Abstract: This paper deals with the response features of apparent ratio of seismic wave velocity (ARWV) on the changes in true ratio of wave velocity in a horizental layered medium in terms of mathematical modelling. The results show that: ① the response features of (ARWV) are associated with the parameters of the structure and its dynamic changes, and the relative position between the hypocenters and the monitoring networks, showing complicated patterns strongly related to the concrete paths of propagation of seismic wave from the source to the receiver; ② the depth of the seismic source would have imporant influence on the response features of ARWV, specially the capacity carrying the anomalous information in the condition of earth media being in anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers; ③ the response features of ARWV is clearly related to the changes of ratio of wave velocity instead of changes of wave velocity itself, i.e. the response could be small as the changes in true ratio of wave velocity is small even in the case of large changes in the wave velocities in comparison with equal conditions. It is suggested that more attention must be paid for all these features in combination with detailed investigation of the velocity structure of the earth media in the studied region and best fitting of hypocenter determination in order to obtain the reliable precursors from the changs in ARWV.

Key words: Apparent ratio of seismic wave velocity, True ratio of seismic wave velocity, Resonse features, Modeling