Seismic refraction

P-wave refraction evaluates the compression wave generated by the seismic source located at a known distance from the array. The wave is generated by vertically striking a striker plate with a sledgehammer, shooting a seismic shotgun into the ground, or detonating an explosive charge in the ground. Since the compression wave is the fastest of the seismic waves, it is sometimes referred to as the primary wave and is usually more-readily identifiable within the seismic recording as compared to the other seismic waves. ==S-wave refraction==

S-wave refraction evaluates the shear wave generated by the seismic source located at a known distance from the array. The wave is generated by horizontally striking an object on the ground surface to induce the shear wave. Since the shear wave is the second fastest wave, it is sometimes referred to as the secondary wave. When compared to the compression wave, the shear wave is approximately one-half (but may vary significantly from this estimate) the velocity depending on the medium. == Two horizontal layers==

ic0 - critical angle V0 - velocity of the first layer V1 - velocity of the second layer h0 - thickness of the first layer T01 - intercept :i_{c_{0}} = asin \left( {V_{0} \over V_{1}} \right) : T = {2h_{0}cos(i_{c_{0}}) \over V_{0}} + {X \over V_{1}} = T0_{1} + {X \over V_{1}} : h_{0}= {T0_{1}V_{0} \over 2cos(i_{c}) } : h_{0} = {X_{cross_{1}} \over 2} \sqrt{{V_{1}-V_{0} \over V_{1} + V_{0}}} == Several horizontal layers==

: h_{n} = {V_{n} \over cos(i_{n})} \left( {T0_{n+1} \over 2} - \sum_{j=0}^{n-1}{h_{j}\sqrt{{1 \over V_{j}^2} - {1 \over V_{j+1}^2}}} \right) ==Inversion methods==

• The General Reciprocal method • The Plus minus method • Refraction inversion modeling (refraction tomography) • Monte Carlo simulation • Genetic algorithms == Applications ==

Seismic refraction has been successfully applied to tailings characterisation through P- and S-wave travel time tomographic inversions. ==See also==