Large earthquakes reveal secrets of Earth’s inner core

The Rotation of the Earth’s Inner Core and the Impact on the Supervolcano Below Yellowstone, Mt. St. Helens

It is said that a person can be relied upon to give a careful and considered opinion if they are said to be grounded. The very meaning of the term comes from the solidity and stability of the ground on which we walk. The media has recently reported on how the core of the Earth is doing some very surprising and unexpected things.

Breathy headlines aside, this recent study confirms earlier results showing that the inner core’s rotation changes over time and helps geologists trying to figure out the mechanism whereby those changes occur. What geologists care about is the interplay between gravitational and magnetic forces within the Earth that speed up and slow down the core’s rotation.

The Earth is not a solid ball; it consists of several layers. The innermost core is the same size as the planet Mars. Surrounding that is the outer core, which is liquid rock. The next layer is the mantle, which is like a stick of consistency. Finally there is the crust, which is the outermost layer– the place where we live.

Scientists are able to make extremely precise measurements under the surface of the Earth, and that is more important than anything else. This is a big deal because it is the only planet we have. What goes on under the Earth has huge potential consequences for humanity.

Consider the supervolcano that is slumbering below Yellowstone National Park. Every half a million years or so (sometimes longer), Yellowstone transforms into a volcano that spews hundreds or thousands times of more ash into the atmosphere than the 1980 eruption of Mt. St. Helens. While some have worried that perhaps the Yellowstone supervolcano is due for another eruption, recent studies have allayed the concern that the danger is imminent. However, given the magnitude of the damage such an eruption would occur, it is imperative that geologists continue to monitor what is going on.

Geophysical seismology as a tool to probe the structure of the Earth’s innermost section with a bell after a large earthquake

And there is much more going on under the Earth’s surface. The Earth’s magnetic field guides ships at sea and lost hikers to safety. It’s easy to believe that the familiar compass will always work, however geologists have shown that the Earth’s magnetic field isn’t constant. Magnetic south becomes north and vice versa when the field flips every few hundred thousand years.

Even if a flip is not imminent, the location of magnetic north changes on human time scales. In the early 1900s, it was located in northern Canada, however it has moved out into the Arctic Ocean and is now approaching Siberia.

Evidence has been mounting for several decades that the planet’s solid inner core is made of distinct layers and their properties have remained a mystery.

To better understand how the innercore’s structure works researchers used multiple seismometers to look at how earthquakes are distorted in the outer core. “Earth oscillates like a bell after a large earthquake, and not just for hours, but days,” says co-author Hrvoje Tkalčić, a geophysicist at the Australian National University in Canberra, Australia.

The study provides a measurement of Earth’s innermost section that was extremely difficult to achieve, according to a researcher at the university. After finding a weak wave at a long distance and enhancing it, you can measure wave speed in the deep interior of the Earth.

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