Relevant migration characteristics of strong earthquakes between the North-South Seismic Belt and North China block

The focal mechanism solutions of earthquakes and in-situ stress mea-surement results showed that there was a regional stress field in nearly radial pattern in Chinese mainland， and the radiation center was located in the eastern Qinghai-Xizang (Tibet) block. In this paper we defined the approximate radiation center (35°N， 100°E) in Chinese mainland as the dynamic source point and then calculated the distance between the dynamic source point and the location of 34 earthquakes with M_S≥6.0 since the year 1900 in eastern part of Chinese mainland (30°N—44°N， 104°E—125°E) so as to analyze the relationship between the distance and earthquake occurrence time. The results showed that a series of M_S≥6.0 earthquakes occurred in North China block after an earthquake with M_S≥7.0 occurred in North-South Seismic Belt in the 20th century， and they generally migrated eastward from North-South Seismic Belt with time. This also suggested that the earthquakes occurred in North China block should be mainly controlled by the influence of the Qinghai-Xizang (Tibet) block’s squeezing to the eastern Chinese mainland under the action of Indian Plate， causing the M_S≥6.0 earthquakes eastward migrating in the North China block. There were four distinct groups of migrations with velocity about 80 km/a. The interval between the first M_S≥6.0 earthquake in North China block and the latest M_S≥7.0 earthquake in North-South Seismic Belt was about 1 month to 11.8 years， and 60% of the M_S≥6.0 earthquakes were located in the area close to (39°N±1.5°). Therefore it could be inferred that the M_S≥6.0 earthquakes probably occur in North China block in recent years after the Wenchuan M_S8.0 earthquake in 2008 and Lushan M_S7.0 earthquake in 2013. Accordingly， we should focus on the junction areas of Shanxi， Hebei， Inner Mongolia， and the circum-Bohai and their surrounding areas.