By measuring the difference in arrival times at a seismometer station they can be used to determine the distance to the epicentre of an earthquake.
They may also be used to estimate the properties of the subsurface and it's structure (refraction and reflection seismology).
Please see the related questions for further information.
A seismograph can locate a seismic wave.
Seismic wave
You need a shotgun and shoot the wave and that's how you stop a seismic wave
the sound wave
In air, the seismic waves(P-wave) are simply sound waves, and travel with the speed of sound (approx. 335 m/s).
medium
The seismic wave that travels fast and increases its speed with depth is called a primary or P-wave. P-waves are compressional waves that can travel through solids, liquids, and gases, and they are the fastest seismic waves.
A P-wave (primary wave) is expected to have the greatest wave speed among seismic waves, traveling through solids, liquids, and gases. P-waves are compressional waves that can travel through the Earth's interior with the highest velocity compared to other types of seismic waves.
deflect
Seismic wave
A seismograph can locate a seismic wave.
The formula to calculate the speed of seismic waves, known as the P-wave velocity, is V D / T, where V is the velocity, D is the distance traveled by the wave, and T is the time it takes for the wave to travel that distance.
The fastest wave is the electromagnetic wave. Of the seismic waves, the P-wave is the fastest seismic wave.
The structure of Earth's interior affects seismic wave speed and direction differently at different boundaries. As P waves enter the mantle, they pick up speed until they enter the core, where the wave paths are bent sharply.
You need a shotgun and shoot the wave and that's how you stop a seismic wave
The bending of a seismic wave as it crosses a boundary is called refraction. This occurs due to the wave changing speed as it moves from one material to another with different properties, causing it to change direction.
Seismic wave velocity is mostly dependent on the material they travel through (things like magnitude do not affect wave velocity). As the earth is relatively uniform, there is virtually no deviation in earthquake 'speed'. (Wave velocity will differ depending on phase, depth, etc. - but that's different.)