Where do travel-time graphs come from?
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 seismograph stations at varying distances away. The velocity of seismic waves through different materials yield information about Earth's deep interior. 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 illustrate arrival times and wave behavior, not to depict reality. The resultant seismograms show that stations around the world record somewhat predictable arrival times.
- Time vs. distance graph of P and S seismic waves
- Seismic waves recorded at different points are a function of distance from the earthquake
- Seismic velocities within the earth have been calculated from these data