Abstract:
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
MS≥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
MS≥6.0 earthquakes occurred in North China block after an earthquake with
MS≥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
MS≥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
MS≥6.0 earthquake in North China block and the latest
MS≥7.0 earthquake in North-South Seismic Belt was about 1 month to 11.8 years, and 60% of the
MS≥6.0 earthquakes were located in the area close to (39°N±1.5°). Therefore it could be inferred that the
MS≥6.0 earthquakes probably occur in North China block in recent years after the Wenchuan
MS8.0 earthquake in 2008 and Lushan
MS7.0 earthquake in 2013. Accordingly, we should focus on the junction areas of Shanxi, Hebei, Inner Mongolia, and the circum-Bohai and their surrounding areas.