Abstract: Based on the statistics of cross-fault deformation anomalies before strong earthquakes during the last forty years, this article analyses the characteristics of the time duration, spatial distribution, amplitude of the anomalies and the relationship of all the three factors. it disgusses the anomaly characteristics of the measurement of cross-fault deformation as well as the maximum spacing of the cross-fault sites and observation cycle of the monitoring of different magnitude of earthquakes. The results suggest that: The anomalies are mainly of medium term as well as short and medium terms, occur more frequently one year before the earthquakes. The time duration of the anomalies is directly proportional to the earthquake magnitude. The spatial distribution of the anomalies also has a phenomenon that it extends as the augment of the epicenter distance. The amplitude of the anomalies enlarges with the increase of time duration and reaches to higher level when the epicenter distance is within 160 to 350 km. The anomaly shape is devided into two main types:trend and mutant. The spacing of monitoring cross-fault sites of different earthquake magnitude can be different: The spacings for monitoring magnitude 7 earthquakes should be less than 450 km, and 300 km, 200 km, 100 km for magnitude 6, 5, 4 earthquakes respectively. The measurement cycle is supposed to be within three months.

Key words: Cross-fault deformation measurement, Earthquake, Anomaly, Period, Epicenter Distance