Earthquakes produce several types of shock waves. The most well-known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the earth's crust, the P-waves travel at around 6.5 km/s while the S-waves move at about 3.5 km/s. The actual speeds vary depending on the type of material they are going through. The time delay between the arrival of these two waves at a seismic recording station tells geologists how far away the earthquake occurred.

The given question is incomplete. The complete question is as follows-

Earthquakes produce several types of shock waves. The most well-known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the earth's crust, the P-waves travel at around 6.5 km/s while the S-waves move at about 3.5 km/s. The actual speeds vary depending on the type of material they are going through. The time delay between the arrival of these two waves at a seismic recording center tells geologists how far away the earthquake occurred. If the time delay is 73 s, how far from the seismic station did the earthquake occur?

553.6 km

Explanation:

Given that,

speed of P-wave = 6.5 km/sec

Speed of S-wave = 3.5 km/sec

Delay time is given to be = 73 seconds

Distance is needed to find,

Since, the distance covered by P wave in 't' seconds, and S wave in "t + 73" seconds

Now, Distance = Speed × Time

⇒ Distance = Speed × (t+73 sec)

For P wave, distance is, D = Pt   ...... equation (1)

and for S wave, distance is, D = S(t+73) ...... equation (2)

As, both the distances are the same, means equation (1) and (2) being equal,

Pt  = S (t + 73)

Pt = St + 73 S

Pt ₋ St = 73 S

t (P ₋ S) = 73 S

t =

Putting this value of t in equation (1), we get,

D = Pt =

Now, by substituting the values of speed of P and S waves in it, we get-

Distance = \frac{73 \times 6.5 \times 3.5 }{6.5 - 3.5}

Therefore, distance = 553.6 kilometers.

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