Abstract: The anomalous strain changes at the borehole strain observation stations in the Capital Circle Area before some earthquakes are analyzed, which shows that the strain curves turned different with their ordinary shapes. The abnormal changes could be classified into 3 types, i.e., step type, pulse type and wave types. Some cases are shown in this paper for describing determination of the strain changes shortly before earthquakes, and some operable criteria to identify the strain precursors are listed.

Key words: Borehole strain, Imminent precursor, Earthquake prediction, Capital Circle Area