Much of what we know about Earth's interior comes from seismic waves generated by earthquakes. Seismic waves are waves of energy that travel through the Earth. Earthquakes produce three basic types of seismic waves: P waves, S waves, and surface waves. Each type has a different type of motion and travels through the Earth at different speeds. Scientists use seismographs to measure these waves, which helps them understand the structure and composition of Earth’s layers.

This post is part of Exploring Earthquakes, a rich collection of resources co-presented by the California Academy of Sciences and KQED. This material is also available as a free iBooks textbook and iTunes U course.

Don’t miss Earthquake, an interactive exhibit at the Academy exploring the seismic forces that impact us today and featuring the Shake House, an earthquake simulator.

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Exploring Earthquakes

Get a new perspective on earthquakes with this rich collection of multimedia resources. You'll learn why earthquakes happen, how they've shaped the Bay Area, and what you can do to prepare for the next one.

Teacher Guide: Earthquakes

Ideas for using videos, articles, and infographics about earthquakes in the classroom.