why did the tangshan Earthquake occur? Explain the plate motions and bounaries please!?

Question

why did it occur? tangshan, china earthquake in 1976

Answer 1

The earthquake was an intraplate earthquake--not located on a plate boundary.
The earthquake occurred on the Tancheng-Lujiang wrench fault system--somewhat inland from the edge of the plate boundary to the east, where the Pacific plate is diving beneath the continent. While the Pacific plate is pushing westward against the continent, the India plate is pushing northward. Big fault systems, like the Tancheng-Lujiang fault system, have formed within the continental plate in response to these pressures.
The Tancheng-Lujiang fault system extends from the the Yangtze River to Russia. The zone of faults is 5000 km long and up to 1000 km wide (Jiawei, 1993). The faults are straight or nearly straight and have steep dips, 70?-80?+ as would be expected in a strike-slip fault.
"Most of the crustal deformation of the Tangshan area was associated with right-lateral slip on a NNE-striking mainshock fault rupture plane together with the ruptures of the two major aftershocks....The focal mechanisms of the Tangshan earthquake sequence are consistent with regional tectonics, that is, extensive right-lateral strike-slip fault movement in a NNE direction and associated NE-SW-directed compression."(Bor-Shouh Huang and Yeong Tein Yeh)

Answer 2

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