Abstract: The "string beads" reflection characteristic is one of important seismic phenomena in identification of carbonation reservoirs of the Ordovician in Tarim basin. Base on forward modeling of wave equation, the difference models for karst cave shape, observation system, cave mode are designed, and the mechanism and its influence factors of the cavern seismic response are analyzed. The result shows that amplitude of "string beads" response is enhanced with cave width increasing, but the length of "string beads" doesn't change; the amplitude of "string beads" first increases and then decreases with cave height increasing; High-density acquisition has better imaging performance and resolution to the small-sized body compared with the conventional observation system. Different response characteristics are corresponding with different patterns of superimposed caves. These understandings provide a means for studying the relationship between the response mechanism and shape of karst cave and the characteristic of "string beads".

Key words: Tazhong area, carbonate cave, forward modeling, seismic response, observation system, influence factor