What's Inside the Earth? (Peru, June 2024)

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  • What's Inside the Earth? Peru
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On June 28, 2024 a magnitude 7.2 earthquake near the coast of Peru. The area experienced 5 foreshocks and 4 aftershocks along with the main earthquake within a 12-day period. No deaths were reported but it initiated a tsunami warning. This earthquake was the result of shallow thrust faulting from the Nazca tectonic plate subducting under the South America plate. It created seismic waves that ricocheted throughout Earth's interior which were recorded at geophysical observatories around the world. The paths of some of those seismic waves and the ground motion that they caused are shown in this poster. Seismologists use these recordings to explore the Earth's deep interior.

Keypoints:

  • Seismic waves propogate outwards from an earthquake in all directions.
  • Seismologists use the recordings of the ground motion caused by these waves to explore the Earth's deep interior.
  • We do not see shear (S) waves passing through the outer core. Because liquids can not be sheared, we infer that the outer core is molten.
  • We do, however, see S waves as they go through the inner core. Because the inner core transmits shear energy, we assume it is solid. 
Wave Propagation: Ripples on a Pond
Video Novice
What's Inside The Earth? An Exploratory Interactive Poster
“What’s Inside the Earth?" is an interactive digital poster designed to engage learners in exploring the vital role seismic waves play in determining the composition and structure of Earth's interior. 
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Station Monitor
Explore earthquakes near you or from around the globe using the new IRIS Station Monitor app! Select from hundreds of seismic stations throughout the world. View up-to-the-minute recorded ground motions or see recordings from previous days and past events. Get information about recent events and choose to annotate wave arrivals.
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.
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Seismic Waves Viewer
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
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
jAmaSeis
jAmaSeis is a free, java-based program that allows users to obtain and display seismic data in real-time from either a local instrument or from remote stations.
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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: S wave shadow zone
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
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.
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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 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
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
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.
Fact-Sheet Novice
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

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