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.
Shear waves (S waves), for example, travel through the Earth at approximately one-half the speed of compression waves (P waves). Stations close to the earthquake record strong P, S, and Surface waves in quick succession just after the earthquake occurred. Stations farther away record the arrival of these waves after a few minutes, and the times between the arrivals are greater.
The tool also illustrates how seismic waves inform our current understanding of Earth’s interior structure. Users will see that between approximately 104 and 140 degrees away from the epicenter, direct P waves do not arrive as they are refracted away from this zone. This suggests the presence of a lower velocity material, Earth’s outer core. Users will also observe that no direct S waves arrive beyond 104 degrees.