What is critical distance in seismic refraction?
In refraction seismic work, that distance at which the direct wave in an upper medium is matched in arrival time by that of the refracted wave from the medium below having greater velocity.
What is crossover distance in seismic refraction?
The crossover distance is the distance from the source at which the critically-refracted energy from the next deepest layer overtakes the critically-refracted energy from the previous layer (in the two-layer case, the energy traveling through layer 1 is direct, not refracted energy, but the idea is the same).
What is a critically refracted wave?
A critical refracted wave travels along the interface between layers and is refracted back into the upper layer at the critical angle. The waves refracted back into the upper layer are called head waves or first-break refractions because at certain distances from a source, they are the first arriving energy.
What is the meaning of critical distance?
Critical distance is the distance between the microphone and the sound source at which the level of room reverberation is equal to the level of the direct sound.
What is the difference between seismic reflection and refraction?
In this sense, reflection method is a very sophisticated version of the echosounding used in submarines, ships, and radar systems. Whereas, in seismic refraction method, principal portion of the wave-path is along the interface between the two layers and hence approximately horizontal.
How do you find crossover distance?
The cross-over distance is related to the refractor depth, h, and the velocities of the overlying medium and the refractor, V1 and V2 respectively, such that xc = 2h[(V2 + V1)/(V2 – V1)]½.
What is critical angle in seismic?
o For refraction seismology, the critical angle is the most important angle value to understand. o If angle (r) equals 90 degrees, then the refracted wave propagates along the boundary interface.
Why is critical distance important?
When designing a sound or a control room, the concept of critical distance is an important factor for positioning loudspeakers and microphones. Critical distance is the distance from the sound source at which the reverberant sound level and the direct signal level are equal.
How do you find the seismic critical angle?
ic = sin-1(V1/V2) o As the critically refracted wave propagates along the boundary, according to Huygen’s Theory of Wavelets, the primary critically refracted wave acts as a source for new secondary wave fronts and ray paths. o These secondary ray paths exit back to the surface at the critical angle.
What is critical angle of reflection?
critical angle, in optics, the greatest angle at which a ray of light, travelling in one transparent medium, can strike the boundary between that medium and a second of lower refractive index without being totally reflected within the first medium.
What is the difference between reflection and refraction survey methods?
Refraction surveys provide us with a layered velocity model as our primary output, reflection surveys will create a ‘true’ image of stratigraphy and structure, with a velocity model requiring further processing.