Abstract: The deviation of micro-epicenter and macro-epicenter is an urgent task in the rapid assessment of earthquake intensity. This paper aims at studying the main area of earthquake rupture and marking the possible position of macro-epicenter through the research of spatial distribution of aftershock frequency N-value within 24 hours after seven greater than M_S6.5 earthquakes, so as to provide reference for emergency rescue. We illustrated the steps and results of determining the minimum completeness magnitude base on the case of the 2008 Wenchuan earthquake, in order to get calculation method and distribution chart of N-value, and determine the macro-epicenter. And finally, we compare and analyze the estimated epicenters with the actual epicenters at each period of the five earthquakes. We concluded that ① at each period of the 24 hours after the catastrophy, the macro-epicenter calculated from aftershock frequency N-value distribution could reduce the deviation referred from the estimated epicenters of micro-epicenter; ② that estimated epicenters at the periods of 2 hours, 4 hours, 12 hours and 24 hours after the earthquake can be used as the correction factor of fast judgement of earthquake intensity, which can meet the timeliness of earthquake quick reponse, and best estimate the epicenter at the period of 24 hours after erathquakes.

Key words: Macro-epicenter, Micro-epicenter, Rapid intensity determination, Aftershock frequency N-value