Mapping The Earth's Interior
Because seismic waves commonly propagate efficiently and interact with internal structure, they provide high-resolution noninvasive methods for studying Earth's interior. One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the earth is liquid. Since S-waves do not pass through liquids, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. In addition, P-waves travel much slower through the outer core than the mantle.
Processing readings from many seismometers using seismic tomography, seismologists have mapped the mantle of the earth to a resolution of several hundred kilometers. This has enabled scientists to identify convection cells and other large-scale features such as Ultra Low Velocity Zones near the core–mantle boundary.
Read more about this topic: Seismology
Famous quotes containing the words earth and/or interior:
“I call heaven and earth to witness against you today that I have set before you life and death, blessings and curses. Choose life so that you and your descendants may live...”
—Bible: Hebrew, Deuteronomy 30:19.
“Anyone with a real taste for solitude who indulges that taste encounters the dangers of any other drug-taker. The habit grows. You become an addict.... Absorbed in the visions of solitude, human beings are only interruptions. What voice can equal the voices of solitude? What sights equal the movement of a single day’s tide of light across the floor boards of one room? What drama be as continuously absorbing as the interior one?”
—Jessamyn West (1902–1984)