What is the 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).
Which instrument is used in seismic reflection method?
The reflection experiment On land, the typical receiver used is a small, portable instrument known as a geophone, which converts ground motion into an analogue electrical signal.
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. The value of xc will always be greater than twice the refractor depth.
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 intercept time?
intercept time The arrival time of a seismic wave, determined from the intercept of the extrapolation of the refracted straight-line segment of a time—distance graph at zero offset. A Dictionary of Earth Sciences. “intercept time .”
What are the limitations of seismic refraction?
Limitations. Both penetration and resolution of the refraction method is inferior to those of seismic reflection if both techniques use the same seismic source and work well in a given situation. Penetration with a hammer is usually up to 30 metres while greater penetration is achieved with explosives or weight drop.
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.
What affects critical distance?
The critical distance depends on the ratio (R) of the direct and reverberant sound. When the critical distance is close to the sound source, it indicates that the reverberation in the room is high. If the critical distance is distant from the sound source, the room has good absorbance.
What is the critical angle for refraction seismology?
A reflected wave enters and exits at the same angle of reflection. different layers. For refraction seismology, the critical angle is the most important angle value to understand. If angle (r) equals 90 interface. One can solve for the critical angle (ic) by calculating
What is seismic refraction?
Seismic refraction is a geophysical principle (see refraction) governed by Snell’s Law. Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, seismic refraction traverses ( seismic lines) are performed using a seismograph (s) and/or geophone (s), in an array and an energy source.
What is the critical distance of a refraction?
The critical distance is the distance at which the refracted wave is first observed according to ray theory (in real life it is observed already at smaller distances, this is due to finite-frequency effects which are not taken into account by standard ray theory).
Can portable seismic refraction equipment be used to make exploration holes?
However, through the use of the portable seismic refraction equipment, the number of borings or core holes required may be reduced and more intelligent location of these, exploration holes can be made.