1. Guided Notes for Seismic Waves and Earth’s Interior
Section 19.2

2. The study of earthquake waves is called seismology.

3. 2) Define seismometer
A seismometer is an instrument used to measure horizontal and vertical motion during an earthquake

4. 3) How a seismometer records seismic waves
A frame is anchored to the ground and a mass is suspended from a spring or wire. The frame vibrates with the ground during an earthquake while the mass is still. The movement of the frame is transferred to the paper with a recording tool attached to the mass.

5. 4) After many years, seismologists have been able to construct global travel-time curves for the initial P-waves and S-waves of an earthquake. These general curves have provided the average travel times of all seismic waves for different distances, no matter where on Earth an earthquake occurs.

6. 5) For any distance from the epicenter, P-waves always arrive first
5) For any distance from the epicenter, P-waves always arrive first. With increasing travel distance, the time separation between P-waves and S-waves increases. This means that waves recorded on seismograms from more distant facilities are farther apart than waves recorded on instruments closer together.

7. 5) continued….
This separation of seismic waves on seismograms can be used to determine the distance from the epicenter of a quake to the seismic facility that recorded the seismogram.

8. 6) P-waves that strike the earth’s core are refracted, or bent, so that beyond a distance of 11,000 km from the epicenter, they disappear. P-waves re-emerge at a distance of 16,000 km from the epicenter. The region between these two distances doesn’t receive direct P-waves and is known as the shadow zone.

9. 7) S-waves do not enter the Earth’s core because they cannot travel through liquids. The disappearance of S-waves has allowed seismologists to reason that the earth’s outer core is liquid.