15. If the incident angle is 45 degrees and the seismic velocity in the first medium is a reasonable value for sediments, and the seismic velocity in the second medium is 4 times slower than in the first medium, then the refracted angle a. Is less than 45 degrees. b. Is more than 45 degrees. c. Is 45 degrees. d. Cannot be determined given this information. 16. Assume that the earth is represented by a horizontal layer overlying a half-space. A simplest refraction survey with minimum instrument requires a. one shot and one geophone b. one shot and two geophones c. one shot and three geophones d. two shots with two geophones 17. You carried out a single-shot seismic reflection survey to find the depth to the basement and the velocity structure. Exact knowledge about the material above the basement and the shape of the basement interface was not known. After carrying out the survey he picked out the first arrivals and plotted the T-X graph as below. What conclusion can you make? a. he can only see one refraction so there is only one layer overlaying the basement b. he can determine the velocity of the basement by measuring the slope of the dashed line c. he can estimate the critical angle using the intercept time of the refraction arrival d. none of the above T 18. The acoustic impedance of a medium a. is equal to the value of the seismic velocity b. depends upon the product of density and velocity c. depends upon the ratio of density and velocity d. depends upon velocity and bulk modulus 19. "Seismic reflections can occur when only when there is a change in seismic velocity". (This is a Right – Wrong question for a final mark. Correct gets one mark; wrong loses a mark) a. TRUE b. FALSE c. Collecting seismic measurement requires contact with the ground while collecting magnetic data can be done at the surface or airborne. d. All of the above 20. Acoustic impedance is used to describe the efficiency of seismic reflection and transmission. Its value depends upon a. critical angle and velocity b. velocity and density c. reflection and transmission coefficients d. layer thickness and velocity