## Determining and Measuring Earth's Layered Interior - Online Student Exploration

Novice

New Version! Major Update!

- New color pallet!
- Interactive questions with feedback for students!
- Improved instructions!
- Embedded instructional videos!

In this learning app, students compare observed seismic data to predictions they make from a model, to determine that the Earth must have a layered internal structure and to estimate the size of Earth's core. In the first step students examine seismic data from a recent earthquake to determine when seismic waves arrived at various points around Earth (observations). Then they use a model that is assumed to have a homogeneous interior with an average seismic wave velocity, to make predictions about when seismic waves should arrive at various points around Earth (predicted data). Students then compare their observations with their predictions to test the hypothesis that the Earth is homogeneous throughout. After comparing and discussing the fit of the predicted data with the observed data, students use a second scale model to further interpret these results. Ultimately, students measure the diameter of Earth's outer core based on their data and can compare it to widely accepted measurements.

#### Objectives:

Students will be able to:

• Demonstrate that Earth can’t be homogenous by comparing a seismic record section to predicted arrivals from a homogeneous Earth model.
• Explain how the internal structure of Earth (concentric layers of different density and composition) is inferred through the analysis of seismic data.
• Explain how models can be used in the scientific process to make predictions that can be compared to observational data.

## Related Lessons

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

Like other waves, seismic waves obey the laws of physics. In this activity Physics students have the opportunity to apply their understanding of the basic concepts of waves (e.g. reflection, refraction and transmission of energy) as they examine seismic data to determine how far it is from the surface to the bedrock.

Lesson Intermediate

## Related Software-Web-Apps

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

Seismic Waves is a browser-based tool to visualize the propagation of seismic waves from historic earthquakes through Earth’s interior and around its surface. Easy-to-use controls speed-up, slow-down, or reverse the wave propagation. By carefully examining these seismic wave fronts and their propagation, the Seismic Waves tool illustrates how earthquakes can provide evidence that allows us to infer Earth’s interior structure.

Software-Web-App Novice

## Related Animations

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 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

The wave properties of light are used as an analogy to help us understand seismic-wave behavior.

Animation Novice

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

The shadow zone results from S waves being stopped entirely by the liquid core. Three different S-wave phases show how the initial S wave is stopped (damped), or how it changes when encountering boundaries in the Earth.

Animation Novice

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

## Related Fact-Sheets

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.

Fact-Sheet Novice

## Related Posters

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

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