Ground Roll Identification and Fresnel zone

  • Thread starter mcmzie
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  • #1
mcmzie
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(1) How do you identify Ground roll on a shot record?
Is it just the polarized nature of the ground roll that leads to its recognition on a shot record?

(2) What is the importance of the Fresnel zone? and What does it depend on?
 

Answers and Replies

  • #2
Integral
Staff Emeritus
Science Advisor
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You make the assumption that we know exactly what you are talking about.


Please tell us what you mean by ground roll and shot record?
 
  • #3
billiards
771
15
On a shot record it will be linear and high amplitude and quite steep (slow). On a single trace (or seismogram) it will be the late arriving packet of high amplitude energy at the end which tails off and sometimes is called the coda.

The Fresnel zone is the zone of sensitivity to the travel time of a ray, it depends on the wavelength of the ray. Did you know, the sensitivity of a ray's velocity is exactly zero to the velocity of the medium exactly on the ray path itself (in contrast to ray theory which adopts an infinite frequency approximation)? The travel time of a ray (a mathematical concept) is actually sensitive to the velocity of the medium around the ray, due to scatterers off the ray which interfere with the wavefront.
 
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