Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Earth Systems 3209 Unit: 4 The Forces Within Earth Reference: Chapters 4, 15, 16, 19; Appendix A & B

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Properties of Seismic Waves Unit 4: Topic 4.3 Focus on...  identify the different seismic waves and describe the properties of each.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Seismic Waves  The source of an earthquake is called the focus and the epicenter is the point on Earth’s surface directly above the focus.  Seismic waves originate at the focus and travel outward in all directions. These energy waves are classified as; 1) Body Waves:  Primary Wave  Secondary Wave  Rayleigh Wave  Love Wave 2) Surface Waves: Text Reference Pages

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador 1)Primary Wave (P-Wave)  P-waves move by compressing and expanding (push-pull motion) the material as it travels. Much like sound waves. Compression RarefactionVibration Direction  Vibrate in the same direction as wave motion.  These waves can pass through solids, liquids, and gases.  These waves have the greatest velocity (6 km/sec) and are the first to reach the seismograph stations.  Originate from the focus and travel in all directions through the body (Interior) of the Earth. Seismic Waves – Body Waves

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador 2)Secondary Wave (S-Wave)  S-waves travel through material by shearing it and vibrate in a direction perpendicular to the wave motion. Vibration Direction  These waves are much like the waves on the ocean.  These waves travel through Earth slower (3.5 km/sec.) and are the second to reach seismograph stations.  Because liquids and gases have no shape, these waves do not pass through liquids or gases, only trough solids. Seismic Waves – Body Waves  Originate from the focus and travel in all directions through the body (Interior) of the Earth.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Surface waves behave like S-waves in that they cause up and down and side to side movement as they pass, but they travel slower than S-waves.  Surface waves differ from body waves in that they do not travel through Earth’s interior, but instead travel along paths nearly parallel to the surface of Earth. Seismic Waves – Surface Waves

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador 1)Love Wave  Surface waves that cause horizontal shearing of the ground. They move in much the same way as a snake slithering across the ground.  Vibrate in a perpendicular direction compared to that of wave motion.  Surface waves are the most destructive and cause the most damage. Direction of Motion Seismic Waves – Surface Waves

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador 2)Rayleigh Wave  Surface waves that cause both horizontal (side-to-side) and vertical (up and down) movement within the ground.  Vibrate in a rolling motion in the same direction as wave motion.  Most of the shaking felt from an earthquake is due to these waves and these waves are the most destructive and cause the most damage. Direction of Motion Seismic Waves – Surface Waves

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Seismograph and Seismogram  P-waves, S-waves, and Surface waves are all recorded on the seismogram as seen below:  These paper records are important when seismologist wants to locate the position of the epicenter of an earthquake.  Seismologist can determine the difference in arrival times between the P-wave and the S-wave.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Seismic Waves - Comparison

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 1: Which description best describes p-waves? A)they move back and forth (compressional wave) and travel through any material. B)they move back and forth (compressional wave) and move only through solids. C)they move side to side (transverse wave) and only travel through liquids. D)they move side to side (transverse wave) and travel through any material. Which seismic wave is the first to reach a seismic station? A)primary wave B) love wave C) secondary wave D) rayleigh wave

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 2: Body waves consist of ________? (A)Primary waves (B)Secondary waves (C)Love waves (D)Both Primary and Secondary waves Which wave is the fastest and moves in a push-pull motion? (A)L (B) primary (C) S (D) Surface

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Your Turn... Take the time and complete the following questions... (Solutions to follow) Question: Contrast the characteristics of Primary and Secondary waves.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Solutions... Question: Answer: P - wave Push - pull waves which vibrate in the same direction in which they move. Fastest earthquake wave and is the first to arrive at seismograph stations. Pass through all states of matter, solids, liquids, and gases. S - wave Shake the particles which cause them to vibrate in a perpendicular direction to their motion. Slower than P - wave and is the second earthquake wave to arrive at seismic stations. Pass only through solids.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Summary... Overview of Points covered: 2 Categories of Seismic Waves: 1)Body Waves  Primary  Secondary 2)Surface Waves  Love  Rayleigh