Tuesday 19 December 2023

Magnitude 6.2 Earthquake in Gansu Province, China, results in at least 126 deaths.

The China Earthquake Networks Center recorded a Magnitude 6.2 Earthquake at a depth of about 10 km, beneath Jishishan County in Gansu Province, slightly before midnight local time (slightly before 4.00 pm GMT) on Monday 18 December 2023. One hundred and thirteen people have been reported dead in Gansu Province following this event, with thirteen fatalities in neighbouring Qinghai Province. Another 597 people have been reported injured in the two provinces, and 20 more missing. Around 155 000 homes have been damaged, with widespread loss of power in the region, which making conditions extremely difficult in an area where night-time temperatures regularly fall below -10°C at this time of year.

Damage to buildings in Jishishan County, Gansu, following a Magnitude 6.2 Earthquake on Monday 18 December 2023. AFP/Getty Images.

Much of western China and neighbouring areas of Central Asia and the Himalayas, are prone to Earthquakes caused by the impact of the Indian Plate into Eurasia from the south. The Indian Plate is moving northwards at a rate of 5 cm per year, causing it to impact into Eurasia, which is also moving northward, but only at a rate of 2 cm per year. When two tectonic plates collide in this way and one or both are oceanic then one will be subducted beneath the other (if one of the plates is continental then the other will be subducted), but if both plates are continental then subduction will not fully occur, but instead the plates will crumple, leading to folding and uplift (and quite a lot of Earthquakes). The collision of the Indian and Eurasian plates has lead to the formation of the Himalayan Mountains, the Tibetan Plateau, and the mountains of southwest China, Central Asia and the Hindu Kush.

Tectonic map of Asia, showing relationships between the India–Asia collision, escape of Indonesian and South China blocks seaward, and extension from Siberia to the Pacific margin. (Note also the opening of back-arc basins including the Sea of Japan and the South China Sea, and extension in the Bohai Basin and eastern part of the NCC.) The North China Craton is also strongly influenced by Pacific and palaeo-Pacific subduction, perhaps also inducing extension in the eastern NCC. The palaeo Pacific and Pacific subduction zones developed in the Mesozoic, and also contributed to the hydration of the subcontinental lithospheric mantle beneath the NCC. Kusky et al. (2007).

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