S and P waves from an earthquake travel at different speeds, and this difference
ID: 2032108 • Letter: S
Question
S and P waves from an earthquake travel at different speeds, and this difference helps in the determination of the earthquake "epicenter" (where the disturbance took place).
(a) Assuming typical speeds of 8.9 km/s and 5.5 km/s for P and S waves, respectively, how far away did the earthquake occur if a particular seismic station detects the arrival of these two types of waves 5.0 min apart?
____ km
(b) Is one seismic station sufficient to determine the position of the epicenter?
No or Yes
Explain.
Explanation / Answer
Given that Both waves travels same distance, which is
D = v1*t1 = v2*t2
also given that
t1 - t2 = 5 min
t1 = t2 + 5 min = t2 + 300 sec
v1*(t2 + 300) = v2*t2
we assumed that t1 > t2, So v1 < v2
v1 = 5.5 km/sec
v2 = 8.5 km/sec
5500*(t2 + 300) = 8500*t2
3000*t2 = 5500*300
t2 = 5500*300/3000 = 550 sec
t1 = 850 sec
D = v1*t1 = 5500*850 = 4675000 m = 4675 km
Part B.
No, one seismic station is not sufficient to determine the position of epicenter. Because the direction of waves in unknown. In general we need 3 seismic station to determine epicenter.
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