Earthquakes produce several types of shock waves. The best known are the P-waves

Question

Earthquakes produce several types of shock waves. The best known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the earth's crust, P-waves travel at around 6.40 { m km}/{ m s} while S-waves move at about 3.50 { m km}/{ m s}. (The actual speeds vary with the type of material the waves are going through.) The time delay between the arrival of these two types of waves at a seismic recording station tells geologists how far away the earthquake that produced the waves occurred.
f the time delay at a seismic station is 38.0 { m s}, how far from that station did the earthquake occur?
One form of earthquake warning system detects the faster (but less damaging) P-waves and sounds an alarm when they first arrive, giving people a short time to seek cover before the more dangerous S-waves arrive. If an earthquake occurs 373 { m km} away from such a warning device, how much time would people have to take cover between the alarm and the arrival of the S-waves?

Explanation / Answer

The knowns for this problem are:

1. P waves travel 6.4km/sec
    S waves travel 3.5 km/sec

P waves are almost twice as fast, and that is why they can be read to use as a warning for the coming slower, more dangerous S waves.

Two questions:
2. If time delay is 38 sec from quake to station, how far from quake?
38 sec divided by 6.4 km/sec 5.93 km
So the answer is the quake is about 5.93 km from the station.

3. If quake is 373 km from people, how long of a warning before S waves arrive?
373 km divided by 6.4 km/sec 58.28 sec
So the answer is the people have about 58.28 seconds before the quake arrives.

I hope this is helpful! Good luck!

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.