9/19/02
Name:
Laboratory Exercise 4
Seismic Reflection Acquisition Survey
We will set up the seismograph and a string of 12 geophones with a 3 m interval and collect six sets or lines of data. One data set/line will be with a 45 meter offset between the shot and the first geophone. The second data set/line will be with a 39 meter offset. . The third data set/line will be with a 33 meter offset and so on (see Ray Path Figure on back). The geophone locations will be the same for each data set/line.
We will divide into six groups of three or four students. Each group will be responsible for collecting one of the six lines of data. In addition, each group will be assigned a Common Depth Point (CDP) and a Common Offset value (see list below).
Group 1 ; shot offset - 45 m, ;CDP - 39, ;common offset - 54
Group 2 ; shot offset - 39 m, ;CDP - 37.5, ;common offset - 51
Group 3 ; shot offset - 33 m, ;CDP - 40.5, ;common offset - 36
Group 4 ; shot offset - 27 m, ;CDP - 36, ;common offset - 39
Group 5 ; shot offset - 21 m, ;CDP - 42, ;common offset - 48
Group 6 ; shot offset - 15 m, ;CDP - 34.5, ;common offset - 45
For your laboratory report, you should turn in the following:
1. A sketch of the ray paths for source to reflector to geophones 1, 4, 8, and 12 from your survey. Assume that the horizontal reflector depth, h, is 25 m. Estimate the arrive time for the reflected p-wave at geophones 1-12 using the formula time = ([x2 +4h2]1/2)/V1. Assume that the velocity is 350 m/sec.
2. A sketch of the ray paths from source to your group's common depth point (CDP) to geophone for ALL surveys (up to 6). Estimate arrive time for each CDP reflected p-wave using the formula and values given in part 1.
3. A sketch of ALL ray paths from source to reflector to geophone from all surveys that have your group's common offset value between shot and geophone (up to six). Estimate arrive time for each common offset reflected p-wave using the formula and values given in part 1.