Seismic Waves and Earth's Core

Earthquakes generate seismic waves that travel through the planet in different ways. Compressional P waves travel through both solids and liquids; shear S waves do not travel through the liquid outer core. Their paths, speeds, and shadow zones helped establish that the outer core is liquid and the inner core solid. Motion in the electrically conducting outer-core fluid sustains the geodynamo that produces most of Earth’s magnetic field.