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).
How do you calculate 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.
Why is the crossover distance important?
cross-over distance (x c) The distance on a seismic refraction survey time-distance chart at which the travel times of the direct and refracted waves are the same. This distance also marks the point when the refracted wave overtakes, and thus arrives before, the direct wave.
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 seismic refraction method?
The seismic refraction method utilizes the refraction of seismic waves by rock or soil layers to characterize the subsurface geologic conditions and geologic structure. The waves are refracted when they cross the boundary between different types (or conditions) of soil or rock.
What is critical refraction?
When light passes from one medium (material) to another it changes speed. When light speeds up as it passes from one material to another, the angle of refraction is bigger than the angle of incidence. For example, this happens when light passes from water to air or from glass to water.
What is Dix equation?
Dix formula The equation by which the interval velocity (v int) can be calculated for a zone between two depths on a seismic section. For two reflectors with reflected-ray travel times t 1 and t 2, and root-mean-square velocities v rms1 and v rms2 respectively, then: v int = [(t 2v rms2 2 – t 1v rms1 2)/(t 2 – t 1)] ½.
What is 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.
What is the difference between seismic reflection and refraction?
In seismic reflection method the waves travel downward initially and are reflected at some point back to the surface, the overall path being essentially vertical. Whereas, in seismic refraction method, principal portion of the wave-path is along the interface between the two layers and hence approximately horizontal.
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 refraction method?
What is a denser medium?
A medium is denser when the speed of light gets reduced when light travels through that medium. When water travels through water, its speed gets reduced. Hence, it is a optically denser medium. Speed of light in air is more than speed of light in water, which means water is optically denser than air.
Which is the cross over distance of a refracted wave?
Cross-over distance is defined as the position where the refracted wave overtakes the direct wave. cyclist and motorist. Imagine a cyclist and motorist depart from the Fall AGU meeting in San Francisco. Both are traveling to a field excursion north of the Golden Gate Bridge in the Marin Headlands.
What is the critical distance and crossover distance?
The critical distance is the closest surface point to the source at which the refracted ray can be observed. The crossover distance is the surface point at which the direct and refracted rays arrive at the same time.
How to calculate travel time of a reflected wave?
The travel time for the reflection is given by travel time reflected wave 2 2 1 ( /2) 2 h v trefl = ∆ + (3) In refraction seismology this arrival is often of minor interest, as the distances are so large that the reflected wave has merged with the direct wave. Note that this has the form of a hyperbola.
How is the slope of a refracted wave defined?
On the T-X plot, the direct passing through the origin. The slope of this interpolated line is time over distance, or the inverse of velocity. The slope of lines on the T-X plot is termed slowness. representing the refracted wave. The distance between the source and distance. Cross-over distance is defined as the position where the