Abstract: The regional deformation anomaly of medium-term phase (1~3 years or more) before strong earthquake occurrence usually shows three aspects of common characteristics: ① For regional vertical deformation, it shows distribution features of anomalous uplift area and concentration belt-high gradient belt of vertical differential deformation (some of them reflect distribution of four quadrants) related to tectonics; ② For horizontal movement, it shows features of centralized high strain area (or zone) of domination shear deformation related to active blocks and faults; ③ It shows common features of regional vertical deformation anomaly area and high strain distribution area of horizontal deformation. Having analyzed preliminarily formation mechanism of these common characteristics of anomaly, it concludes that: these are results, controlled by basically united tectonic stress field of large-range, caused by stress-strain accumulation and certain phase strong earthquakes, according to deformation difference brought about in tectonic position along the boundary zone and within second-order faults of active blocks resulted from unstable and inharmonious features for movement of block system at different levels and deformation of boundary. Based on the above, the meaning of medium-term prediction of strong earthquakes is discussed in the light of common features of regional deformation anomaly and combined with background of geological tectonic activities.

Key words: Medium-term phase of strong earthquakes, Regional deformation anomaly, Common characteristics, Formation mechanism