The seismic CPT tests are conducted at 66 sites where soil liquefaction have or have not occurred during earthquakes. The correlations among the cyclic shear stress ratio, modified shear wave velocity V_<s1>, soil behavior type index I_c and the actual soil performance during earthquakes are examined. The critical V_<s1>-value causing liquefaction for sand is found to increase with I_c if I_c<1.9, while it decreases if I_c>1.9. Based on the above relation, the boundary line separating liquefiable from non-liquefiable conditions is presented in terms of V_<s1> and I_c, which is uniquely expressed regardless of the fines content.
