THE PLANE DISTRIBUTION OF XINGTAI AFTERSHOCKS AND STRONG AFTERSHOCKS ACTIVITY

In this paper, the variation of plane distribution of aftershocks activity with time were obtained by the scan plane distribution ￡or the number of equivalent M-4 earthqukes in each 0.01 square degree. It has beea shown that there is a concentrated energy released zone whose trend is consistent with source stress field. The area of the aftershocks activity is decreased before strong aftershocks and has a convergence tendency toward the zone. However, the area spreads toward the direction perpeadicuar to the trend of the zone and increased at the same time. Finally, we divide the Xiagtai earthquake sequence into the initial, early, medidium and late terms based on he various characteristics of the aftershocks activity pattern in different periods.