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This article explores the study of seismology and how seismic waves help scientists understand the structure and composition of the Earth's interior. It also explains seismometers, seismograms, travel-time curves, and the paths of P-waves and S-waves. The article concludes with the discoveries made about Earth's structure and composition through the study of seismic waves and meteorites.
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19.2: SEISMIC WAVES AND EARTH’S INTERIOR OBJECTIVES: STA NDARDS:
1. What is seismology? What do seismologists study? Explain. • Seismology: the study of earthquake waves. • Seismologist study: • Disasters caused by earthquakes • Seismic waves that penetrate Earth’s interior help scientists to develop models of Earth’s internal structures.
2. What is a seismometer? Explain in detail how they work. • Seismometer: (also called a seismograph) Instrument used to measure horizontal or vertical motion during an earthquake.
CON’T #2: Explanation of how seismometers work: • Vibrations/seismic waves are detected and recorded • This movement is recorded on the paper or stored in a computer – called a seismogram. Some seismometers consists of : • a rotating drum covered with a sheet of paper • a pen or recording tool • a frame anchored in the ground and a mass suspended from a spring or wire • Mass stays at rest as ground and frame shake during an earthquake
What is a seismogram? Draw and label a seismogram (see fig. 19.8 pg. 501) • Seismogram: record produced by a seismometer that can provide individual tracking of each type of seismic wave.
4. Describe a Travel-Time Curve. • Time-travel Curves: • Show the time it takes for the p-waves and s-waves to travel to seismometer stations.
#4 CON’T • P-waves arrive first • S-wave arrive second • Surface waves arrive third • With increasing travel distance, the time separation between the p-wave and s-wave also increases • Can be used to determine the distance from the epicenter of a quake
5. Describe the path of p-waves and s-waves as they travel through Earth’s interior.
5. Path of p-and s-waves as they travel through Earth’s interior. Seismic waves change speed and direction when they encounter different materials. P-waves • Flow direct in the mantle • When they reach the core they are reflected or bent • About 11,000km from the epicenter they disappear • no direct p-waves • Remerge about 16,000km • Between 11,000km and 16,000km = shadow zone
5. Path of p-and s-waves as they travel through Earth’s interior. S-waves • Flow direct in the mantle • Disappear at Earth’s core – cannot travel through liquid • Do not reappear at 11,000km – therefore scientists believe that Earth’s outer core is liquid • inner core is solid.
6. By studying seismic waves, what have scientists discovered about Earth’s structure and composition? • Seismic waves provided detail about Earth’s structure and composition • Seismologists study seismic wave travel time and have determined: • Lithosphere composition: (crust and upper mantle ) • Igneous rocks – granite, basalt, and peridotite • Crust mostly peridotite – containing olivne • Mantle composition: • In the asthenosphere – partially melted Peridotite • Lower mantle is solid – oxides containing iron, silicon and magnesium • Core composition: • Inner part – very dense – probably made of iron and nickel
6. By studying seismic waves, what have scientists discovered about Earth’s structure and composition? Earth’s Composition • Supported by study of meteorites – pieces of asteroids • Formed in the same way the solar system formed • Consist of iron, nickel, and rock similar to peridotite (similar portions to that of Earth) • Meteorites and travel time of seismic waves have helped scientists to INDIRECTLY probe at the composition and structure of Earth’s interior.
