Abstract: In this paper, the authors studied a method, in which the anomaly parameter of seismic precursor is abstracted form the observed data of underground water level, and the spatial distribution patterns of the anomaly parameters in North China was scanned from 1984 to 2002 by using the parameters abstracted as inputs, and than, every pattern was superposed with the numerical pattern or quantitative evaluation about the tectonic activity and seismic risk in North China, to realize combining the spatial scanning of precursor anomaly with active tectonic background. On the above-mentioned basis, the analysis was made entirely for the evolution of short-term patterns of underground water before M_S5.0 shocks which took place since 1985 in North China, so the discriminative criteria of anomaly zones and the characteristics of spatial evolution of short-term precursors of underground water level before strong shocks in North China was established.

Key words: Underground water level, Evolution maps, Short-term precursors, Discriminative mark