Fall 1996
You will "lay out" one spread of 12 geophones, and record data on this spread for each of several "shots." In this experiment, the shot, or energy source, consists of the blow from a hammer striking a plate set on the ground. Individuals in the class with be swinging the hammer.
You will acquire reverse-profile data; that is you will acquire and analyze data recorded by a given geophone spread from individual shots on opposite sides of the spread. Without such information from the two opposite sides, it would be impossible to estimate the dip of the refracting interface or to extract the true refractor velocity from the measured apparent velocity.
Your laboratory report should be written up following the guidelines handed out in class. Include in your writeup the reasons for the choices of parameters such as geophone separation, shotpoint spacing, reason for using reverse profile, etc. Essential results that should be included are listed below.
From measurements made on the direct arrival and subsequent refraction arrivals, you are to estimate (assuming we image only a single interface)
1. The wave speed (seismic velocity) in the uppermost layer
2. The wave speed in the refracting layer
3. The depth and dip of the refracting interface
This is assuming we image only a single interface. If we image more than one interface, you should also estimate the velocity of the third layer, the thickness of the second layer, and the dip of the second interface (as in Burger Chapter 3).
It is likely that the strongest refraction arrival will come from bedrock, as seismic velocity typically increases rapidly at the alluvium/bedrock interface (of course this depends on what the bedrock is). However, these areas have not been explored with seismic techniques before, so we will have to see what the data tell us!
Recommended reading: Burger, Chapter 3.