What is delay time in seismic refraction?
Abstract. “The Delay-Time Method” is a method utilizing the amount of calculated time required for the overburden between the surface and the refractor, and is the difference between the hypothetical time measured if the refractor were on the surface and actual time measured.
What is the 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 does seismic refraction measure?
The seismic refraction method utilizes the refraction of seismic waves by rock or soil layers to characterize the subsurface geologic conditions and geologic structure.
How do you measure the depth of a reflector?
1 Expert Answer For a parabola with vertex(0,0) the equation of the parabola is y = x2/4p where p is the ordinate of the focus, in this case: y=x2/14. The depth of the reflector is the ordinate where y=3.5.
What are the factors needed for refraction to occur?
For refraction to occur substances must be transparent and light ray must pass from region of one index of refraction to another i.e. both substances should have different refractive indices should and the light ray must impinge at an angle other than normal which must not be less than the critical angle.
What are seismic gathers?
A gather is a collection of seismic traces which share some common geometric attribute. The term gather usually refers to a common image point (CIP) or common mid-point (CMP) gather. The stereotypical gather: traces or sorted by surface geometry to approximate a single reflection point in the earth.
What do you need to know about the intercept time?
The information of the intercept time is needed to obtain the depth of first layer using intercept time method which its analysis is described in the next section. The line of reflected energy of the P-waves (V2) which is project back to the time axis to intersect it at a time is called the intercept time.
How is the seismic refraction method used in NDT?
One of NDT which is based on the Primary waves (P-waves) propagate in the layered profile is the seismic refraction method. The method calculates the time intercept of refracted P-waves to find the P-waves velocity and the thickness of the layered profile.
How to calculate the arrival time of a refracted wave?
From elementary geometry it follows that the arrival time trefrof the refracted wave as a function of distance ∆ is given by Travel time refracted wave 1 22 2cos v t v v h i ti refr c refr ∆ = + ∆ = +(5) which is a straight line which crosses the time axis ∆=0 at the intercept time ti refrand has a slope 1/v2.
What is the Book of standards for seismic refraction?
Book of Standards Volume: 04.08 5.1.1 This guide summarizes the equipment, field procedures, and interpretation methods used for the determination of the depth, thickness and the seismic velocity of subsurface soil and rock or engineered materials, using the seismic refraction method.