Extra Resources
- Background (PDF)
- Activities (PDF)
Preview the animations by pressing the play button on them. If you want to view a better version, click the links labeled "Direct Link to Animation". If YouTube is blocked, click the "Direct Link" and wait for it to load.
To save a video, right click one of the Direct Link's below and choose "Save As...".
Introduction
A travel time curve is a graph of the time that it takes for seismic waves to travel from the epicenter of an earthquake (time and distance = zero) to seismograph stations varying distances away. The curves are the result of analyzing seismic waves from thousands of earthquakes, received by hundreds of seismic stations around the world. They are used by seismologists to quickly locate earthquakes. For introductory purposes, we animate only the direct P (red) and S (blue) waves that travel through the crust and mantle, plus the surface (yellow) waves that travel in the shallow crust. We ignore the reflected and refracted waves. By using what we know about the velocity of seismic waves through different materials, seismologists are able refine what we know about Earth’s deep interior.
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.
Direct Link to Creating Travel-time Curves - 6.8MB Quicktime
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.
Direct Link to Static Buildings Version - 4.4MB Quicktime
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.
Direct Link to Earthquakes Scattered Across the Globe - 4.4MB Quicktime
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.
Direct Link to Earthquakes Equidistant from Seismograph Station - 4.4MB Quicktime
Animations By Jenda Johnson Please send any comments or questions to .(JavaScript must be enabled to view this email address)
