Observed and predicted P wave arrivals Questions for discussion following the graphing of the data How does our model data match the observed data? What does this imply about our hypothesis that Earth’s interior might consist of a homogenous material with a constant velocity of 11 km/s? How do travel times from the observed stations compare to the model stations at similar geocentric angles? What are the assumptions of your model? How accurate you think your measurements are and what effect that has on your results? Are there any difficulties you had? What were their impacts on our results? What does this mean in terms of reality? What might this look like on a cross-section of Earth? Lead students to the idea that another scale model might be useful in helping us visualize both the data and allow us to further explore its implications. Observed and predicted P wave arrivals

How does this anomaly in the data translate back to Earth? Instruct students to Indicate the epicenter at zero degrees How does this anomaly in the data translate back to Earth?

Measure the geocentric angle from the epicenter to the anomaly in the data (108 degrees for example). Use your ruler to connect the epicenter to the mark you just drew on Earth’s surface.

Next, repeat this procedure to the bottom of the circle Sample Discussion Questions: What have we determined so far? What sort of structure has the seismic data helped us does this scale model of the P-wave shadow zone help us determine? How? How have we used the seismic waves to help use develop this picture? What might this be similar too? Shape the discussion to lead students to the concept of a shadow. Next, repeat this procedure to the bottom of the circle

Like a tree making a shadow, something is blocking the energy Like a tree making a shadow, something is blocking the energy. Can we tell what it is? Sample Discussion Questions: What have we determined so far? What sort of structure has the seismic data helped us does this scale model of the P-wave shadow zone help us determine? How? How have we used the seismic waves to help use develop this picture? What might this be similar too? Shape the discussion to lead students to the concept of a shadow. But point out that any of the shapes below could fit within the shadow and generate it. We need more earthquakes to further define the shape. While no direct P-waves arrive there it is important to emphasize to students that both P waves and S waves do in-fact arrive in the P-wave shadow zone. The p waves that do arrive have either been reflected, refracted to arrive in this zone. This is very similar to a students shadow on the ground. Their shadow is not the absence of all light. Rather it is an area that is not able to receive direct light but does receive light that has refracted around the student or has reflected off of nearby object

Cut out this shape from your model

Lay the cut out from Earth A on top of Earth B and trace along its edges (indicated with orange)

Next, rotate the cut out and continue to trace its edges What do you think this new inner circle represents?

Closing thought question for students: Considering that seismic evidence for Earth’s core was discovered only in 1906 is it possible that the current model may require further refinements? Actual radius of the core = ~3486km