Analysis of evolution of seismic components induced by a vertical blasthole

Blast ground vibration is the integrated result of body waves and surface waves. However, the contribution of various waves and their evolution laws have not been well studied, and the concept of the influence areas of various waves is rarely mentioned in current studies. In this paper, using the polarization analysis approach, the seismic components and the evolution of various waves induced by a vertical blasthole are analyzed in two case studies. Then, based on the test results, the partition of the influence areas of various waves is discussed. The results indicate that the proportion of different seismic components is not a constant, but rather, the dominant wave may change to another type with r (where r is the distance to the blasthole axis), and the dominant motion directions of various waves are distinct. For a vertical blasthole, the P-wave is a significant component in both near and far fields, and becomes the dominant wave beyond r = 2.3 h (where h is the buried depth of the explosive), furthermore its particle motion gradually rotates to the horizontal direction with r increases. The S-wave only dominates within r = 2.3 h, but its effect can be ignored when the R-wave is well developed. The R-wave is not suddenly created but gradually grows to an identifiable feature at r = 5 h, and it dominates the vertical vibration if r exceeds (43 ~ 45)h (59 ~ 62 m/kg^1/2). Thus, the P-wave is a non-negligible threat to ground structures in vertical-hole blasting. Nevertheless, the P-wave component is commonly ignored in earthquakes, where the S- and R-waves are considered troublesome. The evolution of seismic components induced by blasting has some differences from the expectations in earthquakes.