Seismic Speed Traps: Iron-rich regions may slow deep-Earth vibes

11:00am, April 26, 2006

Large quantities of iron-rich minerals may be responsible for the sluggishness of seismic waves traveling through certain regions deep within Earth, a new analysis suggests.

About 2,900 kilometers below Earth's surface, molten iron from the planet's core meets a thick, overlying mantle of silicate minerals. Vibrations spreading from large earthquakes slow significantly as they pass through some patches of rock just above that core-mantle boundary, says Ho-kwang Mao, a geophysicist at the Carnegie Institution of Washington (D.C.). Those regions, dubbed ultralow-velocity zones, range between 5 and 40 km thick and can measure more than 100 km across.

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