![]() By analyzing the variation in the transmission time of seismic waves from different earthquakes, they concluded that the crystal structure in the inner core is likely different from the structure in the outer layer. The researchers found that the seismic feedback waves repeatedly penetrated points near the center of the Earth from different angles. This can be caused by a different arrangement of the iron atoms at high temperatures and pressures or by a preferential orientation of the growth crystals. In this case, anisotropy is used to describe how seismic waves speed up or slow down as they travel through the inner core material, depending on which direction they are traveling. A material is anisotropic if some physical properties, such as its velocity of light propagation, are unequal in different directions. The researchers studied the anisotropy of the iron-nickel compound that makes up Earth’s inner core. These changes in the movement of the two seismic waves indicates that they're passing through a liquid layer which is the outer core. “Our study is made possible by the unprecedented expansion of global earthquake networks, especially dense networks in countries bordering the United States, on the Alaskan Peninsula and across the European Alps.” At the depth of about 2900 km below the earth's surface, P-waves passing through the earth slow down rapidly and S-waves disappear. Thanh Son Pham of the Australian National University (ANU) in Canberra, first author of the study on the innermost inner core. ![]() “By developing a technique to amplify the signals captured by a ‘dense’ seismic network, we were able for the first time to detect seismic waves bouncing up and down the Earth’s diameter up to five times,” said the observed seismologist. Seismic waves are caused by the sudden movement of materials within the Earth, such as slip along a fault during an earthquake. Until now, seismologists have been able to track the waves as they travel to the antipode and back to the earthquake site, but no further. ![]()
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