Geologists use explosives to map the subterranean.The times for the reflected waves to arrive at a monitoring station can tell a great deal about the composition of the rock structures.Suppose the time it takes for a wave that is reflected from the interface of (1)and (2)is 2 s,and the time for another wave that is reflected between (2)and (3)is 2.5 s and the speed of the wave in layer (1)is 6 km/s and in layer (2)is 4 km/s,how thick is layer (2)?
A)2 km
B)1 km
C)3 km
D)6 km
E)8 km

Question

Geologists use explosives to map the subterranean.The times for the reflected waves to arrive at a monitoring station can tell a great deal about the composition of the rock structures.Suppose the time it takes for a wave that is reflected from the interface of (1)and (2)is 2 s,and the time for another wave that is reflected between (2)and (3)is 2.5 s and the speed of the wave in layer (1)is 6 km/s and in layer (2)is 4 km/s,how thick is layer (2)? 
A)2 km 
B)1 km 
C)3 km 
D)6 km 
E)8 km

Quizplus · Accepted Answer

We can use the formula for wave reflection time:

time = 2 × depth / velocity

First, we can use the information given to find the depth of layer (1):

2 = 2 × depth / 6

6 = 2 × depth

depth = 3 km

Next, we can use the same formula to find the depth of layer (2):

2.5 = 2 × depth / 4

10 = 2 × depth

depth = 5 km

The thickness of layer (2) is the difference between the depths of (2) and (1):

thickness of layer (2) = 5 km - 3 km = 2 km

Therefore, the best choice is B) 1 km.

Geologists Use Explosives to Map the Subterranean