The time vs. distance graph of P, S, and surface
wave arrival times was constructed by analyzing
thousands of earthquakes from hundreds of
seismograph stations around
the world.
Here we show an earthquake near the top of
the globe and graph the arrival times to seismic
stations at varying distances from the hypocenter.
The y-axis shows distance from the earthquake,
and the x-axis shows the elapsed time since
the event.
The seismograms, record the arrivals of the
compressional p , the shearing S and the rolling
surface waves.
Seismic waves travel at different rates, so
the farther a seismic station is from an earthquake,
the further apart the P, S, and surface-wave
arrival times are.
Here we show only direct P and S wave paths
through the mantle and crust.
The final image of this animation will show
more of the complexity within the earth as
waves are reflected, refracted, and damped
due to changes at depth.
Connecting the waves through the stack of
seismograms creates the travel-time curves
that can be used to locate earthquakes .
Simply stated, the time difference between
the arrival P wave and the S wave can be used
to measure the distance from the seismometer
to
the epicenter.
