Abstract: In this paper, the method was studied that the anomaly parameter of seismic precursor being abstracted form the observational data of Rn in underground water, and the pattern of spatial distribution of the anomaly of Rn in North China was scanned from 1985 to 2002 by using the parameters as inputs. And then, the scanned pattern were superposed with the numerical pattern of quantitative evaluation of the tectonic activity and seismic risk in North China, so as to realize the combination of the spatial scanning of precursor anomaly and the active tectonic setting. On the basis of above work, the analysis was made entirely for the evolution of pattern of Rn in underground water before the shocks (M_S≥5.0) took place in North China since 1985, and the discriminative criteria of the short-term Rn anomaly and the characteristics of spatial evolution of anomaly areas before shocks were abstracted. Finally, the discriminative mark of short-term precursor of Rn in underground water before strong shocks in North China was proposed.

Key words: Rn in underground water, Evolution maps, Short-term precursor, Discriminative Mark