8 th Grade Notes Standard 17 Science Learning

8 th Grade Notes: Standard 17 Science Learning Intention: 8. ESS 2. 2 (Seismic Waves & Earth’s Structure) Evaluate data collected from seismographs to create a model of Earth’s structure. Terms/Phrases to Investigate data, seismograph, model, and structure Science and Engineering Practice(s) Develop and Use Models, Analyze and Interpret Data, Crosscutting Concepts Energy and Matter, Patterns, Stability and Change I Can Statement. . . I can create a model of Earth’s internal structure using seismic data.

Seismic Waves: Mechanical Waves Reminder: mech. waves need a medium to propagate (move through). Seismic waves transfer energy through rock formations in the Earth. …mainly caused by the sudden slippage of tectonic plates, but can also be generated by explosions or impacts. The medium’s effects include changes in wave speed, absorption, reflection, and/or refraction.

P-Waves A. K. A. primary waves and/or pressure waves Øare longitudinal waves Øfastest kind of seismic wave Øpushes/pulls as it moves through (called compression) ØCan propagate (move) through solid and liquid rock Øfirst wave felt during earthquakes (before S-Waves) Link (4 sec): P-Wave Animation

S-Waves A. K. A. secondary waves and/or shear waves Øare transverse waves Øonly moves through solid rock Øslower than P-Waves Øup/down or side to side motion Øsecond wave felt during earthquakes (after P-Waves) Link (5 sec): S-Wave Animation

Seismographs What is a seismograph? A. K. A. seismometer Ø an instrument that measures and records seismic waves Ø generally used for detecting and measuring earthquakes Ø also detects/measures volcanic events, explosions, and impacts Link (1: 04): How a Seismograph Works

Seismogram Ø a seismogram is the graph output from a seismograph. Seismogram from California Seismogram from Alaska Ø Richter Scale: a 1 to 9 scale for measuring seismic waves. Ø Each level is ten times greater than the previous level.

Locate anomalies in this seismic data. Then draw a model of Earth’s structure from this data. Crust Slowed Mantle Outer Core Repeated Slowed Repeated Inner Core Constant Stopped Repeated Question: Why did the S-Waves stop at 2900 km?

Draw a model of Earth’s structure from the data. Crust Depth: 0 to 50 km Outer Core Depth: 2900 to 5200 km Mantle Depth: 50 to 2900 km Inner Core Depth: 5200 to 6400 km

Earth’s Internal Structure P-Waves Ømove through solid and liquid rock S-Waves Øonly move through solid rock Link (5: 49): How We Know About Earth's Interior?

Earth’s Internal Structure Ø Seismic waves change speed and refract (bend) as they move through different rock layers. S-Waves stop at liquids. Ø Understanding this enabled us to analyze seismographic data which reveals Earth’s internal structure.

Review Question Layers of rock inside the Earth have been revealed by analyzing seismic data. Geologists have observed that seismic waves change speed as they move downward toward Earth’s center. What is one location where this is revealed in Seismic Data Table 01, and what best explains this phenomenon? a) At a depth of 2900 kilometers the P-Waves slowed from 7. 5 km/s to 0 km/s. This occurred because P-Waves are unable to travel through liquid rock. b) At a depth of 2900 kilometers the P-Waves slowed from 14 km/s to 8 km/s. This occurred as the wave hit the boundary of the mantle and the outer core.

Review Question Layers of rock inside the Earth have been revealed by analyzing seismic data. Geologists have observed that seismic waves can effect the speed of waves as they move downward toward Earth’s center. What is one location where this is revealed in Seismic Data Table 01, and what best explains this phenomenon? a) At a depth of 5200 kilometers the P-Waves slowed from 11 km/s to 10 km/s. This occurred because P-Waves are unable to travel through solid rock. b) After 5200 km, P-Wave speed was a constant 11 km/s all the way to Earth’s center. This occurred as the wave moved from the outer core through the inner core.

Review Question Layers of rock inside the Earth have been revealed by analyzing seismic data. Geologists have observed that seismic waves change speed as they move downward toward Earth’s center. What is one location where this is revealed in Seismic Data Table 01, and what best explains this phenomenon? a) At a depth of 50 kilometers the P-Waves decreased speed from 9 km/s to 8 km/s. This occurred as the wave hit the boundary of the crust and the mantle. b) At a depth of 2900 kilometers the P-Waves slowed from 7. 5 km/s to 0 km/s. This occurred because P-Waves are unable to travel through liquid rock.

Review Question Analyze the P-Wave and S-Wave speed patterns in Seismic Data Table 01 and 02. Then select the model below which best matches the data. (A) Model One (B) Model Two