= Seismology
<Seismology> studies <elastic waves> generated by <earthquakes>, impacts and controlled sources, and uses them to investigate planetary interiors. A <seismometer> converts ground motion into a recorded <seismogram>. Arrival times, waveforms and amplitudes then constrain both the source and the material traversed by the waves.
<P waves> respond to compression and <S waves> to shear. Their different speeds and their reflections or conversions at interfaces help distinguish layers. Locating an <earthquake> requires several stations because its origin time and location must be estimated along with the propagation model. A single late arrival can reflect a deeper source, a slower path or a mistaken <seismic phase> assignment.
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