692 EXPLORATION GEOPHYSICS 



Fig. 427. — Two component seismograms recorded at right angles from one shot-point, 



indicates that pencil marks placed on the records make objectivity in the 

 restudy of the seismograms practically impossible. By not marking the 

 reflections, as is customarily done, this handicap to anyone restudying the 

 records is removed. 



Reflection Grade. — After the seismograms have been studied for 

 reflections and the individual reflections graded, the recorded data are 

 transferred from the seismograms to the computing form (see Figure 428). 

 Columns 1 and 2 contain the grade or quality of the reflection. The 

 grade designation depends somewhat on the experience and objectives of 

 the grader. It is usually possible to give four different grades, which may 

 be designated A, B, C and D, or G, F, P and VP, meaning good, fair, poor 

 and very poor. As stated in a subsequent section, the grade should be 

 based on more than just the appearance of the reflection. It should 

 consider filtering, the degree of mixing, the quality of the weathered correc- 

 tion, the possibility of wave interference, etc., and should give an approxi- 

 mate idea of the reliability of the final plotted result. 



Time Measurements. — Columns 3 to 9 contain the reflection times 

 and move-outs of the same reflections recorded at three different instrument 

 set-ups from the same shot-point, all corrected to datum elevation. In the 

 case at hand, i.e., the simple two-component recording, three of these 



