ON CERTAIN FEATURES OF RUPTURE OF THE NORTHWESTERLY LIYANG-JIEXIU-WUYUAN STRONG EARTHQUAKE BELT

The Liyang-Jiexu-Wuyuan strong earthquake belt became the most active seismic belt in north China after the 1976 Tangshan great earthquake. By studying the source mechanism, rupture process, source parameters and migration of strong earthquakes occurring on this belt, a few special features can be noticed:(1) Direction of the rupture surfaces of all earthquakes ML5.0 strikes northwest, same as the general strike direction of the belt, showing migration of earthquakes along the direction of rupture.(2) Strong earthquakes migrate usually from the center part of the belt towards both directions of the belt in its northwestern and southeastern elongations. Their magnitudes tend to increase, however, after the Pingyao earthquake of magnitude 5.7 on March 9, 1980, such feature of migration and increase of magnitude no longer appear.(3) Until present, all earthquakes have released their energy by moderate and strong earthquakes. The P axes of tE'e principal compressive stress basically coincide with the direction of the general compressive stress. But a few of them do not, showing local conditions may affect the direction.