The Haiyuan Fault is a left-lateral strike-slip fault running about 250 kilometres along the northeastern margin of the Tibetan Plateau in China's Ningxia and Gansu provinces. It marks a boundary where crust pushed eastward by the India-Asia collision slides past the stable Ordos block, accumulating strain in a loess-covered highland.
The fault is famous for the devastating 16 December 1920 Haiyuan earthquake, estimated at magnitude 7.8 to 8.5, which ruptured over 200 kilometres of the fault. The quake triggered enormous loess landslides that buried villages and reshaped whole valleys, and it remains one of the deadliest earthquakes in recorded history.
Studies of the surface rupture and offset streams show the fault has produced repeated great earthquakes over past millennia, with a recurrence interval of roughly a thousand years on some segments. A section near the 1920 rupture is considered a seismic gap, keeping the region under close scientific watch.