Because seismic activity within mid-continents is usually much lower than that along plate boundary zones, even small earthquakes can cause widespread concerns, especially when these events occur in the source regions of previous large earthquakes. However, these small earthquakes may be just aftershocks that continue for decades or even longer. The recent seismicity in the Tangshan region in North China is likely aftershocks of the 1976 Great Tangshan earthquake. The current earthquake sequence in the New Madrid seismic zone in central United States, which includes a cluster of M * 7.0 events in 1811–1812 and a number of similar events in the past millennium, is believed to result from recent fault reactivation that releases pre-stored strain energy in the crust. If so, this earthquake sequence is similar to aftershocks in that the rates of energy release should decay with time and the sequence of earthquakes will eventually end. We use simple physical analysis and numerical simulations to show that the current sequence of large earthquakes in the New Madrid fault zone is likely ending or has ended. Recognizing that mid-continental earthquakes have long aftershock sequences and complex spatiotemporal occurrences are critical to improve hazard assessments.
Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.
Cao JianlingWang HuiWu YanqiangLiu XiaoxiaZhang Jing
