Exploring the Earth Using Seismology

On January 17, 1994 a magnitude 6.9 earthquake near Northridge, California released energy equivalent to almost 2 billion kilograms of high explosive. The earthquake killed 51 people, caused over $20 billion in damage, and raised the Santa Susana Mountains north of Los Angeles by 70 centimeters. It also created seismic waves that ricocheted throughout Earth's interior and 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. 

 

Requesting Posters:

To request hardcopies of E&O materials, please send an email to EandOproduct@iris.edu with the following information:

  1. Names of item(s) you are requesting along with respective quantities.  Please list posters and one-pagers on separate lines.  
  2. Full mailing address, including phone number, where the materials should be sent.
  3. Indicate what purpose the materials will be serving.
  4. Date materials are needed by (if applicable).

PLEASE NOTE: Time-sensitive requests must be sent at least three weeks beforethe date they are needed.  When e-mailing a time-sensitive request, please write "Time-Sensitive Request" in the subject line.


Level: Intermediate

38MB

Optional Files 1 Resource also available in:
Share it

Related Lessons

Learning occurs as 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

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 Animations

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 to this animation.

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 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

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

Related Software-Web-Apps

Watch how earthquake and volcanic activity changes in space and time throughout the earth.

Software-Web-App Novice

The IRIS Earthquake Browser (IEB) is an interactive map 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 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

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.

Software-Web-App Intermediate