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The area of southwestern China struck by a violent tremor on Saturday has witnessed some of the world's deadliest earthquakes.
The area sits on the boundary between two of the Earth's tectonic plates, the Indian and Asian plates, which are constantly grinding against each other.
The region is unusual geologically because of the steep slopes at the boundary between the Sichuan Basin and the Tibetan plateau, according to seismologists.
The elevation rises by about 3,500 metres (11,500 feet) over only about 50 kilometres (about 30 miles).
Earthquakes are frequent along the fringes of the Tibetan plateau, which was raised when India collided into Eurasia starting some 50 million years ago.
It is this powerful thrust that created the Himalayas and its highest peak, Mount Everest, which reaches 8,848 metres (29,029 feet). The mountains continue to reach skyward to this day, propelled by unstable tectonic terrain.
The deadliest earthquake to rock the Tibetan plateau in the 20th century was in 1920 when 230,000 people died in Gansu province. Another quake measuring 8.0-magnitude struck Sichuan in May 2008 leaving nearly 87,000 dead or missing.
Jiang Haikun, an official with the China Earthquake Networks Centre's forecasting department, said Saturday's quake was formed in the same way as the 2008 quake.
Both quakes occurred on the Longmen mountain fault zone, he said, which tended to produce powerful tremors along a 500-kilometre-long belt.