## 1 Introduction  
The seismic P- and S-waves downhole logging method is capable of determining and measuring the distribution and physical properties of soil adjacent to a borehole annulus. In this method, a number of sensors (P- and S-wave geophones) are positioned at different interval depths within the borehole, whereas the seismic source is situated upon the ground surface. The speed of the P-wave movement is higher than that of the S-wave. The advantage of P-wave is that ground water cannot affect its propagation velocity mostly in soil material, hence resulting in a higher precision level [1]. The measurements can be recorded as physical phenomena. Moreover, the artificial physical sources, e.g., electrical and nuclear sources, can be used for the purpose of perturbing the medium and measuring the perturbation response. A number of parameters such as density, orientation, porosity, and lithology of soil in the neighboring area of the borehole (i.e., the physical properties) can be measured through analyzing the available data. In definition, geophysical logging refers to non-disruptive in-situ physical properties of soil [2]. Directly measuring the soil stiffness in situ causes the minimization of material disturbance [1]. In Geotechnics, a key measure in site characterization is to determine the seismic wave velocity [3]. The P- and S-wave velocities are applicable to the calculation of basic elastic material properties, such as the soil bulk modulus and shear modulus. To effectively evaluate the seismic ground motions, these parameters cannot be overlooked [4]. The materials of P-wave velocities can be assessed from field and laboratory observations [5; 6]. In addition, a comparison was made between the obtained values of the P-wave velocity (_Vp_) and parameters such as density, the SPT-N values, velocity index, and friction angle. Remember that the shear wave velocity (S-wave, _Vs_) in soil is dependent upon different parameters, such as the soil type, confining stress, and level of the soil compaction [7]. However, no adequate attention has been paid to the effects of some other parameters like the size and shape of soil material upon _Vs_. Such parameters mainly affect the delegation of the applied normal stress of the soil; this way, they have a direct impact on the _Vs_ magnitude. According to a number of previously conducted studies in this field, the bender elements can be effectively used in determining _Vs_ in different types of materials, e.g., sand, and glass beads. A number of empirical equations in granular materials were proposed by to predict _Vs_ on the basis of size, shape, and the confining stress of material under dry and saturated conditions (e.g., [7]). Formerly, to determine the seismic wave velocity, most researchers and practitioners have made use of the seismic surface refraction and reflection methods. Since borehole receivers emerged and seismic shear wave sources were developed, borehole seismic wave velocity logging methods received more attention. A method that can be simply used to produce seismic shear waves is wooden plank hammering. This technique uses a hammer as energy source at the surface to impact a wood plank and generates shear waves. This is typically accomplished by coupling a plank to the ground near the borehole and then impacting the plank in the vertical and horizontal directions. It can obtain the shear waves that are detectable through the use of downhole receivers. Such receivers are able to effectively measure downhole Vs. Receivers (geophones) are applicable to logging the waves that are generated by seismic shear wave sources in hundreds of meters depths [4]. Table 1 gives a summary of the seismic borehole methods proposed in literature to measure seismic velocity [4; 8]. The methods are the up-hole seismic, downhole seismic, suspension seismic, and cross-hole seismic. These methods are also called PS logging since the measurement of both compression wave (_Vp_) and shear wave (_Vs_) can be done at the same time [9].