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In Situ Shear Wave Velocity Measurements in Rocks - Applications and Synthesis of Vs Values

 

3.0 Applications of Shear Wave Velocity Measurements in Rock

            The Vs of rock materials has many practical applications. Vs has been used in correlations for other parameters or to better understand the behavior of the material. Vs has been used to estimate anisotropy in rocks (Rabbel et al., 1998; Winterstein and Paulsson, 1990), determination of fracture strike (Winterstein and Meadows, 1991), monitoring CO2 injection (Chen and Liu, 2011), underground cavity detection (Bianchi Fasani et al., 2013; Harrison and Hiltunen, 2004; Parker and Hawman, 2012; Robison and Anderson, 2008; Rucker et al., 2005) and many more applications beyond. Shear wave velocity has also been used to better understand discontinuities in rock masses. The effects of other factors such as confining stress, temperature, propagation direction, and faulting have been explored extensively in laboratory settings (Punturo et al., 2005; Agosta et al., 2007). Of significant interest is the effect of rock mass discontinuities on Vs and wave propagation. Winterstein (1992) describes basic cases relating shear wave propagation to fractures in rocks. There has been a significant amount of research into understanding how rock discontinuities such as joints, fractures, and foliation interact with seismic waves (Cha et al., 2009; Ivankina et al., 2005; Misra and Marangos, 2011; Winterstein, 1992).

 

4.0 Synthesis of Vs Values in Rock

 

Several references from the literature discussing in situ Vs measurements in a variety of materials. The reported Vs values have been compiled in Table 1 for comparison. This is an incomplete compilation that identifies possible values of in situ Vs that may be measured in some materials. The values in the table reveal the significant variability in Vs that can be measured in a single geologic unit. Factors such as weathering and the presence of discontinuities have a significant impact on the Vs of rocks. As observed in Table 1, rocks such as limestone can exhibit profound variations in Vs, largely as a function of weathering in the rock mass. Some materials, depending on site conditions, observed an order of magnitude change in Vs over a relatively short distance.

 

 

Table 1: In Situ Shear Wave Velocities of Some Rock Types from the Literature

 Rock Vs Table

*Back calculated from reported values of small-strain shear modulus and mass density.

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