What is Going on in the Earth's Belly?

When Geoscientists first imaged the earth’s interior, they probably thought what any parent first thinks when looking at a sonogram: “what the hell is that?”. Seismic Tomography is perhaps the oldest method of trying to image the interior of a large object we could not easily get a camera inside.

Just like looking inside a pregnant woman with acoustical waves (sonography), seismologist use earth vibrations to image what is going on deep down in the planet. They have used earthquakes, nuclear explosions, and even vibrations related to the ocean, to look at the rattles and shakes of the earth and produce 3D images of what they think the structure is way down below. In a nutshell, that is what Seismic Tomography does.

Unfortunately though, the seismologists who make these images cannot refine their craft as the medical industry has done: they have never put the earth on an operating table and actually looked inside to see if they are using their tool correctly. They have been able to do it in shallow depths, the upper crust, the earth’s most outer layer of “skin”, but getting any deeper is still a very difficult technological feet. So, they have to make assumptions, argue how the computer should display the signals coming from their instruments, and add some “artistry” to how the image is displayed.  With all these variables floating around that can drastically affect the picture they produce, it is a really good thing they at least do not have to worry about malpractice insurance.

Sonogram of Child in Utero

Tomographic Cross Section of Velocity "Anomalies" of the earth