Sunday, September 23, 2018

Subducting Slabs of the Earth's Crust May Generate Unusual Features Spotted Near the Core

Nearly 1,800 miles below the earth's surface, there are large odd structures lurking at the base of the mantle, sitting just above the core. The mantle is a thick layer of hot, mostly plastic rock that surrounds the core; atop the mantle is the thin shell of the earth's crust. On geologic time scales, the mantle behaves like a viscous liquid, with solid elements sinking and rising through its depths.

The aforementioned odd structures, known as ultra-low velocity zones (ULVZs), were first discovered in 1995 by Caltech's Don Helmberger. ULVZs can be studied by measuring how they alter the seismic waves that pass through them. But observing is not necessarily understanding. Indeed, no one is really sure what these structures are.

ULVZs are so-named because they significantly slow down the speeds of seismic waves; for example, they slow down shear waves (oscillating seismic waves capable of moving through solid bodies) by as much as 30 percent. ULVZs are several miles thick and can be hundreds of miles across. Several are scattered near the earth's core roughly beneath the Pacific Rim. Others are clustered underneath North America, Europe, and Africa.
"ULVZs exist so deep in the inner earth that they are impossible to study directly, which poses a significant challenge when trying to determine what exactly they are," says Helmberger, Smits Family Professor of Geophysics, Emeritus.

Earth scientists at Caltech now say they know not just what ULVZs are made of, but where they come from. Using experimental methods at high pressures, the researchers, led by Professor of Mineral Physics Jennifer Jackson, have found that ULVZs consist of chunks of a magnesium/iron oxide mineral called magnesiowüstite that could have precipitated out of a magma ocean that is thought to have existed at the base of the mantle millions of years ago.

The other leading theory for ULVZs formation had suggested that they consist of melted material, some of it possibly leaking up from the core.

Jackson and her colleagues, who reported on their work in a recent paper in the Journal of Geophysical Research: Solid Earth, found evidence supporting the magnesiowüstite theory by studying the mineral's elastic (or seismic) anisotropy; elastic anisotropy is a variation in the speed at which seismic waves pass through a mineral depending on their direction of travel.

One particularly unusual characteristic of the region where ULVZs exist—the core-mantle boundary (CMB)—is that it is highly heterogenous (nonuniform in character) as well as anisotropic. As a result, the speed at which seismic waves travel through the CMB varies based not only on the region that the waves are passing through but on the direction in which those waves are moving. The propagation direction, in fact, can alter the speed of the waves by a factor of three.

"Previously, scientists explained the anisotropy as the result of seismic waves passing through a dense silicate material. What we're suggesting is that in some regions, it is largely due to the alignment of magnesiowüstite within ULVZs," says Jackson.

At the pressures and temperatures experienced at the earth's surface, magnesiowüstite exhibits little anisotropy. However, Jackson and her team found that the mineral becomes strongly anisotropic when subjected to pressures comparable to those found in the lower mantle.

Jackson and her colleagues discovered this by placing a single crystal of magnesiowüstite in a diamond anvil cell, which is essentially a tiny chamber located between two diamonds. When the rigid diamonds are compressed against one another, the pressure inside the chamber rises.

Jackson and her colleagues then bombarded the sample with x-rays. The interaction of the x-rays with the sample acts as a proxy for how seismic waves will travel through the material. At a pressure of 40 gigapascals—equivalent to the pressure at the lower mantle—magnesiowüstite was significantly more anisotropic than seismic observations of ULVZs.

In order to create objects as large and strongly anisotropic as ULVZs, only a small amount of magnesiowüstite crystals need to be aligned in one specific direction, probably due to the application of pressure from a strong outside force. This could be explained by a subducting slab of the earth's crust pushing its way to the CMB, Jackson says. (Subduction occurs at certain boundaries between earth's tectonic plates, where one plate dives below another, triggering volcanism and earthquakes.)

"Scientists are still in the process of discovering what happens to the crust when it's subducted into the mantle," Jackson says. "One possibility, which our research now seems to support, is that these slabs push all the way down to the core-mantle boundary and help to shape ULVZs."

Next, Jackson plans to explore the interaction of subducting slabs, ULVZs, and their seismic signatures. Interpreting these features will help place constraints on processes that happened early in Earth's history, she says.

The study is titled "Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle."
http://www.geologyin.com/2018/09/subducting-slabs-of-earths-crust-may.html#Qx3x2Zsua4VZAmP7.99 Follow us: @GeologyTime on Twitter

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Saturday, September 22, 2018

All quiet before the storm

Good Day to you all, just as well we have doubles as doubles reduce the intensity of the individual earthquakes. The Schumann Resonances above indicate all is quiet. All quiet in the Western Front no aggitation yet. BUT.....you see the clouds in the far horizon, below we see GOES Magnetometer diving solid below 50nT and going. This is no good.

