How do we really know what's inside the Earth? Imaging Earth's interior with seismic waves

Resource 22 Related Resources Lessons Fact-Sheets Animations Interactives Software-Web-Apps Posters How do we really know what's inside the Earth? Imaging Earth's interior with seismic waves Intermediate Resource Files Instructor Guide & Student Worksheets Haiti Record Section Earth Scale Model Blank Graph Slide deck Download All 9MB Students will be able to: -       Describe Earth’s internal structure (layers of different material properties and composition) and summarize how this is inferred through the analysis of seismic data -       Estimate the size of Earth’s core using a record section from a recent earthquake -       Describe how primary and secondary waves propagate through Earth Differentiate between Earth’s asthenosphere and lithosphere (layers of different mechanical properties) Objectives: Students will be able to: Describe Earth’s internal structure (layers of different material properties and composition) and summarize how this is inferred through the analysis of seismic data Estimate the size of Earth’s core using a record section from a recent earthquake Describe how primary and secondary waves propagate through Earth Differentiate between Earth’s asthenosphere and lithosphere (layers of different mechanical properties) Related Lessons Determining and Measuring Earth's Layered Interior Students work first in small groups, and then as a whole class to compare predicted seismic wave travel times, generated by students from a scaled Earth model, to observed seismic data from a recent earthquakes. This activity uses models, real data and emphasizes the process of science. Lesson Novice Build your own seismograph Working in small groups of 3-4,  students design and construct a seismograph using common household and craft materials provided. Students will demonstrate to the class (by shaking their table) how their seismographs records ground motion and if possible, the time of the disturbance occured.  Lesson Novice Related Fact-Sheets Exploring the Earth Using Seismology Earthquakes create seismic waves that travel through the Earth. By analyzing these seismic waves, seismologists can explore the Earth's deep interior. This fact sheet uses data from the 1994 magnitude 6.9 earthquake near Northridge, California to illustrate both this process and Earth's interior structure. NOTE: Out of Stock; self-printing only. Fact-Sheet Novice Related Animations Seismic Shadow Zone: Basic Introduction Seismic shadow zones have taught us much about the inside of the earth. This shows how P waves travel through solids and liquids, but S waves are stopped by the liquid outer core. Animation Novice Seismic Shadow Zones vs Light Shadows The wave properties of light are used as an analogy to help us understand seismic-wave behavior. Animation Novice Seismic Shadow Zones: P wave The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The different phases show how the initial P wave changes when encountering boundaries in the Earth. Animation Novice 1-Component Seismogram: Building responds to P, S, surface waves Seismic waves travel through the earth to a single seismic station. Scale and movement of the seismic station are greatly exaggerated to depict the relative motion recorded by the seismogram as P, S, and surface waves arrive. Animation Novice 3-Component Seismogram Records Seismic-wave Motion We use exaggerated motion of a building (seismic station) to show how the ground moves during an earthquake, and why it is important to measure seismic waves using 3 components: vertical, N-S, and E-W. Before showing an actual distant earthquake, we break down the three axes of movement to clarify the 3 seismograms.  Animation Novice 4-station Seismograph Network Records a Single Earthquake A cow and a tree in this narrated cartoon for fun and to emphasize that seismic waves traveling away from an earthquake occur everywhere, not just at seismic stations A, B, C, and D. A person would feel a large earthquake only at station A near the epicenter. Stations B, C, D, and the cow are too far from the earthquake to feel the seismic waves though sensitive equipment records their arrival. Animation Novice Travel-time Curves: How they are created A travel time curve is a graph of the time that it takes for seismic waves to travel from the epicenter of an earthquake to the hundreds of seismograph stations around the world. The arrival times of P, S, and surface waves are shown to be predictable. This animates an IRIS poster linked with the animation. Animation Novice Layers of the Earth The Earth has 3 main layers based on chemical composition: crust, mantle, and core. Other layers are defined by physical characteristics due to pressure and temperature changes. This animation tells how the layers were discovered, what the layers are, and a bit about how the crust differs from the tectonic (lithospheric) plates, a distinction confused by many. Animation Novice Seismic Tomography (CT scan as analogy) Seismic tomography is an imaging technique that uses seismic waves generated by earthquakes and explosions to create computer-generated, three-dimensional images of Earth's interior. CAT scans are often used as an analogy. Here we simplify things and make an Earth of uniform density with a slow zone that we image as a magma chamber. Animation Novice Seismic Shadow Zone: Basic Introduction Seismic shadow zones have taught us much about the inside of the earth. This shows how P waves travel through solids and liquids, but S waves are stopped by the liquid outer core. Animation Novice Seismic Shadow Zones vs Light Shadows The wave properties of light are used as an analogy to help us understand seismic-wave behavior. Animation Novice Seismic Shadow Zones: P wave The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The different phases show how the initial P wave changes when encountering boundaries in the Earth. Animation Novice Seismic Wave Behavior: Curving paths through the Earth Seismic waves travel a curving path through the earth due to changes in composition, pressure, and temperature within the layers of the Earth.  Animation Novice Related Interactives Shadow Zone Rollover Roll over the buttons to see the difference between P- and S-wave seismic paths as well as their respective shadow zones. Interactive Novice Shadow Zone Rollover Roll over the buttons to see the difference between P- and S-wave seismic paths as well as their respective shadow zones. Interactive Novice Related Software-Web-Apps IRIS Earthquake Browser The IRIS Earthquake Browser (IEB) is an interactive tool for exploring millions of seismic event epicenters (normally earthquakes) on a map of the world. Selections of up to 5000 events can also be viewed in 3D and freely rotated with the 3D Viewer companion tool.  Software-Web-App Novice Seismic Monitor A beautiful map of the latest earthquakes in near-real time. The map also provides links to related resources, news, and connections to 3D maps. Software-Web-App Novice Global Seismogram Viewer Easily view seismograms from stations around the world for large earthquakes. Plots can be used for a variety of activities including to determine the diameter of Earth’s outer core as part of a classroom exercise. Software-Web-App Novice Related Posters Exploring the Earth Using Seismology Seismic waves from earthquakes ricochet throughout Earth's interior and are recorded at geophysical observatories around the world. The paths of some of those seismic waves and the ground motion that they caused are used by seismologists to illuminate Earth's deep interior. Poster Intermediate