摘要
Based on the earthquake data during 1980~2010 in North China region,the authors use the grids with l×l unit size to cover the area and investigate the variation of non-empty box number of earthquakes. The statistics show that in North China the forecasting efficiency is low for “quiescence” type abnormal, the “enhanced” type abnormal has a higher correct alarm rate, and the precursory criterion both by “enhanced” and “quiescence” type abnormal has a higher forecasting efficiency. This means that the precursory of small or moderate earthquakes before large earthquakes mainly displays as “enhanced” activity.