“The material that was there 20 years ago is no longer there. That higher SKS wave speed during the 2018 earthquake can be attributed to the release of light elements such as hydrogen, carbon, and oxygen in the outer core during convection as the Earth cools.” “The difference in wave speed points to low-density regions forming in the outer core in the 20 years since the 1997 earthquake. Zhou said, “Something has changed along the path of that wave so that it can go faster now.” If the thickness is lower in a region of the outer core as the wave penetrates, the wave will travel faster, just as the anomalous SKS waves did in 2018. How fast these waves travel depends partly on the density of the outer core in their path. Back out through the mantle as an S wave.Into the outer core as a compressional wave.It goes through the mantle as an S wave or shear wave.“SKS” represents three phases of the wave: That’s because the SKS waves she studied pass right through it.

In seismic waves and their changes in speed on a decade time scale, Zhou saw a means for “direct sampling” of the outer core. She said, “The changes happening in the outer core aren’t dramatic, but they’re worth confirming and fundamentally understanding.”

Since it’s changing, we also speculate that convection in the outer core changes with time, but there’s no direct evidence.

The magnetic field is not the same every day. It’s moving away from Canada and toward Siberia. Zhou said, “If you look at the north geomagnetic pole, it’s currently moving at a speed of about 50 kilometers per year. Ying Zhou, a geoscientist with the Department of Geosciences at the Virginia Tech College of Science, said, “We only know that in theory, if you have convection in the outer core, you’ll be able to generate the magnetic field.”Īdditionally, scientists have only been able to guess the cause of the gradually observed variations in the magnetic field’s strength and direction, which most likely entail changing flows in the outer core.

Seismac wave