The Kp Index below after a long period of quietness also shows a 5-7 index very Stormy weather ahead!


In conclusion we are in for a few strong shakes within a few days. So keep safe keep Good!



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YOU SEE DOUBLES

If you see Doubles today, no you are not sobber, it is a fact. the early Mexican arrivals confirm we are in a period of encouraging Double Earthquakes. [As we pointed this out, check few previous posts]


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Friday, September 21, 2018

Planets Today, 21st September 2018

Good Day to you all!
Notable today is the MERCURY-SUN conjunction in Virgo, a place where Mercury is strong. On the personal level, restrain a the sun will either burn you out or will say something to hurt or too strong. This conjunction is in semisextile to Venus, so best to talk sweet. The other very intresting aspects and probably more important today is this Uranus square to Mars and Uranus trining to Saturn/Vesta conjunction. Here, we have Mars and Saturn the same degrees and beginning to get out of phase between them but Westa also is close hence we should be seeing strong evidence of double earthquakes. Westa itself is in a perfect square to chiron so one will trigger the other and therefore a sequence, and two is a Double. The Moon is semisquare to Neptune while squaring Jupiter slowly, while Jupiter is semisquare to Westa. So the evidence to me is one can trigger the other, and possible to see Doubles.

Be Safe Be Good!
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Scientists Identified Three Reasons Responsible for Earth’s Spin Axis Drift

A typical desk globe is designed to be a geometric sphere and to rotate smoothly when you spin it. Our actual planet is far less perfect—in both shape and in rotation.

Earth is not a perfect sphere. When it rotates on its spin axis—an imaginary line that passes through the North and South Poles—it drifts and wobbles. These spin-axis movements are scientifically referred to as "polar motion." Measurements for the 20th century show that the spin axis drifted about 4 inches (10 centimeters) per year. Over the course of a century, that becomes more than 11 yards (10 meters).

Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift—contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis. But recently, many researchers have speculated that other processes could have potentially large effects on it as well," said first author Surendra Adhikari of NASA's Jet Propulsion Laboratory in Pasadena, California.
"We assembled models for a suite of processes that are thought to be important for driving the motion of the spin axis. We identified not one but three sets of processes that are crucial—and melting of the global cryosphere (especially Greenland) over the course of the 20th century is one of them."

In general, the redistribution of mass on and within Earth—like changes to land, ice sheets, oceans and mantle flow—affects the planet's rotation. As temperatures increased throughout the 20th century, Greenland's ice mass decreased. In fact, a total of about 7,500 gigatons—the weight of more than 20 million Empire State Buildings—of Greenland's ice melted into the ocean during this time period. This makes Greenland one of the top contributors of mass being transferred to the oceans, causing sea level to rise and, consequently, a drift in Earth's spin axis.

While ice melt is occurring in other places (like Antarctica), Greenland's location makes it a more significant contributor to polar motion.

"There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole—which Greenland is—or from the South Pole (like Patagonian glaciers), it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole," said coauthor Eric Ivins, also of JPL.

Previous studies identified glacial rebound as the key contributor to long-term polar motion. And what is glacial rebound? During the last ice age, heavy glaciers depressed Earth's surface much like a mattress depresses when you sit on it. As that ice melts, or is removed, the land slowly rises back to its original position. In the new study, which relied heavily on a statistical analysis of such rebound, scientists figured out that glacial rebound is likely to be responsible for only about a third of the polar drift in the 20th century.

The authors argue that mantle convection makes up the final third. Mantle convection is responsible for the movement of tectonic plates on Earth's surface. It is basically the circulation of material in the mantle caused by heat from Earth's core. Ivins describes it as similar to a pot of soup placed on the stove. As the pot, or mantle, heats, the pieces of the soup begin to rise and fall, essentially forming a vertical circulation pattern—just like the rocks moving through Earth's mantle.

With these three broad contributors identified, scientists can distinguish mass changes and polar motion caused by long-term Earth processes over which we have little control from those caused by climate change. They now know that if Greenland's ice loss accelerates, polar motion likely will, too.

http://www.geologyin.com/2018/09/scientists-identified-three-reasons.html#GdVCOhZ5HYGMxYgC.99 Follow us: @GeologyTime on Twitter
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Precursors on 21st September 2018


The TEC Rate anomalies this morning is shown here, with a massive drop over Indonesia, as above. This of course does not in my opinion mean anything today, but in due course. However, they do not last long and disappear in minutes. The next to consider is GOES Magnetometer below.
There is a huge spike down to -100 as can be seen above, but I think this should be some kind of problem which was resolved in minutes, hence it returned to normal. We are on a high Tesla field now for a few days and it spirals but does not drop a lot.



Above we see the Schumann Resonances, and there is nothing here to worry about, there was a strong event in Fiji this morning but nothing more....So, time will tell but it looks quiet.

Finally below we see the Kp Index where we can see it is extremely low.






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