RESEARCH ON SEISMIC ACTIVITY CHARACTERISTICS OF MEDIUM-STRONG EARTHQUAKES IN NORTH MARGIN OF ORDOS

From the periodic law aspect of above 6.0 earthquakes in Yinshan seismic zone,the characteristics of medium-strong earthquakes in this area have been studied.There exists the characteristic of a century scale periodicity for above n 6.0 earthquakes in Yinshan seismic zone since AD 849.And since 1900 it has came to the fifth active period.At present,strain energy is at a high state.Therefore above 6.0 earthquakes in this area may be much possible to happen in the future years.Linhe-Wuhai-Bayanhot is the major rupture gap of above 7.0 earthquakes.Above ML5.0 earthquakes jump between eastern and western bordered with the axis of east longitude 110°,where exists a seismogenic zone and earthquake belt of new medium-strong earthquake activities.Since 1970,there have been above ML4.0 seismic gaps or belts before the six above 5.9 earthquakes.From January 1,2000 to September 30,2011,two obvious earthquake belts of ML4.0 earthquakes formed gradually.And Linhe-Wuhai the intersection part of the two belts is the future seismogenic zone.