Where do travel-time graphs come from?


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Travel Time Curves

  • For background on this animation series, download Background from the Resources box.

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Creating Travel-time Curves

IRIS’ travel times graphic for the 1994 Northridge, CA earthquake (described in No.5. Exploring the Earth Using Seismology) is animated to show how travel times are determined. Seismic waves “bounce” the buildings to merely to illustrate arrival times and wave behavior, not to depict reality. The resultant seismograms show that stations around the world record somewhat predictable arrival times. 

Quicktime (6.8 MB)

Static Buildings Version

This version of the animation eliminates the unrealistic building bounce of the upper animation. Although seismographs do record the movement seen in the seismograms, only areas close to the epicenter would feel the event. Instruments are calibrated to record distant long- period events that travel  unfelt across the globe. 

Quicktime (4.4 MB)

Earthquakes Scattered Across the Globe 

This animation uses a gridded sphere is to show that: 

1) the seismic stations don’t need to be lined up longitudinally to create travel-time curves, as they appear in the first animation, and 

2) a single station records widely separated earthquakes that plot on the travel-time curves. 

Remember, a lone seismograph station can only tell how far away the earthquake is, not where it occurred.

Quicktime (4.4 MB)

Earthquakes Equidistant from Seismograph Station

This animation uses a gridded sphere is to show a single station recording five equidistant earthquakes. For demonstration, we are assuming that each earthquake is about a magnitude 7 and the seismic waves are traveling through similar material, thus the seismograms are all the same. 

All the seismologist would know about any of the earthquakes is that they occurred somewhere on the dashed circle in the last frame. 


Quicktime 4.4 MB


Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.

Please send feedback to Jenda Johnson.