage

See also

References

External links