Abstract: During the seismogenic process of strong earthquakes the space-time centralized activity in a definite space-time range is always accompanied. Two quantitive parameters with clear meaning and fine applicability to describe the earthquake space-time uniformity degree have been given on the basis of previous works. Through the study on 5 earthquakes with M_S≥5.5 occurred in Ningxia and its neighboring region and 4 earthquakes with M_S≥6.0 occurred in North china, it is showed that there exists obviously abnormal rise process of C_t and C_d value in couple mouths or around one year before main shocks, indicating that there exists obviously centralized process in earthquake space-time distribution before strong shocks.

Key words: Earthquake time distribution, Space distribution, Uniformity degree