A study on 'jump point' frequencies of zigzag dispersion curves in Rayleigh wave exploration

Zigzag dispersion curves are sometimes found in Rayleigh wave exploration when the media contain low velocity layers. The zigzag dispersion curves are believed to have a relationship with low velocity layers. Especially, there is a relationship between 'jump point' frequencies of zigzag dispersion curves and the parameters of the media. So the 'jump point' frequencies can be seen as a characteristic of the media. However, the relationship has not yet been deeply studied. In this paper, a detaHed research on it is conducted by computing the variation of the 'jump point' frequencies with the media parameters under three different sources. It is found that although the 'jump point' frequencies depend on the source type, there are the same rules for various sources: the S-wave velocities of the low velocity layer and the layer above it have the dominant influence on the 'jump point' frequencies, and followed by their thickness; the other parameters have less effect on the 'jump point' frequencies; the frequencies reduce with the decrease of S-Wave velocity of the loW velocity layer and the increase of S-Wave velocity of the layer above the loW velocity layer; they rediice With the increase of the thickness or depth of the loW velocity layer. The resiHt can be iised as a qtiaiitaiive aiialyCis of loW veloCity layer in the cases iike compaciion test of stibgrade.