Earthquakes and explosions cause seismic waves.
We detect these waves using seismometers.
P-waves are longitudinal. They are fast and can travel through solids and liquids.
S-waves are transversssssssse. They can only travel through solids.
Like usual, when a wave reaches a boundary some of it is reflected.By observing how waves have been reflected and refracted, scientists have been able to observe the earth.
Most of the time, wave speed changes gradually, which results in a curved path. But the path can have a kink when the properties suddenly change.
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