9/5/02
Name:
Laboratory Exercise 2
Seismic Refraction
PART I - Homework Problems
1. What is the wavelength of a 10 Hz wave propagating through bedrock with a velocity of 4500 m/s? What is the wavelength of a wave with a frequency of 150 Hz?
2. A sandstone has a density of 2300 kg/m3, a Young's modulus of 0.14 x 1011 N/m2, and a Poisson's ratio of 0.2. How long will it take a compressional wave to travel 50 m?
3. A rock unit (P-wave velocity = 2500 m/s, S-wave velocity = 1200 m/s) is underlain by a layer with a compressional wave velocity of 4000 m/s and a shear wave velocity of 2000 m/s. Calculate the angles of refraction and reflection for the P- and S-waves produced by an incident P-wave with an angle of incidence of 18°. At what angle of incidence would a compressional head wave be produced?
PART II - Seismic Refraction Acquisition Survey
We will divide into two groups. The first group will work with Robert Little to set up a 12 geophone refraction survey. The second group will work with Dr. Nunn to continue discussion of ray paths and strategies for seismic acquisition surveys.
A. Seismic Refraction Survey - In this section, your group will set up the geophones and the seismograph and collect two sets of data. One data set will be with a 3 meter offset between the shot and the first geophone. The second data set will be with a 30 meter offset. For each survey, please record each step in the step up and acquisition of data and turn it in next week.
B. Ray Path Strategies - In this section, we will examine several different strategies for acquiring seismic data: forward and reverse, split spread with center shot, common offset, and common depth point. Please provide simple sketches of several ray paths that illustrate each technique and turn it in next week.